Equivalent sound level contours. Octave band sound pressure levels may be converted to the equivalent A-weighted sound level by plotting them on this graph and noting the A-weighted sound level corresponding to the point of highest penetration into the sound level contours. This equivalent A-weighted sound level, which may differ from the actual A-weighted sound level of the noise, is used to determine exposure limits from Table 1.G-16.
1910.95(b)(1)
When employees are subjected to sound exceeding those listed in Table G-16, feasible administrative or engineering controls shall be utilized. If such controls fail to reduce sound levels within the levels of Table G-16, personal protective equipment shall be provided and used to reduce sound levels within the levels of the table.
1910.95(b)(2)
If the variations in noise level involve maxima at intervals of 1 second or less, it is to be considered continuous.
TABLE G-16 - PERMISSIBLE NOISE EXPOSURES (1)
______________________________________________________________
|
Duration per day, hours | Sound level dBA slow response
____________________________|_________________________________
|
8...........................| 90
6...........................| 92
4...........................| 95
3...........................| 97
2...........................| 100
1 1/2 ......................| 102
1...........................| 105
1/2 ........................| 110
1/4 or less................| 115
____________________________|________________________________
https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9735
The problem with standard meters is that they are not capable of measuring low frequency noise/sounds and they are not calibrated well most of the time to begin with. In this case I would not trust OSHA on this.
Being a bass player and reading the warnings on my amps or in their respective manuals, plus hearing the sound and feeling the pressure personally, I would be willing to bet that sound pressure production at the sub 1KHz range vs. that graph is way off. In fact more than a few sources I’ve read claim exactly that.
I’ll see if I can find some references.