Ear protection

Thu Sep 24 04:15:00 UTC 2015

So I intended to provide a few short comments on this but got on a
roll. The below may be of more or less use to you but this is the way
I look at things.

Listening to music isn't all that bad a means of dealing with noise
for shorter periods such as the odd onsite engineers have to do
because either you're out of techs or it's a really complicated or
delecate job and it requires more care than the average datacenter
tech or (heaven forbid) remote hands can provide (because they don't
normally do that stuff), especially if you're either using ear buds or
full cup over the hear headphones because the mere fact of wearing
these will probably cut 5-10db off the ambient. (I have a pair I use
for mixing and production use that do much better than that even.)
Second, the presence of music, as long as it ain't overly loud itself,
tends to also not merely cover but it gets the ear doing different
things so it's no longer focusing on the particular frequency set of
the fans.

If you're a datacenter or field tech, noise canceling headphones are
basically a must. If that's not your bag and you don't need to be on
the phone (I strongly advocate electronic means of communication such
as google chat, SMS, irc, or otherwise just because it's more certain
and doesn't require you to shout or listen to very loud background
noise), then go with foam ear plugs. Carry a small package of them in
your bag. They also tend to irritate your ears less than platic ear
plugs and ear buds because the form to the ear, not force tissue
around.

On noise standards, accuracy of the meter isn't really important (as
long as it isn't useless) because it's more of a "I should be thinking
about it" threshold. But make absolutely sure you are measuring the A
weighted noise curve, not the C weighted or your not measuring the
noise that will most impact your hearing. You should also not rely on
your employer providing ear protection. You should take it on yourself
to guard against tinitis. (No fun. I have a touch of it in my left ear
but not from music or concerts. From randomness. Overly loud music or
sharp noises can set it off and it'll annoy me for at least a couple
of hours until it drops back down to easily ignorable levels.) I just
had to do 6 hours of wiring and cable management in some racks I've
been helping assemble, meaning my head and hands were not in the
middle of the aisle, but right behind the machines. It was only when I
stepped away from the racks after the first hour or so to get supplies
that I realized, "MAN, that's loud!" So if you're routinely in that
environment, make ear protection a habit. You can buy a better set of
headphones. You can't buy a better set of ears.

Note also that in the last 15 years, fan speeds and drive speeds have
increased as equipment has gotten more and more dense and as a result
manufacturers have had to up the air velocity in order to cool the
gear and that has generally meant small, steeply pitched, very fast
fans. (This is especially true of servers built to be densely rack
mounted and yet provide capacilities to house lots and lots of drives
in that small footprint. Look at your average 1U crammed with these
small drives. Have to get air through there somehow.) This has caused
a shift in frequency as well as an increase in intensity. So the
characteristics of the noise has changed. That's important because the
current noise is closer to the center of our range of hearing and
don't forget the harmonics. So not only has the noise gotten louder,
it is now in a range where our ears are more sensitive to it and
therefore it is more important to take measures to guard against.

I happen to have a measurement mic and a decent spectrum analyzer
plugin. I may take some measurements just to illustrate the makeup at
various points. May even be worth a paper if I can get some equipment
and colo vendors to cooperate and feed me data.

-Wayne

On Wed, Sep 23, 2015 at 12:13:08PM -0400, Lamar Owen wrote:
> 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.
> 

---
Wayne Bouchard
web at typo.org
Network Dude
http://www.typo.org/~web/