# Building Construction Questions and Answers – Acoustics – Reflection, Reverberation and Absorption

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This set of Building Construction Multiple Choice Questions & Answers (MCQs) focuses on “Acoustics – Reflection, Reverberation and Absorption”.

1. For an echo to be distinguished as separate, it should reach the ear _________ of a second after the direct sound.
a) One-fourth
b) One-fifth
c) One-eighth
d) One-tenth

Explanation: An echo is a defect that is caused due to the reflection of sound waves. For an echo to be distinguished as separate, it should reach the ear one-tenth of a second after the direct sound.

2. Sound waves reflected at a convex surface are diminished.
a) True
b) False

Explanation: Sound waves reflected at a concave surface are diminished while the sound waves reflected at convex surfaces are large and magnified. A convex surface is used to spread the sound waves throughout the room and a concave surface is used for the concentration of reflected waves at certain points.

3. Reverberation time is directly proportional to ____________
a) Effective surface area
b) Lateral surface area
c) Volume of the room
d) Shape of the room

Explanation: The time during which the sound persists is known as the reverberation time. As a result of experiments performed by Professor W.C. Sabine, reverberation time is directly proportional to the volume of the room and inversely proportional to the effective surface area.

4. In the Sabine’s expression for reverberation time t=0.16V/A, A represents __________
a) Area of the room
b) Volume of the room
c) Total absorbing power

Explanation: In Sabine’s expression for reverberation time t=0.16V/A, A represents total adsorbing power. It is expressed in m2 sabines. In this expression, V represents the volume of the room in cubic metres.

5. Rock wool comes under which of the following classifications of absorbents?
a) Porous materials
b) Resonant panels
c) Cavity resonators
d) Composite types

Explanation: Absorbents are broadly classified as porous materials, resonant panels, cavity resonators and composite types. Rock wool is an example of porous material. Other examples of porous materials are glass wool, wood wool, etc.

6. The unit of absorption is ____________
a) Poise
b) Stoke
c) Siemens
d) Sabin

Explanation: The unit of absorption is the open window unit which is known as a sabin. It is named after the scientist who established this unit. The unit of sound absorbed by one square metre of a fully open window is m2-sabin.

7. Reverberation time is independent of the shape of the room.
a) True
b) False

Explanation: Professor Sabine found that the reverberation time is independent of the shape of the room. This time is also independent of the position of the source of the sound and the listener.

8. The absorption of a surface is the product of the __________ of the surface and its absorption coefficient.
a) Length
b) Area
c) Volume
d) Width

Explanation: The absorption of a surface is the product of the area of the surface and its absorption coefficient. The absorption coefficient is used to indicate the sound reducing the effect of an absorber which depends on its area and on the efficiency of the material.

9. In which of the following absorbents, absorption takes place due to the frictional losses occurring due to the to and fro movement of the air contained in the material caused by the sound waves?
a) Cavity resonators
b) Resonant panels
c) Porous materials
d) Composite types

Explanation: In porous materials, absorption takes place due to the frictional losses occurring due to the to and fro movement of the air contained in the material caused by the sound waves. These materials absorb sound generally in higher frequencies.

10. Which of the following types of absorbents can absorb the sound of any frequency?
a) Resonant panels
b) Cavity resonators
c) Porous materials
d) Composite types

Explanation: Cavity resonators can absorb the sound of any frequency. Porous materials absorb sound at high frequencies while resonant panels absorb sound only at lower frequencies.

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