Hearing loss Temporary or more permanent?

One caveat when using the OSHA guidelines is the lobbying that goes into setting them. It costs money to make the workplace quieter. I'd be inclined to use a few dB under the guidelines or to shorten my exposure time. I attended a gathering of audiophiles at a high-end shop in soCal, and in the room with the most expensive stuff the attendees wanted the level so high I left, because it was uncomfortable.

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When I was a grad student decades ago, I worked at a research center aimed at the study of noise-induced hearing loss. Temporary threshold shift (TTS) was a hot topic. Rock concerts were in vogue, and lots of folks were concerned about whether they were injurious to hearing. The answer is they can be depending on where you are and for how long. If you measure carefully enough, you'll discover that even low levels of sound can cause TTS, but recovery is rapid. Buy a Radio Shack sound level meter. I'd use slow trajectory, because the auditory system integrates sound. At this point, I'm not sure what the value of a hearing test could be, but I would avoid prolonged exposure to what seem to you as loud music.

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Bifwynne, I knew some of the people who were on the scientific committees that made the recommendations to OSHA.

Stevecham, I think you're doing the right thing by keeping peaks lower, but you need to know neither the auditory system nor other neural systems ramp up in sensitivity, although your perception may be concentrated with exposure. Adaptation is the mechanism, and thus it's easy to expose yourself to higher and higher levels.

Re fast v slow trajectory for an SL meter: Except for very high level peaks, gun shots usually, noise-induced hearing loss is a cumulative process. The military took advantage of what's called the stapedius reflex, in which the stapes is pulled slight away from the ear drum in response to a loud sound, by sounding a loud horn before firing a large gun. The purpose of such a reflex has been argued, but severe sounds are not part of our natural environment, so it's unlikely it was developed over time to provide protection from such sounds. Using fast trajectory is OK, but it makes it more difficult to estimate the cumulative SPL exposure.

Bifwynne, as a general rule if it feels comfortable to you it's probably OK. If you think you're pushing it, turn the level down a bit. You might start by finding a level where soft jazz (e.g. Bill Evans), Bach, and Mozart feel right, then look at your attenuator to find a reference level. Peaks from that reference in more bombastic music (e.g. Mahler or Stravinsky) are unlikely to do any damage to your hearing. The OSHA guidelines are aimed more at the kind of continuous noise exposure found in a workplace. Bottom line: Use common sense; if it seems loud, it probably is.

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Re A & C weighting: A-weighting is contoured to replicate the hearing sensitivity data of Fletcher and Munson; C-weighting is essentially flat. So you might use the A scale to estimate how loud a sound is and the C scale to determine its level. For hearing protection considerations, I'd use the C scale. Sharp onset acoustic events have broad frequency distribution even though the steady state event might be narrow.

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