1. Sound Absorptive Material
Technical Presentation
Sound Absorptive Material
By Mozart Chan
Wilson Acoustics Limited

2. Topic Covered General properties Rating
Commercial acoustical materials: specific type and properties
How to select and specify
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3. Sound Absorptive Material
When sound waves strike the surface of a material, a fraction of the incident energy is absorbed by conversion to heat.
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4. Sound Absorptive Material
Highly porous material [at least 1.27 cm thick] porous wall friction act with air molecules as damping. Depends only slightly on the frequency
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5. General Properties:
Depth of the space between the face of the material and a rigid backing surface behind it (esp for low frequency)
Gap higher than 1/4 of targeted wave length is preferred
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6. General Properties:
Face covering (perforated board, wire-mesh screen, or perforated sheet metal) exhibit a decreasing peaked absorption-vs.-frequency curve
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7. General Properties:
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8. Sound Absorption Ratings
Sound Absorption Coefficients
Percent of energy absorbed
usually in diffuse field
common practice 6 frequencies:
125, 250, 500, 1000, 2000, 4000 Hz
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9. Sound Absorption Ratings
Sound Absorption Coefficients
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10. Sound Absorption Ratings
Noise Reduction Coefficient (NRC)
Arithmetic value average of sound absorption coefficients at 250, 500, 1000, 2000 Hz
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11. Sound Absorption Ratings
Effects of Mounting
when comparing the absorptivity of two materials, always be sure that the data are for the same mounting conditions.
Type A mounting: Laid directly against rigid solid surface with no airspace
Type B mounting: Spot-cemented to gypsum board with a 20-mm air-space
Type D-20 mounting: Nailed to nominal 20- by 40-mm wood furring strips
Type E-400 mounting: Supported on a metal suspension system with a 400-mm airspace
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12. Effects of Mounting Wood furring strips Type D Mounting
Type B Mounting
Type E Mounting
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13. Commercial acoustical materials: specific type and properties
Classification:
acoustical tiles or boards
special acoustical assemblies
acoustical roof decks
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14. tiles or boards
integral, rigid, self-supporting material furnished in prefabricated units of a definite size and thickness.
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15. special acoustical assemblies
Perforated Metal Pans with Mineral-Fiber Pads.
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16. special acoustical assemblies
Wall Panels
Perforated panel
Absorption Material
Structural Material
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17. special acoustical assemblies
Perforated Panels with Mineral-Fiber Blankets
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18. special acoustical assemblies
Suspended Absorbers
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19. acoustical roof decks
Acoustical materials may be used as an integral part of a roof structure in a one-story building, such as an industrial plant, where the underside of the roof deck forms the exposed ceiling surface of the space below.
i. Acoustical Form Boards for Poured Decks.
ii. Perforated Roof Deck Panels
iii. Structural Roof Insulation
iv. Partial-Height Partitions (Office Dividers)
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20. acoustical roof decks iv. Partial-Height Partitions (Office Dividers)
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21. Selection of Acoustical Materials
other factors:
Flame spread and fire endurance
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22. Selection of Acoustical Materials
other factors:
Mechanical strength, abuse resistance - usually low
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23. Selection of Acoustical Materials
other factors:
Dimensional stability do not change with humidity and temperature
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24. Selection of Acoustical Materials
other factors:
Light reflectance – 4 types of light reflection
a or more
b to 0.74
c to 0.69
d to 0.64
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25. Selection of Acoustical Materials
other factors:
Maintenance, cleanability, paintability
Appearance
Cost
Ease of installation, method of mounting
Space availability for acoustical installation
Weight of acoustical installation
Compatibility with other materials and components
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26. END
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