me5440 lab manual (1 to 6)

Lab Manual for ME5440 page

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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]


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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.


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LabVIEW Based Microphone Calibration: Table 1. Serial Number of Microphones

Channel #1 Channel #2 1/2" Prepolarized Free Field Microphone Serial No. 23417 Serial No. 21908

ICP Microphone Preamplifier Serial No. 2209 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


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3. In the “Creat New NI-DAQmx Task” window, Click “Acquire SignalsAnalog InputSound Pressure” and then choose “a0” and “a1” under “Dev1 (USB-9234)”.

Click “Next” Enter name of the new taskFinish, then the window becomes:


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4. To calibrate the Channel #1, make sure the “Sound Pressure_0” is chosen, and then

click “Calibration” “Calibrate…”type in the Calibrator’s Name “Next” Fill the blank for “Acquisition Duration (s)” and “Sample Rate (Hz)”. 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:


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The piston phone used in this class is B&K piston phone type 4220, Serial No. 704798, sound pressure level is 124.0 dB re 2×10-5 Pa, and Frequency is 250 Hz ±1% in “Measure” position (for fresh batteries).

5. Turn on the piston phone, the sensitivity will be changing in real time.

Click , the sensitivity is committed. Stop clicking and when the value of sensitivity is stable, and write down the sensitivity of this microphone. click “Finish” to close the window

6. Choose the “Sound pressure_1” and repeat step 4 to 5 to calibrate Channel #2.

7. Close the “Measurement & Automation Explorer” window when finished.

8. Based on the calibration result on 08/25/2011: The sensitivity of Channel #1 is 57.3978 mV/Pa. The sensitivity of Channel #2 is 45.2545 mV/Pa.


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LabVIEW based Sound Pressure Level Meter: 1. Left double click “Sound Level Meter.vi”.

2. Setup the parameters for measurement. a. Physical Channels

Set up the physical channels for the microphones. The default setup is shown as the figure below. Note that the index in LabView program starts from zero. Thus the port “ai0” indicates the Channel #1, and “ai0” indicates the Channel #2.

b. Microphone sensitivities Fill the sensitivities that are obtained by microphone calibration.


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c. Sampling period when gathering data Define the sampling period of measurement. Note that the measurement results update every period. If the sampling period of the measurement is set equal one, as shown below, then the paragraphs and sound levels update every one second.

d. Measure method There are two options for the measurement method. “Instantaneous” means that the sound level results shown on front panel are from the recent period of measurement; “Averaging” means that the sound level results are averaged.

e. Number of averages If “Averaging” option is chosen in the “Measure method”, then one need to further define the number of averages. One can define any number of averaging, and the default number of averages is 100 times. When the program is running, the gray box updates how many times are finished. And when the averaging reaches the defined number of averages, the green light will change to light green and the program will stop gathering data from microphones.

f. Weighting Weighting defines the method of calculating the sound levels.


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g. Bandwidth Bandwidth defines the display in the Spectrum.

h. Frequency range If “narrow band” is chosen in “Bandwidth”, one needs to further fill the blanks of “frequency range”. The “Frequency resolution (Hz)” is calculated by program automatically based on the input of “frequency range”. Frequency resolution = (stop frequency – start frequency)/number of lines Note: Don’t increase the “number of lines” higher than default unless required. A higher value need more computer memory and may crash the computer.


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3. Run the program by clicking .

Note that one can choose to see “Microphone 1”, “Microphone 2”, or “Both”. “Microphone 1” or “Microphone 2” shows the data at Channel #1 and #2; “Both” shows both of these two microphones’ data, but the figures are smaller. Time domain waveform, spectrogram and the spectrum are shown in this program. One can move the cursor in the Spectrum to see the dB level of a precise frequency band. If the octave frequency band is chosen, then the frequency showing above the cursor is the central frequency of that band. If it is difficult to drag the cursor to the

target frequency, the one can click on and move the cursor step by stop.

4. Read sound levels Note that the sound levels are shown in dB.


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5. Record the sound levels

Click to save the sound level to a “.txt” file. A “ Choose file to write” window will jump out, remember to write “.txt” with the file name.

When opening the txt file, the first column shows the frequency, the second column shows the sound level at Channel #1, and the third column shows the sound level at the Channel #2.

6. Click until the program stops. 7. Close program.


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LabVIEW Based Reverberation Time Measurement 1. Left double click “T 60.vi”

2. Define the parameters on the left a. Physical Channel Channel #1 is used.

Note: The NI-9234 has totally four channels, and one can use minimum one channel. However, the first port (AI0) must be used; otherwise the data acquisition doesn’t work. In other word, as we only use one microphone in this experiment, we must connect the microphone to the first port (AI0).

b. Sensor sensitivity

Fill in the sensitivity gained in microphone calibration


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c. Weighting The default is “Linear”

d. Trigger Level

Is should be decided based on the experiment environment.

e. Frequency range

The value is fixed in the experiment

3. Click to run program The upper two graphs show data in real time.

The left one is the time domain signal, the right one is the spectrum.

