Acoustical design of spacesUNIT VACOUSTICS AND BUILDING DESIGN 8Site selection, shape, volume, treatment for interior surfaces, basic principles in designing open air theatres, cinemas, broadcasting studios, concert halls, class rooms, lecture halls, schools, residences. Call Centers, Office building and sound reinforcement systems for building types.

Requirements Adequate amt of sound to reach all parts of the roomEven distribution Unwanted noise to be masked to achieve required levelOptimum reverberation time

Acoustical defects to be avoided:Long delayed echoesFlutter echoesSound shadowsDistortion Sound concentrations

Behavior of soundLong delayed echoesIn large halls no strong reflections are received by audience after about 50msAverage speech rate -15- 20 syllables per sec or roughly 1 syllable every 70 ms to 50 ms respectively- corresponds to a delay of about 17mA member sitting at a distance 8.5 m away from a good reflecting rear wall will find difficulty to understand speechAuditorium side walls and ceiling convex to diffuse or absorbent materialCorners acoustic plaster or absorbent materialsBetter to use minimum amt of absorbent material to have minimum volume for a given number of people

Flutter echoesRapid succession of noticeable echoesCan be avoided by making sure that sound source is not between parallel reflecting surfacesAvoid parallel walls and ceiling and floor

Shape of hallRectangular Fan shaped Horse shoe shapedBelow 1000 seat capacity, shape does not matterAs size increases , fan shape becomes preferable because audience is seated closer to the stageRear wall should not be concaveSide walls to be broken up with large diffusing surfaces or absorbent materials

Opera housesHorse shoe shaped mostlyConcave surfaces broken by boxes in tiersAudience absorptionIn opera , clarity is more important than fullness of tone

Seating arrangementsRow of people incident to sound are absorberAdequate vision adequate sound pathLine of sight needs to be raised by 80-100mm for each successive row

Auditoriums Speech, intelligibility first preferenceTheatres, lecture halls, classrooms listening conditions should be good Speech vowels and consonants Vowels formants persons voice, basis tone of speech, natural qualities of speechConsonants intelligibility- high frequency in rapid succession- limited acoustical power

Auditoriums Paths of direct sound waves as short as possibleCompact room shape voulme per seat- 2.3 to 4.3 cu.mLower the volume per seat, lower the acoustic treatment to achieve RTUnamplified speech sound travelling directly from source to listener is hardly understandable beyond 9 to 12 mSo, short delayed reflections from reflective surfaces arrive at listeners position with a path difference of not more than 9 to 10.5 m corresponding to a time delay gap of about 30 ms

Auditorium The speakers should produce a sound level at about 65 dB,A everywhere in the seating area.It should have at least 20 dB of head room so that short lived bursts of sound up to 85 dB,A can be replicated without any hint of speaker or electronic distortion.The natural noise floor of the hall itself should be at least 20 to 30 dB quieter than the speaker level heardA bright and clear sounding auditorium will be providing something like 30 separate early reflections, each arriving well within the first 1/40th second following the initial impact of the direct signal

a) Direct signals leave the speakers and impact the audience.b) Indirect signals are those that bounce off nearby surfaces into the audience.

a) Diffuse late reflections to raise reverberation level.Absorb late reflections to reduce reverberation level.b) Reverberation is residual sound that has lost all sense of direction.

Acoustical shells used to enhance acoustics in stagehouse and audience chamber.

Acoustical clouds and panels used to support acoustics in audience chamber.

Ceiling height that provides sufficient cubic volume for desired reverberance.

Side walls shaped to reflect sound toward side of audience.

Incorporate ways to vary strength and reverberance onstage and in audiencechamber (such as adjustable absorption and coupled volumes).

Quiet so intruding noise does not interfere with performances.

Enclosing constructions that isolate unwanted sound of adjacent spaces and outdoors.

HVAC systems serving auditorium do not produce disruptive noise.

Auditoriums Seating Within an angle of about 140 deg from the position of the speaker- to preserve high frequency speech sounds, which would lose power because of their directional characteristicsRT ideal value through out the entire audio frequency rangeAcoustical finished should have uniform absorption characteristics between 250 and 8000 Hz to preventive excessive absorption of vowel or consonant sounds within this frequency rangeAt frequencies 125-4000 Hz , ration of the level of the speech to that of the background or ambient noise , the intelligibility is seriously affected- if the ratio is large , intelligibility improves

Lecture halls and class roomsConsiderations for speech intelligibilityLecture halls, one half to two third capacity- having absentees into considerationSeldom designed with natural light and ventilation into considerationMechanical and lighting- false ceilingVolume of 425 to 570 cum or audience upto 200 persons will not require sound amplification systemFor rectangular rooms, diagonal seating layout is preferred- it eliminates undesirable parallelism between walls and podium and utilizes splayed front walls as sound reflectors

Classrooms 56- 93 sqm no acoustical problemsRear wall doesnt create acoustic defect because length of the classroom is small and usually bulletin borads, display and cupboards diffuse incident soundProjectors, sound recording, producing units , desk, loudspeakers- have to be considered

Assembly halls