ARCHITECTURAL UTILITIES 3 LIGHTING AND ACOUStiCS THENEW LADDER TYPE CURRICULUM GEORGESALINDA SALVAN ASSISTANT PROFESSOR College of EngineeringandArchitecture Baguio CoMegesFoundation 1980-1988 First andlone graduate of B.S.Architecture,1963 North of Manila,St.LouisUniversity Baguio City Former instructor 1965-1969 at St.LouisUniversity fuap Recipient of various ACE certificates,Architects Continuing Education Program Alicensed Architect,active practitioner and a licensed building constructor,inventor anda board topnotcher. Past president of United Architects Phils.BaguioChapter 1982 and1983 ElectedNationalDirector;UAP,RegionalD.istrict I for the year1987. Conferred the title of " FELLOW"UnitedArchitects Phils. Colege of Fellows,October,1988 JMC P R E S S ~INC. 388 Quezon Avenue,Quezon City Philippine Copyright 1999 by: JMC PREss: INC: -:: and ,. GEORGES. SALVAN Allri ghts reserved. No part ofthis t?ook may be reproduc;ed Inany . manner wlthOot pef'mjssion of the put)lish'er. REVISED EDITION ISBN:971-11-1028-8 Published and Printed by: JMC PRESS, INC. 388 QUEZON AVENUE, QUEZON CITY Tel. Nos.410-95-35871 -91-87 TELEFAX:7124929. Distributed by: GOODWILL BOOKSTORE Glorietta 3 Mall, Ayala Center Ayala Avenue, Makati City Tel.Nos.8939058893-9079 Fax No. (632) 810-9033 e-mail:goodwill@pworld.net.ph. ~.... ' . .. Dedicated to all future Architects and Engineers The hope for a functional, comfortable and convenient designs for better living. ACKNOWLEDGEMENTS The completion of this book was made into reality through the patient and consistentco-operation and efforts of my draftsmen and BCF graduates in architecture, Mr. Rey Puno for heading the overalllayout and paste-up dummies and his assistants,Mr. Jerry Jun Suyat and Edgar Peralta, who spent sleepless nights to meet this deadline. Special thanks are also acknowledged to Mr.Roy Pagador,who designed the cover page and to Frederick Palasi who designed the chaptercovers. To the ones who lent unselfishly their Books, like Dean Avelino Cruz of the Baguio Colleges FoundationEngineeringandArchitecturedepartment,andmostespeciallytoMr.ValS. Gutierez who lent his acoustical Design for architects Book. To the ladies,Miss Reesa Angela Palaganas, Teresa Cuares and Imelda Dumasi, who helped in the typingofthelengthy manuscripts andwho also helpedinthe proofreading of the texts,with Mr.Fiorito Amon. To Mr. Luis V. Canave, who guided me on the complete process of publishing and printing a book,andto Mr.FranCiscoC.Mali.csi,TeresitaG.Espinoza,Eduardo C.Villanuevaand ParaidesG.Aragonesfor their untiringcooperationinpreparingthe manuscriptsin com puterized typesetting. To the many students of architecture whose curiosity and interest in lighting and acoustics to be in abook form have been a source of inspiration. And lastlythe author wants to acknowledge his heavy indebtedness to the various authors listed in the Bibliography. v PREFACE acoustics and lighting is an exact science and practical art. The architect who oas..;a .workingknpwledgeof thesesubjectscanplanadequatelyfor .theacousticsand lighting o(the buildings hedesigns.It is .the purpose of this bookto presentworking principles of this .science and art in a simple,useful, and convenient form.Architectural de-signing based on these principles wiU,assure the constr.uction of rooms and buildings which are disturbing glare I')Oises and provide the optimum conditions for reading, listening to either speech or music.Functional acoustical and lighting design demands scientific,aesthetic,and practical planning. Acousticaldesigningin architecturebeginswiththepreliminarysketchesonthe dratting board and continues throughout all stages of planning and construction. Good acoustics will beassuredinthebuildingsanarchitectdesignsifhehasanunderstandingofthe technological principlesof architectural acousticsandknows how to apply them. For many years an artificial dichotomy existed in the field of lighting design, dividing it into two disciplines:architectural lighting andutilitarian design the former trendfound expres-sion in architectural building design that took little cognizance of vision needs,but that dis-playedaninordinatepenchantforincandescentwallwashersandarchitecturallighting elements while regarding the added-on utilitarian lighting with partially justified asperity. The latter, trendsawallspacesintermsofroomorcavityratiosanddesignedlightingwith foocandlesandf inancialconsideration(pesoordollar)astherulingconsiderations.That both these trends have in large measure been eliminated is due in large measure to the work of the Illuminating Engineering Society liES}, and its members and new found energy con-sciousness that followed the 1973 arab oil Embargo. The latter spurred research into satisfy-ing real vision need within a framework of minimal energy use, and convinced architects that in addition to seeing the building, it must be possible to see within the building.The architec-turaldesignermust thentakecognizanceof these factors: 1.The manifoldramifications of daylighting 2.Theintimateinterrelationbetweentheenergyaspectsofartificialandnatural lighting,heating and cooling. 3.Theeffectoflightingneedsoninteriorspacearrangement,forexample,the desirability of grouping similar l ightingrequirementtasks. 4.The characteristics,means of generation,effects,and utilization techniquesof ar-tificial lighting. As a result of the need to consider these and other interrelatedfactors,many of which are mutually incompatible,the architect is faced withmany tread-off type decisions.The pur-poseof thisbookis thentwofold:toprovidethebackgroundthat willhelpthearchitect makethese decisions correctly andto makehim or her proficient inthe use of lighting as a design material. This book is intended as a practical guide to good acoustical and lighting design in architec-ture. It is written primarily for architects, students of architecture, and all others who wish a non-mathematicalbutcomprehensivetreatiseonthissubjects.Usefuldesigndatahave beenpresentedin suchamanner that thetext canserveas a convenient handbook inthP. solution ofmost problemsencountered in architectural acousticsandlighting. vii This book is compased of two sections. The first section discusses about "Acoustics" and is further divided into two parts.The general principles and procedures on which all acoustical designing sliould be based considered in chapters 1 to 10 specific applications of these prin-ciples andprocedures are describedin chapter 11these applications include the design of auditoriums,theatres,schoolbuildings,commercialandpublicbuildings,homes,apart-ments andhotels,churches,radio andtelevision,sound-recording studios. The secondsectiondiscussed"LIGHTING" andis also further divided into two parts The general principles and procedures lightsources on which all the lighting designing should be based are considered in chapters 12 to 15. Specific applications of these principle$ and pro-cedures aredescribed in chapter 16.These applications include the lighting applications on Residentialoccupancies,Institutional andEducational buildings,Commercial Interiors,In-dustriallighting,andotherDesignTopicssuchasAutomaticenergy control,Emergency lighting. Buildingretrofit, RoodlightingandStreetlighting.A :short discussionfollowson Disco-lighting. viii TABLEOFCONTENTS PART 1ACOUSTICS . Chapter1FUNDAMENTALS OF ARCHITECTURAL ACOUSTICS .............................................. .-:. .. . . ... ... ... .. . ..... . . . . .1 Chapter Sound Theory, 2 General,2 Wl'lat iS Sound, 2 Propagation of Sound, 4 Velocity of Propagation,5 Speed of Sound. 5 Frequency,6 Wavelength, 8 Wave Form,10 Sound magnitude;12 Sound pressure,12 Acoustical power,14 SoundIntensity,14 Intensity level,the Decibel;18 2HUMAN RESPONSETO SOUND How we hear,24 Sensitivity of the ear, 26 Sound pressurelevel,27 Loudness level,Phon scale,31 The Sone Scale, 33 Sound Fields in an EnclosedSpace,35 SoundPower andPreuure levelsinFreeSpace,39 Other Factors in Hearing, 40 Effects of Noise on Hearing,41 Calculation of MaskingSpectrafrom Sound-PressureSpectra,42 Loudness. Calculations for a Case of Typical Room Noise,46 Chapter3SOUND SOURCES ................................................................. . Di rectionality of Sound Sources, 48 Speech and Music, 49 Noise, Music and Speech,49 Speech;51 Speech Power, 53 Other Sounds, 56 . . Properties of Musical Sounds,56 Effects of a Room on Speech and Music, 58 Noise Criteria, 60 Negative effects of noiee, 60 Noise andAnnoyance,60 ix 23 47 Chapter.4ACOUSTICS ..! .. ......... . . . ..... ::.......... .... ........... . ........ .... ................65 Sound in Enclosures,66 Sound Absorption,66 Reverberation,07 Reflection andDiffraction of SoundinRooms,69 Ref1ectiooof -Sound, 70 Soim f....-, Musical nota (combination of several pure tones) Thefollowingfigureshowsthefrequencyrangesofsomecommondevicesand phenomena.Thefrequenciesshowninthe figureallstandintheratioof2: 1to each other, that is-, 16:32:63:125: 250 and so on.Borrowing again from musical terminology, they areoneoctave apart. Frequeocvlhertzlandwavelength(em) ofcommonaudioitems A$SUmedvelocity:344mJSec 2H 20 16,531.5 22001100 Piano ..._Middlec Pipeorgan Svmohonyorchestra Speech Funclamentals Telephone conversation Hearingran9e HiFi 4186 Overtones (! .. E 5 (! ~ " ' ~ 0 s ~~ 5 ~ 8 . 20,000 Figure of Frequency Rangesof CommonInstruments. Wavelength andTypes of Propagation Hertz :>. ,c:m The wavelengthof asoundmay bedefinedasthe distance between similar points on successive waves or the distance the sound travels in one cycle of vibration, That is, in 1/ second. is called its wavelength and is denoted by the Greek letter lambda )..The reia tionshipbetweenwavelength,frequency,andvelocityof a soundisexpressedas 8 or).f= c where>.""' wavelength, in ft or M c=velocity ofsound, in fps or min/sec f=frequency of soundHz Low-frequencysoundsarecharacterizedbylongwavelengthsandhigh-frequency sounds by short wavelengths. Sounds with wavelengths ranging fromY:zinch to 50 feet or 1.25 em to 15.25 mcan be heard by humans. Asimple nomograph is shown in the figure, which permits rapid determination of wavelength given f requency, and vice versa. WavelengthinFrequency Wavelength feetandinchesinhertzinmeters 113 TO34.4 15 20 56-20 17.2 - 50 30 10 22.6 20 506.88 70 5.0 11.3 10 100 4.0 3.0 3.44 150 6.6 5 200 2.0 1.72 - 4 300 1.01meter 3 2.3 2 50069em 700 0.5 1. 