Basic Concepts of Sound Contents Definitions d B
Basic Concepts of Sound Contents: Definitions d. B Conversion Sound Fields d. B ± d. B BA 7666 -11, 1
Sound BA 7666 -11, 2 860499/1
Sound and Noise BA 7666 -11, 3 860500/1
Terminology of Sound RMS Peak d. B Fast Slow Impulse Percentile level Sound Pressure Logarithmic scales Pascal Weighting Leq RMS L 10 L 90 1/1 and 1/3 Octave Analysis Statistical analysis Constant percentage bandwidth Noise Dose BA 7666 -11, 4
![Pressure vs. Power Pressure p [N/m 2 = Pa] Analogy Lp [d. B] Temperature](http://slidetodoc.com/presentation_image/29148bbb9939cece6fec45b6b635bbdf/image-5.jpg "Pressure vs. Power Pressure p [N/m 2 = Pa] Analogy Lp [d. B] Temperature")
Pressure vs. Power Pressure p [N/m 2 = Pa] Analogy Lp [d. B] Temperature t [°C] Power P [W] Sound Source Electrical Heater BA 7666 -11, 5
Basic Parameters of Sound Under free-field conditions: P 2 P BA 7666 -11, 6 861218/2 The Sound Intensity vector, describes the amount and direction of flow of acoustic energy at a given position r 2 r 1 Power: P [W] Intensity: [J/s/m 2] = W/m 2 Pressure: p [Pa = N/m 2]
Propagation of Sound t=0 Compression t = 1/4 T t = 1/2 T Extension t = 3/4 T Minimum compression t=T No compression BA 7666 -11, 7 Maximum compression
![Sound Pressure [Pa] 100 000 Pascal Time BA 7666 -11, 8 860504/1](http://slidetodoc.com/presentation_image/29148bbb9939cece6fec45b6b635bbdf/image-8.jpg "Sound Pressure [Pa] 100 000 Pascal Time BA 7666 -11, 8 860504/1")
Sound Pressure [Pa] 100 000 Pascal Time BA 7666 -11, 8 860504/1
![Sound Pressure [Pa] Atmospheric Pressure New York 100 000 Pascal Mexico City BA 7666](http://slidetodoc.com/presentation_image/29148bbb9939cece6fec45b6b635bbdf/image-9.jpg "Sound Pressure [Pa] Atmospheric Pressure New York 100 000 Pascal Mexico City BA 7666")
Sound Pressure [Pa] Atmospheric Pressure New York 100 000 Pascal Mexico City BA 7666 -11, 9 Acoustic Pressure Variations
![Range of Sound Pressure, p [Pa] 100 10 1 0. 01 0. 000 01](http://slidetodoc.com/presentation_image/29148bbb9939cece6fec45b6b635bbdf/image-10.jpg "Range of Sound Pressure, p [Pa] 100 10 1 0. 01 0. 000 01")
Range of Sound Pressure, p [Pa] 100 10 1 0. 01 0. 000 01 BA 7666 -11, 10 860505/2
Basic Concepts of Sound Contents: Definitions d. B Conversion Sound Fields d. B ± d. B BA 7666 -11, 11
![Range of Sound Pressure Levels Sound Pressure, p [Pa] 100 10 1 0. 01](http://slidetodoc.com/presentation_image/29148bbb9939cece6fec45b6b635bbdf/image-12.jpg "Range of Sound Pressure Levels Sound Pressure, p [Pa] 100 10 1 0. 01")
Range of Sound Pressure Levels Sound Pressure, p [Pa] 100 10 1 0. 01 0. 000 01 BA 7666 -11, 12 860508/2 Sound Pressure Level, Lp 140 120 100 80 60 40 20 0 [d. B]
d. B – decibel Lp = 20 log d. B re 20 Pa (p 0 = 20 Pa = 20 × 10 -6 Pa) Ex. 1: p = 1 Pa Lp = 20 log BA 7666 -11, 13 Ex. 2: p = 31. 7 Pa Lp = 20 log 50 000 = 20 log 1. 58 × 10 -6 = 94 d. B = 124 d. B
Perception of d. Bs Change in Sound Level (d. B) BA 7666 -11, 14 Change in Perceived Loudness 3 Just perceptible 5 Noticeable difference 10 Twice (or 1/2) as loud 15 Large change 20 Four times (or 1/4) as loud
Conversion to d. B using Charts Lp d. B re 20 Pa 200 150 100 94 d. B 50 0 0. 0001 p 0 = 20 Pa BA 7666 -11, 15 0. 01 0. 1 1 10 1000 10 000 Pressure [Pa]
