the best Active *Noise* Reduction technology existing

[[email protected]]

Hi,

I am trying to decide on an Active Noise Reduction (ANR) headset or
earplugs. I have looked at the Sony, Bose, Shure and other models, but
almost all reviews/comments mix two very different issues: noise
reduction and sound quality.

In my case, I have no interest whatsoever in sound quality, what I am
looking for is the absolute best noise reduction possible. I have
tried the Bose Quiet Comfort II, and they appear extremeny effective,
but only in the middle-low frequency range. Also, I have a feeling
that ANR earplugs might be more effective.

Various manufacters claims various degrees of noise reduction. As for
Bose, they do not even release their technical specs (although would it
not be possible for any lab to measure them across a frequency range
and publish the results?).

Recently I met a guy who was working in the US Navy on the deck of
aircraft carriers. He said that the headsets they had cancelled out
everything, that nothing could be heared at all when he was wearing
them. Since this hardly constitutes a secret technology, is it known
who designs these headsets for the US Navy? Is this technology used
for the civilian market by some manufacturer?

Can anyone give me some pointers as to how I could go about finding the
best ANR headset/earbuds out there?

Many thanks,

M.

 

[Rene Tschaggelar]

Hi,

I am trying to decide on an Active Noise Reduction (ANR) headset or
earplugs. I have looked at the Sony, Bose, Shure and other models, but
almost all reviews/comments mix two very different issues: noise
reduction and sound quality.

In my case, I have no interest whatsoever in sound quality, what I am
looking for is the absolute best noise reduction possible. I have
tried the Bose Quiet Comfort II, and they appear extremeny effective,
but only in the middle-low frequency range. Also, I have a feeling
that ANR earplugs might be more effective.

Various manufacters claims various degrees of noise reduction. As for
Bose, they do not even release their technical specs (although would it
not be possible for any lab to measure them across a frequency range
and publish the results?).

Recently I met a guy who was working in the US Navy on the deck of
aircraft carriers. He said that the headsets they had cancelled out
everything, that nothing could be heared at all when he was wearing
them. Since this hardly constitutes a secret technology, is it known
who designs these headsets for the US Navy? Is this technology used
for the civilian market by some manufacturer?

Can anyone give me some pointers as to how I could go about finding the
best ANR headset/earbuds out there?

Depending on what you try to attenuate, they may not
work as desired. While they are able to attenuate the
lower frequencies, they produce higher frequencies
that are making you more tired.
In smaller airplanes I feel better with switching
the active compensation off.

Rene

 

[Noral Stewart]

Affordable for industrial situations if appropriate.
http://www.protechcommunications.com/hearing_protection.html

Good reading before you go this way.
http://www.aearo.com/pdf/hearingcons/anr.pdf

The military side of things.
http://www.sdltd.com/_consulting/project_info/hearing_protection.htm

http://www.adaptivetechinc.com/anr_earplug.php?mm=6

 

[Scott Dorsey]

I am trying to decide on an Active Noise Reduction (ANR) headset or
earplugs. I have looked at the Sony, Bose, Shure and other models, but
almost all reviews/comments mix two very different issues: noise
reduction and sound quality.

Why not use both at the same time? It is fairly standard practice to use
foam plugs underneath active ear protection devices.

In my case, I have no interest whatsoever in sound quality, what I am
looking for is the absolute best noise reduction possible. I have
tried the Bose Quiet Comfort II, and they appear extremeny effective,
but only in the middle-low frequency range. Also, I have a feeling
that ANR earplugs might be more effective.

For the most part, none of the active noise reduction systems work much
above 1 KHz or so.

My feeling is the Sennheiser pilot headsets are definitely better in an open
cockpit plane (lots of repetitive impulse noise) than the Bose pilot ones.
The consumer (open ear) ones are all pretty lousy.

Various manufacters claims various degrees of noise reduction. As for
Bose, they do not even release their technical specs (although would it
not be possible for any lab to measure them across a frequency range
and publish the results?).

That's the way Bose is. Bose products are 90% marketing, and 10% technology.
Some of them (like the headsets) work okay, just at much higher cost than
they should. If you look at the over-ear Bose sets for pilots, though,
they will have some minimal specifications on the data sheet.

Recently I met a guy who was working in the US Navy on the deck of
aircraft carriers. He said that the headsets they had cancelled out
everything, that nothing could be heared at all when he was wearing
them. Since this hardly constitutes a secret technology, is it known
who designs these headsets for the US Navy? Is this technology used
for the civilian market by some manufacturer?

These are over-ear earcup devices. The high frequencies are blocked out
mechanically, the low frequencies are blocked out with active noise
cancellation. You can then use foam earplugs underneath them for additional
high frequency cancellation.

