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Noise and Vibration ControlBasic Principles & Materials

1.    NOISE PROBLEM
SOURCE PROPAGATION MEDIUM RECEPTOR


2.  
FOUR  FUNDAMENTALS QUESTIONS

            QUESTION 1 : Do we have a noise problem?
            QUESTION 2 : What is it which causes this noise problem?
            QUESTION 3 : How the noise of this source is generated?
            QUESTION 4 : How the noisr of this source is propagated&
 

3.    HOW TO CONTROL NOISE AND VIBRATIONS

3.1     Control at the source:  
                    . Shut down equipment that are not in use;
                    . Ensure preventive maintenance;
                    . Modify process;
                    . Modify operating parameters;
                    . Replace components;
                    . Replace noisy equipment;
                    . Install damping material;
                    . Install vibration isolators;
                    . Install silencers.

3.2     Propagation Reduction:
                    . Relocate (the source or the receptor);
                    . Improve Room Acoustical Absorption;
                    . Install Acoustical Screen;
                    . Install Acoustical Enclosure;
                    .
Install Acoustical Lagging.

3.3     Reduction at Reception:
                    . Install Acoustical Screen;
                    . Install Booth;
                    . Implement Work Shift Rotation;
                    .
Wear Hearing Protection Devices
 


4.    MAT
ERIALS

        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:
                            -
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:
              
     .
Damps metallic surface resonance;
                    . Glued on the inside or outside of the surface;
                    . Optimal Efficiency: 70% of the surface.

4.8    Vibration Isolator:
                   
.
Reduces mechanical vibration propagation;
                    . Two main types : spring-type and Neoprene-type;
                    . To be installed under the machinery;
                    . Sometimes, an inertia base shall be added under the machinery;
                    . Install flexible joints at the equipment inlet and outlet;
                    . Efficiency depends on the static deflection and the operating speed.

4.9    Silencer:
                   
.
Three main types:
                            -
dispersive silencer (for compressed air);
                            - dissipative silencer (for ventilation systems);
                            -
reactive silencer (for engines, compressors, pumps, etc.)
                    .
Take into account the static pressure loss caused by the silencers.
 

5.    STEP FOR NOISE REDUCTION PROJECT:

                    . Identify sources and their individual contribution (frequency analysis, dose rate measuring);
                    . Find sound propagation paths
;
                    . Study control measures
;
                    . Select acoustical materials
;
                    . Implement solutions;

              
     . Evaluate and adjust.

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