Lab Manual for ME5440page 1 ME5440: Industrial Noise Control Laboratory Manual Dr. Sean F. Wu Fellow, ASA, ASME University Distinguished Professor Department of Mechanical Engineering Wayne State University Detroit, MI 48202 Tel: (313)577-3884 (Office) Fax: (313)577-8789 E-mail: [email protected] Copyright 2011 Lab Manual for ME5440 page 2 Preparation of Lab Reports A great deal of literature has been written on the technique and style of report writing and many different formats exist to satisfy different institutions and purposes. The following short format is offered as a guide to the elements of a technical report. This format represents a consensus opinion of many writers and is not be interpreted as the only acceptable format for a technical report. 1. Title Page: This page should include the title of the experiment, course name and number, instructor, group members, date of report, and author. 2. Summary: The summary should indicate the following paragraphs with proper subtitles: (a) Objectives (b) Experimental Setup (including the major equipment used) (c) Results and Discussion: This paragraph should include the experimental results and calculations using words, graphs, and tables, and comparisons of the measured data with the theoretical or expected values. Also, discussions of the results obtained, any interesting phenomena observed, and reasons why they may happen should be included. (d) Conclusion: This paragraph should describe what you have learned from this experiment and what other people can learn from your experiment. 3. References: Include all references that can support your calculations, reasoning, and conclusions. All reports must be typed in double space on one side of the paper (8 ½’’ by 11’’). Each page should be numbered and have a minimum margin of 1’’ on all sides. The report should be bounded with a report cover. Copyright 2011 Lab Manual for ME5440 page 3 LabVIEW Based Microphone Calibration: Table 1. Serial Number of Microphones 1/2" Prepolarized Free Field Microphone ICP Microphone Preamplifier Channel #1 Serial No. 23417 Serial No. 2209 Channel #2 Serial No. 21908 Serial No. 2274 1. Left double click on desktop, or find the software at “StartProgram National InstrumentsMeasurement & Automation” A window will be opened as: 2. Click “My systemData NeighborhoodNI-DAQmx Tasks” and then click “ Create New NI-DAQmx Task” on the right Copyright 2011 In the “Creat New NI-DAQmx Task” window. Click “Next” Enter name of the new taskFinish. Click “Acquire SignalsAnalog InputSound Pressure” and then choose “a0” and “a1” under “Dev1 (USB-9234)”. then the window becomes: Copyright 2011 .Lab Manual for ME5440 page 4 3. and then click “Calibration” “Calibrate…”type in the Calibrator’s Name “Next” Fill the blank for “Acquisition Duration (s)” and “Sample Rate (Hz)”. make sure the “Sound Pressure_0” is chosen. The Default is value is shown as below: Click “Next” Change the “Frequency” and “Sound Pressure” to value of the piston phone as shown below: Copyright 2011 . page 5 To calibrate the Channel #1.Lab Manual for ME5440 4. Lab Manual for ME5440 page 6 The piston phone used in this class is B&K piston phone type 4220. click “Finish” to close the window 6. Turn on the piston phone. Choose the “Sound pressure_1” and repeat step 4 to 5 to calibrate Channel #2. Based on the calibration result on 08/25/2011: The sensitivity of Channel #1 is 57. Stop clicking and when the value of sensitivity is stable. Serial No. The sensitivity of Channel #2 is 45.3978 mV/Pa. Close the “Measurement & Automation Explorer” window when finished. 704798. 5. sound pressure level is 124. Click .2545 mV/Pa.0 dB re 2×10-5 Pa. Copyright 2011 . 8. and write down the sensitivity of this microphone. the sensitivity will be changing in real time. and Frequency is 250 Hz ±1% in “Measure” position (for fresh batteries). the sensitivity is committed. 7. Setup the parameters for measurement. Thus the port “ai0” indicates the Channel #1. a. and “ai0” indicates the Channel #2. Left double click “Sound Level Meter. Microphone sensitivities Fill the sensitivities that are obtained by microphone calibration.vi”. Copyright 2011 . Physical Channels Set up the physical channels for the microphones. Note that the index in LabView program starts from zero. b.Lab Manual for ME5440 page 7 LabVIEW based Sound Pressure Level Meter: 1. The default setup is shown as the figure below. 2. “Averaging” means that the sound level results are averaged. then the paragraphs and sound levels update every one second. “Instantaneous” means that the sound level results shown on front panel are from the recent period of measurement. the gray box updates how many times are finished. f. Measure method There are two options for the measurement method. Weighting Weighting defines the method of calculating the sound levels. Number of averages If “Averaging” option is chosen in the “Measure method”. then one need to further define the number of averages. Copyright 2011 . and the default number of averages is 100 times. And when the averaging reaches the defined number of averages. One can define any number of averaging. When the program is running. the green light will change to light green and the program will stop gathering data from microphones. as shown below. Sampling period when gathering data Define the sampling period of measurement. If the sampling period of the measurement is set equal one.Lab Manual for ME5440 page 8 c. e. d. Note that the measurement results update every period. h. A higher value need more computer memory and may crash the computer. Copyright 2011 . Frequency resolution = (stop frequency – start frequency)/number of lines Note: Don’t increase the “number of lines” higher than default unless required. The “Frequency resolution (Hz)” is calculated by program automatically based on the input of “frequency range”. Bandwidth Bandwidth defines the display in the Spectrum. Frequency range If “narrow band” is chosen in “Bandwidth”.Lab Manual for ME5440 page 9 g. one needs to further fill the blanks of “frequency range”. Read sound levels Note that the sound levels are shown in dB. Note that one can choose to see “Microphone 1”. If the octave frequency band is chosen. Copyright 2011 . “Microphone 2”. Time domain waveform. the one can click on and move the cursor step by stop. Run the program by clicking page 10 . spectrogram and the spectrum are shown in this program. but the figures are smaller. If it is difficult to drag the cursor to the target frequency. 