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4. MATERIALS
Generally, the higher the noise frequency, the more effective the materials.
4.1
Sound-Absorbing Material:
.
Absorbs sound waves (reflected airborne noise);
.
Porous and flexible;
.
Examples:
acoustic tiles, fiberglass, acoustical foam, etc.
4.2
Sound-Barrier Material:
.
Reduces sound propagation (direct airborne noise);
.
The heavier, the more effective;
.
Examples: cement barrier wall, plywood, gypsum, steel plate, etc.
4.3 Composites
Material:
.
Sound-absorbing material joined to a barrier material;
.
Absorbs sound waves and reduces noise propagation;
.
Examples:
acoustical foam with barrier material, etc.
4.4
Acoustical Lagging:
.
Sound-absorbing material (inside) joined to a barrier material (outside);
.
Blocks noise travelling through thin metallic partitions;
.
Examples:
isolating wool and plate, foam and vinyl, etc.
4.5
Acoustical Curtain:
.
Reduces sound propagation (screen, acoustical enclosure, etc.);
.
Examples: clear
strip curtain, absorbing vinyl curtain, etc.
4.6
Acoustical Enclosure:
.
Reduces
airborne sound propagation;
.
Walls are made of:
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sound-absorbing material on the inside (ex.: isolating wool, etc.);
-
barrier material on the outside (ex.: plywood, gypsum, steel plate, etc.);
-
protective material (optional, ex.: wire netting, perforated plate, film, etc.)
. Leaks must be reduced to a minimum or eliminated;
.
Plan access,
lightning, ventilation, and fire protection.
4.7
Damping Material:
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Damps metallic
surface resonance;
.
Glued on the inside or outside of the surface;
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Optimal Efficiency: 70% of the surface.
4.8
Vibration Isolator:
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Reduces mechanical vibration propagation;
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Two main types : spring-type and Neoprene-type;
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To be installed under the machinery;
.
Sometimes, an inertia base shall be added under the machinery;
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Install flexible joints at the equipment inlet and outlet;
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Efficiency depends on the static deflection and the operating speed.
4.9 Silencer:
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Three main types:
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dispersive silencer (for compressed air);
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dissipative silencer (for ventilation systems);
-
reactive silencer (for engines, compressors, pumps,
etc.)
.
Take into
account the static pressure loss caused by the silencers.
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