lab4 - 1 Physics 198 PHYSICS OF MUSIC Laboratory 4 Name...

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1 Physics 198 PHYSICS OF MUSIC Laboratory 4 Name ________________________________ Partner(s) ___________________________________ This laboratory deals with sound intensities, sound levels, hearing sensitivity and a brief introduction to digital analysis of sound. Goals : I. To become familiar with sound level meters and review the relationship between sound intensities and levels. II. To measure hearing sensitivity limits as a function of frequency. III. To digitally record and visually examine sound waves. Apparatus : Dell Optiplex 620 Computer equipped with SpectraPlus sound analysis software, USB audio interface box (M-Audio, FastTrack) for headphones (Sennheisser EH150 ) and microphone (Shure MD58), microphone stand, signal (function) generator (BK Precision) connected directly to a (Realistic) speaker and “tee’d” to an oscilloscope, sound level meter (Realistic).; selection of tuning forks and devices to strike them. There is now a networked printer for all lab setups rather than on each table as in the photo.
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2 PART I. Sound Intensities and Intensity Levels. Turn on the sound intensity level meter and check its battery by placing the dial on “BATT” and check that the meter falls in the “batt” range indicating that it is ok. If the battery is dead ask the instructor for a new one. The meter has two ranges: “A” that is similar to the human ear in response, and “C” that has a “flat” response largely independent of frequency. Use range “C” and “slow response” for this lab. Turn the switch so that to the range centered on 70 dB. If the needle were centered, the sound level would be 70 dB; if it were 4 units to the left of zero, the level would be 66 dB and if it were 4 units to the right the level would be 74 dB, etc. You may or may not have a reading on the 70 dB range, depending on how noisy your fellow students are at the time. Try whistling or singing to get a feel for how the level changes. Ask your partner to sing at moderate volume or recite poetry and hold the meter at a distance of about one to two feet from his/her mouth. Approximate sound level for poetry _____________; for singing ______________. Now turn the “output level” knob on the “BK Precision 4011” function generator all the way down, and push in the button that gives 20 dB of attenuation. (This is one of four buttons labeled “Normally left out.”) Turn on the generator and set it to about 262 (close to middle C) Hz sine wave. (The sine, square and triangle wave selector buttons are on the top right of the device.) Adjust the generator output to obtain a sound level of about 80 dB at a distance of about 1 foot (approximately 0.30 meters) from the center of the speaker enclosure. (You may have to remove the 20 dB of attenuation to achieve this level.) Turn off the function generator after you have heard the 80-dB sound. It turns out that a remarkably small amount of sound power is necessary for a reasonable listening sound
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lab4 - 1 Physics 198 PHYSICS OF MUSIC Laboratory 4 Name...

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