Architectural Acoustics

• Factors Affecting Architectural Acoustics

1.Reverberation Time• When the reverberation time is too high, the sound produced by

the speaker will persist for a long period of time.• Similarly ,when the reverberation time is low, sound dies quickly

and becomes inaudible in a short amount of time.• In order to improve the sound, reverberation time of a hall should

be increased to an optimum value.

Remedies :-• Decreasing total absorption coefficient of the wall• Placing sound reflection boards inside a hall

2. Loudness• Reverberation time of a hall is directly proportional to loudness.• Low loudness results in existence of sound for a shorter period

while high loudness results in existence of sound for a longer period.

• Therefore sound produced by the speaker should be within audible range.

Remedies :-• Placing sound absorbing boards to reduce loundness• Placing sound reflecting boards to increase loudness

3. Echelon Effect• Unwanted sounds are produced when people walk on

staircase or floors or hard paved paths due to poor finishing of the floor surface, structural effects, etc.

• The above mentioned unwanted sound are termed as ‘echelon effect’ .

Remedies :-• Finishing the floors or stairs very finely.• Using carpet to caver floors and stairs.

4. Structure-Borne Sound• Sound waves generated inside a hall are known as structure-

borne sound.• They are produced due to apparent motion of benches &

footsteps & propagated through walls and floors.

Remedies :-• Using rigid structures so as to rest the vibrations.• Introducing discontinuities in the path of sound.• Converting floor and ceilings with suitable sound absorbing

materials & anti-vibration mouths.

5. Echo• If the time interval between direct sound and reflected

sound is less than 1/15 of a second, the reflected sound is helpful in incresing loudness.

• But if the time interval is less than that, then the sound arrives later and will cause confusion.

Remedies :-• To prevent unnecessary reflection of sound.• Covering long distance walls and ceilings with suitable sound

absorbing materials.

6. Focusing due to walls and ceilings• Sound produced by speaker undergoes multiple reflections at

ceilings and walls. • Reflected sounds from ceilings and walls should not be focused on

particular point, rather it should be distributed throughout a hall.• Generally a plane surface reflects sound uniformly but a curved

surface does not. So reflection of sound from a curved surface produces a harmful effect.

Remedies :-• Radius of curvature of ceilimg should be kept twice the height of

the building• Distribution of sound waves from a concave surface should be

made uniform

7. Resonance within a building• Sound waves get amplifies when the frequency of vibration

of air particles matches with the hall’s natural frequency of vibration.

• Thus, it results in an unwanted sound effect in side a hall.

Remedies :-• Model-Hall or a model auditoriun should be kept inside a

vessel which contains water.• The water-wave particle movememnts are studies and are

used for the construction of actual hall or auditorium.