1Ike 0.4 34em 0.56 Bin. 6in. 2kc 0.2 17cm 4in. 3kc 0.1 0.235kc7em 2in. 7kc 0.05 0.1110kc3.4em 9 Wave Form Thewaveformof soundwave describes,by means of a graphicalrepresentation,the precise nature of a complete to and-fro oscillationof the vibrating particles ina sound field. Thus below is a graph of the simple harmonic wave form of the sound generated by agentlystrucktuningfork;itgivesasthefunctionofthetimetheinstantaneous displacement (plotted vertically) of a typical vibrating particle. Sine Wave eachcomplete cycle in the sinewave graph corresponds to a complete cycle of the tun-ing fork or of the sound wave it generates. Although the displacements arerepresented as transverse to the time axis, the actual displacements of the particles in the sound field are parallel to the direction of propagation of the sound wave.that is.the wave motion is longitudinaL The wave forms of musical tones are somewhat more complicated. For example the next figure shows the wave formsof sustained tones produced by a tuning fork, a violin and anoboe.Theserecordsareforsustainedmusicaf tonesof thesamefundamentalfre-quencyandapproximatelythesameamplitudeofvibration.However,theydiffer markedly in their wave forms.Although not simple harmonic. the wave formsfor these tones are periodic;they repeatat definite intervals.Theyarecalledcomplexwaves in contradistinction to simple harmonic waves. It is possible, by mathematical or instrumen-.tal means, or both, to analyze complex wave forms, like those characteristic of the oboe orany other instrument.into aseries of simple harmonicvibrations.Thus,a complex tone (or its graphical representation as a complex wave form) may be regarded as made up of a series os Simple harmonic tones (or waves). Usually the frequencies of these com-ponent simple harmonic tones are integral multiples of the frequency of the fundamental component. whichissometimes referredto asthe gravest component. 10 TUNINGFORK VIOLIN OBOE 11 Sound Magnitude Whenwe speakof sound magnitude,we think of loudness,which is a subjective,ear-oriented reaction not linearly related to the physical quantity of sound.The level (quanti-ty)of soundpressure,sound pre$surelevel(SPL),sound intensity, and soundintensity level(ll), allofwhichare different fromeachother,and fromsubjective loudness.To clearly understand these concepts, a comprehension of how we hear and how sound is propagated infree space is necessary. SoundPressure The most elementary type of vibration is that which has a single frequency and is called simple harmonic motion. It is the form of vibration which characterizes a "pure" tone; for example, that given by a good tuning fork which has been struck gently. The form of this vibration andthe corresponding form of the pressure variationwhich is propagated out-wardly in the surrounding mediumasa soundwaveisshowninthis figure. Sine Wave This is a sine wave; a curve having this shape can be obtained by plotting, on rectangular coordinate paper, the sine of an angle against the angle itself. Thus a tone produced by a simple harmonic sound source is often called a "pure" tone because it contains only one frequency. The total pressure in a sound field,at a specified point and instant of time t, is given by the sumof the undisturbed atmospheric pressure Ps and the alternating pressure due to the soundwave. 12 The latter is given by P8 sin(21rlt+9 where: P 8 ==maximum pressure amplitude f= frequencyof vibration t=time e;:::phase angle when t==O Thisparticular(simpleharmonic)type of wave motionis importantbecauseallsound waves can be shown to be made up of a number of different simple harmonic waves. The effectivesoundpressureP isthe square root of the time averageof the square Pasin (2tcft+ 9). The term sound pressure is generally used to designate the effective value of the sound pressure. An extraordinarily small sound pressure can be detected by the ear. The following figure indicates the pressure due to noise in various locations;it shows that atthe threshold of audibilitythe sound pressure is on 0 .0000000035 pound per square inch. SOUND SOUNDPR'e!ISURBPRE:ilUI1f ucf4NNf'JN..IZ 'IH FRONT N'/1> BELOWMUZZLE (e(Jli!VIILENTMJRNftl PRESSURE} l'tfRe.SHC:>LDPPAIN ELECTRIC POWER.SUBSTAne>l'f Sl/8WAY ST/ITIC>N, TRI\INPASSING f:I.ECTRIC tROM f ORI../IRGcHOTEL 1\Vf:RAGI!':FAC"K->RY AVERAGe RE:Sit>f:NCE WJllfRA.DK, {AUDIENCf:Nl:SI!:.MOTIOI'CPICTWU:THfATER AVfR....CeRf.SIDI!NCE. WITH0VTRADIO L..___....._;;.. CI=000=::.'!:

TH/t/!.SHOLDOFAYD/8/UTY 13 Acoustical Power Therateofemissionofacousticalenergyfrommostsourcesofsound,andthecor-respondingpressuresintheirresultingsoundfields,arevervsmall.Forexample,the average acoustical power radiatedby a person speaking in an auditorium is of the order of 25 to 50 microwatts (a microwatt is one million of a watt). It would require, therefore, no fewer than1 5 ,000,000.such speakers to generate a single horsepower of acoustical energy.With such minute amounts of sound power in unamplifiedspeach. the resulting soundpressureinanauditoriumiscorrespondinglysmall;oftentheaveragesound pressureislessthan0.1dyne .persquarecentimeter.Incontrastwiththemere50 microwatts output of a typical speaker,the acousticalpower required for good hearing conditions for speech throughout anauditorium, is10,000 microwatts in a room having a volumeof about100,000 cubicfeet . Mostmusicalinstrumentsradiateasomewhatgreaterpower thandoestheaverage human voice. The table below gives the approximate peak power for a number of typical instruments. These valuesare small comparedto acousticalpower out-putof a largeair-raidsirendevelOpedduring worldwar II. TheApproximate PeakSoundPower Output of Conversation Speech and of SeveralMusicalInstruments (BellTelephone laboratories) Source ConversationnlSpeechfemale male Clarinet Bass Viol Piano Trumpet Trombone BassDrum, 0 .90 x0.38 Orchestra,75 pieces Sound Intensity Peak Power in Watts 0 .002 0.004 0.05 0.16 0.27 0.31 6.00 25.00 10 to 70 The sound intensity in a specified direction at a point in a sound f ield is defined as the rate of flow of sound energy througha unit areaat that point,the unit areabeingperpen-dicular to the specified direction. Sound Intensity is usually expressed in watts per square centimeter. Asanillustration,we. shallcalculatethe 1 00centimeterfromthebellofa clarinet.Forlow-frequency tones,theclarinetapproximatesapointsource;that is,it radiates sound nearly uniformly in all directions.(The soundwaves from a perfect point source,whichis far fromany reflectingsurfacearespherical.)let usassumethat the total power output W for a sustained tone from the clarinet is 0.002 watt. Since the area 14 Sofa sphere is 4'lr times the square of the radius; the area of a sphere100 centimeters in radius is 125,600 square centimeters. Thus the power passing through each square cen-timeters. Thus the power passing through each square centimeter of this sphere. flowing in the outward directiot'l- the intensity I- is I- ~=0 .002 watt/125,600 cm2 =1.59 x1 o-s watt/cm2 Since the area of a sphere increases as the square of its radius, we note that the intensity of free3sound waves originating at a point source diminishes inverse.ty as the square of the distance from the source. The sound intensity at any distance from the s o u ~ c eis expressedalsoas Where I=the sound intensity in w/cm2or w/ m2 P= acoustic power inwatts A=area in cm2 1m2) Sincethesound radiatesfreelyin alldirections, w/cm2 Where ris. theradiusofanimaginaryenclosingsphere(inEnglishunitsthisis = - --'- P__ 930 X4..-2 w/ft2 since there are930 cm2 inone sq.ft.}The intensities atdistances r1 andr2 from the source stand in the ratio of 15 which is the formula for the classic Inverse Square Law, stating that intensity is inverse ly proportional to distance from the source. Anotherfigurebelowshowgraphicallyhow asoundpulseis attenuatedinstrength (but not in wave form) as it travels outward from the source by action of distance. The threshold of hearing, that is, the minimum sound power intensity that a normal ear can detect. is , o-16 w/cm2 (actually the ear responds to pressure, as will be explained. The maximum sound intensity that the ear can accept without damage is approximate-ly 10-3 w/cm, this gives a range of 1013 or 10 million million to one 10,000,000,000,000:11. 0 ... 1 0 ~ - - . . . . . . . . . . _ ___ Distance 16 The table below gives the reader an idea of the physical significance of these numbers. Two problems arise immediately when dealing with quantities of this type; t he numbers themselvesareverysmalland the ratiosarevery large.Furthermore.the humanear responds logarithmitically,not arithmetically to sound pressure(and intensity); that is doubling the intensity of a sound does not double its loudness- the changeisbarely perceptible. Tosolve theseproblems it would bemuch more convenientifwewere to construct a scale that: a.Started at zero for the minimum sound!intensity or pressure) that we could hear. b.Used whole numbers rather than negative powers of 10. c.Had some fixed relationship between an arithmetic difference and a loudness change;say10 unitsequalsadoublingor(halving}of loudness.Thus.on suchascale.thedifferencebetween20and30,and60 and70,would always be a doubling of loudness. Such a scale is the decibel scale. TABLE Intensity (w/cm21 Intensity Level -DecimalExponential

