hobbyist wrote:Unacceptable levels are where my ears can be further damaged.
For me that is a hard line at 85dB and if you might cross it I will already have earplugs in use.
There is a fundamental misunderstanding here about what causes hearing damage.
There is a direct risk from instantaneous high levels -- gun shots and impacting machinery etc -- but we're talking 135dBC SPL as the lower action level and 137dBC SPL as the upper action level -- in Europe; I can't be bothered to look up the US equivalent, but it's probably higher... The absolute maximum instantaneous peak level allowed in Europe by law is 140dBC SPL.
These values are legal limits -- the lower action level is where hearing protection must be offered, the upper level is where hearing protection must be worn, and no-one must ever be exposed to levels above the peak value.
These instantaneous peak values are the only sound levels which can be assessed with a simple SPL meter.
But you are extremely unlikely ever to come across situations with instantaneous sound levels anywhere near those figures in normal life.
More commonly, long term noise-induced hearing damage comes from 'sound exposure
', which is the continuous sound level integrated over time
Decades of meticulous research has arrived at a 'safe' figure for daily sound exposure (normalised over an 8-hour working day) of 85dB LEPd. In Europe, to play extra safe, they reduced that to 80dB LEpd. In the US they still have 85dB as the daily exposure first action level.
So, in Europe, if someone has a daily (8-hour) noise exposure of more than 80dB LEpd (or sometimes noted as LAeq), they have to be offered hearing protection (but they don't have to use it if they're idiots). If the exposure exceeds 85dB LEpd they have to wear hearing protection (by law). And no-one can ever be exposed to more than 87dB LEpd, even when wearing hearing protection.
But note again the suffixes used here -- they are extremely important: We are talking about sound exposure over time, not simple SPL levels!
In situations where the sound exposure could exceed these values over an 8-hour period, either the source sound level has to be reduced (eg, by enclosure), the hearing protection improved, or the personal exposure time shortened. Halving the exposure duration reduces the exposure figure by 3dB.
However, measuring the LEpd value is non-trivial and requires specialist metering/logging equipment -- although there are some apps for smart phones that can give a useful approximation. The last time I looked the least expensive device capable of properly measuring LEpd (LAeq) was the NTI XL2 costing in excess of £1300.
The important point to take away from all this, really, is that saying "For me that is a hard line at 85dB" is entirely meaningless and ignorant!
At moderate-to-loud volume levels hearing damage is entirely determined by exposure
-- integrated volume over time -- not instantaneous or even short term averaged SPL.
And none of this has any relevance whatsoever to the SMPTE pro-studio acoustic alignment level which just happens to share a similar numerical value.