Ron Wanttaja wrote:

James Robinson wrote:

Further, don't be lulled into thinking ANR will help prevent hearing
loss. ANR has a number of issues that can give a false sense of
security. The best protection is a passive ear muff. With some
designs, ANR can actually increase sound levels.

When I can, I wear foam earplugs under the ANR. However, I dislike
to, as the "as-heard" volume isn't quite high enough, and I lose
sidetone. I wear the plugs if I'm going to actually fly somewhere,
fishing them out from under the helmet when I get near the
destination.

That's a good practice.

The problem with ANR is that its effects are deceptive, and the value it
provides against hearing loss is limited.

ANR typically only works at the lower frequencies of the sound spectrum.
If you see graphs of the effectiveness, it is the highest at low
frequency, and it drops off as the frequency increases toward about 500
Hz. Above 500 Hz, ANR is typically ineffective.

The dBA sound curve is the closest representation of what frequencies can
be heard by humans. It drops off below 500 Hz, meaning that humans don't
hear low frequency sounds that well. The curve is also said to be
representative of the sound frequencies that will cause permanent hearing
damage. That suggests that low frequencies are not as damaging as higher
frequencies.

Putting all that together says that ANR is most effective in the
frequency ranges that have the least impact on hearing damage, and has no
effect in frequency ranges that can cause the greatest hearing damage.

When people switch ANR on and off, the effect is therefore deceiving.
They think it is doing more than it actually is.

In practical terms, I was part of a study where we looked at using ANR in
an industrial application to try to reduce long-term hearing loss claims.
After extensive study and research, the medical department determined
that while ANR could improve the clarity of things like voice
communication in high noise environments, it had so little value in
reducing hearing loss, that the extra investment wasn't justified.

Instead, ear plugs or passive muffs were considered the best protection,
with both used at the same time where the sound levels were the highest.
The company didn't prohibit the use of ANR muffs if employees wanted to
purchase their own, but the muffs still had to have a passive noise
reduction rating above a minimum amount.