NotationNotation Notation Examples 0.001 10-3 130 dbPainful 0.0001 10- 4 120 db 0.00001 10-5 110 db75-piece orchestra 0.000001 10- 6 100 db 0.0000001 10-7 90dbShouting at 5 ft 0. ()(X)()()00)110-9 70dbSpeech at 3ft. 0.00000000001 10-11 50dbAverage office 0.0000000000001 10- 13 30dbQuiet unoccupied office 0.00000000000001 10- 14 20 dbRural ambient 0.000000000000001 10- 15 10 db 0.0000000000000001 10- 16 0dbThreshold of hearing 17 Intensity level(ll) the Decibel(db) Theword"level" indicates aquantity relative to abasequantity.Intensitylevelis the ratiobetween agiven intensity and a base intensity. If we express intensity level as where: I IL=10 log-lo IL= intensity level in decibles = intensity in watts per square centimeter 10 = base, that is,1016 w/cm2 (threshold of hearing) thenwehaveestablishedascalethatsatisfies thethreeconditionssetforthinthe previoussection.ThequantityIL.intensitylevel.isdimensionless,sinceitindicates simply a ratio between two numbers.It is measured in decibles (dblfor convenience in expressing the l arge numbers involved. The previous table above show the great conve-nience of using the logarithmicdecibelscaleascomparedto either decimalnotationor exponentialnotation.Thetablebelowgivesashort listingofsubjectiveloudness changes expressed indb. Note that 10 db indicates a doubling of loudness,asspecified; 20 db is loudness doubled twice, that is, four times as loud. The difference in db between any two intensity levels, expressed as a function of these respective intensities, is '2,, 10log- - 10 log-'olo 12,, 10(logiO- logiO) A ll = ll2- IL, 12 = 10 logJ, Example:Two soundsourcesproduceintensitylevelsof 50 and60db,res-pectively,atapoint.Whenfunctioningsimultaneously.whatisthetotal soundintensity level?(Weassume identicalfrequencycontentandrandom phase; that is, the phase relationship between the two sources changes in a random manner.) 18 .. Solution: (a) rL= 10 log _1_ so 60 6.0 ,, and50 5.0 105 10 I = 101og-1-to-t6 I :::log-1-10-16 It = - -10- te = (l0- 16)106=10-10 w/cm2 = 10 1og-12-1o-16 '2 = log -----:---+- . 10-16 12 a - -lo- 16 =- 10-11 w/cm2 =10-10+l0-11 =(10 Xl0-11)+10- 11 = 11X10- 11W/cm2 tlxto-11 (c)ll combined=10 log 16 10-= 10 (log11+log195) 10(1.04+5) = 10 (6.041 = 60.4db which is a fraction larger than the original60 db of the stronger sound. Example:Assumetwonoisesignalsof60 dbeach.Whatisthecombined strengthindecibels? Solution:Onemethodwouldbe tocalculatelevelsasintheexampleabove. A shorter methodis to find the difference between the two signals andto add it to either one.Using the equation; 6 1L=ILcomb- IL1 ==10 log+ 1 = 10 logI comb ,, 21 10 log -11-1 = 10 log 2 = 10 (0.3010) = 3db 19 Thisanswergivesustheextremetyimportantfactthatdoublingasignalintensity raisestheintensity levelby 3db.Unour case,thecombinedintensity levelwouldbe 60 db+3db or 63 db).Similarly, quadrupling a signal's intensity raises the received level by 6db (see table below). Change in Level. Decibels 3 sa 7 10 20 TABLE Subjeotive Change InLoudness Barely perceptible Perceptible Clearly perceptible Twice or half astoud Four times or one-quarter as loud Example:Given a sound source that produces sound intensity IL at a distance d 1 from the source (the reader can substitute any numbers desired, or follow the problem with symbols),what are the intensities at twice the distdnce? Three times?four times? Solution: from the equation .61L101og+ 1 .,d22 andequation __ = 12d12 ....!.L(2d112 or12=ld1 )2=4 .:.. substituting in the first equation,we have IL=10 log+ 2 =10 log1/4. =10 1-0.6) =-6 db Whichtells us that soundintensity level (not pressure)is reducedby 6db.Similarly, whendistanceistripled,intensity levelis reducedby 9.5 db,and when distanceis quadrupled,it is reducedby12 db. 20 Tosummarize,then,intensitylevelincreasesI decreases)3dbwitheverydoubling (halving)ofpower anddecreases(increases)6db witheverydoubling(halving)of distance. The following figures illustrate these relationships. The ear responds to sound pressure,not pressurelevel(SPUis equalnumericallytointensity level(atleast for normaltemperatureandpressure,ex.;forouruseinarchitectural acoustics),sothat theforegoingexamplesandmanipulationsofintensitylevelare equally applicable to soundpressure level. Thecombinedeffectoftwosoundsdependsupontheirfrequencycontent.Inthe above examples, we assumed signals either of identical frequency and random phase, or of verywide-frequencyspectrum- so wide that phase phenomena arenot signifi-cant.In architectural acoustics work, such anassumption is generally valid. 100 I i -90 k v r-80 7\l I v l 60 I t-l----VII !I I I I 50 II. I I! I ! 40 I! I 30 J! I t-1{I I 20 /11 f I 10 ! l I 01234567891011121314 Ri!ductioninsoundintensitvlevelII L)andsoundprll$Sllrelevel(SP Llindecibel! 10 X 8X -T-0 c:l. "0 c ::J 0 .. 6X .5 el "' :!! .... 4X .5 45678910 1ncreaseinsoundprt!$Wre (SPl)indecibels 21 Soundlevels Bell \IL -12 db 10urce__...:.,:..._____+--tl---+ 2d----22 :.: ~ " J .. ... . . .. . ... . ~.. SoundPropagationAcousticPower and SoundPressurelevel HOW WE HEAR The hearing mechanism, shown in cross section in thefigurebelow canbedivided into three parts: the external ear, the middle ear,and the inner ear.The external ear consists of an external appendage. called the pinna, and the ear canal. which is closed at the inner end by the eardrum. The outer ear is funnel shaped and serves as a sound-gathering input terminal to the auditory system,. Soundenergy travels through the auditory canal (outer ear}andsets in motion the components of themiddle ear. The middle ear contains three tiny bonesor ossideswhich transmit vibrations from the eardrum to the inner ear.These bones- the hammer, anvil, andstirrup- constitute a lever mechanism that communicates the vibrations of the drum to the membrane of the ovalwindow,whichistheentranceto theinnerear.Thestirrupactsasapistonto transmit vibrations into the fluidof the inner ear.Thisfluid motion causes movement of haircellsin thecochlea,whichinturnstimulatesnerves at their bases,which in turn transmit electrical impulses along the eight cranial nerve, to the brain. These impulses we asSOUND.Thustheactionofthemiddleearisthatofanefficient mechanicaltransh>rmercoupling vibrations inthe air to the liquid in the internal ear. ,.. ,:. \'. 24 Whenyouhear:1;SoUncl- nvoo- .... tr..,.! tht0 The frequency scale of the spectrogram is linear, and it covers 3500 cycles, asshown by theverticalscaleto theleft of the figure.Thetime stale is also linear andis marked in secondsalong the horizontal axis.Thus,on the spectrograms,a sustained puretoneof 1750 cycles produces a single dark horizontal line mid-way between the top and bottom of therecord.Thegreater thepressureofthe sound,thedarker istheline.Thespec-trogram of street fl9ise shows that the peaks of power occur at random. The figure below is the spectrogram of noise from a ventilating fan. Note the regularity of the pattern and also the predominance of certatr frequencies. 50 00 .10.2o.30.4O.!o0.5.0 .70.8O.jj1.01.1 TIMEIN

I Music is generally, though not always, made up Ordered sound. The powef peaks co:1: at periodic intervals, as illustrated in the f igure below which is a spectrogram of a portion of aclarinetsolo.Thisrecordalsoindicatesanothercharacteristicofmost musical tones. The overtone structure is harmonic. The component frequencies in this figure are integral multiples of thefundamentalfrequency. BbDEbFcc81> 3000,,.-"" .-'::::::------... _";:__.. 1/ --:;- .....,.'""';"' _.. :......-- -. '>ZCOO-.yal .:r'*. v .. z'r:..;:.-

ol - --------------------------------------------------------------Speech . ... . ------- - .._-_-__;_-___...;_ '__,.__....___.__ ___..._....;..__.__ __o c.1o.2o.3o.4o.so.oo.7o.ao.91.01.11.21. .:11.41.s1.61.11.e1.92.02.1 TIMEINSECONDS Theear'ssensivityismaximuminthespeechfrequencyandnormalenergyrange. Speech sounds vary in the length between 30and 300 msec so that the ear perceives them individually and clearly. Speech is comprised of phonemes, which are individual and distinctive sounds that to an extent fromlanguage to language, that is, certain ones exist in one language not in another, Since certain phonemes carry more information than others,itis_thesewhichgoodarchitecturalacousticsmustbeparticularlycarefulto preserve intact, to preserve intelligibility. In English,consonants carry much moreinfor-mation than vowels, as can readily demonstrated by writing a sentence firstwithout sonants and then without vowels: 51 ._.. Most speechenergyisconcentratedinthe 1 00- to 600- Hzrange 0eeeeoeaee tOO- 600eae Mst spch nrgy S cncntrtd n th 1 00 - 600 Hrtz rng 1 0 ~ ~ ~ ~ - - - - - - - - - - ~ ~ - - - - ~ - - - - ~ 4050100200 50010002000500010,000 Fri!Quencvinheru 162351 Themalevoicecentersitsenergyaround500Hz;thefemaleabout900Hz.It is, however,in the high frequencies that consonants have most of their energy. Phonemes such as "s" and "sh" have most of their energy above 2khz and both are particularly im-portant in conveying Intelligence. Speechconsists of both orderedanddisordered sound. Thespectrograms in thisfigure belowiflustratethespokenwords,AcousticalDesigninginArchitecture.Notethat the hiss"s" in the word''acoustical" (Akussss) produces much the same record as street noise does. This "s" sound is non-periodic as contrasted with the vowel sounds, which show a definite overtone structure with the bursts of peak power coming at regular inter-valsof time,asshown by the vertical striations. 52 vi 0.: u30 00 z >- 2000 u z w lOCO ~ 0 w a: u. PLOSIVE RESONANCE BARS 0 A 0,20.40.60.8LO1. 21. 41. 61.8 TIME. INSECONDS couSTICAL:;;..D...;; E;..._S::......._..;,.._..;G;..._N_ _I _N..;.G .;;.NARCHrTECTu Nomal speech averages between 40and50 db sound pressure level at3to 4ft, with a dynamic range of from about 30 db for a soft speech to about 65 db for loud speechat thesamedistance. Extremes of speechare10db for a Whisperand80 db for a shout, but in both these instances intelligibility is sharply reduced because of lack of consonant power. Indeed,in shouting. emphasis is necessarily on vowels so that it is generally ac-ceptedthat70 db SPLisabout the upper limit of fully intelligible humanspeech.Note that singers who frequently exceed 90 db so at great loss of intelligibility}. Another result of the high-frequency content of consonants and hence intelligibility is its directiveness. The higher the frequencythe greaterits directivity and the less its diffraction (ability to turn corners).Therefore, intelligibility of speech is greatest directly in front of the speaker andleastbehindhim.Thehigh-f,requencytonesaremosteasilyabsorbedandleast reflectedanddeffracted. Speech Power The average person is surprised at the exceedingly minute amount of energy contained in speech. As mentioned in chapter I. approximately 1 5,000,000 lecturers speaking at the same time generate acoustical energy at a rate of only 1 horsepower. When the speech power of a single speaker is diffused in a large auditoruim, the sound pressure in the room is reduced to extraordinarily small values. Under such circumstances, it is easy to unders-tand why it is difficultto hear well in a large room, and why very feeble sources of ex-traneous noise may produce serious interference with the speech. For example, the noise of adistantventilatingfanormotor,theshufflingof feetonthefloor,thejarringofa nearbydoor,or thewhisperingor coughingof inconsiderate" spectators"may be suffi-cientto maskmany of thespeechsounds,and.especiallYthe feebleconsonants,which reach an auditor in a large auditorium. Since the amountsof acoustical power generated in speech are very small, the acoustics ofauditoriumsusedprimarilyforunamplifiedspeechmust becarefullycontrolledto 53 2.0 RE make the best p o s s i b l ~use of the usually inadequate speech power.In large auditorium, as might beexpected, the amplification of speechis anindispensable requirement. Theinstantaneousspeechpower,therateatwhichsoundenergyisradiatedbya speaker,varies considerablywith time.Its maximum valueinany given time interval is the peak speech power.Theaverage speechpower has, in general, a very much lower value than the peak value and depends on the method of averaging (That is, on the length of time over which the average is taken)and on the inclusion or