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BA7667-11, 1 Measuring Sound Contents: The Microphone The Sound Level Meter L eq Statistics and Noise Dose.

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Presentation on theme: "BA7667-11, 1 Measuring Sound Contents: The Microphone The Sound Level Meter L eq Statistics and Noise Dose."— Presentation transcript:

1 BA , 1 Measuring Sound Contents: The Microphone The Sound Level Meter L eq Statistics and Noise Dose

2 BA , 2 Measuring Microphones /1

3 BA , 3 The Polarised Condenser Microphone Principle of Operation Z V in Q = CV /1

4 BA , 4 How much does the diaphragm move ? V V d d = For typical measurement microphone: – diameter 12.5 mm – thickness of diaphragm 5 µm – distance between diaphragm and backplate 20 µm – polarisation voltage 200 V – sensitivity 50 mV/Pa For 94 dB = 1 Pa the diaphragm moves V d V 50 mV 20 µm 200 V == d = 5 nm Diameter of diaphragm Pressure (level re 20µPa Diaphragms movement 12.5mm1Pa(94dB)5nm (5 x 10 –9 m) 12.5mm0.02Pa(60dB)1 Å(10 –10 m) 12500km (thickness of diaphragm 5km) 0.02Pa(60dB)0.1m(10 –1 m) Pa(20dB)0.001m(10 –3 m)

5 BA , 5 Directional Characteristics 90° 0° 180°0° 2 kHz 8 kHz 12 kHz ° ° 180° /1

6 BA , 6 Types of Microphones Random incidence Pressure Free field

7 BA , 7 Free Field Correction p0p0 pmpm log dB p0p0 pmpm f 27k 1/81/41/2124 2k5k10k20k50k100k D (D=1/2) Hz D

8 BA , 8 Free Field Correction L dB ° 30° 60° R 90° 120° Frequency 0° 90°

9 BA , 9 Measuring in Accordance with Standards: IEC ANSI 70° – 80°

10 BA , 10 Use of Free Field Microphones

11 BA , 11 Use of Random Incidence Microphones /1

12 BA , 12 Measuring Sound Contents: The Microphone The Sound Level Meter L eq Statistics and Noise Dose

13 BA , 13 Hold The Sound Level Meter RMS Peak Fast Slow Impulse 87.2 Time LpLp p

14 BA , 14 Sound Level Parameters p Pa PeakPeak – Peak RMS = Average = p Pa Time Average Crest factor = Peak RMS

15 BA , 15 Basic Sound Level Parameters p Pa PeakRMS p Pa Crest factor = Peak RMS Time

16 BA , 16 Time Weighting p LpLp Time Slow (1 s) Fast (125 ms) Impulse (35 ms) Impulse (1.5 ) Slow (1 s) Fast (125 ms) LpLp

17 BA , 17 Peak Hold p LpLp Time LpLp

18 BA , 18 Time Weighting p LpLp Time Impulse Fast Slow LpLp

19 BA , 19 Time Weighting Fast LpLp Time Slow Time LpLp

20 BA , 20 The Digital Display LpLp Time

21 BA , 21 Measuring Sound Contents: The Microphone The Sound Level Meter L eq Statistics and Noise Dose

22 BA , 22 Equivalent Level, L eq L eq T LpLp Time

23 BA , 23 LpLp Time L eq Measuring L eq

24 BA , 24 L eq for Transient Noise LpLp Time L eq Transient

25 BA , 25 Sound Exposure Level and its Origin LpLp Time SEL 1SEL 2

26 BA , 26 Time Sound Exposure Level, SEL 1 s L eq L dB(A) SEL t

27 BA , 27 Measuring Sound Contents: The Microphone The Sound Level Meter L eq Statistics and Noise Dose

28 BA , 28 Level Sampling Time dB(A) Time dB(A) Sample

29 BA , 29 Noise Level Distribution Distribution of levels Time dB(A) dB(A) Time Noise Level Distribution dB(A) Sample

30 BA , 30 Cumulative Distribution L 10 L 50 L %50%90% Time dB(A) Distribution of levels Time dB(A) Noise Level Distribution

31 BA , 31 Percentile Levels Cumulative Distribution L 10 L 50 L %50%90% Time dB(A) Noise Level Distribution Time L 10 L 50 L 90 dB(A)

32 BA , 32 Statistical Analysis of Noise Levels Cumulative Distribution L 10 L 50 L %50%90% Time dB(A) Distribution of levels Time dB(A) Noise Level Distribution Time dB(A) Sample

33 BA , 33 Percentile Levels, L N Time L 10 L 90 dB(A) 100% Time ab 10% time a + b = 10% time

34 BA , 34 Noise Dose Measurement in Practice

35 BA , 35 Definition of Noise Dose 8 hours in = 100 % Noise Dose The actual dB level depends on National Legislations. In some countries the level is 80 dB

36 BA , 36 Noise Dose Examples 8 hours4 hours % 50% 100% 200% dB(A) 8 hours4 hours 85 dB(A) 8 hours4 hours 85 dB(A) 8 hours4 hours 85 dB(A)

37 BA , 37 Daily Personal Noise Exposure, L EP,d Time dB(A) T 0 = 8 hours Work period T e L Aeq,Te Example: L Aeq,Te = 89.2 dB and T e = 4 hours MorningLunchGo Home

38 BA , 38 Standards ISO 9612 Guidelines for the measurement and assessment of exposure to noise in a working environment ISO 1999 Determination of occupational noise exposure and estimation of noise-induced hearing impairment IEEC Directive EEC/86/188 The protection of workers from the risk related to the exposure to noise at work OSHA Occupational Safety and Health Act International The European Union USA and others

39 BA , 39 Exchange Rate Time L dB(A) L eq = (85 + Exchange Rate) dB L eq = 85 dB 8 hours 4 hours Exchange Rate, q 8 hours 4 h.

40 BA , 40 ISO vs. OSHA L eq dB(A) hour2 hours4 hours8 hoursTime 3 dB 5 dB ISO (q = 3) OSHA (q = 5) Logarithmic time axis

41 BA , 41 Noise Dose and Peak Time L EP, d L C, pk No peaks above this level allowed L p dB

42 BA , 42 Conclusion The sensitivity of a microphone depends on the direction of the noise - that is why there are free-field and random- incidence microphones Sound level meters are integrated measurement equipment with standardized time weightings and measurement parameters The L eq is the energetic average of the noise over a period of time and is one of the most important noise measurement parameters The Noise Dose and Daily Personal Noise Exposure (L EP,d ) are ways of showing how much noise exposure a person has received in relation to legal limits

43 BA , 43 Literature for Further Reading Acoustic Noise Measurements Brüel & Kjær (BT ) Noise Control - Principles and Practice Brüel & Kjær (188-81)


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