4.Lab Manual for ME5440 3. One can move the cursor in the Spectrum to see the dB level of a precise frequency band. then the frequency showing above the cursor is the central frequency of that band. “Both” shows both of these two microphones’ data. or “Both”. “Microphone 1” or “Microphone 2” shows the data at Channel #1 and #2. the first column shows the frequency. 6. A “ Choose file to write” window will jump out. Copyright 2011 .Lab Manual for ME5440 page 11 5. Record the sound levels Click to save the sound level to a “. When opening the txt file.txt” file. Close program. the second column shows the sound level at Channel #1.txt” with the file name. remember to write “. and the third column shows the sound level at the Channel #2. Click 7. until the program stops. Define the parameters on the left a. Sensor sensitivity Fill in the sensitivity gained in microphone calibration Copyright 2011 .Lab Manual for ME5440 page 12 LabVIEW Based Reverberation Time Measurement 1.vi” 2. Physical Channel Channel #1 is used. otherwise the data acquisition doesn’t work. and one can use minimum one channel. the first port (AI0) must be used. as we only use one microphone in this experiment. we must connect the microphone to the first port (AI0). However. Note: The NI-9234 has totally four channels. b. Left double click “T 60. In other word. The left one is the time domain signal. clapping) 5. The measurement will stop when the impulsive sound reach the trigger level. Weighting The default is “Linear” d. 4. Play the impulsive sound (for example. Click to run program The upper two graphs show data in real time. Frequency range The value is fixed in the experiment 3. Trigger Level Is should be decided based on the experiment environment.Lab Manual for ME5440 page 13 c. Copyright 2011 . e. the right one is the spectrum. Copyright 2011 . Change the frequency band to find the T60 for each frequency band.Lab Manual for ME5440 page 14 6. time graph is shown on the left lower corner. For example. if 1000 Hz is chosen. then a detailed SPL vs. The “T60(ms)_manual” can be decided manually by moving the two yellow cursors in the “SPL vs. time” graph.Lab Manual for ME5440 page 15 The “T60(ms)_auto” is updated automatically. which is calculated by computer. It uses the curve from the peak to the first positive inflection point next to it. Copyright 2011 . The graph on the right lower corner shows the T60 vs Frequency. Moving the yellow cursor can see the detailed value of the frequency and T60. which uses the “T60(ms)_auto”.Lab Manual for ME5440 page 16 7. Copyright 2011 . In the saved txt file. Click page 17 to save the T60 values. and the second column is value of “T60(ms)_auto”. the first column is the central frequency of each frequency band. Copyright 2011 .Lab Manual for ME5440 8. Move the cursor to the right most position on the same line and select V/PA.. Once the internal program checks are completed successfully. Check and set microphone sensitivity to the specified value. T to Total by pressing key repeatedly. Mark measurement microphone positions according to Table 1. (g) Move cursor one step up and set MEASUREMENT to CH. or to move cursor to the 3rd position on Ch. Set the microphone at the position of measurement point #1. Use Field Select keys <. If it is 200 V. Lay the sound source on the center of the chamber floor. Place the sound source at the origin of the Cartesian coordinate system. press Reset and 9 on the numeric keypad simultaneously. as well as the usage of B&K Dual Channel Signal Analyzer Type 2032. the 3rd line from the bottom of the screen. 2. Set input type to PREAMP by using Field Entry key or repeatedly. and wave propagation in a free field. 10. SPECTRUM AVERAGING. 6. 1669464. Input of Channel A and B of B&K 2032. Then press 49m and ENT on numeric keypad. (d) Move cursor two steps up and set FREQ SPAN to 400Hz using Field Entry key. Calibrate the microphone by using the B&K Pistonphone Type 4220 as follows: (a) Place a ½’’ adapter on the Pistonphone head. (c) Move cursor one step up and change WEIGHTING to HANNING by pressing the Field Entry key. set Pol. 3. the sensitivity is 49 mV/Pa. A. power amplifier. serial no. Turn on the power of B&K 2032. 1 Determination of Cut-off Frequency of a Free Field Objective: To familiarize the basic concepts of wavelength. Voltage to 200 V. for the ½’’ B&K Prepolarized Condenser Microphone Type 4189. Plug the power cord of B&K Dual Channel Signal Analyzer Type 2032 to an outlet. Move cursor to the third line from the top and change Ave. If it is 0 V. (b) Fit the Pistonphone on a ½’’ microphone and switch on the Pistonphone. . 5. Voltage on B&K 2032 to 0 V. Procedures: 1.Lab Manual for ME5440 page 18 Experiment No. Connect microphone cables to Preamp. then one step to the right and select 100 averages by typing 100 and ENT on the key pad (f) Move cursor one step up and set TRIGGER to FREE RUN. Check the Polarization Voltage of the microphone in use. speaker. 7. 4. 9.A. (e) Move cursor one step up and set AVERAGING to LIN. For example. cut-off frequency. 