Auditorium Design Guidelines

Auditorium design guidelines

“The design of various types of

auditoriums (theatres, lecture halls,

churches, concert halls, opera houses,

and cinemas) has become a complex

problem in contemporary architectural

practice because, in addition to

aesthetic, functional, technical, artistic

and economical requirements, an

auditorium often has to accommodate

Requirements for Good Acoustics

The following points are fundamental to the provision of good acoustics within a modern auditorium

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 whatever function is required.

The room should be free from acoustical defects (distinct echoes, flutter echoes, picket fence echo, sound shadowing, room resonance, sound concentrations and excessive

reverberation).

Background noise and vibration should be sufficiently excluded in order not to interfere in any way with the function of the

Guidelines for adequate loudness

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 direct sound to every listener.

Guidelines for adequate loudness

As a general rule, however, the gradient along

aisles of sloped auditoria should not be more than 1:8 in the interests of safety.

In addition, the reflectors should be positioned in such a way that the time-delay

between the direct and reflected

sound is as short as possible,

preferably not

exceeding 30 msec and definitely not more than 80

Recommended Volume-per-Seat

Values (m³) for Auditoria.

TYPE OF AUDITORIUM min opt max for Speech 2.3m³ 3.1m³ 4.3m³ Concert Halls 6.2m³ 7.8m³ 10.8m³ Opera Houses 4.5m³ 5.7m³ 7.4m³ Catholic Churches 5.7m³ 8.5m³ 12.0m³ Other Churches 5.1m³ 7.2m³ 9.1m³ Multipurpose Halls 5.1m³ 7.1m³ 8.5m³ Cinemas 2.8m³ 3.5m³ 5.6m³

Diffusion of Sound

In order to provide a high degree of sound diffusion within in an enclosure an abundant supply of surface irregularities, such as

exposed structural elements, offered

in small rooms, the application of surface irregularities 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. ceilings, serrated enclosures, protruding boxes, sculptured surface decorations, and deep window reveals must be provided.

Control of Reverberation

RT = (0.161V)/A where:

V = the volume of the enclosure (m³) and

A = the total absorption within the enclosure (Sabine).

A look at this formula clearly shows that the larger the room, the longer the reverberation time and the greater the absorption

required. Thus, the RT can be changed within the same auditorium by enlarging or reducing it's volume (ex: raising or lowering the ceiling, using more balconies, etc). It is often the case that the RT at low frequencies is most troublesome as this is the area at which porous absorbers are least effective. Thus, panel absorbers and bass traps may have to be considered.

Control of Reverberation

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 use absorber on the bottom of fold-up seating.

when occupied, the absorption effect is reduced as it faces the floor whilst unoccupied if is folded up and faces the stage.

Better Placement of Reflectors:

The basic concern is the

availability of direct sound

to all the audience at the

same time. To maintain

this reflectors are best

used.

Also to correctly placing

these will enhance the

indirect rays to reach the

public at the earliest.

Elimination of Defects

The basic defects attributable to room

geometry:

echoes

sound concentrations,

sound shadowing,

distortions,

coupled spaces and

room resonance.

SOUND CONCENTRATON

Sometime referred to as 'hot-spots', these are

caused by focused 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 it to focus the sound outside or

ECHOES

These 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, distinct from 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.

SOUND SHADOWING

Most noticeable under a balcony, it is basically the situation where a significant portion of the reflected sound is blocked by a protrusion that itself doesn't contribute to the reflected

component. In general, avoid balconies with a depth exceeding twice their height as they will cause problems for the rearmost seats beneath them.

Solution:

Redesign the protruding surface to provide reflected sound to the affected seats or get rid of the protrusion.

Coupled Spaces

When 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 two spaces, 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

ROOM RESONANCE

Room resonance is similar to distortions in

that it causes an undesirable tone

colouration, however, room resonance results

from particularly emphasized 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

ELECTRO ACOUSTICS

System Specifications

Any such sound amplification system is expected to meet the following criteria:

It should properly transmit a wide range of frequencies (30 - 12000 Hz) in order to maintain the correct

balance between fundamentals and harmonic frequencies.

It should possess a high dynamic range, reproducing sounds from a whisper to a shout without distortion. It should remain undetected. The illusion of a natural sound source should be preserved in spite of the use of amplification equipment.

TYPES OF SYSTEM

ARRANGEMENTS

There are three types of

arrangements

Central

Distributed

stereophonic

Centrally located

Also known as a high level system, this is essentially a single cluster of loudspeakers located near the source. Such a system gives maximum realism as the

amplified sound, whilst increasing loudness and clarity, is still associated with the original source.

Distributed system

Basically a number of

loudspeakers spaced throughout

the auditorium. This is also known

as a low level system as each

individual speaker operates at a

low amplification level to service

only a small part of the whole

stereophonic

Two or more loudspeaker clusters at

strategic positions within the

auditorium. Such systems are used

when there are a number of different

sources to be amplified or the source is

quite mobile. By using two or more

microphones, each connected to their

own cluster of speakers, the spatial

relationship between the sources is

preserved in the amplified sound.

Guidelines for speaker placement

Every listener must have a sight line to the particular speaker designed to supply them with amplified sound.

A loudspeaker cluster (particularly the central type) may require a great deal of space

.

Concealed loudspeakers must be hidden behind sound-transparent materials such as thin cloth or gauze, never behind a reflective panel.

Loudspeakers should always radiate sound energy wholly at the audience, not at any sound-reflecting surfaces.

Loudspeakers should never be directed at the pickup