1. Dept. of Mech. Engineering University of Kentucky 1 Two Vacuums Shopvac Bosch

2. Dept. of Mech. Engineering University of Kentucky 2 Bosch Vacuum Exhaust flows through foam

3. Dept. of Mech. Engineering University of Kentucky 3 Shopvac Vacuum

4. Dept. of Mech. Engineering University of Kentucky 4 Sound Quality Bosch (original) Bosch (w/o foam) Shopvac Bosch (w/o 1 st peak)

5. Dept. of Mech. Engineering University of Kentucky 5 Sound Quality: Jury Test Note: Rate each vacuum on a scale from 1 to 10 where 1 is “very quiet” and 10 is “very loud.”

6. Dept. of Mech. Engineering University of Kentucky 6 Foam Inside Bosch Vacuum

7. Dept. of Mech. Engineering University of Kentucky 7 Sound Intensity (Shopvac)

8. Dept. of Mech. Engineering University of Kentucky 8 Sound Intensity (Bosch)

9. Dept. of Mech. Engineering University of Kentucky 9 Sound Intensity (Bosch)

10. Lesson 2 Noise Measurements Slides © 2006 by A. F. Seybert

11. 11 Dept. of Mech. Engineering University of Kentucky Instrumentation PC Spectrum analyzer Display Function Generator sine wave square wave Loud- speaker Sound level meter

12. 12 Dept. of Mech. Engineering University of Kentucky SLM Calibration 94 dB tone @ 1 kHz Adjust until display reads 94 dB Calibrator Calibration should be checked each time SLM is turned on and before it is turned off.

13. 13 Dept. of Mech. Engineering University of Kentucky Pure Tone Sounds Pure tones are sounds at a single frequency

14. 14 Dept. of Mech. Engineering University of Kentucky time Frequency Spectrum Fourier Series of a Square Wave

15. 15 Dept. of Mech. Engineering University of Kentucky Reference Quantities and Decibel Scales Example: what is the sound pressure level of a pure tone sound having a peak sound pressure of 1 Pa? Definition of the decibel:

16. 16 Dept. of Mech. Engineering University of Kentucky Typical Sound Pressure Levels Source/Environment L P (dB) p rms (Pa) Launch noise, near payload bay1602,000 Heavy artillery near gunner’s head140 200 Large jet engine, 30 m120 20 Inside textile factory (uncontrolled)100 2 Shouted male voice, 1 m 80 0.2 Two-person conversation 60 0.02 Residential neighborhood, night 40 0.002 Empty symphony hall 20 0.0002 Average threshold of hearing (1 kHz) 0 0.00002

17. 17 Dept. of Mech. Engineering University of Kentucky Sound Level Meter Block Diagram Micro- phone Meter Filter Circuit Amp Weighting Networks Rectifier RMS Meter To oscilloscope or analyzer if desired pipi Sound pressure e0e0 e1e1 e2e2 e3e3 e4e4 A, B, C, flat Fast/Slow

18. 18 Dept. of Mech. Engineering University of Kentucky The Electrodynamic (Moving Coil) Microphone Sound Waves Vibrate Diaphragm Voltage output from coil is Proportional to velocity Of Diaphragm (the inverse of a loudspeaker)

19. 19 Dept. of Mech. Engineering University of Kentucky The Piezo-electric Microphone

20. 20 Dept. of Mech. Engineering University of Kentucky The Condenser (Capacitor) Microphone

21. 21 Dept. of Mech. Engineering University of Kentucky Condenser Microphone - Schematic Sound Waves Diaphragm (foil, 0.0001” thick) Air gap, 0.001” Back plate with damping holes case Quartz insulator e0e0 Polarization voltage EbEb e0e0 Polarization voltage EbEb Variable capacitance Equivalent Circuit Protective Grid