4. Play the impulsive sound (for example, clapping)

5. The measurement will stop when the impulsive sound reach the trigger level.


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6. Change the frequency band to find the T60 for each frequency band.

For example, if 1000 Hz is chosen, then a detailed SPL vs. time graph is shown on the left lower corner.


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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. The “T60(ms)_manual” can be decided manually by moving the two yellow cursors in the “SPL vs. time” graph.


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7. The graph on the right lower corner shows the T60 vs Frequency, which uses the “T60(ms)_auto”. Moving the yellow cursor can see the detailed value of the frequency and T60.


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8. Click to save the T60 values.

In the saved txt file, the first column is the central frequency of each frequency band, and the second column is value of “T60(ms)_auto”.


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Experiment No. 1 Determination of Cut-off Frequency of a Free Field

Objective: To familiarize the basic concepts of wavelength, cut-off frequency, and wave propagation in a free field, as well as the usage of B&K Dual Channel Signal Analyzer Type 2032. Major Equipment: B&K Dual Channel Signal Analyzer Type 2032, speaker, power amplifier, and signal generator. Procedures: 1. Lay the sound source on the center of the chamber floor. 2. Mark measurement microphone positions according to Table 1. Place the sound

source at the origin of the Cartesian coordinate system. Set the microphone at the position of measurement point #1.

3. Plug the power cord of B&K Dual Channel Signal Analyzer Type 2032 to an outlet. 4. Connect microphone cables to Preamp. Input of Channel A and B of B&K 2032. 5. Check the Polarization Voltage of the microphone in use. If it is 0 V, set Pol. Voltage

on B&K 2032 to 0 V. If it is 200 V, set Pol. Voltage to 200 V. 6. Turn on the power of B&K 2032. 7. Once the internal program checks are completed successfully, press Reset and 9 on

the numeric keypad simultaneously. 8. Use Field Select keys <, >, , or to move cursor to the 3rd position on Ch. A., the

3rd line from the bottom of the screen. Set input type to PREAMP by using Field Entry key or repeatedly. Move the cursor to the right most position on the same line and select V/PA. Check and set microphone sensitivity to the specified value. For example, for the ½’’ B&K Prepolarized Condenser Microphone Type 4189, serial no. 1669464, the sensitivity is 49 mV/Pa. Then press 49m and ENT on numeric keypad.

9. Move cursor to the third line from the top and change Ave. T to Total by pressing key repeatedly.

10. Calibrate the microphone by using the B&K Pistonphone Type 4220 as follows: (a) Place a ½’’ adapter on the Pistonphone head; (b) Fit the Pistonphone on a ½’’ microphone and switch on the Pistonphone; (c) Move cursor one step up and change WEIGHTING to HANNING by pressing

the Field Entry key; (d) Move cursor two steps up and set FREQ SPAN to 400Hz using Field Entry key. (e) Move cursor one step up and set AVERAGING to LIN, 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. (g) Move cursor one step up and set MEASUREMENT to CH.A. SPECTRUM

AVERAGING.


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(h) Move cursor two steps up and to the right most position and select TOTAL by pressing Field Entry key repeatedly.

(i) Move cursor one step up to the fourth position from the left and select RMS, then one step left to set 20U by typing 20 on the key pad, and finally to the 1st position from the left on the same line and set 130dB by typing 130 on key pad.

(j) Move cursor to the 2nd position from the left on the top line and select AUTO SPEC CH.A.

(k) Press Input Autorange once. (l) Press Start to start calibrating the microphone on Channel A. Observe the display

of auto-spectrum on the screen. The SPL (sound pressure level) value at 250 Hz should be 124 dB. Press Cursor once followed by the key repeatedly to move to cursor line to 250 Hz. The value of Y should be 124 dB. If the difference is more than 05. dB, then move cursor to Ch. A. line at the bottom and adjust the microphone sensitivity. If the difference is less 05. dB, calibration is done.