omission of the pauses between syllables and sentences inthis time interval. An extensive investigation of the conversationalspeechpower output of individuals of two groups, 6 men and 5 women, was conducted by Dunn and White. "Long-time-inter-val averages" were obtained by averaging data over time intervals of a minute or mor.e of continouous speech, including all natural pauses between syllables and sentences. Their results show that the long-time-interval average power output varied from one individual to another within the group of 6 men, ranging from 10 to 91microwatts. The short-time-intervalaverageandpeakpower outputsof typicalspeakers,speakingat aconversa-tionallevel,canbeandoftenaremuchhigher.Calculationsof thesequantitieswere made for 1/8 second intervals, a length of time of the order of magnitude of the duration of a syllable.At least 1 percent of the1/8 second intervals had an average power in ex cess of 230 microwatts for men and 150 microwatts for women, and a peak power in ex-cess of 3600 microwatts for men and 1800 microwatts for women. This study indicates that the average male person produces a long-time-interval average sound-pressure level of about 64 db at a distance of 1 meter, directly in front of him, when he talks in a .normal conversationalvoice;the average for women, is about 61db at a distance of 1 meter. Theabovedataareforconversationalspeechinaquietlocationintheabsenceof reflectingsurfaces.Noise,thesizeoftheroominwhichapersonisspeaking,his distance from the auditor, the acoustical condition of the room, and other factors affect thepoweraoutputofhisspeech,andespeciallythesound-pressuredistribution throughout theroom.If anoisycondition prevails,Hewill raisehis voice inorder to "override" the noise. He will, in general, increase his power output as his distance from anauditor is increased.Furthermore. it is well known that a speaker attempts to raise the power output of his voice when he is speaking in an auditorium, and the larger the auditorium, the more he exerts himself. Tests conducted in a small auditorium (27,000 cubic feet) approximately 25ft x80ft x 13 ft high or 8 m x 25 m x 4 m high. indicatethat the averagespeechpower in this large auditorium was approximately 50 microwatts. These results confirm a reasonable expec tation based upon everyday observations, namely, that a speaker increases the power of ,his voice in his attempt to discount the effect of the size of the auditorium in which he is !speaking. He attempts to speak sothat he will be heard by all auditors in the room.That .hefallsshortof therequirementsforgoodhearinginlargeauditoriumswillbemade manifest inthe chapter on auditoriums. Thepercentageof thespeechpowerlyingbelowagivenfrequency,for theaverage speaker is given in thisfigure. 54 Thepercentageofthespeech power lying below a given frequen-cy,forthe averagespeakeris given in this figure. ..-- 1---- There is relatively little power In the frequencies of 1000 cycles, the frequency range that characterizes most consonants. The figure below shows how the total power of average conversationalspeechisdistributedinfrequency.Thelevelof speechpowerpercycle is plotted as a function of frequency.Since theSE! curves represent data averaged over a long time interval, their shapes are affected by the frequency of occurence of the speech components aswell as by their acoustic power. If these curves were "corrected" for the sensitivity of theearsothat the ordinatesrepresentedthe loudness of the variousfre-quency components as heardby the ear,the maximumwould occur between500 and 1 000 cycles. - 10 v ~ l \ tHv-=-,-*....q"''::: .. .. l - - - - - i---1--- 1- - 601()0zoo50010002()()():;,o()()10,000 f'ReQI.Jel'lCYINCYCLE8PERSl:cNO 55 Other Sounds is much broader and complex than speech in frequency and dynamic range.It has no direct parallel to intelligibility. "Reception" of music is a combination of physiological andpsychological phenomena.As such, it is beyond most of the purposes of this study, but will be briefly examined in the discussion of roomacoustics, auditoriums, and halls. Noise is variously defined asunwanted sound, sound with no intelligence content.and broadbandsounddepending onthelistener andthe situation. Properties of Musical Sounds The physical characteristics of musical sounds differ from those of speech in several im-portant respects.Inthey arenot so..Theseparatetonesof musicoftenaresustainedforanappreciablef;actionofa secondorlonger,andthe change in frequency is nearly always ordered in conformity with the relations among the frequencies which make upthe musical scale. This is illustrated by a comparisonof the speech spectrogram in the figure onpage 53 with one of a portion of a clarinet solo,figure onpage 51. The separate tones that comprise music are in general made up not of a single simple har-monic vibration,but of long and complexseries.. ofsucn \iibrations.In someinstances, theovertonesmaybemuchmoreprominent fromthefuriaamental.Thenumberand prominenceof theseovertones,together with the differencesintheir ratesof build-up and decay, are the chief determinants of the tonalcharacteristics of various musical in-struments. The overtones from most string and pipe instrument are, at least very approx-imately, harmonic. The differences in the overtone structure of different musical tones on the samepitch areillustrated inthe figurebelow. ClARINET cr.ARINA ACCORDION

------::;:t10:: 1 fR!!G.jU!!HC.iIN cvcu:.sPIORSt;C()tm (b) Mechanics of Absorption fOI'example,thefigurethawsthatfiberboenbsuchas Ma11onite,andacousticaldiesuchas Acouati-celotexare much mOI'a absorptive at frequencies of 128 and 266 cycles whentheyarenailedtowoodstrips- and canvibrateas panels - than when they are or oth wise fasten-ed a rigid surface. fltaster on lath OY studs provides muchmoreabsOI'ptionatlowfrequenciesthandoestne same type of plaster applied directly to solid masonry walls. In general, the r&te at which a flexible p&nel absorbs acous-ticalanergyof vibration,to Itslternaldampingcoefficient. andto thefrictional losses at the edges of its mounting. Absorption by porous materials normaRy is large at high fre-quencies and smal at low frequencies.AbsOI'ption by panel vibt'ation is small at high frequencies but may be large at low frequencies. Both of these types of absorption are important Inthe control of sound In rooms. By using them in the proper proponlon.It is posslbfe to control the absorption ofsound throughout the al.ldible range of frequencies. This because a necessity In sound recording andradiostudios and isoften desirable elsewhere. We have already learned the definition of sound absorption of sound..inthe lastchapter andits relevance to room reverberationcharacteristics.Re-examining 'absorpti on asan acoustic phenomenom, we refer to the figure below so that we may understand the ap-plication of absorption mat erial.Referto the figure Ia) below hetvyCOf'lcretebarr ier a0.02 89 lal Actionof an Incomingsound wavestrikingaheavybarrier. Much of theenergyIsreflected. aomeiaabtorbed.andlittleis transmitted. ;:""Acousticabsorbent "material - ~ . ~... ~ :..:: :. lblActionof acousticabsorbent material alone.Verylittle energy Isreflected.someisabeorbed. and most Is transmitted. (c)Whenabsorbent Is appfied to the heavy wall,it "traps" sound preventingreflection.whilewall massactstoreducetransmis sion. Inanuntreated room of normal construction, when the sqund waves strij(e the Walls or ceiling. a small portion is absorbed andmost of the sound is reflected. The exact propor-tions abviously depends on the nature of construction. When acoustical figure (c) above, some of the energy. in the..sound waves is dissipated befQre the sound reaches the wall. The transmitted portion is slightly reduced but the reflection is greatly reduced. The dif-ferencebetween the two situations is shown graphically-inthisfigure (b} Intheuntreatedspace(a) reverberant(reflected)sound constitutes the greater portion of receivedsoundinmuchofthe room. these reflections are largely eliminated in lbl by walland ceil-Ingabsorption.Notethatdirect wave is completely unaffected. Referring to the figure below, the result of adding absorptive material to a room is shown ingreater detail . Distancefromr.ft. 101001000 (I Room30ftwide,10ftIOfl9.30fthigh Surfacearec 2 31,200sqft (1 a"10logc:,2+t0.5 R= ..!!.. . 1- Subjective Loudness Changesand Corresponding Intensity Level Changes Change inSubjective Change Level. Decibelsin loudness 3Barelyperceptible 6"Perceptible 7Clearly perceptible 10Twice or half as loud 20Four times or one-quarter as loud sh(the change encountered when distance to the souce in a free fields Is doubled (halved). 91 Medium Here,theresultofaddingabsorptive material toaroomisshowningreater detail. The difference between a room with averageabsorptionof 0. 1"andthesame room with 6/aof 0. 7is1 5db,whichisa reduction in loudness of approximately one and half times. See table We will no,vexamine the acoustic materials themselvesand the effect of varying type quantity, thickness,andinstallation methods. Absorptive Materials Therearethreefamiliesof devices for sound absorption-(a)Fibrous materials {b)Panelresonators tclandVolume resonators Alltypesabsorbsoundbychangingsoundenergyintoheatenergy.Onlyfibrous materials andpanelresonatorsareusedcommonly in buildings.Volume resonatorsare used principally as enclosures for absorbing a narrow bandof frequencies. The "FIBROUS" material or porous absorb the frictional drag produced by moving the air insmallspaceswithinthematerial.Theabsorptionprovidedbyaspecificmaterial depends on its thickness, density, and porosity and resistance to air flow.For example, materialsmustbethicktoabsorblowfrequencysoundeffectively.Sincetheaction depends on absorbing energy by "pumping" air through the material. the air paths must extend from one side to the other.A fibrous materialwith sealedpores is useless as an acousticabsorbent!Therefore,paintingwill generally ruinaporous absorber).Asimple test is to blow smokethrough the material. tfthe smoke passes through freely andthe material is porous,fibrous, andthick it should be a good sound absorbent. Porosity pro-videdit isabove70%,doesnot muchaffectabsorption.Belowthis figuresoundab-sorbency decreases asporosity decreases.The table in the next pages gives absorbent materials andfor building materials andfurnishings.Severalimportant conclusions can be drawn from examination of this table. (a)Forabsorbent materials, absorption is normally in higher at high frequencies thanat low. (b)Absorption is not always proportional to thickness,but depends on the type of materialbeing usedandthe method of installation.