8. and signal generator. Copyright 2011 . >. set Pol. Major Equipment: B&K Dual Channel Signal Analyzer Type 2032. g. (Now you can view the data thus collected. Click Acquire Data on the STARAcoustics diagram. (Now STARAcoustics is ready to take data. A. line at the bottom and adjust the microphone sensitivity.5 dB. Open the door and move microphone to the next location according to Table 1 and close the chamber door. Turn on the signal generator and select random signals. Then close grid. The STARAcoustics diagram will appear. Click New Project. set Directions to X only. Open STARAcousticss on computer by double clicking STARAcoustics icon. 26. (i) Move cursor one step up to the fourth position from the left and select RMS.5 dB. Compare these values between two spectra with doubling of distance. The SPL (sound pressure level) value at 250 Hz should be 124 dB. 17. Select Cancel on the next screen.. 14. and finally to the 1st position from the left on the same line and set 130dB by typing 130 on key pad. 27. Click Analyzer on the next screen. select a group name under c:\acoustic\me5440. 12. (l) Press Start to start calibrating the microphone on Channel A. 24. If one dimensional grid is used. 18. #3 vs. Repeat Step 9 to calibrate microphone on Channel B. Press Input Autorange on B&K 2032. #6. Turn on the power amplifier and adjust output power to a desired level.A. and close Project Slate. Observe the display of auto-spectrum on the screen. If the difference is less 0. 16. The value of Y should be 124 dB. 35. #2. 15. Press Cursor once followed by the key repeatedly to move to cursor line to 250 Hz. 34. (k) Press Input Autorange once.) 21. #4. then one step left to set 20U by typing 20 on the key pad. Check SPL values at each frequency band. Open any measurement file and display sound pressure spectrum. Click OK followed by Close. 11. Copyright 2011 . 23.) 33. 19. Click Mesh Generator on the STARAcoustics diagram and set X&Y to start from 1 to 16 with 15 divisions. 22. Click Show Measurement on the STARAcoustics diagram. Repeat Steps 24 and 25 until all measurements are taken. etc. calibration is done. Press Start on B&K 2032 to collect sound pressure spectrum at the measurement point #1. select Yes Hamming windows followed by OK. Exit the chamber and close the door. #1 vs. 25. change SMS_DEMO to BK2032. Click Accept on computer screen to transfer data to the computer. 36. then move cursor to Ch. #5 vs. Click Show Grid/Vector to view the grid thus generated. 20. Click Type and select Autopower and unselect Crosspower. e. (j) Move cursor to the 2nd position from the left on the top line and select AUTO SPEC CH. followed by OK. 13. then OK. Close BK2032 Analyzer Control and Measurement Display screens and go back to the original STARAcoustics diagram. If the difference is more than 0.Lab Manual for ME5440 page 19 (h) Move cursor two steps up and to the right most position and select TOTAL by pressing Field Entry key repeatedly. 5 1.0.0. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 X (m) 0.5 .0 0.0 0 0 0 0 0.0 . Measurement scheme.0 0 0 0 0 0. Table 1.0 .5 1. 3.0 .5 1.1.0 . page 20 Find the cut-off frequency at which the difference in SPL values between two spectra is less than 6 dB. 4.5 .0 0 0 z (m) 0 0 0 0 0 0 0 0 0.5 .5 1.5 1.5 1. 5.1.5 1. No.5 .0 0. 2.0 Write a report and answer the following questions: 1.0 0. Copyright 2011 .5 1. Try to explain your observations and answer these questions. What is the cut-off frequency of this chamber? What sound field is it for frequency below the cut-off frequency? What sound field is it for frequency above the cut-off frequency? Why do you place the sound source on the floor? Will the same procedure work if the sound source is set at certain distance above the floor? You may have your own observations and questions.5 1.0.Lab Manual for ME5440 37.0 0 0 0 0 0 0 y (m) 0 0 0 0 0.1.0.0 0.1. 7. If it is 200 V. 13. 9.) 3. Measure and record the ambient noise spectrum by pressing Input Autorange once followed by Start. average to Lin. For the ½’’ B&K Prepolarized Condenser Microphone Type 4189. Press Cursor once followed by the key repeatedly to move the cursor line to 250 Hz. Copyright 2011 . Fit the Pistonphone on a ½’’ microphone and switch on the Pistonphone. A. Move cursor to the third line from the top and change Ave. Once the internal program checks are completed successfully. Press Start and Auto Scale. 15. Connect microphone cable to Preamp. 12. Follow the instructions shown on the screen and insert Start-Up disk 1 and 2. The value of Y should be close to 124 dB.0mV on Ch. 2.5 mV/Pa. Input of Channel A of B&K 2133. Voltage on B&K 2133 to 0 V. 1783577. Move cursor to Averaging line and change Exp. 16. set Pol. The SPL (sound pressure level) value at 250 Hz should be 124 dB. press Reset and 9 on the numeric keypad simultaneously. Procedures: 1. If the difference is less 0. serial no. Check the Polarization Voltage of the microphone in use. 11. (Use an adapter for the old model cable that has a long 7-pin head. Turn on the power of B&K 2133. T to Total by pressing key repeatedly. Press Auto Scale to get a better view of display. 5. Place a ½’’ adapter on the Pistonphone head.5m and ENT on the numeric keypad. set Pol. average and set average time to 4 s. Calibrate the microphone by using the B&K Pistonphone Type 4220 as follows: 10. This can be done by pressing 52. 2 Measurement of Sound Pressure Levels in a Noisy Environment Objective: To measure sound pressure levels of various sources in a noisy environment and to familiarize the use of B&K Real Time Frequency Analyzer Type 2133. >. Observe the display of auto-spectrum on the screen.5 dB. Press Input Autorange once. 14. Voltage to 200 V. line at the bottom and set microphone sensitivity to the specified value. . 4.5 dB. If the difference is more than 0. New model cable has a short 7-pin head and does not need an adapter. If it is 0 V. line at the bottom and adjust the microphone sensitivity. the sensitivity is 52. Use Field Select keys <. 6. Major Equipment: B&K Real Time Frequency Analyzer Type 2133 and various sound sources. average by pressing key once.Lab Manual for ME5440 page 21 Experiment No. then move cursor to Ch. press Stop. Move cursor on B&K 2133 to Averaging line and select Exp. A. Plug the B&K Real-Time Frequency Analyzer Type 2133 to power outlet. and to move cursor to 50. 