11. Repeat Step 9 to calibrate microphone on Channel B. 12. Exit the chamber and close the door. 13. Open STARAcousticss on computer by double clicking STARAcoustics icon. 14. Select Cancel on the next screen. The STARAcoustics diagram will appear. 15. Click New Project, select a group name under c:\acoustic\me5440, followed by

OK. 16. Click Analyzer on the next screen, change SMS_DEMO to BK2032, select Yes

Hamming windows followed by OK, and close Project Slate. 17. Click Mesh Generator on the STARAcoustics diagram and set X&Y to start

from 1 to 16 with 15 divisions. Click OK followed by Close. 18. Click Show Grid/Vector to view the grid thus generated. Then close grid. 19. Click Acquire Data on the STARAcoustics diagram. 20. Click Type and select Autopower and unselect Crosspower, then OK. If one

dimensional grid is used, set Directions to X only. (Now STARAcoustics is ready to take data.)

21. Turn on the signal generator and select random signals. 22. Turn on the power amplifier and adjust output power to a desired level. 23. Press Input Autorange on B&K 2032. 24. Press Start on B&K 2032 to collect sound pressure spectrum at the measurement

point #1. 25. Click Accept on computer screen to transfer data to the computer. 26. Open the door and move microphone to the next location according to Table 1

and close the chamber door. 27. Repeat Steps 24 and 25 until all measurements are taken. (Now you can view the

data thus collected.) 33. Close BK2032 Analyzer Control and Measurement Display screens and go

back to the original STARAcoustics diagram. 34. Click Show Measurement on the STARAcoustics diagram. 35. Open any measurement file and display sound pressure spectrum. 36. Check SPL values at each frequency band. Compare these values between two

spectra with doubling of distance, e.g., #1 vs. #2; #3 vs. #4; #5 vs. #6; etc.


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37. Find the cut-off frequency at which the difference in SPL values between two spectra is less than 6 dB.

Table 1. Measurement scheme.

No. X (m) y (m) z (m) 1 0.5 0 0 2 1.0 0 0 3 - 0.5 0 0 4 - 1.0 0 0 5 0 0.5 0 6 0 1.0 0 7 0 - 0.5 0 8 0 - 1.0 0 9 0.5 0 0.5 10 1.0 0 1.0 11 - 0.5 0 0.5 12 - 1.0 0 1.0 13 0 0.5 0.5 14 0 1.0 1.0 15 0 - 0.5 0.5 16 0 - 1.0 1.0 17 0 0 0.5 18 0 0 1.0

Write a report and answer the following questions: 1. What is the cut-off frequency of this chamber? 2. What sound field is it for frequency below the cut-off frequency? 3. What sound field is it for frequency above the cut-off frequency? 4. Why do you place the sound source on the floor? 5. 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. Try to explain your observations and answer these questions.


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Experiment No. 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. Major Equipment: B&K Real Time Frequency Analyzer Type 2133 and various sound sources. Procedures: 1. Plug the B&K Real-Time Frequency Analyzer Type 2133 to power outlet. 2. Connect microphone cable to Preamp. Input of Channel A of B&K 2133. (Use an

adapter for the old model cable that has a long 7-pin head. New model cable has a short 7-pin head and does not need an adapter.)

3. Check the Polarization Voltage of the microphone in use. If it is 0 V, set Pol. Voltage on B&K 2133 to 0 V. If it is 200 V, set Pol. Voltage to 200 V.

4. Turn on the power of B&K 2133. 5. Follow the instructions shown on the screen and insert Start-Up disk 1 and 2. 6. Once the internal program checks are completed successfully, press Reset and 9 on

the numeric keypad simultaneously. 7. Use Field Select keys <, >, , and to move cursor to 50.0mV on Ch. A. line at the

bottom and set microphone sensitivity to the specified value. For the ½’’ B&K Prepolarized Condenser Microphone Type 4189, serial no. 1783577, the sensitivity is 52.5 mV/Pa. This can be done by pressing 52.5m and ENT on the numeric keypad.


9. Calibrate the microphone by using the B&K Pistonphone Type 4220 as follows: 10. Place a ½’’ adapter on the Pistonphone head; 11. Fit the Pistonphone on a ½’’ microphone and switch on the Pistonphone; 12. Move cursor on B&K 2133 to Averaging line and select Exp. average by pressing

key once; 13. Press Input Autorange once; 14. Press Start and Auto Scale. Observe the display of auto-spectrum on the screen. The

SPL (sound pressure level) value at 250 Hz should be 124 dB. Press Cursor once followed by the key repeatedly to move the cursor line to 250 Hz. The value of Y should be close to 124 dB. If the difference is more than 05. dB, then move cursor to Ch. A. line at the bottom and adjust the microphone sensitivity. If the difference is less 05. dB, press Stop.

15. Move cursor to Averaging line and change Exp. average to Lin. average and set average time to 4 s.

16. Measure and record the ambient noise spectrum by pressing Input Autorange once followed by Start. Press Auto Scale to get a better view of display.


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17. 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. Press Auto Scale to get a better view of display.