This is typical of the David Clark ground support sets:
http://www.davidclark.com/HeadsetPgs/h3530.htm
You'll notice that the David Clark website gives actual measured attenuation
numbers across the band, rather than made-up crap or single-frequency
marketing numbers like Bose shows.

Can anyone give me some pointers as to how I could go about finding the
best ANR headset/earbuds out there?

Your deck crew guy is probably issued a set of David Clarks. Sennheiser
also makes some that are okay.

The big question is what kind of noise you're trying to block out. If
you're sitting in a 747 or a Stearman, the noise patterns are very different.
--scott

 

[hank alrich]

This is typical of the David Clark ground support sets:
http://www.davidclark.com/HeadsetPgs/h3530.htm
You'll notice that the David Clark website gives actual measured attenuation
numbers across the band, rather than made-up crap or single-frequency
marketing numbers like Bose shows.

A few years ago I was on the tractor cleaering the road in a snowstorm.
A tree branch that I overlooked whapped me on the side of the head and
knocked the David Clark's off and onto the ground, where a tractor wheel
rolled over one earpiece. I sent them to DC for repair and at no charge
they sent them back fixed. Their quality and service are top notch.

 

[-hh]

Why not use both at the same time? It is fairly standard practice to use
foam plugs underneath active ear protection devices.

Wearing both is what I do when I'm carrying my NC headphones. The net
effect is quite good.


Part of the challenge is that there's no clear "Underwriters
Laboratory" standard (control) to benchmark test against.

Bose products are 90% marketing, and 10% technology. Some of them
(like the headsets) work okay, just at much higher cost than they should.

Truer words haven't been said about the $300 Bose headphones. There
are some dramatically less expensive alternatives out there that are
probably 90% the pragmatic performance potential, such as the "Plane
Quiet NC6" headphones which sell for a bit over $50. Here's a review:

http://www.thetravelinsider.info/roadwarriorcontent/planequietnc6headphones.htm

FWIW, Sharper Image catalog has a NC headphone that looks suspiciously
familiar to the NC6. It might be worth a visit to your local store to
see a copy in person.

Your deck crew guy is probably issued a set of David Clarks. Sennheiser
also makes some that are okay.

CONTROL also made the famous 'Cone of Silence', which was extremely
effective, but hard to use

FWIW, a couple things about the practical use of a travel-oriented NC
headset: some designs can be quite bulky, so do pay attention to how
they fold (or not) for how much room they'll take up in your carry-on.
Ditto for if they have a detachable cable (its just one more thing to
lose). Also, many of them (including my NC6's) have smaller "on the
ear" rather than large "over the ear" designs, which can have a
tendency to pinch your ear onto your eyeglasses and become
uncomfortable to wear after a few hours of continuous use. Afterall,
it does you little good to have the "perfect" set if they end up being
too big / too heavy to be worth carrying.


-hh

 

[Bernhard Mayer]

Recently I met a guy who was working in the US Navy on the deck of
aircraft carriers. He said that the headsets they had cancelled out

are those active or just the same type we use on the shooting range
during arms drill?

Can anyone give me some pointers as to how I could go about finding the
best ANR headset/earbuds out there?

Honestly, I have been through the Bose (the new one), the Sennheiser
250 and 350, the AKG 28 and the JVC. They all sort of work with Bose
taking the lead (well, you'd expect that for twice/three times the
price), but they will only cancel out some of the engine noise. The
difference is noticable and you'll have a nicer flight. You will still
hear some humming from the engine and you will hear everything that is
above a certain frequency (voice included).

However, these headphones are only worthwhile if you need to actually
use them as headphones to watch a movie or listen to the radio/MP3.

If you just want a good sleep, go to Walmart or your local drugstore
and pickup some of the in-ear noise blockers. They cost 10 cent or
something in that range and will block out *everything* resulting in
much better noise suppression than any headphone.
(if they are made by 3M, they are the ones we use for military
exercises - they are pretty good and comfortable)

If you want a headphone that blocks all the noise (and, well, works as
a headphone) I would pick one of those higher price SHURE headphones at
99,- or 199,-. Just by itself, they block noise as efficiently as those
Walmart thingies. If you pick the right headphone, they will be
comfortable enough to wear for the duration of a red eye flight.

 

[Scott Dorsey]

are those active or just the same type we use on the shooting range
during arms drill?

They might be the DC passive ones, but I know the Air Force guys are
being issued the DC active ones. The actives are really amazing... low
frequency cancellation from the active hardware, good padding for the high
frequency rejection.