8. Can you tell the type of environment (e. 20. Repeat Steps 16 – 18 to measure and record spectra in both linear and A-weighting at a location that is approximately equal distance to all three sources. 28. measure and record the noise spectra of the second source at the same location as that in Step 22.) based on your measured noises at location A and location B? You may have your own observations and questions. and speaker at locations A. Turn off the first and second sources. 27. Compare the measured noise spectra and total SPL with the calculated ones by using L p 10 log10 10 L1 10 10 L2 10 where L1 and L2 are the SPL values of the first and second sources obtained in Steps 22 and 23. 24. Press Auto Scale to get a better view of display. 21.g. Try to explain your observations and answer these questions. free field. 18. reverberant. Press Cursor once and record the SPL values in each 1/3-octave band by pressing or repeatedly. Set three sources. 26. and Ls implies the SPL values of the centrifugal blower alone. with the engine and air flow running together). respectively. measure and record the noise spectra of the third source and compare them with those calculated in Step 27. and C. What have you learned from this experiment? How do you obtain the noise spectrum of a machine in a noisy environment? Where should you take noise measurement in a noisy environment? In this experiment. 3. 19. Lb indicate the SPL values of the background noises (e. Turn off the first source and turn on the second source. 2. a vacuum cleaner. a vacuum cleaner at location A. for example. semireverberant. 22. Calculate the noise spectra of the third source by using Ls 10 log 10 10 Lc 10 10 Lb 10 where Lc represents the combined SPL values with all machines running together. Write a report and answer the following questions: 1. 23.g. Turn on the power of the third source. hand drill. Measure and record the noise spectra with the first source on. 4. B. do your measurements agree with your calculations in Steps 21 and 24? 5. Move cursor to the beginning of the second line from the top and press 20 on the numeric keypad followed by ENT to record the A-weighting spectrum.Lab Manual for ME5440 page 22 17... Turn on the power of the first source at location A and measure the noise spectra again with the second source on. Turn on the first source. respectively. Press Auto Scale to get a better view of display. 25. for example. Copyright 2011 . measure and record the noise spectra at the same location as that in Step 24 with all three sources running together. etc. ADJ. potentiometer on the side of the sound level meter with a small screwdriver. 6.1 dB. B&K Pistonphone Type 4220. The display should indicate 124 dB 0. and a shop vacuum cleaner. Procedures: 1.2 are area-averaged total SPL values measured on hemi-spherical surfaces S1 and S2 . WEIGHTING: “Lin” EXT. Repeat Step 4 for a hemi-spherical surface at r 2 m. Set a shop vacuum cleaner in the center of an open space and turn on its power. Calibrate the B&K Precision Sound Level Meter Type 2230: (a) Set controls of the sound level meter as follows: Power: “On” REF-OPERATE: “Operate” FSD: “120” RESET: “All” FREQ. Calculate the radiated sound power level from the vacuum cleaner by using LW 10 log10 10 L p .Lab Manual for ME5440 page 23 Experiment No. Major Equipment: B&K Precision Sound Level Meter Type 2230. (d) If an adjustment is necessary. 3. respectively. turn the SENS. 4. 5. FILTER: “Out” DISPLAY: “SPL” TIME WEIGHTING: “Fast” DETECTOR: “RMS” (b) Fit the pistonphone over the microphone using an ½’’ adapter (c) Switch on the pistonphone and wait for the display to stabilize. 2 10 10 log 10 S1 1 S1 S2 where Lp . Measure the total ambient SPL values in both linear and A-weighting of the room in which experiments are to be conducted.1 10 10 L p . 3 Measurement of Sound Power Levels in a Semi-Reverberant Environment Objective: To measure sound power levels of a source in a semi-reverberant environment and to familiarize the use of B&K Precision Sound Level Meter Type 2230. Copyright 2011 . 2. Set the radius of a hemi-spherical surface at r 1 m and take the SPL measurements at all ten points as shown in Table 1.1 and Lp. 773 0. 8.446 -0.151 10 0.452 8 -0.327 0. 9.151 9 0.327 -0.566 0.757 5 0.856 0. and S1 and S2 are the total “transparent” areas of the measurement surfaces at r 1 m and r 2 m.495 -0. Does the result of Step 6 agree with that of Step 8? Why? 4.446 0. excluding the reflecting surface on the ground. Try to explain your observations and answer these questions.452 6 -0. Table 1.773 0.757 3 0.892 0 0.856 0. Repeat Steps 4 to 6 to measure the total radiated acoustic power level from the vacuum again. Should the total radiated acoustic power from the vacuum cleaner change with the measurement points? 3.757 4 0. j where Si .495 0.989 0 0. respectively.Lab Manual for ME5440 page 24 1 Lp . j is the jth segment of the surface Si . Turn on the power of a centrifugal blower as background noises.452 7 -0.i 10 log10 Si 10 8 L j 10 j 1 Si . x y z 1 0 0 1 2 -0. What have you learned from this experiment? 2. No. 7. Can we use this method to measure sound powers when the background noise levels are non-negligible? You may have your own observations and questions.653 0 0. Copyright 2011 . Coordinates of ten-point measurement scheme. Compare the two results to see if they agree with each other.151 Write a report and answer the following questions: 1.566 0. (c) Move cursor on B&K 2133 to Averaging line and select Exp. The value of Y should be close to 124 dB.0mV on Ch. Voltage to 200 V. serial no.5m and ENT on the numeric keypad. If it is 0 V.5 dB. New model cable has a short 7-pin head and does not need an adapter. Input of Channel A of B&K 2133. and acoustic absorption coefficient and to familiarize the use of B&K Real Time Frequency Analyzer Type 2133. >. 8. 