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| APPENDIX |
Appendix B | B |
Glossary of Terms |
Background Noise, effects of
Background noise can cause considerable error in measurement when its level is high relative to the level of a noise source of interest. If you can make measurements both with and without the contribution of a noise source of interest, you can mathematically subtract the background noise from the combined measurement, yielding the level of the noise source of interest alone. The accuracy of this determination improves as the difference between the two measurements increases.
To remove background noise
1.Obtain a measurement that includes the contribution of the noise source of interest (the combined measurement).
2.Make a second measurement under exactly the same conditions as in Step 1 but without the presence of the noise source of interest (the background noise measurement).
3.Determine the decibel difference between these two measurements.
4.Find that difference on the
5.Find the point on the curve directly above this difference.
6.Read the corresponding value on the
7.Subtract the correction value from the combined measurement.
Example: Measurements with and without the noise source of interest are 91 dB and 90 dB, respectively. For a difference of 1 dB, the background noise correction value is 7 dB. Therefore the level for the noise source of interest without the noisy background is 84 dB.
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