Module 2: Sound Absorption, Reflection and Transmission

Sound Absorption

the measure of the amount of energy removed from the sound wave as the wave passes through a given thickness of material.

Marble

— surfaces in churches creates a very reflective sound effect on users. Reverberation is too long that it affects the quality of sound.

Wood

aside from its beauty, it produces a very natural sound effects especially in residential buildings.

Acoustic ceiling boards

For best quality sound, we use —— (usually perforated gypsum boards or equal). This material can have a very large amount of sound absorption

Material’s Mass Density

To the same porous material, its ——- increases, the absorption efficiency to high frequency sound decreases

Material’s Thickness

Increasing the —— can enhance the absorption to low frequency sound, but it makes little difference to high frequency sound

Material’s Porosity

more pores in smaller sizes increases the sound absorption effect.

weak

Materials with bigger pores has —— sound absorption effect.

• direct sound from source

• indirect reflections from adjacent surfaces and objects

Sound in buildings is composed of:

transmission, absorption, or reflection of sound energy

The interaction of sound with a building component can result in ——- of sound energy

Sound Insulation

known as sound absorption

Sound Insulation

one of the most important features in building materials, with the purpose to maintain a living comfort, reducing noise and sound reflected by surfaces

Insulation materials

applied to walls to control their acoustic performance

Acoustic absorbers

have been extensively used in noise control to minimize the sound reflected by surfaces and have the ability to contrast sound transmission

Sound Reflection 

Waves are reflected when the density of matter is too high for the wave to pass through or be absorbed

reflected

waves are —— when the density of matter is too high for the wave to pass through or be absorbed.

because of that, the wave is — (or bounces off) and then moves in a different direction than it was originally traveling

• echo or

• reverberation

reflection of sound waves off of surfaces can lead to one of two phenomena:

echo

when sound waves are reflected, there is often an —- because the sound wave is traveling in various direction bouncing off matter

reverberation

the process of a sound wave repeatedly reflecting in a space 

Echo

sound waves which have been reflected back to a listener with sufficient magnitude and time delay

echo

occur when a reflected sound wave reaches the ear more than 0.1 seconds after the original sound wave was heard

died out

if the elapsed time between the arrivals of the two sound waves is more than 0.1 seconds, then the sensation of the first sound will have —-

echo

the arrival of the second wave will be perceived as a second sound rather than the prolonging of the first sound

reverberation

the persistent of sound in an enclosed space as a result of repeated reflection or scattering of sound

Reverberation

often occurs in a small room with height, width, and length dimensions of approximately 17 meters or less

prolonged

If a reflected sound wave reaches the ear within 0.1 seconds of the initial sound, then it seems to the person that the sound is ——

reverberations

The reception of multiple reflection off of walls and ceilings within 0.1 seconds of each other causes ——— —the prolonging of sound

Flutter Echo

occur between hard parallel walls where the sound repeatedly bounces back and forth

Flutter Echo

Whispering Gallery

If you stand facing the wall in any of the four corners, and whisper, your words will be carried to the corner diagonally across from you and can be heard by someone in that corner

Long Reflective Hallways

Flutter Echo in a modern plastered room

Concave Reflector

Focuses Reflections

Convex Reflector

Scatters Reflections

Attenuation and sound insulation

descriptive terms used to denote performance in reducing sound transmission

Transmission loss

____ of a wall or a floor is a number of decibels by which the level of air-borne sound is decreased in passing through the structure

Air-borne transmission

produced by sources that radiate directly into the air

Impact transmission

produced by a direct mechanical impact such as footsteps, a slam

Sound Transmission Class

a single number used to characterize the air-borne isolation properties of a partition

Sound Transmission Class

determined from the measure Transmission Loss of a partition at different frquencies.

Mass Law

the degree of variation of the energy of sound transmission through a partition will depend first of all on the mass or weight or unit area of a panel. (Porous materials_

Sound absorption coefficient

defined as the ratio of the sound energy absorbed by a surface to the sound energy incident on that surface, taking values between 0 and 1

Sound absorption coefficient

The ratio of the absorbed sound energy to the incident energy 

Noise reduction coefficient

the descriptor most often used