dB weighting

[drummerboi316]

When measuring dB for an outdoor concert at FOH using a sound level meter, what is the correct settings to get accurate OSHA measurements. A or C weighting / fast or slow?

Thanks!

 

[DaveySimps]

OSHA looks for A weighting slow response.

~Dave

Decibel levels hearing protection and the OSHA

http://www.osha.gov/dts/osta/otm/noise/health_effects/physics.html

 

[museav]

When measuring dB for an outdoor concert at FOH using a sound level meter, what is the correct settings to get accurate OSHA measurements. A or C weighting / fast or slow?

To get accurate measurements for OSHA compliance you need to measure the exposure over an 8 hour period. That generally requires a dosimeter or similar device. Even for shorter measurement periods a simple sound level meter does not address the time factor relevant to exposure or 'dose'. The only OSHA value that would seem to be directly relevant with a simple sound level meter is the 140dB maximum allowable peak level, everything else has a time factor involved.

One exception to this may be if you took the perspective of the goal being to avoid an exceedance during the time period of the event, in which case you could insure that by never exceeding the allowable level for the duration of the event, e.g. never exceed 100dBA for a 2 hour show, thus you know the show in and of itself does not reflect an exceedance. However, that only addresses that portion of the total 8 hour exposure period defined by OSHA. And it would result it lower levels than may be possible if you were able to account for the time factor and related exposure.

Keep in mind that OSHA has two action levels. The Table in 1910.95.b.2 that many reference applies to engineering and administrative controls, i.e. actively reducing the exposure, and in effect defines a 90dBA, 8 hour TWA (Time Weighted Average) limit. However, 1910.95.c and 1910.95.d define that a hearing conservation program that includes monitoring and audiometric testing must be established whenever the 8 hour TWA level exceeds 85dBA without any personal hearing protection, 5dB below the levels defined to require engineering and administrative controls.

Also consider that OSHA is addressing long term noise exposure in the workplace, which explains the 8 hour exposure period and why it refers to employers and employees. It may be a reasonable guideline for other applications but is not necessarily directly relevant or applicable to other situations.