Conversion to d. B using Tables d. B to 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. 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 000 1. 012 1. 023 1. 035 1. 047 1. 059 1. 072 1. 084 1. 096 1. 109 0. 501 0. 447 0. 398 0. 355 0. 316 0. 251 0. 200 1. 158 0. 126 0. 100 6 7 7 9 10 12 14 16 18 20 1. 995 2. 239 2. 512 2. 818 3. 162 3. 981 5. 012 6. 310 7. 943 10. 000 0. 891 0. 841 0. 794 0. 708 0. 631 0. 562 1. 0 1. 5 2. 0 3. 0 4. 0 5. 0 1. 122 1. 189 1. 259 1. 413 1. 585 1. 778 0. 0316 0. 0100 0. 0032 10 -3 10 -4 10 -5 30 40 50 60 80 100 31. 62 100 316. 2 103 104 105 BA 7666 -11, 16 Pressure Ratio db Pressure Ratio
![Simple Rules for Conversion Sound Pressure, p [Pa] Sound Pressure Level, Lp d. B](http://slidetodoc.com/presentation_image/29148bbb9939cece6fec45b6b635bbdf/image-17.jpg "Simple Rules for Conversion Sound Pressure, p [Pa] Sound Pressure Level, Lp d. B")
Simple Rules for Conversion Sound Pressure, p [Pa] Sound Pressure Level, Lp d. B re 20 Pa 20 10 2 × 100 × 10 × 4 BA 7666 -11, 17 114 × 3 × 2 1 94 0. 3 0. 2 86 84 80 0. 1 74 40 d. B 20 d. B 12 d. B 6 d. B 10 d. B
Basic Concepts of Sound Contents: Definitions d. B Conversion Sound Fields d. B ± d. B BA 7666 -11, 18
Types of Sound Sources Point source Line source r: Lp 2 r: Lp 3 d. B Plane source r: Lp 2 r: Lp 6 d. B r: Lp BA 7666 -11, 19 860510/1 2 r: Lp
Anechoic and Reverberant Enclosures BA 7666 -11, 20 860511/1
Pressure Field l Loudspeaker l l BA 7666 -11, 21 Enclosure Microphone
Sound Fields Lp Near field Free field Reverberant field 6 d. B A 1 BA 7666 -11, 22 860512/2 2 × A 1 Distance, r
Directivity Index Source Location Directivity Factor Directivity Index, d. B Free field 1 0 L = Lp On a flat plane 2 3 L = Lp + 3 d. B At a junction of two planes 4 6 At a junction of three planes 8 BA 7666 -11, 23 L = Lp + 6 d. B 9 L = Lp + 9 d. B
Pressure Increase at Walls Lp L = Lp + 6 d. B L = Lp + 3 d. B BA 7666 -11, 24
Basic Concepts of Sound Contents: Definitions d. B Conversion Sound Fields d. B ± d. B BA 7666 -11, 25
Two Sound Sources Lp 1 = X d. B Lp 2 = X d. B Lp 1 + Lp 2 = X + 3 d. B BA 7666 -11, 26
Addition of d. B Levels L+ d. B Example: L 1 L 2 L L+ Lt 3 2 = 55 d. B = 51 d. B = 4 d. B = 1. 4 d. B = 55 + 1. 4 = 56. 4 d. B 1 0 0 BA 7666 -11, 27 860512/2 4 d. B 5 10 15 L d. B
![Subtraction of Noise Levels LS+N [d. B] BA 7666 -11, 28 LN [d. B]](http://slidetodoc.com/presentation_image/29148bbb9939cece6fec45b6b635bbdf/image-28.jpg "Subtraction of Noise Levels LS+N [d. B] BA 7666 -11, 28 LN [d. B]")
Subtraction of Noise Levels LS+N [d. B] BA 7666 -11, 28 LN [d. B]
Subtraction of d. B Levels L d. B Ex: LS+N LN L L LS 6 5 4 = 60 d. B = 53 d. B = 7 d. B = 1 d. B = 60 1 = 59 d. B 3 2 1 1 2 3 BA 7666 -11, 29 4 5 6 7 L d. B 8 9 10 LS ~ LS+N
Addition of many d. B values Addition of sound levels : L 1 + L 2. . . + LN = ? For L 1 = L 2 = L 3. . . = LN 10 log N 12 10 8 Examples: N = 2: LTotal = L 1 + 3 d. B N = 10: LTotal = L 1 + 10 d. B 6 4 2 0 0 BA 7666 -11, 30 5 10 15 N
Conclusion l Sound pressure level in d. B is related to 2 * 10 -5 Pascal. l The range of human hearing is 130 d. B. l To add or subtract d. B-values use charts or formulas BA 7666 -11, 31
Literature for Further Reading BA 7666 -11, 32 l Acoustic Noise Measurements Brüel & Kjær (BT 0010 -12) l Noise Control - Principles and Practice Brüel & Kjær (188 -81)
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