acoustical properties of materials

Acoustical Properties of Materials

Chapter 8

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Sound

Response of human ear to pressure fluctuations in the air caused by vibrating objects.

Sound wave is a back & forth vibratory motion passed from particle to particle through a medium

Sound frequency is the number of back and forth cycles that occur in one second ( measured as Hertz)

Audible frequency range lies between 20 Hz & 20,000 Hz

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Sound wave produced by tapping on wall

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Wavelength

Distance between peaks in a sound wave

Speed = Frequency X Wavelength

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Sound pressure (loudness) measured on decibel scale

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Types of sound: Airborne sound

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Types of sound: Structure-borne sound (impact sound)

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Airborne sound falling on a building assembly

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Airborne sound & building assembly

Sound is reflected, absorbed & transmitted Transmission rate varies with weight of assembly

Heavy-weight assemblies are poor transmitters - good insulators

Light-weight assemblies, poor insulators

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Sound transmission loss (TL): the loss of sound pressure level as sound passes through an assembly

Measured in decibels (dB) Difference in sound pressure level between

the source side and receiver side The greater the TL of a wall, the better it is as

a sound insulator TL varies with frequency, generally higher TL

with higher frequency sound

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Sound transmission loss

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Sound Transmission Class (STC)

Single number index- average of TL over frequencies ranging from 125 Hz to 4 kHz

Used to compare building assemblies

Regulated by code in some building types

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Decibel scale

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Improve STC of light weight assemblies by

Adding fibrous insulation in stud cavities

Decoupling gypsum board layer

Use multiple gypsum board layers

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Stud wall assemblies

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Resilient Channel

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Resilient Clip

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Impact Insulation Class (IIC)measure of structure-borne sound

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Sound absorption

Sound originating within room attenuated only through sound absorption

Noise reduction coefficient used to compare efficacy of materials (0-1)

Higher NRC, the more sound absorptive the material

Materials .2 NRC or higher are sound absorptive

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Ceiling tiles

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Partitions: fabric-wrapped fiberglass panels absorb sound