Most shooting range hearing protectors are piston-type protectors that
are only effective against impulse noises. They have a diaphragm that
seals and unseals the chamber. This way you can hear people talk, but
when there is a short shockwave from a gunshot, the chamber seals and
most of the gunshot noise is kept out. Really ingenious idea. I think
it was a German idea in WWII that we adopted.

Honestly, I have been through the Bose (the new one), the Sennheiser
250 and 350, the AKG 28 and the JVC. They all sort of work with Bose
taking the lead (well, you'd expect that for twice/three times the
price), but they will only cancel out some of the engine noise. The
difference is noticable and you'll have a nicer flight. You will still
hear some humming from the engine and you will hear everything that is
above a certain frequency (voice included).

The Sennheiser PXC 250 and 350 have really very poor high frequency rejection
because they don't have a good ear seal. Skip those and take a look at
the HMEC250 as an entry-level unit and the HMEC450 as one with better
sealing. Yes, they are more money, but they work much, much better.

Which Bose units did you try?

Honestly, you cannot expect any of the "over-ear" units to be effective
at all at higher frequencies. And if you are on jets, it's the higher
frequencies that are a major problem. With a piston engine craft, the
active noise cancellation can deal with a lot of the noise, but on a jet
you're relying a lot on the ear cup design to eliminate the noise.

If you just want a good sleep, go to Walmart or your local drugstore
and pickup some of the in-ear noise blockers. They cost 10 cent or
something in that range and will block out *everything* resulting in
much better noise suppression than any headphone.
(if they are made by 3M, they are the ones we use for military
exercises - they are pretty good and comfortable)

I recommend using these WITH the noise-cancelling headsets. This gives
you much better high frequency rejection than either one alone, and it
also helps a lot of you have problems with pressure equalization and ear
popping as well.

I will say that the noise cancelling systems are more effective than
plugs at low frequencies, and generally less effective than plugs at
high frequencies. And it's the low frequency stuff that tends to give
you the headaches after ten hours in the air on a C-130.

If you want a headphone that blocks all the noise (and, well, works as
a headphone) I would pick one of those higher price SHURE headphones at
99,- or 199,-. Just by itself, they block noise as efficiently as those
Walmart thingies. If you pick the right headphone, they will be
comfortable enough to wear for the duration of a red eye flight.

I did not know Shure made any headphones... I know they make some IEM
earpiece for monitoring, but no actual sealed phones.
--scott

 

[Angelo Campanella]

The Sennheiser PXC 250 and 350 have really very poor high frequency rejection
because they don't have a good ear seal.

etc. snip.

HEY! This is GREAT!. Let's keep up the dialog on ANR headsets and
hopefully soon earplugs as well. The public true knowledge extant so far
has been woefully inadequate. The topic needs a good wringing out here.

1-What Units are available?

2- What are the low frequency quantiative noise reductions feasible?

3- What are the maximum exterior amplitude vs octave band limits (10Hz -
1kHz) where clipping and degradation might occur?

4- What ANC circuit prinicples apply. electronic design hints and kinks.
It is high time this no longer be a trade or personal secret, INHO. I
saw two types at Oshkosh over a year ago (David Clarks?); a chepo
'analog' that allowed a tad of engine noise to purvey, and a 'digtal'
that pertty much wiped out everything up to midband, but had a whisper
of digutal noise in its place.

5- Ways to meld speech sound from the local environment, narrowband and
just enought to get a high AI, into our ear.

6- Anytihing else we can tout as a plus.

Angelo Campanella

 

[Scott Dorsey]

HEY! This is GREAT!. Let's keep up the dialog on ANR headsets and
hopefully soon earplugs as well. The public true knowledge extant so far
has been woefully inadequate. The topic needs a good wringing out here.

1-What Units are available?

Well, that's the problem. First of all, we have millions of Chinese
factories making cheap ANR headsets. Philips is selling one for $19 at
K-Mart. Sporty's and Aircraft Spruce sell similarly cheap ones for
under $50. There is an over-the-ear unit sold at Lowe's, rebadged by
John Deere. Most of these units don't make good ear seals and none of
them come with real specifications or any OSHA approval.

Then, on the other side of the line, we have Sennheiser, Telex, David Clark,
and a couple others. These units come with real specifications for noise
reduction although it's sometimes not clear how much of the reduction is
from the ANR and how much is from the padding and baffling. Yes, there is
a cutover frequency at which one becomes more effective than the other, but
I'm not sure I know how sharp it is.

What is interesting is that Bose is trying to play both sides of the line.

2- What are the low frequency quantiative noise reductions feasible?

Well, the David Clark H3530 claims 14.3 dB of attenuation at 125 Hz,
21.5 dB at 250 Hz. Now, that is the combination of the ANR and the
passive stuff, but I am willing to bet at 125 it's entirely due to ANR.
I have seen a little bit better numbers on some Sennheiser sets, but
I am not sure where the theoretical limit is. Be interesting to do some
modelling.