90 to '10 ;17nc;ident "!.-:, Soull4 --._.Rtfloeeteoll Ill 1'4ottriol to....f-.:.-=-..... -'-i+-il_._I+-1 40501002005001 0001000soooFrequenevinHt '92 V11riation of absorption coefficient with thickness of feh absorbent.Note parti-cularlythltt. beyond1kHz.allthick-nessesgivethesamea,whereasat lowfrequenciesthe absorptionis pro portionaltothickness.Furthermoreit requires a very tt.avy layer to give ap preciable absorption at low frequency. NOTE: It is clear from this figure that beyond a nominal thickness except at very low frequency, or when installed discontinuousy, as in (c)below. (c)It is possible to obtain an agreater than1.0 by using very thick blocks.See "Fiber Blocks" in the table.These are installed at a distance from each other and the edge absorption is very large,particularly at high frequecies. (d)Installation methods have a pronounced effect. See Table on coefficients of absroption on chapter IX .Air-Borne NoiseTypes of Acoustical Materials Most commercially available acoustical materials are included in one of the three follow-ing catergories: ( 1 lPre-fabricated Units -These include acoustical tile, which is the principal type of materialavailablefor acoustical treatment;mechanicallyperforated units backedwith absorbent material; andcertainwall boards, tile boards andab-sorbent sheets. (2)Acoustical Plaster and Sprayed- Onmaterials.thesematerialscomprise plastic and porous materials applied with a trowel; and fibrous materials. com-binedwith binder agents,which areappliedwith(sprayedon)anair gun of blower. (3)Acoustical Blankets- Blankets are made up chiefly of mineral or wood wool, glassfibers,kapokbatts,andhairfelt.Thephysicalcharacteristicsofthe materials ineachof these catergor;eswillnow be considered. Prefabricated Acoustical Units Prefabricated acoustical materials have beensubclassified in order that similar products may be grouped together. Prefabricated units are separated into three types described in detail below. These groups include tile, absorbent material covered by mechanically per-foratedunits,andcertain building boards andsheets. Perhapsthemostoutstandingfeatureof anacousticaltileis its"built-in"absorptive value. The tile is a factory-made product; the absorptivity is relatively uniform from tile to tileof thesamekind.Thismakesiffoolproof,ahighlydesirablecharacteristics.The amount of absorption added to a room by acoustical tile therefore is quite independent of the skill, of the persons who install the material.Another merit possessedby acoustical tile is its relatively high absorptivity.Ina factory made product it is possible to control such factors as prorosity (including the number and size of pores), flexibility, density, and the punching of drilling of holes - factor which are paramount in determining the absorp-tivity of materials, and factors such which often are difficult to control in certain types of acousticalplasters.Inadditiontilecanbegivenstructuralanddecorativeproperties which usually arewell adapted to the requirementsfor artistic interiors.Because of its high absorptivity, acoustical tile is well adapted to rooms in which a relatively small sur-face is availablefor acoustiCal treatment. 93 Severalacousticalunits likeacousti-celotex,frbetetone.cushiontone,andsanacoustic tile,have the advantagethat they canbe decoratedwithoil-basepaint withouthaving theirhighabsorptivityimpaired.Thispropertyisduetothemechanicallymadeholes which permit the sound waves to reach the interior of the tile and be absorbed as a result of viscous forces inthe tiny pores of the material. The principal disadvantages of an acoustical tile its limitations for architectural treatment andits cost comparedwith that of other acoustical materials. It is impossible to conceal entirely the points between adjacent tiles, andfor this reason such treatments should be limited to rooms or surfaceswherea tile or ashl ar effect isnot objectionable. With types to tile is possible to secure the appearance of a cont inuous or monolithic surface by using tight unbeveled joints and by decorating an entire surface. But in rooms with low ceilings. or in other roomswith tile of the walls.theashlar effect is noticeable with any tYpe of decoration. Forthis reason, the edgeisfrequently beveledaroundthe tile to emphasize, rather than attempt to conceal, its masonry effect. The bevels also serve to "conceal" slight irregularities inthe fining of the tiles. Most types of acoustical tile on the market are relatively costly.In comparing the cost of acoustical tile with that of other types of acoustical treatment it should be borne in mind that the cost per square foot should not be consideredalone.Acoustical tiles often are two of three times more absorptive than acoustical plasters, and for this reason as much absorption may be attainedwith one square foot of tile aswith two or three square feet of plaster. TheU.S.FederalspecificationsSS-A-11 8- aclassifiesprefabricatedunitsintofour types. Thesetypes and the.irsubclassifications arelisted below,together with nameof oneormorerepresentativecommercialproducts.Thefigureshowsthesurfaceap-pearance of the different types of materials. "Type I.Cast Units havinga pined or granular- appearingsurface" "Class A.All- mineralunits composed of small granular of finely divided particles with portland cement bider." The masonry like surface appearance of the units makes them particular-ly suited for installation in buildings of the monumental types and in some churches. These tiles are rated as incombustible. Paints normally reduces their sound absorptive properties, but decoration is seldom required. The surfacesof materials inthis classarereasonablysmooth. .. TypeIA Tile,R.GuostovinoCo.) 94 "Oass B.All- nliia units composed of smallgranulesor finely divided parOdes. with lime or gypsum binder." Type1-8(Muffietone,St andard.C 1 1 l o t p ~Corp.) "ClassC.Unitscomposedofsmallgranulesorfinelydivi dedparticlesof mineral or vegetable originwith inco'mbustible mineral binder. Typ.,IC(Soflone,AmericanAcoustic,,Inc.) " TypeII.Unitshavingperforatedsurface;the perforations to bearrangedina regular pattern." " Class A. Units having a perforated surface which acts as a covering and sup-.portforthesoundabsorbentmaterialtobestronganddurableand substantially rigid." In this type of unit an absorptive pad, blanket, or rigid element (frequently consisting of compressedmineralwool)is covered by perforated sheet metal or board. The perforated covering does not reduce the absorption . to the areacovered.For example,the absorption coefficient of a btanket coveredwith perforated sheet steelwhich exposes only1 5percent of theabsorptivematerialmayhaveacoefficient,upto4000cycles, almost as high as ifthe cover+ngwere not there at alii This is due to dif-fraction,which is discussed in chapter 4. 96 Type II- Afabricated units canbe painted repeatedly without impairing their absorption, if reasonable care is taken not to fill or bridgethe holes with paint.If the holesare1/8 inchdiameter or longer,it is highly im-probable that they will ever become bridgedl;>ypainting.Sincethe per-foratedcoveringsoffergoodmechanicalprotectionfor theabsorptive material, the units can be installed in locations where they will besubject to considerable wear and tear. Most units of this class are incombustible. Manyaremoisture-resistantandhencefindapplicationinswimming pools,kitchens,etc.Someofferinterestingpossibilities forcombining acoustical construction with air conditioning and lighting control.For ex-ample, ther are metal pan units andspecial flush-type fluorecent lighting ficturesthat can be interchanged. - ------- - ------------- - -- ..- . -----TypeII-A ArmstronqCorkCoJ Other brands ACOUSTEEL ACOUSTIMETAL ARPHON PERF ATONE SANACOSTIC UNIT TRANSITEACOUSTICAL UNIT CELOTEX "CORP. NATIONAL GYPSUMCO. A. B.ARK I(Sweden) UNITED STATES GYPSUMCO. JOHNS- MANVILLE JOHNS- MANVILLE "Class B.Units having circular perforations extending into the sound absor-bent material." ... Prefabricatedunitsofthisclassusuallyhavelargeperforationsand therefore are especially serviceable in installations that require frequent redecoration.Laboratoryandfieldtests show that these tilesmaybe paintedrepeatedlywithoutnoticeablereductionoftheir . sound-absorptive properties. Thepresenceofholesinporousmaterials,asinacousticelotexor cushiontone has the effect of greatly increasingly the absorptivity of the material.The holes increase both the superficial areaand the effective porosityofthematerial.Theperforationscanbeusedtoconcealthe heads of nails or screws when used for attaching the units to wood fur-ring strips or wood decking. 96 .. ,. Type11-8(Acousti-Celotex ConeTile, CelotexCorp.) Otherbrands: ACOUSTI-CELOTEXMINERAL TILECelotex Corp. ACOUSTIFIBRENationalGypsum Co. cuSHIONTONEArmstrong Cork Co. FIBERTONEJohns- Manville PAXTILESNewalls-Co.,Lt d. (England) STENITPLATT AA. B.Arki(.Sweden) " Cl ass C.Units havi ng slots or grooves extending into the sound absorbent material .'' The action of the slots or grooves is similarto that ofthe holes in the tiles oft he preceding classif ication. -,. -I I I II Type11-C U.S.GypsumCo.) Other brand: TREETEX(Type ClTreetex,ltd.(Sweden& England) "TYPE Ill Units having a fissuredsurface." Thistype,includes tiles di fferingwidelyIn composition.Some consist largel y of f ilamentsor mineralwoolgranul es;i n others,vermiculite or cork is t he princi palingredient: The action of the f issures in causing ab-sorption of sound by t he unit s is very similar to t hatof t he perforations intypeII- B.Theset ileshavesurfacesthataresandedorplaned smooth. The may be painted without loss ofabsorption if the fi ssures are numerousandarenot filledwith paint . TypeIll(Corkou$lic,CorkCo.) Other brands: ACOUSTONE FISSURETONE TRAVERTONE UnitedStates Gypsum Co. Celotex Corp. Cork Co. "TYPE IV Units having a felted fiber surface." "Class A.Units composed of long wood fibers." Units of thisclass aremade of woodshavingsof excelsior,generally pressedtogetherwith a mineralbinder. The wood fibers may befine, medium or coarse. TypelVA(Absorb-A-Noise,Lufe...StevensonCoJ Other brands: ABSORB-ATONE L.W.lNSULATtONBOARD PORE X SONOFHERM Luse-stevenson Co. Brown andTawse,Ltd.(England) Porete Manufacturing Co. Sono- Therm Co. "Class B.Units composed of fine felted vegetable fiber or woodpulp." lncluded in this class are small tiles and also acoustical fiberboards.In general,thesematerialsarenot fireproof.Thefiberboardsprovidea means of obtaining absorption at relatively low cost. They are commen ly manufactured in large panels, K feet wide, and 8, 10, or 1 2 feet long. The use of fiberboards presents a difficulty in the matter of decoration and redecoration.Oil,lead,andother non-porous paints will close the surface pores of the materials and hence, destroy the absorptive valve. 98 Ontheother hand, 1hin dyesandstains,stencildesignswith heavier paint dusted on with apounce-bag can beusedwithout impairing the acousticalvalveof thematerial.Inspiteof theselimitations,certain acoustical fiberboards are useful for the control of noise and reverbera-tion in buildings. There f!re many school ahd industrial jobs, where cost is an important consideration, in which fiberboard& may be used to ad-vantage. TypetVB{Ec:onac:oustic,National GyptumCo.) Other brands: ACOUSTILITE FIBRACOUSTIC LLOYD BOARD NUWOOD BEVELLAP TILE lnsulite Co. Johns- Manville Lloyd boards,Ltd. (England) Wood Conversion Co. "Class C.Units comprised of mineral fibers." Type IV-C10-T Ductliner, Celotex Corp: I Type IV- C( Q-T Ductliner,Celotex, Corp.) Other brands: AIRACOUSTIC SHEETS FIBERGLASSACOUSTICAL TILE P.AXFELT 99 Johns - M a n v ~ l e Owens- Corning fiberglass Newalls Insulation Co., Ltd.