Services Acoustics

8/8/2019 Services Acoustics

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Akash Raju 1rv06at006

Vikrant chandragiri 1rv06at068

ACOUSTICAL ANALYSIS, MATERIAL STUDYACOUSTICAL ANALYSIS, MATERIAL STUDY

M L R C O N V E N T I O N C E N T R E

B R I G A D E M I L L E N N I U M ,

B A N G A L O R E .


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M L R C O N V E N T I O N C E N T E R

I N T R O D U C T I O N


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A c o u s t i c a l M a t e r i a l s


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I N T R O D U T I O N T O



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ARCHITECTURAL PLANNING


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DETAILS


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ACOUSTIC ANALYSIS


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We feel specially thankAr. Vi al,Wh help get all the inf r ati n

Of MLR c nventi n center.

We thank r teacherPr fess r O.P Bawane

All wing s t d an exciting pr ject like this.

The pr ject was very inf r ative, and will helpUs in all perspectives f r r exa inati ns.

INFORMATION COURTESY: PARADIGM ARCHITECTURE(Principal Architects)


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There should be adequate loudness in every part of the auditorium, especially in remote seats.

The sound energy should be uniformly distributed within the room.

Optimum reverberation characteristics should be provided in the auditorium to facilitate whateverfunction is required.

The room should be free from acoustical defects (distinct echoes , flutter echoes, picket fenceecho, sound shadowing, room resonance, sound concentrations and excessive reverberation).

Background noise and vibration should be sufficiently excluded in order not to interfere in any waywith the function of the enclosure.

In order to provide a high degree of sound diffusion within in an enclosure an abundant supply ofsurface irregularities, such as exposed structural elements, coffered ceilings , serratedenclosures, protruding boxes, sculptured surface decorations, and deep window reveals must be provided.These must also be of various sizes in order to affect all frequencies.For reasons of economy and aesthetics, particularly in small rooms, the application of surfaceirregularities is often difficult. In such cases a random distribution of absorbing material of the

alternate application of reflective-absorptive materials provide an alternate, though less effective means .The use of dedicated diffusers is particular ly important in concert halls , opera houses , radio/recordingstudios and rehearsal rooms. The beneficial effect of acoustic diffusers upon the sound quality ofauditoria is often quite marked as they retain the sound energy within the room whilst negating echoand standing wave effects.


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The auditorium should be shaped so that the audience is as close to the sound source as possible.In larger auditoria the use of a balcony brings more seats closer to the sound source.

The sound source should be raised as much as is feasible in order to secure a free flow of directsound to every listener.

The floor on which the audience sits should be properly raked as sound is more readily absorbedwhen it travels at grazing incidence over the audience. As a general rule, however, the gradient alongaisles of sloped auditoria should not be more than 1:8 in the interests of safety. The audience floor oftheatres for live performance, especially open or arena stages should be stepped.

The sound source should be closely and abundantly surrounded by large sound-reflective surfaces in order to increase the soundenergy received by the audience. It must be remembered that the dimensions of the reflecting surfaces must be comparable with

the sound waves to be reflected. In addition, the reflectors should be positioned in such a way that the time-delay between thedirect and reflected sound is as short as possible, preferably not exceeding 30 msec and definitely not more that 80 msec.

The floor area and volume of the auditorium should be kept at a reasonable minimum, thus shortening the sound paths.

Type of Auditorium Minimum Optimum Maximum

Rooms for Speech 2.3 3.1 4.3

Concert Halls 6.2 7.8 10.8

Opera Houses 4.5 5.7 7.4

Catholic Churches 5.7 8.5 12.0

Other Churches 5.1 7.2 9.1

Multipurpose Halls 5.1 7.1 8.5

Cinemas 2.8 3.5 5.6

Recommended Volume-Per-Seat Value for Auditoria


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All orators, actors, musicians and especially singers, will expect a reasonable reverberation time so they donot sound too stark or dry. The optimum reverberation times of a room implies the following:

Favourable RT vs frequency characteristics.

