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Acoustical Properties of Materials

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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  1. Acoustical Properties of Materials Chapter 8

  2. 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

  3. Sound wave produced by tapping on wall

  4. Wavelength Distance between peaks in a sound wave Speed = Frequency X Wavelength

  5. Sound pressure (loudness) measured on decibel scale

  6. Types of sound: Airborne sound

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

  8. Airborne sound falling on a building assembly

  9. 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

  10. 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

  11. Sound transmission loss

  12. 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

  13. Decibel scale

  14. Improve STC of light weight assemblies by • Adding fibrous insulation in stud cavities • Decoupling gypsum board layer • Use multiple gypsum board layers

  15. Stud wall assemblies

  16. Resilient Channel

  17. Resilient Clip

  18. Impact Insulation Class (IIC)measure ofstructure-borne sound

  19. 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

  20. Ceiling tiles

  21. Partitions: fabric-wrapped fiberglass panels absorb sound

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