Sound is a disturbance in air that travels as a wave havinq a frequency of between 20 and 20,000 hertz and having an amplitude great enough to be heard. Noise is merely a sound that is, subjectively, unwanted because of intensity, frequency, or location.

Sound is sensed by a microphone which converts the pressure fluctuations of the sound wave to an electrical signal. This signal is conditioned by the circuitry of a sound level meter and the intensity is indicated in unit of decibels (~). The term decibel is defined to be equal to 10 times the logarithm to the base 10 of the ratio of two power quantities. Power can be in watts horsepower, or in the case of sound, pressure squared. The advantage of a decibel scale is that smaller numbers can be used in calculations.

It was noted that in addition to intensity, sound is further characterized by frequency of the sound wave. Since response of the human ear is not the same for all frequencies, various weighting systems have been devised to correlate the sound level meter readings to human response to sound. The "A" weighted scale is presently accepted as resulting in the closest correlation.

The test site was the kart track of Johnson Park, Milwaukee, Wisconsin. Track layout and microphone positions are shown in figure 1.

Data was obtained on the afternoon of June 15, 1993. Ambient conditions were:

Temperature: 73 F
Barometer: 29.97 inches Hg
Wind: SSW 7 mph
Background Noise Level: 53 ~A

For the microphone positions shown on figure 1, test results were:

Position A B C
High 80.5 72 66
Low 76 70 64
Avg. 78.25 71 65

Military Jet Takeoff at 50'X
Oxygen TorchX
Turbofan Aircraft Takeoff at 200'X
Riveting MachineX
Rock-N-Roll BandX
Passing SubwayX
Newspaper PressX
Motorcycle at 25'X
Food BlenderX
Power Mower at 25'X
Garbage DisposalX
Passenger Car 65 MPH at 25'X
Vacuum CleanerX
Electric Typewriter at 10'X
Quiet Residential StreetX
Bird CallsX
Soft MusicX
Rustling Leaves X
Threshold of HearingX
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