Sound Absorptive Material Technical Presentation Sound Absorptive Material By Mozart Chan Wilson Acoustics Limited www.wal.hk

Topic Covered General properties Rating Commercial acoustical materials: specific type and properties How to select and specify Wilson Acoustics Limited www.wal.hk

Sound Absorptive Material When sound waves strike the surface of a material, a fraction of the incident energy is absorbed by conversion to heat. Wilson Acoustics Limited www.wal.hk

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 Wilson Acoustics Limited www.wal.hk

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 Wilson Acoustics Limited www.wal.hk

General Properties: Face covering (perforated board, wire-mesh screen, or perforated sheet metal) exhibit a decreasing peaked absorption-vs.-frequency curve Wilson Acoustics Limited www.wal.hk

General Properties: Wilson Acoustics Limited www.wal.hk

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 Wilson Acoustics Limited www.wal.hk

Sound Absorption Ratings Sound Absorption Coefficients Wilson Acoustics Limited www.wal.hk

Sound Absorption Ratings Noise Reduction Coefficient (NRC) Arithmetic value average of sound absorption coefficients at 250, 500, 1000, 2000 Hz Wilson Acoustics Limited www.wal.hk

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 Wilson Acoustics Limited www.wal.hk

Effects of Mounting Wood furring strips Type D Mounting Type B Mounting Type E Mounting Wilson Acoustics Limited www.wal.hk

Commercial acoustical materials: specific type and properties Classification: acoustical tiles or boards special acoustical assemblies acoustical roof decks Wilson Acoustics Limited www.wal.hk

tiles or boards integral, rigid, self-supporting material furnished in prefabricated units of a definite size and thickness. Wilson Acoustics Limited www.wal.hk

special acoustical assemblies Perforated Metal Pans with Mineral-Fiber Pads. Wilson Acoustics Limited www.wal.hk

special acoustical assemblies Wall Panels Perforated panel Absorption Material Structural Material Wilson Acoustics Limited www.wal.hk

special acoustical assemblies Perforated Panels with Mineral-Fiber Blankets Wilson Acoustics Limited www.wal.hk

special acoustical assemblies Suspended Absorbers Wilson Acoustics Limited www.wal.hk

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) Wilson Acoustics Limited www.wal.hk

acoustical roof decks iv. Partial-Height Partitions (Office Dividers) Wilson Acoustics Limited www.wal.hk

Selection of Acoustical Materials other factors: Flame spread and fire endurance Wilson Acoustics Limited www.wal.hk

Selection of Acoustical Materials other factors: Mechanical strength, abuse resistance - usually low Wilson Acoustics Limited www.wal.hk

Selection of Acoustical Materials other factors: Dimensional stability do not change with humidity and temperature Wilson Acoustics Limited www.wal.hk

Selection of Acoustical Materials other factors: Light reflectance – 4 types of light reflection a- 0.75 or more b- 0.70 to 0.74 c- 0.65 to 0.69 d- 0.60 to 0.64 Wilson Acoustics Limited www.wal.hk

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 Wilson Acoustics Limited www.wal.hk

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