18. Press Cursor once and record the SPL values in each 1/3-octave band by pressing or repeatedly. Press Auto Scale to get a better view of display.

19. Set three sources, for example, a vacuum cleaner, hand drill, and speaker at locations A, B, and C, respectively.

20. Turn on the first source, for example, a vacuum cleaner at location A. 21. 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. 22. Measure and record the noise spectra with the first source on. 23. Turn off the first source and turn on the second source, measure and record the noise

spectra of the second source at the same location as that in Step 22. 24. Turn on the power of the first source at location A and measure the noise spectra

again with the second source on. 25. Compare the measured noise spectra and total SPL with the calculated ones by using

101010

21 1010log10 LLpL

where L1 and L2 are the SPL values of the first and second sources obtained in Steps 22 and 23, respectively.

26. Turn on the power of the third source, measure and record the noise spectra at the same location as that in Step 24 with all three sources running together.

27. Calculate the noise spectra of the third source by using

101010 1010log10 bc LL

sL

where Lc represents the combined SPL values with all machines running together, Lb indicate the SPL values of the background noises (e.g., with the engine and air flow running together), and Ls implies the SPL values of the centrifugal blower alone.

28. Turn off the first and second sources, measure and record the noise spectra of the third source and compare them with those calculated in Step 27.

Write a report and answer the following questions: 1. What have you learned from this experiment? 2. How do you obtain the noise spectrum of a machine in a noisy environment? 3. Where should you take noise measurement in a noisy environment? 4. In this experiment, do your measurements agree with your calculations in Steps

21 and 24? 5. Can you tell the type of environment (e.g., free field, reverberant, semi-

reverberant, etc.) based on your measured noises at location A and location B? You may have your own observations and questions. Try to explain your observations and answer these questions.


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Experiment No. 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. Major Equipment: B&K Precision Sound Level Meter Type 2230, B&K Pistonphone Type 4220, and a shop vacuum cleaner. Procedures: 1. 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. WEIGHTING: “Lin” EXT. 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. The display

should indicate 124 dB 0.1 dB. (d) If an adjustment is necessary, turn the SENS. ADJ. potentiometer on the side of

the sound level meter with a small screwdriver. 2. Measure the total ambient SPL values in both linear and A-weighting of the room in

which experiments are to be conducted. 3. Set a shop vacuum cleaner in the center of an open space and turn on its power. 4. 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. 5. Repeat Step 4 for a hemi-spherical surface at r 2 m. 6. Calculate the radiated sound power level from the vacuum cleaner by using

LS

S SWL Lp p

10 10 10 10

11010 10

101

1 2

1 2log log, ,

where Lp ,1 and Lp ,2 are area-averaged total SPL values measured on hemi-spherical

surfaces S1 and S2 , respectively,


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LS

Sp ii

Li j

j

j

, ,log

10

11010

10

1

8

where Si j, is the jth segment of the surface Si , and S1 and S2 are the total

“transparent” areas of the measurement surfaces at r 1 m and r 2 m, respectively, excluding the reflecting surface on the ground.

7. Turn on the power of a centrifugal blower as background noises. 8. Repeat Steps 4 to 6 to measure the total radiated acoustic power level from the

vacuum again. 9. Compare the two results to see if they agree with each other.

Table 1. Coordinates of ten-point measurement scheme.

Write a report and answer the following questions: 1. What have you learned from this experiment? 2. Should the total radiated acoustic power from the vacuum cleaner change with

the measurement points? 3. Does the result of Step 6 agree with that of Step 8? Why? 4. 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. Try to explain your observations and answer these questions.

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Experiment No. 4 Measurement of Reverberation Time and Room Constant

Objective: To measure reverberation time, room constant, and acoustic absorption coefficient and to familiarize the use of B&K Real Time Frequency Analyzer Type 2133. Major Equipment: B&K Real-Time Frequency Analyzer Type 2133, a hammer used to produce impulsive signals, and a soft foam whose acoustic absorption coefficient is unknown. Procedures: 1. Plug the B&K Real-Time Frequency Analyzer Type 2133 to power outlet. 2. Connect microphone cable to Preamp. Input of Channel A of B&K 2133. (Use an

adapter for the old model cable that has a long 7-pin head. New model cable has a short 7-pin head and does not need an adapter.)

3. Check the Polarization Voltage of the microphone in use. If it is 0 V, set Pol. Voltage on B&K 2133 to 0 V. If it is 200 V, set Pol. Voltage to 200 V.

