Abstract
Noises were measured many times on 60, different types of pneumatic machines such as reciprocating and turbo compressors, axial and centrifugal fans, turbo refrigerators and superchagers, at distances ranging from 1 to 30 meters. The results of statistical observation on the calculated value of a noise rating number, sound levels and spectra may be summarized as follows: 1) Like tha case of ship campartment noises, discussed in Report (1), good correlation was reached between the calculated value (LL, PNL, NRN) of the sound rating number of pneumatic machines and the sound level A calculated from the original spectra. 2) The difference between the noise rating number and the sound level A came to 13 (LL), 14 (PNL), and -2 (NRN), each of which was very close to the corresponding value in the case of ship noises. The noise rating number is expressed in terms of the sound level A by averaging the values of the difference published in several literature and the difference mentioned above, as follows: LL=A+13±3, PNL=A+14±2, NRN=A-3±1. 5, In this respect, the sound level A is considered as a good single measure of noises. 3) Noises measured in the neighborhood of each machine has spectrum which has less enagy at low frequencies and more energy at middle and high frequencies, than ship noises with the sound level A rated about 95±10dB.
