[183982] in North American Network Operators' Group
Re: Ear protection
daemon@ATHENA.MIT.EDU (Lamar Owen)
Wed Sep 23 12:22:02 2015
X-Original-To: nanog@nanog.org
Date: Wed, 23 Sep 2015 12:13:08 -0400
From: Lamar Owen <lowen@pari.edu>
To: NANOG <nanog@nanog.org>
In-Reply-To: <295C9FCB-3121-4756-9FD1-847644808E12@neilltech.com>
Errors-To: nanog-bounces@nanog.org
On 09/23/2015 10:09 AM, Keith Stokes wrote:
> Since I=E2=80=99m in our colo facility this morning, I decided to put s=
ome numbers on it in my little isolated corner with lots of blowers runni=
ng.
>
> According to my iPhone SPL meter, average SPL is 81 - 82 dB with peaks 8=
8 - 89 dB.
>
>
With SPL that close to the recommended maximum, the accuracy of the SPL=20
measurement is rather critical. I would not trust my smartphone's mic=20
to have sufficient accuracy to protect my hearing unless it is=20
calibrated to a known source SPL using pink noise of a particular=20
weight. The calibration SLM should be a 'real' SLM, such as a Bruel &=20
Kjaer Type 2250 or similar with proper transducers. (Yes, I know, a B&K=20
2250 will set you back nearly $4K, but, just what is your hearing=20
worth? A pair of hearing aids will set you (or your insurance company=20
at least) back $4K too....). I used a vintage B&K transducer with a=20
custom-built SLM-rated spec-an years ago at a local manufacturer's sound=20
testing lab; the manufacturer makes ballasts and luminaires for HID=20
lighting, and measuring ballast noise is a big deal. But reasonably=20
accurate SLM's are available for less than $500 (some are available for=20
less than $100, but you get what you pay for....).
The particular whine of high-speed fans is a known risky noise source,=20
particularly white noise, due to the high frequency content (140dB SPL=20
at 45Hz is not as harmful as 140dB at 3kHz or 15kHz due to the outer=20
ears' acting as waveguide-beyond-cutoff attenuators (and cavity=20
resonators, too, for that matter). Spinning drives are no better,=20
particularly 15k RPM drives.
If it's at all uncomfortable, wear the earplugs. You're already having=20
to shout to be heard anyway.