4. Turn on the power of B&K 2133. 5. Follow the instructions shown on the screen and insert Start-Up disk 1 and 2 as

requested. 6. Once the internal program checks are completed successfully, press Reset and 9 on

the numeric keypad simultaneously. 7. Use Field Select keys <, >, , and to move cursor to 50.0mV on Ch. A. line at the

bottom and set microphone sensitivity to the specified value. For the ½’’ B&K Prepolarized Condenser Microphone Type 4189, serial no. 1783577, the sensitivity is 52.5 mV/Pa. This can be done by pressing 52.5m and ENT on the numeric keypad.


9. Calibrate the microphone by using the B&K Pistonphone Type 4220 as follows: (a) Place a ½’’ adapter on the Pistonphone head; (b) Fit the Pistonphone on a ½’’ microphone and switch on the Pistonphone; (c) Move cursor on B&K 2133 to Averaging line and select Exp. average by pressing

key once; (d) Press Input Autorange once; (e) Press Start and Auto Scale. Observe the display of auto-spectrum on the screen.

The SPL (sound pressure level) value at 250 Hz should be 124 dB. Press Cursor once followed by the key repeatedly to move the cursor line to 250 Hz. The value of Y should be close to 124 dB. If the difference is more than 05. dB, then move cursor to Ch. A. line at the bottom and adjust the microphone sensitivity. If the difference is less 05. dB, press Stop.

10. Press Measurement on Field Select once.


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11. Press 19 on the numeric keypad followed by ENT to recall the default measurement setup No. 19 for measuring reverberation times.

12. Move cursor to the top line and change Spectrum to Slice by pressing once. 13. Move cursor to Averaging line and change the average time to 1 128 s. 14. Move cursor to Start on line and set: Ch. A. 2kH 90 dB Delay -40 ms. 15. Move cursor to Ch. A. line at the bottom and set Preamp. value to 4V by pressing 4

on the numeric keypad followed by ENT. 16. Press Clear Buffer on Measurement keypad followed by Command/Execute on the

keypad to the right of the screen to clear the buffer. 17. Press Auto Accept on Measurement keypad. 18. Press Start on Measurement keypad and wait for the message “Waiting for trigger.” 19. Generate impulsive signals by hammering the hammer on a hard, steel surface. If the

message “Triggered” does not appear, then hit the steel surface again a little louder. If an “overload” message appears, then move the microphone a little further away from the impulsive signal. When the signal is accepted, the analyzer will automatically start next measurement by displaying “Waiting for trigger” again. Repeat this process until all measurements are completed.

20. Move cursor to the beginning of the second line from the top of the screen. 21. Press 52 on the numeric keypad followed by ENT to select the default setting for

calculating the reverberation times. 22. Press Auto Scale on Display keypad. 23. Move cursor to the top line and change Main to Delta by pressing once. 24. Move cursor to the third line and change [ ] to Reverb. T by pressing repeatedly. 25. 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. 26. 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. 27. The value of Reverb. T is T60 for the 1/3-octave band centered at 1 kHz. 28. Move the cursor to the second line from the top and change the frequency to any

other value by pressing or repeatedly, and record the corresponding T60 . 29. Alternatively, 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. 30. Move cursor to the next line and press 51 on the numeric key pad followed by ENT. 31. Move cursor to the top line and change Delta to Main by pressing repeatedly. 32. Press Auto Scale to get a better view of display. 33. Press Cursor once and then press or repeatedly to find T n60, for all frequency

bands. 34. Measure the volume and total surface area of the room in which experiments are

being conducted. 35. Calculate the average absorption coefficient n in each frequency band by using

nn

V

T S

016

60

.

,

where V and S are the volume and the total surface area of the room, respectively. 34. Calculate the room constant Rre n, in each frequency band by using


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RS

re nn

n,

1

35. Place a soft foam against a hard wall and repeat Steps 16 to 33 to determine T n60, and

n in each frequency band. 36. Calculate the acoustic absorption coefficient n for this foam in each frequency band

n

n n

n

V S S T

T S

016 60

60

. ,

,

where S is the area of the foam, S is the total surface area of the room, and n is

the average absorption coefficient of the room for the nth frequency band. 37. Take the soft foam out of the room and open all the windows of the room. 38. Determine the acoustic absorption coefficient using the Eyring and Millington-Sette

formulations, respectively, and compare the results with those of Step 36. 39. Repeat steps 16 to 36 to determine the absorption coefficient for the open windows. Write a report and answer the following questions: 1. What have you learned from this experiment? 2. Can the soft foam be placed in the center of a room? Under this condition, do

you expect to get the same values for the absorption coefficient? 3. What should the acoustic absorption coefficient for an open window be? 4. Does your measured acoustic absorption coefficient for the open windows agree

with the expected value? 5. Explain why this may be the case. You may have your own observations and questions. Try to explain your observations and answer these questions.