(England .. Acoustical Plaster and Sprayed- onMaterials The use of selected types of acoustical plastic materials has proved highly satisfactory for the treatment of offices, school rooms, corridors, and many public building. They can be used inmost placeswhere ordinary lime or gypsum plaster can be used without ~ l t e r ing the architectural effects. Two coats of acoustical plaster may be aplied instead of the finishcoatin theordinaryplaster treatment foran addedlittle costpersquaremeter. Thesematerials have dificiencies in regardto cleaning anddecorating.Although these shortcomings are not seroius in localities where the air is relatively clean, They are an im-portant consideration where air is laden with smoke or dust. As plastic materialsare im-proved and as the correct manner of their a_pplication is more fully understood and prac-Ct:) =----- _J 117 LEC"I'UP.Eltfl0M Theyserve the samepurpose as do the front splays of the side walls. TheLAW of REFLECTION(angle of reflection equals angteof incidence) canbeusedto deter-mine the most propitious angle of inclination. Similarly, a splay between the ceiling and the rear wall can be designed to reinforce the sound in the rear of the room, and at the same time to prevent echoesfrom the rearwall. Concave surfaces such as domes, cylindrical arches, and barreled ceilings should be avoided wherever possible. If they are required by the architectural style, the radius of curvature should be either at least twice the ceiling height, or less than one-half the ceiling height. ceiling H 118 If coves, bey or oa-r smalt concave surfaces are employed, their radii of curvature shouktbe quite -.181comparedtotheceilingheight .Themostseriousdefects (sound foci or echoes) occur whenthe radiusof curvature of aceilingsurface is about equal to the ceiling height . ...1 ~ .... In order to avoid flutter echoes, a smooth ceiling should not be strictly parallel to the floor.If the floor and ceiling are both smooth, level and highly reflective, the flutter between the floor and ceilingwill be very prominent. 4.SIDEWALLS Splay Thesidewallsshouldreinforcethesoundthat reachest herearpartsofalarge room.Thisise!ipeciallydesirableforauditoriumsinwhichasound-amplification - asloping or beveled surface or angle asof the sideof a doorway, a spreading expansion, enlargement system is not utilized for allspoken and musical programs.The location of thewall is,of course determined principally by the general contour of the floor plans. The angle that any portion of the wallsurfaces,suchasasplaymakeswith the wall contour line should be such to reflect sound beneficially to those seats where the sound level isnot adequate.Thelawofreflectioncanbe usedtodeterminethisangle.Thesidewalls shouldbedesignedsothatthesoundsthey reflecttotheaudiencewillnotbetoolong delayed. Some parts of the side walls may be suspected of causing probable echoes or undu-ly delayed reflections; this may happen in very largeauditoriums. In such instances the supported surfaces should not be reflective. Instead they should either be made "acoustically rough"to diffuse the sound,or they should becoveredwith highly absorptive material.Examples of side walls based on good acoustical designing for different types of roomsare given in the chapter of Auditorium design. 5.REARWALL In the design of allrooms,large concave rear walls should be avoided. il{{(/111 \\\\\\\\\ 119 Unfortunately,theyareof commonoccurencebecauseit seemssosimpleand economical to most architects to have the rear wall follow the curvature of the last row of seats.Wallswith this shapeare responsiblefortroublesomeechoesand delayedreflectionsinmanytheatersandauditoriums.Thisisillustratedbelow whichis a longitudinalsection showing a vertical rearwall. Sound rays reflected from the ceiling near the rear wall at P are next reflectedfrom the rear wall at Q to seats in the vicinity of R; there results an echo at R if the path dif-ference at R exceeds 65 feet (about 20 meters).Sound rays striking the rear wall at Mare reflected to the ceiling at N, and then to 0at the back part of the stage. Often thesereflectionsfromconcaverearwallsarecon.centratedinregionsnearthe microphonesof thesound-amplificationsystem;then feedbacktroubleis induced. These detrimental reflections can be converted into beneficial ones by introducing a ceilingsplay between the ceiling and the rearwall,as shown in the sectionalfigure below. L,_.-----____ ""': __ _ 120 Here the rays SP' and SM' arereflected to the rear seats; thus I or 2db are added to the sound level in that area. Absorptive material on the rear wall eliminates the echo at R.Concavesurfacesincertainsituations canbemadeaseffectiveassplays,and theyaresometimesbetteradaptedthansplaystothegeneralappearanceofthe room.However,unlessproperlydesigned,theycanleadtofocusingeffects.In some designs, splays between the ceilingandside walls are useful in prevention of long-delayed reflections and in directing advantageous reflections to the audiences. If reflections from either a vertical or tiltedwall are capable producing echoes, the of-fendingsurface shouldbetreatedwith absorptive material.Therewill stillbesome reflectionfrom thissurface,but the soundlevelis thusreducedsogreatly that its detrimental effects are negligible. Insome large rooms, reflectionfrom a portion of the rearwall canbeutilized effec-tively by tilting thewall; .for example,see"balcony recess"below. Properrear wall design can increase the sound level in an auditorium .where the increase is most need-ed.Caution must be observed, however, to avoid the concentration of reflections in smallareas,especiallyfor excessive path- length differences between the direct andreflectedsoundsinroomswhere therearwallisrelativelyhighorwherethe seatingarearisesrapidly, it is not advisable to ti lt the entire rear wall , to do somight : reflectthe direct sound toward the front of the room so that echoes could be produc-ed. 6.BALCONYRECESS Gooddesign of a baicony recessusually requiresa shallow depthanda highopen-ings.For anauditorium or legitimate theater, the depth should not exceed twice the height of the opening. h This plan permits sound to flow readily into the space under the balcony. Good design also requires that the reverberation time in the balcony recess approximately that of the main part of the auditorium.(seereverberationin coupledspaces,chapter 5) By applying the above rules, it is possible to design the recess so that the sound level in this space is about the same as it is'in other equally distant parts of the auditorium. However, if the opening is low and the recess relatively deep, the sound level will be considerably lower in this area, especially at the rear of the recess. For example, if the depth is equal to four times the height of the balcony opening, the teve1 may be 8 db lower at the rear wall than it is at the opening. In large auditoriums and theaters, it is advisable to "break up" the '"rearwall in order to provide proper diffusionof sound throughout the balcony recess. A i8,jje unbroken concave rearwall always should be avoided,sin.ce it invariably .Qives ri5e to a nort-uniform distribution of sound. Trouble of this kind atso may arise from large' Wrticar surfacesof glass in front of the standee rail. 121 The balcony rail(front) should not be overlookedwhen the acoustical design of an auditoriums is being worked out. Since it is frequently a large, concave, surface hav-inga width that is large comparedto the shorter wavelengths of speech andmusic, thebalconyfrontcangiverisetoanechoor" s l ~ pback".Bytiltingthissurface downwardandmakingit convexit is sometimespossibletoutilizetheresulting reflections to increase the sound level at the rear of the auditorium. Otherwise , the front should be highly absorptive or should have a contour such that reflections from it willbediffusedandnot concentrated in smallareas. Thebalconysoffit andrearwallshouldbedesign9dso that alarge portionofthe soundcomingdirectlyfromthesourcewillbereflectedto theauditorsunder the balcony, and the remainder absorbed by the rear wall. An example of one such plan is showninfigure(a)below,whichis asectionof thebalconyrecess. of the philips theater in Eindhoven. Measurements made in a scale model indicate that this design leads to a distribution of sound on the floor of the auditorium that is fairly uniform: see figure (b)below. (b) If the time lag between the direct sound and the reflections from the rear wall is short, theauditorwillnot beawareof thedirectionfromwhichthesereflectedsounds come.Hewillhaveillusionthatallthesoundcomesdirectlyfromthestage,for auditory local izationispoor in the vertical direction.Furthermore, it is much more dif-ficult to discriminate between sounds coming from directly ahead or behind than bet-ween sounds coming from one side or the other. Hence, these reflected contributions may be utilized effectively. In contrast to the section of fig. (a) is t ~ esection shown in fig (b) . Here the rear wall reflectssound to the front part of the auditorium. 122 Volume Per Seat The most desirable volume for a room is closely correlated with the design of the ceiling. There is nofixedoptimum ratio betweenceilingheight andwidthandlength.Theop-timumheight,andthereforetheoptimumvolumeperseat,isdependent onboththe seating capacity of theroomandthepurposestheroomis to serve. The optimum volume per seat for a room is the lowest valueconsistent with the visual and aesthetic requirements,with the comfort of the audience, and with the generalap-pearance. Thus, although it is desirable to have a low value of volume per seat, it should not be attained by seating the auditors so close to each other that they do not have suffi-cientlegroomorbysacrificingotherfunctionalfeatures.Inmotionpicturetheaters seati ng1000 people, the optimum volume per seat may be as small as125; for theaters witha seating capacityof 2000, the volume not exceed about175 cu.ft .per seat.In music rooms seating more than 1500, a volume per seat of 200 cu. ft . has been found to give satisfactory results. There are many advantages in keeping the volume per seat at a low value.The building costisgreatlyreduced.Maintenancecostsforlighting,cleaning,redecorating,air-conditioning,etc.arecorrespondingly lowered.There are also important acoustical ad-vantages. Thu$, suppose that a given reverberation ti me is sought. Then, from reverbera-t ion time equation of the smaller volume of the room the fewer will be the units of absorp-tion 0.049v Sl-2.30 iog10t1- V2" AIR SFJ\CE 39db 1/4'rAIRSPACE 1/4" PLATESLASS The transmission loss of a DOOR increases with increased weight; the T.l. also increases withfrequency.Most doors of ordinary construction have an average transmission loss of 20 to25 db; some specially manufactured doors have T.L.'s ashigh as40 db.The generaltrendoftheT .L.frequencycharacteristicsfollowsapproximatelythatofthe corresponding curve for rigid partitions. The effectiveness of any door in providing sound insulation depends largely on the seal around the edges. For example, tests on one steel door showed that the placement of a rubber strip on the outer step of the jamb increased the T .l. 4 db. A force of 400 pounds on the panel made still better contact at the edges, and the T.L.was increa'sed another 4 db. The average T.l.'s for a number of different types of doorsgiven below: Doono solid 1 3/4", with cracks as ordinarily hung 256 cycles= 15 db 512 cycles= 20 db 1024 cycles=22 db 156 solid 1 3/ 4" welllseasoned and airtight 256 cycles= 18 db 512cycles= 21db 1 024 cycles= 26 db Wood,heavy,approximately2 Y2 "thick,rubbergasketsaroundsides and top; specialfelt strippushes down asdoor closes, eliminating any crack under door; 12.5 lb per sq.ft. 256 cycles= 30 db 512 cycles=29 db 1024 cycles=25 db Noise Insulation Requirements In Sweden requirements regardingsound insulation have beeninforce since1946. The Swedish regulations specify the minimum transmissionlosses againstair-borne sound for partitionsandfloor-ceilingconstructionsgivenbelow. AVERAGEMINIMUMINSULATIONREQUIREMENTSINDECIBELS Frequency. Range 100-500500-3000100-3000 Type of Roomcyclescyclescycles Hospitals445650 Dwelling rooms425448 School rooms364842 Work rooms344640 *Transmissionloss measuredin decibel$withsound-level meter incorporatinganappropriate frequency-weightingnetwork. Noise-insulationrequirementsforroomsandbuildingsshouldbecalculatedjustas routinelyasarereverberationrequirements;oftentheyaremuch more important.The nomogram in the figure below is anaid in the determination of the approximate minimum insulat ion requirements. Average noise conditions which may exist outside the. room are listed in the column at the left of the chart. The acceptable noise conditions are listed in the column to the right.Insulationneeds are estimated in the following way_ After an estimate or survey of the exterior noise conditions, the appropriate level on the scale to the left is selected. This point is connected by a straight line through a point on the scale to the rightwhichcorrespondsto thedesirednoiseconditions.Thenthepoint of in-tersection of this straight line with that of the center scale determines the approximate minimum insulationrequirement.The weight Unpounds per squarefoot of wall section) of a single rigid partition that will provide this insulation is indicated. 