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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

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



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




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 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



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





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



Partitions fabric wrapped fiberglass panels absorb sound
Partitions: fabric-wrapped fiberglass panels absorb sound