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Experiment No. 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. Major Equipment: B&K Real-Time Frequency Analyzer Type 2133, B&K Intensity Probe Type 3545, Remote Control Unit ZH0354, and a radio as an unknown noise source. Procedures: 1. Plug the B&K Real-Time Frequency Analyzer Type 2133 to power outlet. 2. Plug the Intensity Probe cable to Probe/Remote Control socket on B&K 2133. 3. Check the Polarization Voltage of the microphone in use. If it is 0 V, set Pol. Voltage

on B&K 2133 to 0 V. If it is 200 V, set Pol. Voltage to 200 V. In this case, the Polarization Voltages of both microphones must be checked and the Pol. Voltage on both channel of B&K 2133 must be set accordingly.

4. Connect B&K 2133 to computer using an HP 10833B cable by plugging it to the Interface Bus (IEEE - 488) in the back of B&K 2133 and to the LPT1 port of the computer.

5. Turn on the power of B&K 2133. 6. Follow the instructions shown on the screen and insert Start-Up disk 1 and 2 as

requested. 7. Once the internal program checks are completed successfully, press Reset and 9 on

the numeric keypad simultaneously. 8. Press Measurement on Field Select once. 9. Press 12 on the numeric keypad followed by ENT to select the default setup for

measuring sound intensity. 10. Use Field Select keys <, >, , and to move cursor to 12.5mV on Ch. A. line at the

bottom and set microphone sensitivity to the specified value. In this case, both microphone’s sensitivities through Ch. A. and Ch. B. must be set correctly according to the specified values.

11. Move cursor to Averaging line and change Exp. to lin. and set time to 4 s. 12. Move cursor to Buffer line and change Empty to Multi 10,1,1. 13. First, do some tests. Press Auto Accept once. 14. Press Start and whistle towards the probe. 15. Reverse the probe direction and repeat Step 13. 16. Repeat Steps 13 and 14 until all ten measurements are completed. 17. Press Graph Format twice to get dual graph format. 18. Move cursor to the first line of the top graph and change Input to Buffer. 19. Move cursor to the second line and change Mean_spec to Intensity. 20. Move cursor to the beginning of the third line and press Auto Scale. 21. Move cursor to the first line of the bottom graph and change Input to Buffer.


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22. Move cursor to the second line and select Mean_spec. 23. Move cursor to the beginning of the third line and press Auto Scale. 24. More cursor to the second line on number 1 and press Align on Display. This enables

one to view the first set of intensity and mean spectrum measurements simultaneously.

25. Press key to view the second set of intensity and mean spectrum measurements simultaneously.

26. Move cursor to the top line and change Spectrum to Slice to view the amplitudes of sound intensities at a particular frequency band.

27. Move cursor to the second line and step through various frequency bands. 28. 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. 29. Now begin the measurements of intensities of a radio. Turn on a radio and set it in

between stations so as to generate white noises. 30. Open STARAcousticss on computer screen by double clicking STARAcoustics icon. 31. Select Cancel on the next screen. The STARAcoustics diagram will appear. 32. Click New Project, select c:\acoustic\me544, and type a file name followed by OK. Click Analyzer on the next screen, change SMS_DEMO to BK2133, select No

Hamming windows followed by OK, and close Project Slate. 38. Click Mesh Generator on the STARAcoustics diagram and set X&Y to start from 1

to 3 with 2 divisions. Click OK followed by Close. 39. Click Show Grid/Vector to view the grid thus generated. Then close grid. 40. Click Acquire Data on the STARAcoustics diagram. 41. Move cursor to the second line from the top of the screen of B&K 2133 and change

Mean_spec to Intensity, and Buffer to Input. 42. Move cursor to Buffer line and set Multi 3, 3, 3 to measure acoustic intensities on a

3 3 grid in x, y, and z directions. 43. Press Clear Buffer followed by Command/Execute. 44. Press Auto Accept. 45. 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. 46. Click Accept on computer screen to transfer data to the computer. 47. Move cursor to the third line from the top on B&K 2133 and change Abs. Lin. to dB

re by pressing once. 48. Move cursor to 0.8 Hz in the next line and rest the X scale to 100 Hz by pressing 100

on the numeric keypad followed by ENT. 49. Move the intensity probe to the next grid point and press Start to collect the intensity

and mean spectrum at that point. 50. Repeat Steps 41 to 44 until all measurements are completed. 51. Close BK2133 Analyzer Control and Measurement Display screens and go back to

the original STARAcoustics diagram. 52. Click Show Measurement on the STARAcoustics diagram. 53. Open any intensity measurement file and display the intensity spectrum. 54. Pull down Analysis and click Compute Results Data …. 55. Click Compute on the next screen. 56. Close Show Measurement and go back to the STARAcoustics diagram.