6. (d) Press Input Autorange once. set Pol. Press Cursor once followed by the key repeatedly to move the cursor line to 250 Hz. 2. Once the internal program checks are completed successfully. Voltage on B&K 2133 to 0 V. Use Field Select keys <. This can be done by pressing 52. Press Measurement on Field Select once. 7. If the difference is less 0. a hammer used to produce impulsive signals. Check the Polarization Voltage of the microphone in use. press Stop. 9. press Reset and 9 on the numeric keypad simultaneously. room constant. Procedures: 1. 10.5 dB. and a soft foam whose acoustic absorption coefficient is unknown. Observe the display of auto-spectrum on the screen. average by pressing key once. (Use an adapter for the old model cable that has a long 7-pin head. 4. Turn on the power of B&K 2133. line at the bottom and adjust the microphone sensitivity. (b) Fit the Pistonphone on a ½’’ microphone and switch on the Pistonphone. For the ½’’ B&K Prepolarized Condenser Microphone Type 4189. (e) Press Start and Auto Scale. the sensitivity is 52. then move cursor to Ch.5 mV/Pa. Plug the B&K Real-Time Frequency Analyzer Type 2133 to power outlet. 1783577. Major Equipment: B&K Real-Time Frequency Analyzer Type 2133. set Pol. If it is 200 V. A. If the difference is more than 0. . A. Move cursor to the third line from the top and change Ave. The SPL (sound pressure level) value at 250 Hz should be 124 dB. and to move cursor to 50.Lab Manual for ME5440 page 25 Experiment No. 4 Measurement of Reverberation Time and Room Constant Objective: To measure reverberation time. Calibrate the microphone by using the B&K Pistonphone Type 4220 as follows: (a) Place a ½’’ adapter on the Pistonphone head. Copyright 2011 . Connect microphone cable to Preamp. 5. Follow the instructions shown on the screen and insert Start-Up disk 1 and 2 as requested. T to Total by pressing key repeatedly.) 3. line at the bottom and set microphone sensitivity to the specified value. Move cursor to the top line and change Main to Delta by pressing once. Press Start on Measurement keypad and wait for the message “Waiting for trigger.n for all frequency bands. line at the bottom and set Preamp. V 016 T60 . 23.” 19. Press Clear Buffer on Measurement keypad followed by Command/Execute on the keypad to the right of the screen to clear the buffer. A. T is T60 for the 1/3-octave band centered at 1 kHz. Alternatively. The value of Reverb. Press 52 on the numeric keypad followed by ENT to select the default setting for calculating the reverberation times. steel surface. T by pressing repeatedly. 14. 13. 16. Move cursor to the third line and change [ ] to Reverb. Move cursor to Averaging line and change the average time to 1 128 s. 27. 21. Calculate the average absorption coefficient n in each frequency band by using . Calculate the room constant Rre . 20. Generate impulsive signals by hammering the hammer on a hard. 12. A.Lab Manual for ME5440 page 26 11. 33. Press Auto Accept on Measurement keypad. Move cursor to Ch. Move cursor to the second line and change the value of Z to adjust the width of the shaded area that covers the decay of reverberation time by pressing repeatedly. 15. Press Auto Scale on Display keypad. 31. 26. Press 19 on the numeric keypad followed by ENT to recall the default measurement setup No. Move the cursor to the second line from the top and change the frequency to any other value by pressing or repeatedly. n in each frequency band by using n Copyright 2011 . and record the corresponding T60 . When the signal is accepted. value to 4V by pressing 4 on the numeric keypad followed by ENT. Move cursor to Start on line and set: Ch. If the message “Triggered” does not appear. one can obtain T60 for all 1/3-octave bands by moving cursor to the top line and change Slice to Spectrum by pressing repeatedly. 28. then move the microphone a little further away from the impulsive signal. Press Cursor once and then press or repeatedly to find T60. 30. then hit the steel surface again a little louder. 32.n S where V and S are the volume and the total surface area of the room. Measure the volume and total surface area of the room in which experiments are being conducted. Move cursor to the top line and change Spectrum to Slice by pressing once. 19 for measuring reverberation times. 35. 34. Move cursor to the next line and press 51 on the numeric key pad followed by ENT. 17. 25. 22. 34. 29. the analyzer will automatically start next measurement by displaying “Waiting for trigger” again. respectively. Repeat this process until all measurements are completed. Move cursor to the beginning of the second line from the top of the screen. 18. Move cursor to the right of the top line and change the value of Z1 to position the cursor line at the beginning of the decay by pressing repeatedly. 2kH 90 dB Delay -40 ms. If an “overload” message appears. Press Auto Scale to get a better view of display. Move cursor to the top line and change Delta to Main by pressing repeatedly. 24. respectively. 38. 37. 36. Take the soft foam out of the room and open all the windows of the room. Copyright 2011 . and n is the average absorption coefficient of the room for the nth frequency band. Write a report and answer the following questions: 1. n S where S is the area of the foam. Try to explain your observations and answer these questions. Does your measured acoustic absorption coefficient for the open windows agree with the expected value? 5. n n S 1 n 35. Can the soft foam be placed in the center of a room? Under this condition. Calculate the acoustic absorption coefficient n for this foam in each frequency band n 016 . What have you learned from this experiment? 2. n and n in each frequency band. Repeat steps 16 to 36 to determine the absorption coefficient for the open windows. V n S S T60. 39. Place a soft foam against a hard wall and repeat Steps 16 to 33 to determine T60. S is the total surface area of the room.Lab Manual for ME5440 page 27 Rre . Determine the acoustic absorption coefficient using the Eyring and Millington-Sette formulations. Explain why this may be the case. do you expect to get the same values for the absorption coefficient? 