An advantageous ratio of reflected to direct sound reaching the audience and

A steady, smooth growth and decay of sound energy.Once the RT has been decided upon, reverberation control consists of establishing the total roomabsorption and ensuring it is adequately provided for. This means selecting the correct acoustical finishesfor room surfaces as well as considering the effects of occupation and fittings. To calculate this at theearliest stages of design the Sabine formula is usually used.

A look at this formula clearly shows that the larger the room, the longer the reverberation time and the greater the absorptionrequired. Thus, the RT can be changed within the same auditorium by enlarging or reducing it's volume (eg: raising or lowering theceiling, using more balconies, etc).

Since the absorption of materials varies with frequency, so to will the RT. It is therefore essential to specify and calculate the RT fora number of frequencies throughout the audible range. It is often the case that the RT at low frequencies is most troublesome as thisis the area at which porous absorbers are least effective. Thus, panel absorbers and bass traps may have to be considered.

In almost every large auditorium, the audience provides most of the absorption (0.45 Sabine per person). If you rely upon this andthe attendance rates sometimes vary, then the listening conditions may suffer. The most effective (and most expensive) compensation

for low attendance is to use upholstered seating with the same overall absorption coefficient as a single person. Some auditoria useabsorber on the bottom of fold-up seating. Thus, when occupied, the absorption effect is reduced as it faces the floor whilstunoccupied if is folded up and faces the stage.

As a general rule, sound-absorbing materials should be placed on those surfaces most likely to produce acoustic defects.


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The basic defects attributable to room geometry have been touched in a previous lecture and consist ofechoes, sound concentrations, sound shadowing, distortions, coupled spaces and room resonance.

1. EchoesThese are probably the most serious and most common defect. They occur when sound is

reflected off a boundary with sufficient magnitude and delay to be perceived as another sound, distinctfrom the direct sound. As a rule, if the delay is greater than 1/25 sec (14m) for speech and 1/12 sec(34m) for music then that reflection will be a problem.

Solution: Either alter the geometry of the offending surface or apply absorber or diffusion.

2. Sound concentrationSometime referred to as 'hot-spots', these are caused by focussed reflections off concave surfaces. The intensity of

the sound at the focus point is unnaturally high and always occurs at the expense of other listening areas.Solution: Treat with absorber or diffusers, better still, redesign

3. Sound shadowingMost noticeable under a balcony, it is basically the situation where a significant por tion of the reflected sound is

blocked by a protrusion that itself doesn't contribute to the reflected component. In general, avoid balconies with a depthexceeding twice their height as they will cause problems for the rear-most seats beneath them.

Solution: Redesign the protruding surface to provide reflected sound to the affected seats or get rid of theprotrusion.

4. DistortionsThese occur as a result of wildly varying absorption coefficients at different frequencies. This applies an undesirable

change in the quality and tone colouration (of frequency distortions) to sound within the enclosure.Solution: Balance the absorption coefficients of acoustical finishes over the whole audible range.


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5. Coupled spacesWhen an auditorium is connected to an adjacent space which has a substantially different

RT, the two rooms will form a coupled space. As long as the airflow is unrestricted between the twospaces, the decay of the most reverberant space will be noticeable within the least reverberant. This will be

particularly disturbing to those closest to the interconnection.Solution: Add some form of acoustic separation (a screen or a door) or match the RT of

both rooms.

6. Room resonanceRoom resonance is similar to distortions in that it causes an undesirable tone colouration, however, room resonance

results from particularly emphasised standing waves, usually within smaller rooms. This is a significant concern when designing

control rooms and recording studios.Solution: Apply subtle changes in overall shape of the room or find out which surfaces are contributing and use largesound diffusers.

SpeechThe acoustics of a space designed for speech must primarily ensure definition andintelligibility, remembering, of course, that understanding in the speech communication processdepends as much upon gesture and facial movements as it does on vocal projection.The audience's expectations regarding the actual quality of the speech signal is not too critical, aslong as the speaker's voice and accent are recognisable and the vocal information is understandable.

MusicMusic audiences, on the other hand, have inherited quite a developed expectation of particular sound qualities for various stylesand eras of music.Whilst definition is a prerequisite for speech, excessive clarity in music gives the subjective impression of brittleness or dryness. In

addition, it accentuates unwanted bowing or fret noise, making the musicians job even more difficult.

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