Applied Noise Control. D. W. Herrin, Ph.D., P.E. University of Kentucky Department of Mechanical Engineering

Transcription

1 D. W. Herrin, Ph.D., P.E. Department of Mechanical Engineering

2 Outline of Topics 1. Introduction 2. Noise Control at Source 3. Noise Control of Transmission Path 4. Protection at Receiver 5. Summary 2

3 Introduction Source Path Receiver Path Source Receiver 3

4 Outline of Topics 1. Introduction 2. Noise Control at Source 3. Noise Control of Transmission Path 4. Protection at Receiver 5. Summary 4

5 Reduce Impact Forces Noisy Design Quiet Design 5

6 Application Cutting of Cardboard Noisy Design Quiet Design 6

7 Reduce Speed and Pressure Operate at low speed Use large-diameter low-speed fan 7

8 Reduce Flow Velocities and Pressures A 50% reduction in velocity may lower noise by db Pressure reduction may lower noise 8

9 Balance Rotating Parts Method: add counter weights or remove some weights One of the main sources of machinery noise 9

10 Reduce Flow Resistance Noisy Design Quiet Design 10

11 Design of Quiet Flow System Noisy Design Quiet Design 11

12 Isolate Vibrating Elements in Machine Noisy Design Quiet Design 12

13 Application Machinery Noise Reduction 13

14 Reduce Radiating Area Noisy Design Quiet Design 14

15 Noisy Design Hoods and Protective Covers Quiet Design 15

16 Apply Damping Material 16

17 Adding Coatings to a Plate 17

18 Reduce Noise Leakage Noisy Design Quiet Design 18

19 Effect of Enclosure Sound Leaks 19

20 Avoid Flow Past Hollow Openings Noisy Design Quiet Design 20

21 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

22 Outline of Topics 1. Introduction 2. Noise Control at Source 3. Noise Control of Transmission Path 4. Protection at Receiver 5. Summary 22

23 Absorptive Material Foam Closed-cell Foam is not absorptive material Open-cell Foam is absorptive material 23

24 Absorptive Materials 24

25 Absorptive Materials 25

26 Absorption Coefficient absorption coefficient = absorbed energy incident energy 26

27 Ideal Case Anechoic Room 27

28 Room Treatment 28

29 Ceiling Treatment 29

30 Pipe Lagging 30

31 Separate Source and Receiver Free Field 6 db SPL decrease for each doubling of distance 31

32 Noisy Design Sound Barriers Quiet Design 32

33 SPL for Different Barriers 33

34 Application Auto Plant Barrier Noisy Design Quiet Design 34

35 Application Road Barrier 35

36 Partial Enclosures 36

37 Complete Enclosure 37

38 Enclosure with Ventilation Openings Untreated Treate d 38

39 SPL Comparison of Different Openings 39

40 Enclosure 40

41 Install Muffler or Silencer Noisy Quiet 41

42 Industrial Silencers 42

43 Application Muffler for a Large Engine 43

44 Application Fan Inlet Muffler 44

45 Flexible Couplings 45

46 Vibration Isolators 46

47 Application Electric Motor 47

48 Application Compressor 48

49 Modify Equipment Layout Noisy Layout Quiet Layout 49

50 Outline of Topics 1. Introduction 2. Noise Control at Source 3. Noise Control of Transmission Path 4. Protection at Receiver 5. Summary 50

51 Ear Protection Devices 51

52 Other Approaches Booth Hearing Conservation Programs and Education Exposure Control 52

53 Outline of Topics 1. Introduction 2. Noise Control at Source 3. Noise Control of Transmission Path 4. Protection at Receiver 5. Summary 53

54 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

55 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

56 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