3. n T60. What should the acoustic absorption coefficient for an open window be? 4. You may have your own observations and questions. and compare the results with those of Step 36. 19. Copyright 2011 . both microphone’s sensitivities through Ch. and Ch. Press Graph Format twice to get dual graph format. 3. Remote Control Unit ZH0354. 12. Press 12 on the numeric keypad followed by ENT to select the default setup for measuring sound intensity. Move cursor to Averaging line and change Exp. and set time to 4 s. Procedures: 1. Move cursor to the second line and change Mean_spec to Intensity. 5 Measurement of Sound Intensity Objective: To measure sound intensity and acoustic power flow and to familiarize the use of B&K Real Time Frequency Analyzer Type 2133. Voltage on both channel of B&K 2133 must be set accordingly. the Polarization Voltages of both microphones must be checked and the Pol. Voltage to 200 V. Move cursor to the first line of the bottom graph and change Input to Buffer. Connect B&K 2133 to computer using an HP 10833B cable by plugging it to the Interface Bus (IEEE . 17. Once the internal program checks are completed successfully. Press Measurement on Field Select once. B&K Intensity Probe Type 3545. 15.488) in the back of B&K 2133 and to the LPT1 port of the computer. Move cursor to Buffer line and change Empty to Multi 10. 8. Plug the Intensity Probe cable to Probe/Remote Control socket on B&K 2133. and to move cursor to 12. 16. 9. 13.Lab Manual for ME5440 page 28 Experiment No. A. to lin. 6. set Pol. In this case. B. Follow the instructions shown on the screen and insert Start-Up disk 1 and 2 as requested. 2. First. press Reset and 9 on the numeric keypad simultaneously. line at the bottom and set microphone sensitivity to the specified value. set Pol. and a radio as an unknown noise source. Press Auto Accept once. Press Start and whistle towards the probe. >. Voltage on B&K 2133 to 0 V. Move cursor to the first line of the top graph and change Input to Buffer. Turn on the power of B&K 2133. If it is 200 V. 10. In this case. 11. 14. 4. 20. Use Field Select keys <. A. 21. Plug the B&K Real-Time Frequency Analyzer Type 2133 to power outlet. Major Equipment: B&K Real-Time Frequency Analyzer Type 2133. must be set correctly according to the specified values. 5. Move cursor to the beginning of the third line and press Auto Scale. If it is 0 V. 7. Reverse the probe direction and repeat Step 13. do some tests. 18. Check the Polarization Voltage of the microphone in use.5mV on Ch.1.1. Repeat Steps 13 and 14 until all ten measurements are completed. . 23. 45. y. select c:\acoustic\me544. Select Cancel on the next screen. Click Show Measurement on the STARAcoustics diagram. Press Graph Format repeatedly on Display to get back the single graph format and move cursor to the top line and change Slice to Spectrum. This enables one to view the first set of intensity and mean spectrum measurements simultaneously. and z directions. Click Mesh Generator on the STARAcoustics diagram and set X&Y to start from 1 to 3 with 2 divisions. select No Hamming windows followed by OK. 52. 30. Move cursor to the third line from the top on B&K 2133 and change Abs. Open any intensity measurement file and display the intensity spectrum. Press Clear Buffer followed by Command/Execute. to dB re by pressing once. Copyright 2011 . 29. 31. Turn on a radio and set it in between stations so as to generate white noises. 39. 46. 40. Click New Project. and type a file name followed by OK. 44. Move cursor to the beginning of the third line and press Auto Scale. Move cursor to the second line and select Mean_spec. Click Show Grid/Vector to view the grid thus generated. 51. 27. More cursor to the second line on number 1 and press Align on Display. 43. Close Show Measurement and go back to the STARAcoustics diagram. Click OK followed by Close. 47. Move cursor to the top line and change Spectrum to Slice to view the amplitudes of sound intensities at a particular frequency band. 50. and close Project Slate. Pull down Analysis and click Compute Results Data …. Click Acquire Data on the STARAcoustics diagram. 42. Lin. 48. The STARAcoustics diagram will appear.8 Hz in the next line and rest the X scale to 100 Hz by pressing 100 on the numeric keypad followed by ENT. change SMS_DEMO to BK2133. 53. Press key to view the second set of intensity and mean spectrum measurements simultaneously. Click Accept on computer screen to transfer data to the computer. 24. 3. Move cursor to 0. 55.Lab Manual for ME5440 page 29 22. Move cursor to the second line and step through various frequency bands. 26. 32. Then close grid. Now begin the measurements of intensities of a radio. Click Compute on the next screen. 3 to measure acoustic intensities on a 3 3 grid in x. 28. 25. Open STARAcousticss on computer screen by double clicking STARAcoustics icon. Move the intensity probe to the next grid point and press Start to collect the intensity and mean spectrum at that point. Press Auto Accept. Move cursor to Buffer line and set Multi 3. 38. 56. and Buffer to Input. 41. Move cursor to the second line from the top of the screen of B&K 2133 and change Mean_spec to Intensity. Click Analyzer on the next screen. Close BK2133 Analyzer Control and Measurement Display screens and go back to the original STARAcoustics diagram. Repeat Steps 41 to 44 until all measurements are completed. Move the intensity probe to the first grid point in front of the radio and press Start to collect the first set of intensity and mean spectrum measurements. 54. 49. This will display dynamically the intensity vector at the selected frequency band. Change the vertical scale to dB. Write a report and answer the following questions: 1. in a directory. click Band #. and click Compute. Contour. click Show Measurement and open any intensity file. power1. Normal Shape. 59. Select Dynamic Vector. Pull down Intensity. Pull down Analysis and select Composite Sound Power. Copyright 2011 . Will background noises affect intensity measurements? 