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57. Click Show Grid/Vectors. 58. Pull down Intensity, click Band #, and select a frequency band followed by Ok. 59. Select Dynamic Vector. This will display dynamically the intensity vector at the

selected frequency band. 60. Pull down Intensity and select another Band # to view the intensity vector at a

different frequency band. 61. Other types of display such as Static Vector, Contour, Normal Shape, and

Complex Shape can be obtained in a similar manner. 62. To calculate the time-averaged acoustic power, click Show Measurement and open

any intensity file, say, 001x001x.int. Change the vertical scale to dB. 63. Pull down Analysis and select Composite Sound Power, and click Compute. 64. Save file, say, power1, in a directory. 65. Open file power1 to view the power spectrum. Write a report and answer the following questions: 1. What have you learned from this experiment? 2. Will background noises affect intensity measurements? 3. Will background noises affect the power levels resulting from the intensity

measurements? You may have your own observations and questions. Try to explain your observations and answer these questions.


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LabVIEW Based Modal Analysis

Login: SeanWu Password: ME4410 Folder: Desktop/ME5440

DATA Acquisition

Open DAQ file: Desktop/ME5440/Template/”ME5440_Modal.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. Setting up the Data Acquisition file, a) Press F2 and wait to see if the cables and signals are good. (See level meter: Red indicates overload, 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, make sure you are on “Display” in Task List (left side). The below changes may be necessary at the beginning and when a data acquisition needs some control. The following changes are restricted to “Measurement Organizer” window.

1. To change “Level” (trigger values as a % of Range) and “Delay”, right-click: Setup > properties

2. To change “Span” (frequency range) & “Lines” (frequency resolution), right-click:: FFT Analyzer > properties

3. To change “Averages”, right-click:: FFT Analyzer > properties

4. To change excitation “Window”, right-

click: Force > properties > Signal tab a. In “Window” pull down “Transient” for impact

hammer measurement. b. Use “Shift” to assign start window and “Length” to

stop window. 5. To change response “Window”, right-click: Acceleration >

properties > Signal tab a. In “Window” pull down “Exponential” for impact

hammer measurement. b. Use “Shift” to assign start window and “Tau” to

stop window.


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II. 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. This process is called ranging. Click on “ORGANISERS” in Task List (left side). 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. Use four times (+6 dB) the maximum value for determining range.

b) To change “Range” of impact hammer signal, right-click: Force > properties > Channel tab> change values in “Max Peak Input”

c) To change “Range” of accelerometer signal, right-click: Acceleration > properties > Channel tab > change values in “Max Peak Input”

III. Collecting data:

a) Press F2 (ARM) followed by F5 (START) a. Hit the object at a marked position for obtaining the Frequency Response Function for the

predetermined number of averages. b. To save this data Press F7 (SAVE). The data on the screen will be saved as

“Measurement” in the tree of the “Measurement Organizer” window. Rename this saved file with indexes corresponding to the excitation location and response location. For example if you applied excitation at point 1 in Z-direction and measured response at point 2 in Z-direction, the assigned name should be “0001Z0002Z”.

c. Copying the FRF to excel spreadsheet:

i. To do this, make sure the “Frequency Response H1” is the active curve (red colored) in the FRF/Coherence display window.

ii. Right-click and select “Copy Active Curve”. Paste this data to your excel sheet. The 2nd column represents the X-axis frequency and the 3rd column represents Y-axis dB (m/sec^2/N, ref 1).

d. Repeat the above two steps for all the marked locations. e. Exporting FRF data to STAR

MODAL: i. In the “Function

Organizer” right click “Frequency Response H1

(ACCELERATION,FORCE)” and select Properties. Leave the “Frequency Response H1(ACCELERATION,FORCE)” window open.

ii. In the newly opened “Frequency Response H1 (ACCELERATION,FORCE)” window, under “Measurement” select the file you like to export (example: 0001Z0002Z).


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iii. Go to “Function Organizer” right click “Frequency Response H1(ACCELERATION,FORCE)” and click “Save” and select “STAR Binary”.

iv. Fill the “STAR Binary File properties” window with appropriate measurement location and directions for the file selected in step ii.

v. Hit “OK” and “Save” the file created in the “Group 1” folder you had created initially.

vi. Repeat step ii-v for all measurement locations.

