D. W. Herrin, Ph.D., P.E. Department of Mechanical Engineering
Outline of Topics 1. Introduction 2. Noise Control at Source 3. Noise Control of Transmission Path 4. Protection at Receiver 5. Summary 2
Introduction Source Path Receiver Path Source Receiver 3
Outline of Topics 1. Introduction 2. Noise Control at Source 3. Noise Control of Transmission Path 4. Protection at Receiver 5. Summary 4
Reduce Impact Forces Noisy Design Quiet Design 5
Application Cutting of Cardboard Noisy Design Quiet Design 6
Reduce Speed and Pressure Operate at low speed Use large-diameter low-speed fan 7
Reduce Flow Velocities and Pressures A 50% reduction in velocity may lower noise by 10-20 db Pressure reduction may lower noise 8
Balance Rotating Parts Method: add counter weights or remove some weights One of the main sources of machinery noise 9
Reduce Flow Resistance Noisy Design Quiet Design 10
Design of Quiet Flow System Noisy Design Quiet Design 11
Isolate Vibrating Elements in Machine Noisy Design Quiet Design 12
Application Machinery Noise Reduction 13
Reduce Radiating Area Noisy Design Quiet Design 14
Noisy Design Hoods and Protective Covers Quiet Design 15
Apply Damping Material 16
Adding Coatings to a Plate 17
Reduce Noise Leakage Noisy Design Quiet Design 18
Effect of Enclosure Sound Leaks 19
Avoid Flow Past Hollow Openings Noisy Design Quiet Design 20
Tips for Controlling Noise Use plastic containers instead of containers made of heavy glass Substitute rubber or plastic trash cans for noisy metal cans Use wood or fiberboard cabinets instead of metal units Select sliding or folding closet doors made of wood or laminate instead of metal doors Replace small high-speed fans with larger, slowermoving units Change usual procedure of operation 21
Outline of Topics 1. Introduction 2. Noise Control at Source 3. Noise Control of Transmission Path 4. Protection at Receiver 5. Summary 22
Absorptive Material Foam Closed-cell Foam is not absorptive material Open-cell Foam is absorptive material 23
Absorptive Materials 24
Absorptive Materials 25
Absorption Coefficient absorption coefficient = absorbed energy incident energy 26
Ideal Case Anechoic Room 27
Room Treatment 28
Ceiling Treatment 29
Pipe Lagging 30
Separate Source and Receiver Free Field 6 db SPL decrease for each doubling of distance 31
Noisy Design Sound Barriers Quiet Design 32
SPL for Different Barriers 33
Application Auto Plant Barrier Noisy Design Quiet Design 34
Application Road Barrier 35
Partial Enclosures 36
Complete Enclosure 37
Enclosure with Ventilation Openings Untreated Treate d 38
SPL Comparison of Different Openings 39
Enclosure 40
Install Muffler or Silencer Noisy Quiet 41
Industrial Silencers 42
Application Muffler for a Large Engine 43
Application Fan Inlet Muffler 44
Flexible Couplings 45
Vibration Isolators 46
Application Electric Motor 47
Application Compressor 48
Modify Equipment Layout Noisy Layout Quiet Layout 49
Outline of Topics 1. Introduction 2. Noise Control at Source 3. Noise Control of Transmission Path 4. Protection at Receiver 5. Summary 50
Ear Protection Devices 51
Other Approaches Booth Hearing Conservation Programs and Education Exposure Control 52
Outline of Topics 1. Introduction 2. Noise Control at Source 3. Noise Control of Transmission Path 4. Protection at Receiver 5. Summary 53
Move the machinery to a new location, more distant from the area where quiet is required Provide vibration isolation to reduce the radiation from surface on which the machinery is mounted Use a partial enclosure around the machine Use a complete enclosure around the machine, or use a booth to house the operator when it is impractical to quiet the machine Reduce the leakage paths that permit noise to leak through openings in the enclosure Reduce impact forces Summary 54
Summary Apply vibration-damping materials to the housing of the machine Insert flexible connectors between the machine and conduit, cable, piping, or ductwork connected to it Use an inertia block, where appropriate Reduce or modify surfaces that radiate noise Reduce resonance effects in mechanical and acoustical systems Use sound-absorptive material Modify or replace noisy parts (gears, bearings etc.) Reduce unbalance in rotating systems 55
Summary Use ducts lined with sound-absorptive material Use wrapping or lagging on pipes or ducts to increase their sound insulation Reduce or eliminate aerodynamically generated noise 56