3.Lab Manual for ME5440 page 30 57. 001x001x. Save file. Other types of display such as Static Vector. What have you learned from this experiment? 2. Pull down Intensity and select another Band # to view the intensity vector at a different frequency band. Click Show Grid/Vectors. and select a frequency band followed by Ok. 64. To calculate the time-averaged acoustic power. 62. 60. say. say. Try to explain your observations and answer these questions.int. 58. 61. 65. Will background noises affect the power levels resulting from the intensity measurements? You may have your own observations and questions. and Complex Shape can be obtained in a similar manner. 63. Open file power1 to view the power spectrum. To change “Span” (frequency range) & “Lines” (frequency resolution). b. b. To change response “Window”. make sure you are on “Display” in Task List (left side). right-click:: FFT Analyzer > properties 4. To change excitation “Window”. Setting up the Data Acquisition file. right-click:: FFT Analyzer > properties 3. In “Window” pull down “Transient” for impact hammer measurement. right- 5. In “Window” pull down “Exponential” for impact hammer measurement. Use “Shift” to assign start window and “Length” to stop window.Lab Manual for ME5440 page 31 LabVIEW Based Modal Analysis Login: SeanWu Password: ME4410 Folder: Desktop/ME5440 DATA Acquisition Open DAQ file: Desktop/ME5440/Template/”ME5440_Modal. To change “Averages”. right-click: Setup > properties 2. (See level meter: Red indicates overload. click: Force > properties > Signal tab a. right-click: Acceleration > properties > Signal tab a. Use “Shift” to assign start window and “Tau” to stop window. Copyright 2011 . To change “Level” (trigger values as a % of Range) and “Delay”. 1. Red with X mark indicates cabling/ instrument problems) b) Select a proper tip for the impact hammer (switch between hard plastic and hard rubber as necessary to avoid double hit and overload problems) c) To prepare collecting data.pls” Use “SaveAs” to store it in a new folder (create new one and name it as “Group 1”) to preserve the original file I. The below changes may be necessary at the beginning and when a data acquisition needs some control. a) Press F2 and wait to see if the cables and signals are good. The following changes are restricted to “Measurement Organizer” window. b) To change “Range” of impact hammer signal. In the newly opened “Frequency Response H1 (ACCELERATION. e. Rename this saved file with indexes corresponding to the excitation location and response location. ii. The 2nd column represents the X-axis frequency and the 3rd column represents Y-axis dB (m/sec^2/N. Hit the object at a marked position for obtaining the Frequency Response Function for the predetermined number of averages. ii. a) Hit the object at the location where you had fixed the accelerometer position (also known as Drive Point) and observe for the approximate maximum Force and Acceleration in the “Monitor” windows. In the “Function Organizer” right click “Frequency Response H1 (ACCELERATION. d. Exporting FRF data to STAR MODAL: i. Leave the “Frequency Response H1(ACCELERATION.Lab Manual for ME5440 page 32 II. Copying the FRF to excel spreadsheet: i. To do this. under “Measurement” select the file you like to export (example: 0001Z0002Z). c. right-click: Acceleration > properties > Channel tab > change values in “Max Peak Input” III. Repeat the above two steps for all the marked locations. To save this data Press F7 (SAVE). For example if you applied excitation at point 1 in Z-direction and measured response at point 2 in Z-direction. ref 1). Click on “ORGANISERS” in Task List (left side). Right-click and select “Copy Active Curve”. The data on the screen will be saved as “Measurement” in the tree of the “Measurement Organizer” window. Use four times (+6 dB) the maximum value for determining range. right-click: Force > properties > Channel tab> change values in “Max Peak Input” c) To change “Range” of accelerometer signal. This process is called ranging. Collecting data: a) Press F2 (ARM) followed by F5 (START) a.FORCE)” and select Properties. make sure the “Frequency Response H1” is the active curve (red colored) in the FRF/Coherence display window. Paste this data to your excel sheet. Ranging: For accurate measurements it is necessary to determine the maximum input forces and maximum responses that will be experienced during the test and adjust the measurement scale. b.FORCE)” window.FORCE)” window open. Copyright 2011 . the assigned name should be “0001Z0002Z”. 3. f. Repeat step ii-v for all measurement locations. Go to “Measurement Points” tab and click “Assign Default” for the system to assign the measurement locations to the geometry locations. In “Setup” input the location and direction of “Driving point (reference) DOF” (for example: 7Z corresponds to accelerometer position and direction used as reference in a fixed response test). Creating Model : Click Model and select “Setup” > Templates. 5. Go to “Lines” tab and connect the points sequentially as shown below by inputting the connecting points in the “From” and “To” spaces. 4. e. Press “Create New” to create a template. Go to “Function Organizer” right click “Frequency Response H1(ACCELERATION. Click Project > New. b. vi. d. You will now see the geometry we had created in 4 different views in the main window. b. Go to “Components” tab and create a new component which will contain the points and lines we had created before.FORCE)” and click “Save” and select “STAR Binary”. Insert “STAR Security Key” floppy disk in the floppy dive. a.z locations of the pints measured to create the geometry. Input the x. In the “Project Parameters” assign the Units (Same as your measurements). Copyright 2011 . Go to constraint and create dependent measurements (that is create measurement data for dummy locations). Importing Measurements: Click Measurements and select “Setup” a. iv. Choose “Fixed Response” radio button for roving hammer method.y. Select “Modal” and hit Run to open STAR Modal application. Hit “OK” and “Save” the file created in the “Group 1” folder you had created initially. Click “OK”. v. c. Post Processing 1. 