156 Inmanycases,itisadvisabl etout ilizeacompoundpartitionhavi ngantransmission loss. The use of this f igure will yield t he minimum average requirements f or insulation againstcondit ions of noise. This nomogramshould be regarded only as an aid in establishing an approximate lower limit ofthe amount of sound insulat ionrequired to meet specified conditions - not as the final means for determining the types of wall con-struction, doors, windows,etc., that will give sati sfactory sound insulation. .SCVlJRCI: f.Yf' NCll'e tloi:IYI'V.I'I OR CYc;n ; i : (t'AIRI..YCl.(),IS)l i UUi f'FlC t i M0 PERiO.T!! TRAFFIC. ; Tt i REE11112P LIINE3: 1\T3000 I'T; I i QUIET.:STREET' : OCC"'SI"'NI\L TR. III'F ICf Q\111!-T; SVBUR.DAN GARDENt RVSTt.e01" Ll !l iVBSI INOBNTI.I!l!llllti!I!'U! INSUI..I\TJONREQVIIti!O ""'"""' WeiGHTOF HOMOGENE'Otl3TYP!!C>F SiRUCTl!P-2,S T/tVCTllPfi 1..s n-RSQ r-r stliDV m: SL131!PII-IO S PECIAL

ftWRITING (DJXW TYPEWJ! JT tN"'\""'.,_,.... SVU() Minimumrequirementsfor the amplifier power-handling capacity inthe 11011-ndsystem of amotionpictue theater. 1 he amplifier ratmg is shown asa functi onof theseating capacity of the house.For ex ample, a theater seating1 000 should be equipped with an amplifier having a power out put of at least 20 watts lengths greater thanabout150feetshouldbeavoidedin order to prevent a noticeable delay in the arrival of the sound to persons in the rear of the theater.Itrequires about 1/7 second for sound to travel1 50 feet. The lack of synchronism between sight and sound becomesquiteannoyingwhenthedifferenceexceedsabout117second.Sincethe length .of.the theater may be as great as double the width, it is necessary to design the sidewalls,floor,andceilingsoasto minimize the attentionof the soundtransmitted toward the rear seats.Sound which is propagated over an abrsorptive surface,suchas anaudienceoranacousticallytreatedceiling,isgreatlyanenuated.Hencethefloor should rise steeply toward the rear, the loudspeakers and screen should be well elevated, and the ceiling and side walls shoukt neither be highly absorptive nor obstruct unduly the flowof soufld from front torear. Splays and other functional deviations in the walt and ceiling contours can be used to give the proper diffusion without hindering theeffi cient transmission of sound to the rearof the auditorium. 209 The motion picture research council recommends, for proper viewing and listening condi-tions,thatthefirstrowof seatsbeat least20 feet (6.00 m.)from the screen- for screenwidhtsnot greater than16 feet (4.80 m.).Forwider screens,the first rowof seats should be back an additional15 inches for each foot of screen width over 16 feet. SCREEN 6.00m. 20ft. ... ~:!'drl FiRST ROW OFSEA'TS SCREEN 1 ~feet +.eom. -EACH0.3Dm c . l ~ rrr..--------, ..,..., LLlJJJ 4-.som. 16feet ex. if the width of the screen is 20 feet or 4feet more than16 feet (6.00 or 1.20 more than 4.80 m.)add15 inches or (0.33 m.)for thefirst row of seat. SCREEN If thereis abalcony,its depthshouldnot bemore thanthreetimesthe height of the balcony opening. A relatively deeper overhang can be tolerated here than for a legitimate theater,since the average speech levels in a cinema are somewhat higher.The balcony soffitshouldslopedownwardtowardtherear,andshouldnotbeabsorptive.(See chapter 6onAcoustical Designof Rooms)for other features of design. A volume per seat of 1 25 to 1 50 cubic feet is a good figure to use in determining the op-timumvolume,thelowervaluebeingpreferable.Thedesignof ahousewithalow volumeperseathasseveraladvantagesoverdesignswiththevisuallargervalues, acoustically and otherwise. The bui\ding cost is reduced;the cost of the corresponding smallerair- conditioningequipmentand,toamuchlesserextent,ofthesound-amplificationsystem)arelikewise reduced;andthe optimumreverberationcanbeob-tained with the use of little or no special sound absorbents added to the walls and ceiling, if thick carpets are used on the aisles and heavily upholstered chairs are installed. The op-timumreverberationtimesformotion picturetheaterscanbedeterminedfromthese figures. 210 1.0 .--.. ------- -- -- ----- ..---- --- .. . . - - -- --1- .... ..----- .. ,. ..;r l;o- - - ..._. - .:/ . .-'

/ ,< .-,--+-1- - /m. . -- - -vW,4,;j

--4 { '...

:.r,/: I- --.PT. - :r-e'itS . :'l?//d/ V,/.. -.. . c :.,.:;;...;...-: --.f-"' --r .-- . - - -- - t- ---- --. ... t- .. - ----r--- -- --- I---,..-- - -z.o .J.l! o.c 0-610 w:to41)so 60ao100200300 oo.'iOO7001000 VOLUMCIll1 liOI.!SIINI>-'OPCU8lCF-eET Optimum reverberation time at 512cvoles for different tvpes of rooms as afunetion of room volume. ,... II:.. - ...- - - '---- ---- __ ..----gI.ZI--j// ////- f--- - 1--- - - 1----'l//.:7?7-,. t-----1-- - 1- 1-- -- +----1-- - ...- - --Aftercalculationof thetotalsquare-foot-units(Sabins}ofabsorptionsuppliedbythe upholsteredchairs,audience,carpeting,andthewallsandceiling,thetotalrequired number of sabins of absorption that must be addedis obtained by subractingfromt he totalnumberof requiredunitstheunitsofabsorptionfurnishedbychairs,audience, (assume a2/3 capacity audience), and allthe boundaries of the auditorium. Absorptive material should be appliedto the rear wall to eliminate "slap-back". Additional absorp-tivemay be appliedto the sidewalls in.accordance with the general princi ples andrecommendations _of Chapter 6. Treatment of the walls behind the screen with highly absorptive material prevents sound radiatedfrom the back of the loudspeakers from the being reflected to the audience. It atsosuppressesacousticalresonancesthatGCcuronsomestages.Mineral- wool blanketsbeen used in many theaters to treat this area. The surface of the backstage acoustical treatment should be very dark, preferable black, in order to avoid light reflec-tionfromit.As indicatedin Chapter5,theabsorptioncharacteristicsof anacoustical material can be enhanced, especially at low frequencies, by furring it out from the wall.If a blanket consisting of glass wool is used,it should be at_teast 2or 3inches thick and have a density of about 4pounds per cubic foot. The floor between the screenand the firstrowofseatsalsoshould behighlyabsorptive,. inordertoprevents'oundfrom reaching the audience in the front seats be reflection from this area. Such reflections con-tribute' to the loss of "inti.mac;.v";that is,the loss of fee\ingthat the soundis actually coming fron1 the screen. They be suppressed bythe stage floor with heavy carpetsover1-inch ozite or similar abs.orptive pad. 211 In many respect the acoustical problems of motion picture and legitimate theater are similar. Both should be properly insulated against noise according to the principles of Chapters 8 to 10.Ingeneral.aslightlygreaternoiselevelcanbetoleratedinmotiontheatersthanin legitimatetheatersbecauseofthehigherspeechlevel .Theaverage"film"(background! noise" level is about 35 db, whereas the average audience noise level in a cinema is about 40 to 45 db.Since the projection booth is a potential source of noise, all available interior sur-facesshouldbeheavilytreatedwith fireproofacousticalmaterial,suchasa 2- to 3-inch mineral-woolblanket covered with perforatedtransite.Doublepanes of glassof different shouldfit tightlyintheir framessothat thereareno thresholde1acks.It alsoishelpful to cover with absorptive material the peripheral surfaces separatmg the double windows.The wall between the projection room and the auditorium should have a tn!lnsmission loss of not less than 35 db at 128cycles and not less than 45 db512to 2048 cycles. School Auditoriums The school auditorium usually serves a wide range of functions. It Is used asan assembly room,largeclassroom,theater,cinema,concerthall,communityauditorium,andit houses a host of other activities.Theelements of design given in Chapter 6, regarding shape,size,reverberation,and diffusion, are applicable here. Furthermore, the principles andpracti ceofnoisecontrolasdescribedinChapter8to1 0shouldbefollowed scrupulously. Inregard to theatrical uses,most school administrator and instructors of drama expect the impossiblewhen they produce stage plays in a large auditorium without the benefit of ahigh-qualitysound-amplificationsystem.Auditoriumswhichareto beusedwithout sound-amplication, evenifonly occasionally, shouldnot have volumes in excessofthe following: For elementary schools, about 40,000 cubic feet; For highschools,about 50,000 cubicfeet; For colleges anduniversities about so.ooocubic feet; (These volume include the volume of the recess under the balcony but not the volume of the stage recess.) A great deal of dissatisfaction will be eliminated .bYavoiding the design of largerauditoriumsforschools.If for anyreasonit shoutdbecomenecessary to con-struct.alarger auditorium,provisionshouldbemadeforsoundreinforcementfor speakerswithweakvoices,foroccasionalmusicalprograms.Nothinglessthana stereophonicsoundsystemwillbeentirelysatisfactoryfortheatricalpurposes(see Chapter7). ... The auditorium shouldbel()catedin aquiet sectionof the campus.If it forms a part of another building, . itshould bethoroughly insulatedfromtheremainderof thebuilding. ihere should be two sets of tightly fitting doors betwe.en the auditorium and the corridorsor theoutdoors.If a highdegreeof insulationis required,it will behelpfulto dispense with windows. With the increase in airplane traffic,it has.become increasingly necessary to eliminate windows; with. the good air-conditioning systems avai(able,th.ey are no longer a necessity. Any noise from the ventilating or other mechanical equipment shouldbeadequatelysup'pressed.The floorshouldbecovered with linoleumorsome 212 other soft covering. The chairs should be heavily upholstered,of a rigid,substantial con struction,' andsecurely fastened to the floor so that there will be no creaking or squeak ing.: It is necessary to makea compromisebetweentheoptimumacousticalpropertiesfor speechandfor music in Orderthat the. the schoolauditoriummay best serveits diverse tiSes.Theexacfcalculationof reverberationinvolvesa three-spaceproblem:thestage recess; the main part of the auditorium,and the recessunder the balcony.However,if the stage has an enclosed set and if the balcony recess is not tt>o deep, the calculation of reverberation time reduces to a one-space problem. In order to make this simplification, it is assumed that each of these three spaces contains an appropriate amount of absorption topermitauniformaveragerateofgrowthordecayofsoundinallpartsofthe auditorium.Thecompletesetof hangingsrequiredforthestageseningordinarilywill supply a sufficient amount of absorption for the stage recess.In fact, a full set of stage hangings may make the stage too dead for musical settings. For this reason it is advisable to provide an enclosed wood veneer or heavily painted canvas set for musical programs, suchas' shownbythedottedlinesinthepreviousfigure,longitudinalsectionofa legitimatetheater.If upholsteredchairsareprovidedandtheaislesofthefloorare carpeted,therecessunder the balconyordinarilywillnot requireadditionalabsorptive treatment of its side wallsjn the strips, panels, or patches. to give added diffusion; ifnone is requited,it may benecessar'y to introduce splays,Of other means of insuringproper difussion. An example of good side wall design is shown inthis fiQure. 