Re: Ear protection

[Lamar Owen <lowen () pari edu>]

On 09/23/2015 10:09 AM, Keith Stokes wrote:
> Since I’m in our colo facility this morning, I decided to put some numbers on it in my little isolated corner with lots 
> of blowers running.
>
> According to my iPhone SPL meter, average SPL is 81 - 82 dB with peaks 88 - 89 dB.
With SPL that close to the recommended maximum, the accuracy of the SPL 
measurement is rather critical.  I would not trust my smartphone's mic 
to have sufficient accuracy to protect my hearing unless it is 
calibrated to a known source SPL using pink noise of a particular 
weight.  The calibration SLM should be a 'real' SLM, such as a Bruel & 
Kjaer Type 2250 or similar with proper transducers.  (Yes, I know, a B&K 
2250 will set you back nearly $4K, but, just what is your hearing 
worth?  A pair of hearing aids will set you (or your insurance company 
at least) back $4K too....).  I used a vintage B&K transducer with a 
custom-built SLM-rated spec-an years ago at a local manufacturer's sound 
testing lab; the manufacturer makes ballasts and luminaires for HID 
lighting, and measuring ballast noise is a big deal.  But reasonably 
accurate SLM's are available for less than $500 (some are available for 
less than $100, but you get what you pay for....).

The particular whine of high-speed fans is a known risky noise source, 
particularly white noise, due to the high frequency content (140dB SPL 
at 45Hz is not as harmful as 140dB at 3kHz or 15kHz due to the outer 
ears' acting as waveguide-beyond-cutoff attenuators (and cavity 
resonators, too, for that matter).  Spinning drives are no better, 
particularly 15k  RPM drives.

If it's at all uncomfortable, wear the earplugs.  You're already having 
to shout to be heard anyway.