BA , 1 Basic Concepts of Sound Contents: Definitions dB Conversion Sound Fields dB ± dB

BA , 2 Sound /1

BA , 3 Sound and Noise /1

BA , 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

BA , 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]

BA , 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   /2

BA , 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

BA , 8 Sound Pressure Pressure [Pa] Pascal Time /1

BA , 9 Sound Pressure Pascal Atmospheric Pressure Mexico City New York Pressure [Pa] Acoustic Pressure Variations

BA , Range of Sound Pressure Pressure, p [Pa] /2

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

BA , 12 Sound Pressure, p [Pa] Range of Sound Pressure Levels Sound Pressure Level, L p [dB] /2

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

BA , 14 Perception of dBs Change in Sound Level (dB) Change in Perceived Loudness Just perceptible Noticeable difference Twice (or 1/2) as loud Large change Four times (or 1/4) as loud

BA , 15 Conversion to dB using Charts dB re 20  Pa Pressure [Pa] p 0 = 20  Pa 94 dB LpLp

BA , 16 Conversion to dB using Tables dB to Pressure Ratio Pressure Ratio  db  Pressure Ratio Pressure Ratio  db  Pressure Ratio

BA , 17 Simple Rules for Conversion Sound Pressure Level, L p dB re 20  Pa Sound Pressure, p [Pa] × 100 × 10 × 2 × 3 × 4 6 dB 10 dB 20 dB 40 dB 12 dB

BA , 18 Basic Concepts of Sound Contents: Definitions dB Conversion Sound Fields dB ± dB

BA , 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 /1

BA , 20 Anechoic and Reverberant Enclosures /1

BA , 21 Pressure Field Loudspeaker Microphone Enclosure

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

BA , 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 Directivity Index, dB

BA , 24 Pressure Increase at Walls L = L p + 3 dB L = L p + 6 dB LpLp

BA , 25 Basic Concepts of Sound Contents: Definitions dB Conversion Sound Fields dB ± dB

BA , 26 Two Sound Sources L p1 = X dB L p2 = X dB L p1 + L p2 = X + 3 dB

BA , 27 Addition of dB Levels Example: L + dB  L dB L1L2LL+LtL1L2LL+Lt 55 dB 51 dB 4 dB 1.4 dB = 56.4 dB ========== 4 dB 1.4 dB /2

BA , 28 Subtraction of Noise Levels L S+N [dB] L N [dB]

BA , 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  L dB L S ~ L S+N 

BA , 30 Addition of many dB values Addition of sound levels : For L 1 = L 2 = L = L N Examples: N = 2: L Total = L dB N = 10: L Total = L dB log N N L 1 + L L N = ?

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

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