213 Thefigurebelowshowsasectionof ahighschoolauditoriumthat incorporatesthe essential characteristicsof goodacoustical design.Thefollowingfeatureswere given carefulconsideration during the design and construction of the auditorium the floor pl an, the elevation of seats, the diverging proscenium splays, the functional ceiling, the shape and dimensions of the balcoriy recess, the control of reverberation and diffusion by alter-natehorizontalstripsof absorptivetileandreflectiveplasterforthesidewalls,the upholstery of the chairs, the_stage furnishings (including an enclosed reflective stage set for musical programs), the planned insulation against outside noise, the control of inside noise, and the sound-amplification system. 31. 5 Scale:3/16= 1'0" I I I ,, II 111 II 6a 6b 1.Acoustically treated pfojection booth with sound-amplificatiO{l equipment and controls for sound monitoring. 2.Ceiling planes reflect sound to.allparts of the auditorium. 3.Three-channelpublic address systemto reproducestage sound in "auditory perspec-tive." 4.High-fidelity bass-compensateddynamicspeakerforlowtones;high-frequency dtrectional'homs for high tones. 5.Backstage treated with acoustical plaster to reduce "stage echoes." 6.Acoustical treatment on walls; over-all distribution in alternate bands of {a)acoustic tile and(b)hardwall plaster. 7.Proscenium splays;horn-like shape of stage opening projects sound to audience. 8.Upholsteredseats;absorptionvalueofeachseatequivalenttothatofa person's clothing. 9.Double doorsto foyerinsulate against external noises. 10.Slantingrear walls on main floor and balcony reflect sound down toward rear seats. 11 .Acousticalty treated foyer to reduce external noises. 12.Streamlined balcony improves flow of sound to rear seats. Manyschoolauditoriums,especiallyinsmalltownS, 8reusedfor communityof light in the wave spectrum with relation to other wave phenomena of various frequencies. 214 CivicAuditoriums Many schools auditoriums, especially in smallare used for community purposes-town meetings.debates,concerts,andavarietyofothergatherings.But asatown grows to a city. there develops a need for a separate civic auditorium to serve the above purposes and anumber of others such asdances,bazaars,conventions, andactivities that require (1) a level hardwood floor and (2) readily removable chairs. The present sec-tion is concernedwith the latter type of auditorium. The two features just mentioned in-troduceacousti calproblemsthatdo not occurin theusualauditorium. Thelevelfloor, especially if it ext ends more than about 1 5. 50 meters (50 ft) from the stage, requires t he stage to be as high lineswill allow. The portable chairs generally will not be upholstered, or they will have only thin pads of soft andabsorptive material on the seat s andbacks. Thesechairsfurnishmuchlessabsorptionthandofullyupholsteredones(thefixed chairs should be heavily upholstered, of the type previously advocated in this chapter for theaters and school auditoriums.). It usually will be necessary to compensate for the lack of absorption in the chairs by the introduction of absorptive strips, panels, or patches on the walls and ceiling in such amounts as will provide the optimum reverberation and good diffusion. The optimum reverberation characteristics will be provided in most cases asif the curve whichappliestoschool auditoriumsin this figureisu-sed. l.t,.---.,--.--,--,--,-,..,.,---.--r--,--r--r-r-r"'T'"I .t.ot---+--+---+-+-t--H-t-l,...---- +--4--t--!--t--61..-lrl -b-: t.6Z'/"//// 'l' /h // Z1'7 V: :""1'77'/ /h 'LU' I h'/ 111 -u.7Ill!'/."')\Ot'lotlptcTV 1.0...... -0.0 Since civic auditoriums are often used for smallaudiencesand since the chairs areoften upholstered, it is advisable to provide the optimum reverberation for one half of capacity audience.Ifaroomhasavolumeofmorethanabout50,000 cubicfeet,asound-amplification system is necessary. The loudspeakers should be located somewhat higher than they would be in anauditorium with a sloping floor. All the acoustical problems consideredin the previous sections of this chapter,namely those relating to theaters, cinemas, and school auditoriums, are likely to arise in planning the acoustics of civic auditoriums, and it is recommendedthat these sections be careful-ly reviewed.The acousticalproblems relatingto thedesignof amunicipalauditorium become increasingly complex and difficult as theof the auditorium increases. Echoes andinterfering reflections beconte much more probable,and therefore appropriate plans should be worked out at the very start of the design to avoid these defects and to insure a good distribution of soundto seats. Acoustical studiesshouldbe made ofallfeasible shapes and arrangements supplemented by model testing, if there are anyuncertainties determining the best plans. 215 Existingmunicipalauditoriumsarenotoriouslydefectiveinregardtoacoustics .. Until recently,mostofthemwere excessivelyreverberant.Many ofthese havebeen''cor-rected" by "acoustical treatments", that is, by adding acoustical tile or plaster to the en-tireceilingortoalmostevery availablesurfacethat canbeso. treated. TNs hasgiven quite satisfactoryresultsin manycases.However,in some instances,the auditoriums havebeenovertreated,or mistreatedbyplacing the absorptivemateriali(lthewrong places.and the correction of &ther serious defects has been overlooked. F& example,a study was made of a municipal auditorium seating1,800 persons.At the time of-construction, acoustical plaster was applied to all side walls rear walls was treated with a thin acoustical tile,and the entire ceiling was treatedwith thin fib.erboard applied directly to concreteceiling slabs.Thestage was furnishedwith overhead,sideandrear hangingsof unlined velours.Asaresultthe auditoriumwassomewhat overtreatedat medium and high frequencies.Complaints were made about the acoustics, most of them by the artists who sang or playedsolo instruments in this audit9rium. They averred that theirvoiceswere "smoothered". that they feelunable to "project"sound out into the audience. The management, heeding: these complaints, addedstillmore absorptive treatment- a burplap type of material festooned between the exposed trusses- and made the situa-tion worse.Instead, the following correctives should have beensupplied: , .Astage settingofinchplywoodwith overheadandsidesplays. 2.A suspended ceiling designed in accordance with the principle of chapter 6. To glve benefictal reflections and made of a material that would add considerable absorption at the high frequencies. 3.of the thin absorptive tile on the rearwall with a material that is highly absorptive .ttt low as well as high frequencies. 4.Ahigh quality sound amplification system, Thesecorrectiveswouldnot pro-yjde' idealacousticsinthisauditoriumbut they . wooldeliminatetheobjec-tionable defectsand make the buildingquitesatisfactory for its many func-tions. : .. 216 - . .. .. ....... ... ...~.......; ...... ....~. PHYSICS OF LIGHT LIGHT ASRADIANT ENERGY Light is "visually evaluated radiant energy" or more simply, a form of energy which per-mits us to see.If light is considered as a wave, similar to a radio wave or an alternating current wave, it has a frequency and a wave length. The figure below shows the position of light in the wave spectrum with relation to other wave phenomena of various frequencies. ' I IIIII I I i ! IFMTV Gamma !:2 Radio Cosmic rays ; X rays; > Radar Sound I ray5 ' i Short '' ;:Iwave ' IIIII \10110121010 108 106 1o10060 \Frequency in hertz(cycles per second) \ \ \ \ '- ........................ _ 1/rsiblelight-, "'arometers (10-9meters)'', 50:EOO700'800, ' VaoletRed BlaticLt.=-di:Olrr:rared Orange:-!eaters From the chart we see that even the longest wavelength light (red) is a much higher fre-quency than radio and radar, and that visible light comprises only a very small part of the wave energy spectrum. Yet it is this energy that makes possible our sight and with which wearehereconcerned.Colorisdeterminedbywavelength.Startingat thelongest wavelengths with red, we proceed through the spectrum of orange, yellow, green, blue, indigo,and violet to arriveat the shortest visiblewavelengths (highest frequency) When a light source produces energy over the entire Visible speCtruminapproximately equal quantities, the combination ofas is the case with the sun, whereas a source producing energy over only a "SmallseCtion of the spectrum pro-duces its characteristics colored light. Examplesare the blu&-greenclear mercury lamp andthe yellow sodium lamp. ' ; . . . .--::.. .. '.( 218 Fundamental &..a.l8 .of Light 'of lighting is possible because light is predictable, that is, it follows certaintaws andexhibitscertainfixedcharacteristics.Althoughsome of these areso well known asto appear self-evident,a review is in order. The luminoustransmittanceof amaterialsuchasafixture or diffuser is ameasure of its capabilitytotransmitincidentlight.Bydefinition,thisquantityknownvariouslyas transmittance,transmissionfactor,or coefficient of transmissionis theratioof the total emittedlightto the totalincident light.In the caseof incident lightcontainingseveral componentspassingthroughamaterialthat displaysselectiveabsorption,this factor becomesanaverageoftheindividualtransmittancesforthevariouscomponentsand mustbeusedcautiously.Apieceoffrostedglassandapieceofredglassmayboth havea70%transmissionfactorbut obviouslyaffecttheincidentlightdifferently.In generalthen,transmissionfactorsshouldbeusedonlywhenreferringtomaterials displayingnonselectiveabsorption.Clearglass,forinstance,displaysatransmittance between 80 and 90%,frostedglassbetween 70 and85%, and solidopalglassbetween 15 and 40%. Similarly,theratio of reflectedto incident light is variouslycalledreflectance,reflectance factor,andreflectancecoefficient.Thusif half of the amount of thelight incident ona surfaceisbouncedback,thereflectanceis50%or0.50.Theremainderisabsorbed, transmittedor both.The amount of absorption andreflectiondependson the type of the material and the angle of light incidence, since light impinging upon a surface at small (graz-ing)tends to bereflectedrather thanabsorbedor transmitted. c: .! 1: a.. 100 90 III , T !_Effect of anile of ineiden on the percent of light reflected 80 70 fiO 50 40 30 20 10 ,_ by clear plate glass I

Ill J1 Gtass I I/"II One surface of &lass- Bothof g!HS- ! ; !/ / ! ........... 0 -, .. 0102030..40506070.SO9() Angle of incidence,fromthe normal 219 Anexampleof almostperfect reflectionfromanopaquesurfacewould. bethat i roma well-silvered mirrorwhile almost complete absorption t akesplace on an object covered . with lamp black or matte finish black paint. The effect of the material finish on reflec