Originally Posted by Bill Fitzmaurice
Originally Posted by homeboydeluxe
Also is it not the case that the ear is simply more sensitive at mid frequencies (Intelligibility) and that bass frequencies are still capable of damaging the ossicles and other workings of the inner ear?
Damaging frequencies closely follow equal loudness curves, so we are far less likely to suffer damage from lows or highs as we are the midrange. Exposure to 105-110dB broadband for a couple of hours a day shouldn't be a problem. That's plenty loud enough for any sane person. But of course that means that at 28 you've only recently arrived at that milestone.
Yikes! IMO, 105-110 dBA is WAY too much for two hours. OSHA specifies 90 dBA average over eight hours, and for each 5 dB above that, cut the exposure in half. So that would put the "safe" exposure at 105 dBA at one hour and 110 dBA at 30 minutes. However, I believe that the OSHA standards are way too liberal for real safety. Here's a quote from the OSHA website:
"OSHA sets legal limits on noise exposure in the workplace. These limits are based on a worker's time weighted average over an 8 hour day. With noise, OSHA's permissible exposure limit (PEL) is 90 dBA for all workers for an 8 hour day. The OSHA standard uses a 5 dBA exchange rate. This means that when the noise level is increased by 5 dBA, the amount of time a person can be exposed to a certain noise level to receive the same dose is cut in half.
"The National Institute for Occupational Safety and Health (NIOSH) has recommended that all worker exposures to noise should be controlled below a level equivalent to 85 dBA for eight hours to minimize occupational noise induced hearing loss. NIOSH has found that significant noise-induced hearing loss occurs at the exposure levels equivalent to the OSHA PEL based on updated information obtained from literature reviews. NIOSH also recommends a 3 dBA exchange rate so that every increase by 3 dBA doubles the amount of the noise and halves the recommended amount of exposure time.
"Here's an example: OSHA allows 8 hours of exposure to 90 dBA but only 2 hours of exposure to 100 dBA sound levels. NIOSH would recommend limiting the 8 hour exposure to less than 85 dBA. At 100 dBA, NIOSH recommends less than 15 minutes of exposure per day."
I'm with NIOSH on this one!
Bill is correct that noise-induced hearing loss normally affects the midrange (2-4 kHz), which is exactly where speech consonants live. This is why it's more difficult to understand conversations in a noisy environment. Plus, NIHL is cumulative and insidious; it often doesn't manifest until years after the exposure, when it's too late.
As for measuring the levels in your theater, I use the AudioTools iPhone app from Studio Six Digital
. The app is $20, and to get a realistic measurement over time, it's best to use the add-on called SPL Graph, which is another $6. I also sprung for the calibrated microphone, which is $200. That's pretty expensive, but as a professional in this field, I felt it was a worthwhile investment. You can probably do without the microphone, but the iPhone's internal mic overloads somehwere around 100 dBA or so. I think Android phones do much better in this regard, but I don't know what SPL apps are available for it.
For more about hearing protection, loss, and compensation for loss, please watch my Home Theater Geeks podcast episode 209 here