Post Processing 1. Insert “STAR Security Key” floppy disk in the floppy dive. 2. Click open: Desktop/”STAR” to launch STAR software. Select

“Modal” and hit Run to open STAR Modal application. 3. Click Project > New, to create a new project file in the “Group 1”

folder. 4. Creating Model : Click Model and select “Setup” > Templates.

a. Press “Create New” to create a template.

b. Go to “Points” tab and input the number of points you had conducted the experiment for. Input the x,y,z locations of the pints measured to create the geometry.

c. Go to “Lines” tab and connect the points sequentially as shown below by inputting the

connecting points in the “From” and “To” spaces.

d. Go to “Components” tab and create a new component which will contain the points and lines we had created before.

e. Go to “Measurement Points” tab and click “Assign Default” for the system to assign the measurement locations to the geometry locations.

f. Click “OK”. You will now see the geometry we had created in 4 different views in the main window.

5. Importing Measurements: Click Measurements and select “Setup”

a. In the “Project Parameters” assign the Units (Same as your measurements). 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). Choose “Fixed Response” radio button for roving hammer method.

b. Go to constraint and create dependent measurements (that is

create measurement data for dummy locations).


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c. Choose “Ok”

d. Click Measurements and select “Import” > “STAR v5” e. By default the above window chooses “Measurements” and

“Freq response”. If different choose as per the above figure and hit “OK” for importing the FRF data.

f. Locate your folder destination and select it.

5. Analyzing Measurements: Click Analysis and select “Function” > Modal peaks

a. 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.

b. 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.

c. Click Analysis and select “Function” > Advanced Modal Peaks d. Click “Create” to create the analysis file in the “Star Files” folder created before and then

click “Next”


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e. Select “Bandwidth” for the analysis and hit Process. f. Change “Model size estimator” values to 10 & 20 and click “Next” g. In the stabilization diagram pick the lowest black circle (F&D Still stable) lying below

the peak values. h. Click “Real” for mode shape type and hit “Calculate” to calculate the modal

participation. Click “Next”. i. Click “Autofit All” and hit “Next” j. Select the “Mode” for click “Overlay” and play to see the modes.


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Experiment No. 6 Modal Analysis Objective: To measure and analyze the modal parameters, i.e., the natural frequencies, damping ratios, and mode shapes of a simple structure using an impulse-frequency response technique and digital frequency spectral analyzer. Major Equipment: HP 3582A Spectrum Analyzer, HP 54501A Digital Oscilloscope, PCB Model GK291B01 Impulse Hammer Kit which includes Model 086B01 hammer and Model 309A miniature accelerometer, and a steel cantilever and clamping fixtures. Procedures: 1. Clamp a steel cantilever beam on fixtures. Measure the free length, width, and

thickness of the beam. The values of the modulus of elasticity and density can be found in mechanics of materials books.

2. Use bees wax to attach the miniature accelerometer near the tip of the beam so that it will respond to the first three modes. Note that if the accelerometer is mounted at a nodal point for a particular mode, that mode will not be present in the modal response measurement at that point.

3. Mark the beam with a pencil at evenly spaced positions along the beam (i.e., 2”, 4”, 6”, 8”, 10”, and 12” from the fixed end). These are the positions where the impulse hammer will be used to excite the beam.

4. Set up the spectrum analyzer with the impulse hammer output connected to Channel A and the accelerometer output connected to Channel B. Select the Uniform Window and Both Channels on the input. Set up the analyzer for averaging of the transfer function data with four averages.

5. Tap the beam several times while checking the overload lights on each channel. Adjust the input sensitivity knobs on each channel so that the overload lights do not come on during impact. The optimum sensitivity setting is one “click” above the position where the overload light comes on.

6. For the first position at 2” from the clamped end of the beam, tap the beam four times to get the averaged transfer function data. Select the frequency span so that the peaks corresponding to the first three modes appear on the spectrum. Moving the cursor dot along the spectrum and using the function selection buttons, 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 1.0, disregard the measurement and repeat the test until an acceptable coherence is obtained. Observe the time domain responses on the oscilloscope – note the changes in the response as the impact hammer is moved to different locations.

7. 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.


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8. For at least one measurement position, 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. Check your results for a different measurement point – the frequency and damping should be the same for all positions. Only the magnitude and phase information which govern the mode shape will change from one position to another.

Requirements

1. Using the theory of flexural vibration discussed in the class, calculate the natural

frequencies and mode shapes for the first three modes of a cantilever beam. The mode shapes should be normalized to the maximum deflection for that mode (i.e., let the maximum deflection be unity and other deflections be fractions of unity).

2. Based on the measured data, calculate the imaginary part of the transfer function. Plot the mode shape for each of the first three modes. As with the theoretical mode shapes, normalize the amplitude of the mode shape.

3. Calculate the damping ratios for each of the first three modes using the half-power method. Are the damping ratios position dependent?

4. Compare your experimental mode shapes to the theoretical ones. Are the natural frequencies position dependent? Are the mode shapes position dependent?

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