22. 22 Dept. of Mech. Engineering University of Kentucky Characteristics of the Condenser Microphone High sensitivity – 25 to 50 mV/Pa Requires polarizing voltage of 150-200 V dc (needed to initially charge the microphone); determines sensitivity Wide frequency response (limited by diaphragm resonance frequency at high frequency and venting at low frequency) Good linearity over a wide range of sound levels High output impedance – requires signal conditioning close to diaphragm Susceptible to humidity when temperature is close to the dew point Delicate B&K 4190 ½” microphone: Sensitivity: 50 mV/Pa Polarization: 200 V dc Frequency range: 5 Hz – 10 kHz (+/- 1 dB); resonance freq. = 14 kHz SPL range: 15 dB – 148 dB (3% distortion) Operating temperature range: -30 to 150 degrees C

23. 23 Dept. of Mech. Engineering University of Kentucky Characteristics of the Condenser Microphone Sensitivitas tinggi - 25 sampai 50 mV / Pa Membutuhkan tegangan polarisasi dari 150-200 V dc (diperlukan untuk awalnya mengisi mikrofon); menentukan sensitivitas Respon frekuensi yang luas (dibatasi oleh frekuensi resonansi diafragma pada frekuensi tinggi dan ventilasi pada frekuensi rendah) linearitas baik pada berbagai tingkat suara Keluaran impedansi tinggi - memerlukan pengkondisian sinyal dekat dengan diafragma Rentan terhadap kelembaban saat suhu mendekati titik embun Halus B&K 4190 ½” microphone: Sensitivity: 50 mV/Pa Polarization: 200 V dc Frequency range: 5 Hz – 10 kHz (+/- 1 dB); resonance freq. = 14 kHz SPL range: 15 dB – 148 dB (3% distortion) Operating temperature range: -30 to 150 degrees C

24. 24 Dept. of Mech. Engineering University of Kentucky Frequency Analysis of Noise Uses of frequency analysis: Noise source diagnostics (resonances, etc.) Qualification testing of prototypes Conformance to company, industry, or international standards Other Types of frequency analysis: Narrowband (FFT based) – best frequency resolution (reveals narrow peaks due to resonances, harmonics); lots of data Octave band – best for broadband noise – limited data One-third, one-twelfth octave bands – narrower versions of octave band filters

25. 25 Dept. of Mech. Engineering University of Kentucky Octave Band Filters Frequency (Hz) 63 125 250 1000 500 Each octave band filter has a fixed center frequency and is twice as wide as the one before it. Each octave band filter may be divided into three one-third octave band filters for more frequency resolution. etc. 0.707 x center frequency

26. 26 Dept. of Mech. Engineering University of Kentucky Octave Band Filters (Partial List) Center Frequency (Hz)Lower Band Limit (Hz)Upper Band Limit (Hz) 634488 12588177 250177355 500355710 10007101420 200014202840 400028405680 8000568011360 160001136022720

27. 27 Dept. of Mech. Engineering University of Kentucky One-Third Octave Band Filters (Partial List) Center Frequency (Hz)Lower Band Limit (Hz)Upper Band Limit (Hz) 5044.756.2 6356.270.8 8070.889.1 10089.1112 125112141 160141178 200178224 250224282 315282355

28. 28 Dept. of Mech. Engineering University of Kentucky Example Same Spectrum, Various Frequency Bands

29. 29 Dept. of Mech. Engineering University of Kentucky Equal Loudness Contours Experiment: ask subjects to compare a second tone to one at 1 kHz by increasing or decreasing the level of the second tone until it the two tones have equal loudness. Sounds at lower frequency must have a higher SPL to be judged equivalent in loudness to the tone at 1 kHz. The hearing mechanism does not have a flat frequency response.

30. Tugas 1. dikumpul paling lambat senin, 26 Maret 2012 Buat makalah tentang : – Piezo electric microphone – Condensor microphone – 1 oktaf, 1/3 oktaf, narrowband Tulis sumbernya: buku, artikel, internet, dsb. Kirimkan hasilnya ke email: suudi@unila.ac.id atau ke suudipolda2@gmail.comsuudi@unila.ac.idsuudipolda2@gmail.com