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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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Presentation Transcript
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

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
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
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