2. to create a new project file in the “Group 1” folder. Go to “Points” tab and input the number of points you had conducted the experiment for.Lab Manual for ME5440 page 33 iii. Click open: Desktop/”STAR” to launch STAR software. Fill the “STAR Binary File properties” window with appropriate measurement location and directions for the file selected in step ii. Lab Manual for ME5440 page 34 c. f. e. 5. Click Measurements and select “Import” > “STAR v5” By default the above window chooses “Measurements” and “Freq response”. d. In the “Identify Modal peaks” dialog box click the Directions for which you have collected measurements and pick the calculation method as “Magnitude2” and click OK. Choose “Ok” d. Click Analysis and select “Function” > Advanced Modal Peaks Click “Create” to create the analysis file in the “Star Files” folder created before and then click “Next” Copyright 2011 . Locate your folder destination and select it. In the “Identify Modal peaks” dialog box click the Directions for which you have collected measurements and pick the calculation method as “Magnitude2” and click OK. If different choose as per the above figure and hit “OK” for importing the FRF data. Analyzing Measurements: Click Analysis and select “Function” > Modal peaks a. b. c. Change “Model size estimator” values to 10 & 20 and click “Next” In the stabilization diagram pick the lowest black circle (F&D Still stable) lying below the peak values. Click “Next”. g. i. Copyright 2011 . f. page 35 Select “Bandwidth” for the analysis and hit Process. Click “Real” for mode shape type and hit “Calculate” to calculate the modal participation. Click “Autofit All” and hit “Next” Select the “Mode” for click “Overlay” and play to see the modes. h.Lab Manual for ME5440 e. j. 4”. 2. 10”. Copyright 2011 . Select the frequency span so that the peaks corresponding to the first three modes appear on the spectrum. Measure the free length. Tap the beam several times while checking the overload lights on each channel. Observe the time domain responses on the oscilloscope – note the changes in the response as the impact hammer is moved to different locations.0.. Select the Uniform Window and Both Channels on the input. PCB Model GK291B01 Impulse Hammer Kit which includes Model 086B01 hammer and Model 309A miniature accelerometer. Adjust the input sensitivity knobs on each channel so that the overload lights do not come on during impact. 3.e. damping ratios.Lab Manual for ME5440 page 36 Experiment No. 6. that mode will not be present in the modal response measurement at that point. Note that if the accelerometer is mounted at a nodal point for a particular mode. record the frequency and the value of the transfer function at each peak – remember that the transfer function has both magnitude and phase! Check the coherence function at each peak also – if the coherence is not close to 1. width. HP 54501A Digital Oscilloscope. Use bees wax to attach the miniature accelerometer near the tip of the beam so that it will respond to the first three modes. Set up the analyzer for averaging of the transfer function data with four averages. These are the positions where the impulse hammer will be used to excite the beam. Clamp a steel cantilever beam on fixtures. Mark the beam with a pencil at evenly spaced positions along the beam (i. 6 Modal Analysis Objective: To measure and analyze the modal parameters. Repeat steps 5 and 6 for the other positions along the beam until the transfer function data has been collected for each excitation and response measurement point. and thickness of the beam. and 12” from the fixed end). and a steel cantilever and clamping fixtures. Major Equipment: HP 3582A Spectrum Analyzer. and mode shapes of a simple structure using an impulse-frequency response technique and digital frequency spectral analyzer. 2”. 5. 7. disregard the measurement and repeat the test until an acceptable coherence is obtained. The optimum sensitivity setting is one “click” above the position where the overload light comes on. 6”. Procedures: 1. tap the beam four times to get the averaged transfer function data.e. 8”. The values of the modulus of elasticity and density can be found in mechanics of materials books. the natural frequencies. i. For the first position at 2” from the clamped end of the beam. Moving the cursor dot along the spectrum and using the function selection buttons. Set up the spectrum analyzer with the impulse hammer output connected to Channel A and the accelerometer output connected to Channel B. 4.. let the maximum deflection be unity and other deflections be fractions of unity). calculate the imaginary part of the transfer function. Calculate the damping ratios for each of the first three modes using the half-power method. use the Set Center control to Zoom in on each peak and take the necessary data to calculate the damping ratio by the half-power method. Are the natural frequencies position dependent? Are the mode shapes position dependent? Copyright 2011 . The mode shapes should be normalized to the maximum deflection for that mode (i. calculate the natural frequencies and mode shapes for the first three modes of a cantilever beam. Using the theory of flexural vibration discussed in the class. For at least one measurement position.Lab Manual for ME5440 page 37 8. Requirements 1. Based on the measured data. As with the theoretical mode shapes. 2. Check your results for a different measurement point – the frequency and damping should be the same for all positions. Compare your experimental mode shapes to the theoretical ones.. Are the damping ratios position dependent? 4. Plot the mode shape for each of the first three modes. normalize the amplitude of the mode shape. 3. Only the magnitude and phase information which govern the mode shape will change from one position to another.e.