| Acoustic sizes must be adapted to the perception range of the human ear in a way that also makes technical sense. Depending on the frequency, the real sound pressure level is adjusted with certain values to the sensitivity of the ear. There are valid international evaluation curves for these adjustment
values.
Some areas of application for different evaluation curves are given below.
A - Evaluation curve for LN = 30 - 60 Phon.
B - Evaluation curve for LN = 60 - 90 Phon.
C - Evaluation curve for linear audibility range.
D - Evaluation curve for aircraft noise.
An evaluated sound level is indicated by having the letter of the evaluation curve e.g., dB (A) suffixed.
The A-evaluation curve is the one primarily used in measuring the noise of compressors and other machinery. Sound measurement as standardised in DIN 45635 uses A-evaluated sound pressure levels. |