1. BA 7666-11, 1 Basic Concepts of Sound Contents: Definitions dB Conversion Sound Fields dB ± dB

2. BA 7666-11, 2 Sound 860499/1

3. BA 7666-11, 3 Sound and Noise 860500/1

4. BA 7666-11, 4 Terminology of Sound dB L eq RMS Sound Pressure Constant percentage bandwidth Noise Dose Logarithmic scales Pascal Fast Slow Impulse RMS Peak Weighting 1/1 and 1/3 Octave Analysis Percentile level Statistical analysis L 10 L 90

5. BA 7666-11, 5 Pressure vs. Power Temperature t [°C] Power P [W] Electrical Heater Analogy Pressure p [N/m 2 = Pa] Sound Source L p [dB] Power P [W]

6. BA 7666-11, 6 Basic Parameters of Sound Under free-field conditions: Power:P [W] Intensity:  [J/s/m 2 ] = W/m 2 Pressure:p [Pa = N/m 2 ] The Sound Intensity vector,  describes the amount and direction of flow of acoustic energy at a given position P P2P2 P2P2  r1r1 r2r2   861218/2

7. BA 7666-11, 7 Propagation of Sound t = 0 t = 1/4 T t = 1/2 T t = 3/4 T t = T Compression Extension Minimum compressionMaximum compression No compression

8. BA 7666-11, 8 Sound Pressure Pressure [Pa] 100 000 Pascal Time 860504/1

9. BA 7666-11, 9 Sound Pressure 100 000 Pascal Atmospheric Pressure Mexico City New York Pressure [Pa] Acoustic Pressure Variations

10. BA 7666-11, 10 100 10 1 0.1 0.01 0.001 0.000 1 0.000 01 Range of Sound Pressure Pressure, p [Pa] 860505/2

11. BA 7666-11, 11 Basic Concepts of Sound Contents: Definitions dB Conversion Sound Fields dB ± dB

12. BA 7666-11, 12 Sound Pressure, p [Pa] Range of Sound Pressure Levels 140 120 100 80 60 40 20 0 Sound Pressure Level, L p [dB] 100 10 1 0.1 0.01 0.001 0.000 1 0.000 01 860508/2

13. BA 7666-11, 13 dB – decibel Ex. 1: p= 1 Pa LpLp = 20 log = 20 log 50 000 = 94 dB Ex. 2: p= 31.7 Pa LpLp = 20 log = 20 log 1.58 × 10 -6 = 124 dB (p 0 = 20  Pa = 20 × 10 -6 Pa) L p = 20 log dB re 20  Pa

14. BA 7666-11, 14 Perception of dBs Change in Sound Level (dB) Change in Perceived Loudness 3 5 10 15 20 Just perceptible Noticeable difference Twice (or 1/2) as loud Large change Four times (or 1/4) as loud

15. BA 7666-11, 15 Conversion to dB using Charts dB re 20  Pa 200 150 100 50 0 0.00010.01110010 000 Pressure [Pa] p 0 = 20  Pa 94 dB LpLp 0.1101000

16. BA 7666-11, 16 Conversion to dB using Tables dB to Pressure Ratio Pressure Ratio  db  Pressure Ratio Pressure Ratio  db  Pressure Ratio 1.00 0.989 0.977 0.966 0.955 0.944 0.933 0.923 0.912 0.902 0.891 0.841 0.794 0.708 0.631 0.562 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.5 2.0 3.0 4.0 5.0 1.000 1.012 1.023 1.035 1.047 1.059 1.072 1.084 1.096 1.109 1.122 1.189 1.259 1.413 1.585 1.778 0.501 0.447 0.398 0.355 0.316 0.251 0.200 1.158 0.126 0.100 0.0316 0.0100 0.0032 10 -3 10 -4 10 -5 6 7 9 10 12 14 16 18 20 30 40 50 60 80 100 1.995 2.239 2.512 2.818 3.162 3.981 5.012 6.310 7.943 10.000 31.62 100 316.2 10 3 10 4 10 5

17. BA 7666-11, 17 Simple Rules for Conversion Sound Pressure Level, L p dB re 20  Pa Sound Pressure, p [Pa] 114 74 80 84 86 94 10 0.1 0.2 0.3 1 20 2 × 100 × 10 × 2 × 3 × 4 6 dB 10 dB 20 dB 40 dB 12 dB

18. BA 7666-11, 18 Basic Concepts of Sound Contents: Definitions dB Conversion Sound Fields dB ± dB

19. BA 7666-11, 19 Types of Sound Sources r: L p 2r: L p  6 dB r: L p 2r: L p  3 dB r: L p 2r: L p Plane source Point source Line source 860510/1

20. BA 7666-11, 20 Anechoic and Reverberant Enclosures 860511/1

21. BA 7666-11, 21 Pressure Field Loudspeaker Microphone Enclosure

22. BA 7666-11, 22 Sound Fields Near field Far field Free fieldReverberant field LpLp Distance, r A1A1 2 × A 1 6 dB 860512/2

23. BA 7666-11, 23 Directivity Index Source Location Free field L = L p L = L p + 3 dB L = L p + 6 dB L = L p + 9 dB On a flat plane At a junction of two planes At a junction of three planes Directivity Factor 1 2 4 8 Directivity Index, dB 0 3 6 9

24. BA 7666-11, 24 Pressure Increase at Walls L = L p + 3 dB L = L p + 6 dB LpLp

25. BA 7666-11, 25 Basic Concepts of Sound Contents: Definitions dB Conversion Sound Fields dB ± dB

26. BA 7666-11, 26 Two Sound Sources L p1 = X dB L p2 = X dB L p1 + L p2 = X + 3 dB

27. BA 7666-11, 27 Addition of dB Levels Example: L + dB 3 2 1 0 051015  L dB L1L2LL+LtL1L2LL+Lt 55 dB 51 dB 4 dB 1.4 dB 55 + 1.4 = 56.4 dB ========== 4 dB 1.4 dB 860512/2

28. BA 7666-11, 28 Subtraction of Noise Levels L S+N [dB] L N [dB]

29. BA 7666-11, 29 Subtraction of dB Levels Ex: L S+N L N  L L  L S 60 dB 53 dB 7 dB 1 dB 60  1 = 59 dB ========== L  dB 6 4 2  L dB 1 3 5 11023456789 L S ~ L S+N 

30. BA 7666-11, 30 Addition of many dB values Addition of sound levels : For L 1 = L 2 = L 3..... = L N Examples: N = 2: L Total = L 1 + 3 dB N = 10: L Total = L 1 + 10 dB 0 2 4 6 8 10 12 051015 10 log N N L 1 + L 2..... + L N = ?

31. BA 7666-11, 31 Conclusion Sound pressure level in dB is related to 2 * 10 -5 Pascal. The range of human hearing is 130 dB. To add or subtract dB-values use charts or formulas

32. BA 7666-11, 32 Literature for Further Reading Acoustic Noise Measurements Brüel & Kjær (BT 0010-12) Noise Control - Principles and Practice Brüel & Kjær (188-81)