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