Acoustical properties of materials
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Acoustical Properties of Materials. Chapter 8. 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

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Acoustical Properties of Materials

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Acoustical properties of materials

Acoustical Properties of Materials

Chapter 8


Sound

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


Sound wave produced by tapping on wall

Sound wave produced by tapping on wall


Wavelength

Wavelength

Distance between peaks in a sound wave

Speed = Frequency X Wavelength


Sound pressure loudness measured on decibel scale

Sound pressure (loudness) measured on decibel scale


Types of sound airborne sound

Types of sound: Airborne sound


Types of sound structure borne sound impact sound

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


Airborne sound falling on a building assembly

Airborne sound falling on a building assembly


Airborne sound building assembly

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


Sound transmission loss tl the loss of sound pressure level as sound passes through an assembly

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


Sound transmission loss

Sound transmission loss


Sound transmission class stc

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


Decibel scale

Decibel scale


Improve stc of light weight assemblies by

Improve STC of light weight assemblies by

  • Adding fibrous insulation in stud cavities

  • Decoupling gypsum board layer

  • Use multiple gypsum board layers


Stud wall assemblies

Stud wall assemblies


Resilient channel

Resilient Channel


Resilient clip

Resilient Clip


Impact insulation class iic measure of structure borne sound

Impact Insulation Class (IIC)measure ofstructure-borne sound


Sound absorption

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


Ceiling tiles

Ceiling tiles


Partitions fabric wrapped fiberglass panels absorb sound

Partitions: fabric-wrapped fiberglass panels absorb sound


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