a. It depends very much on the design of the headphones. In principle they
do, and in practice they can, provide a very substantial reduction in the
noise reaching the ear.
b. No, you are not replacing one damaging sound by another, you are just
cancelling (to some extent) the original sound.
c. If you are looking for a means of reducing the noise exposure, you will
need to consider both the noise and the design of the headset. Active noise
reduction (ie sound cancelling) works best at fairly low frequencies up to
about 1 kHz. So if the noise is mostly high frequency, then it won't work,
in fact can make things slightly worse. If the noise is mostly low
frequency, the reduction in noise is likely to be of the order of 10 dB or
so. If you are serious about reducing noise exposure, then the headset
should incorporate as much conventional passive protection as possible, so
that you have the benefit of both active and passive protection.
d. Using sound cancelling, the headphones can be lighter and more
comfortable than conventional passive ear muffs. This is fine, assuming you
can still get the noise at the ear to "safe" levels, and you are happy with
the cost and complication of an active system. If it isn't enough then you
will have to go to relatively heavy and bulky headphones which give good
passive as well as good active reduction of sound.
e. If the noise is very intense then the active system may not be able to
cancel it, especially if the passive protection isn't good.
So, as always, the answer is to evaluate the noise and then consider how
best to deal with it. There isn't one simple answer that will fit all
Maury Freedman <mauryf at earthlink.net> wrote in article
<38DF66A8.97AA965F at earthlink.net>...
> I have a layman's question about excessive machinery noise. Do those
> sound canceling headphones provide any substantive protection? The
> theory of reproducing sound out of phase to cancel the primary sound
> seems like it would work to make the original sound seem less loud, but
> are you replacing one damaging sound with another? In other words, is
> it only beneficial from a comfort standpoint, or is there any real
> medical benefit - such as a set of padded cushions might produce?
>> Please fee free to post here, but an e-mail would be really appreciated.
>> mailto:mauryf at earthlink.net>> Thanks! Maury