3- What are the maximum exterior amplitude vs octave band limits (10Hz -
1kHz) where clipping and degradation might occur?

That's an interesting question. In the case of the David Clark units,
they use seperate speakers for the ANR system and for the actual comms,
so the headroom of the ANR system is not degraded by the comm usage.
But the actual measurement of where the system bottoms out... that isn't
published at all. So I am making the assumption that it is well above
any level that would be of interest, but it might be worth making a call
to DC to find out.

4- What ANC circuit prinicples apply. electronic design hints and kinks.
It is high time this no longer be a trade or personal secret, INHO. I
saw two types at Oshkosh over a year ago (David Clarks?); a chepo
'analog' that allowed a tad of engine noise to purvey, and a 'digtal'
that pertty much wiped out everything up to midband, but had a whisper
of digutal noise in its place.

I don't think any of the DC units use any digital stuff. I know that the
Chinese cheapies don't, although I haven't taken them apart. I should
probably get a $20 K-Mart special just to disassemble and see what's inside.
I'm assuming it's probably one does-everything-IC.

My experience with all of the things is that they work pretty well on random
low frequency noise, and okay on repeititive impulse noise. This goes for
the $20 specials as well. But the high grade ones actually have decent high
frequency rejection from passive stuff, and the crappy ones do not.

I was actually surprised how effective the $50 special from Sporty's was
on our Convair at work, but on the B-200 they really weren't worth a damn.

5- Ways to meld speech sound from the local environment, narrowband and
just enought to get a high AI, into our ear.

In the case of the cheapies, they don't have any high frequency rejection
at all. By 1 KHz, it's all gone. So there is no need to do this, because
speech comes through audibly without any problems. In the case of the higher
end units, they're intended to plug into intercom systems anyway. Much
better than shouting through that rubber hose...

6- Anytihing else we can tout as a plus.

No more headaches after 12 hours in a jumpseat. Lots of other things still
hurt, though.
--scott

 

[Tony]

Well, the David Clark H3530 claims 14.3 dB of attenuation at 125 Hz,
21.5 dB at 250 Hz. Now, that is the combination of the ANR and the
passive stuff, but I am willing to bet at 125 it's entirely due to ANR.

I have done some indicative tests using a few types of ANR headphones on an
acoustic manikin. (Manikin measurement is not the right way to do these
tests for several reasons - but it is easy and convenient for a rough
indication of performance.)

Normal ear muffs have quite significant attenuation in the 125 Hz band -
good ones could do around 15 dB. However, one thing I found, is that on
the manikin, at least some circumaural headphones show an *amplification* of
ambient sound at low frequencies. I presume this is because they cannot
have the damping material that is fitted in standard ear muffs. I've done
these manikin tests only on ANR headphones, and of course the amplification
changes to attenuation when the ANR is switched on. I've not had the
chance to investigate this amplification further, but there is a real effect
present as I could hear it when I wore the headphones myself. At a guess I
would say it could be a resonance of the mass of the shell assembly and the
springiness of the enclosed air and seals, but I haven't measured the mass
or tried to do any calculations. Anyone else?

An example - with Sennheiser Noiseguard headphones, in the 125 Hz 1/3 octave
band, the amplification with ANR off was around 10 dB (rather variable
between different trials when the headphones were re-fitted to the manikin),
and the attenuation with ANR on was about 17 dB, so the ANR is certainly
doing something, but the net effect is not much better than a good pair of
passive muffs. If the effective attenuation is really 27 dB, that is way
above what muffs could do by themselves.

Incidentally, the crossover frequency between active and passive attenuation
was about 500 Hz on those headphones. The 500 or 630 Hz band seems fairly
typical.

 

[Angelo Campanella]

Normal ear muffs have quite significant attenuation in the 125 Hz band -
good ones could do around 15 dB. However, one thing I found, is that on
the manikin, at least some circumaural headphones show an *amplification* of
ambient sound at low frequencies.

Quite so. I've known and experienced that for decades. It's not touted
commercially because it undermines a huge amount of lore (that earmuffs
are the 'answer').

Its source is the mass-spring resonance that always occurs when a mass
(cup) encloses a volume of air (that captured inside the cup). The
resonance frequncy so occuring is approximately via the panel resonance
formula; 170*SQRT(WD) wher W is the area mass of the panel in pounds per
square foot and D is the thickness of the air under that panel. This is
around 100+-Hz for earmuffs. Its maximum amplitude idepends on the
damping available. But it is likely about 10 dB.

When ANC is introduced, 10dB of its attenuation capability is used to
counter this effect. My experience is that common ANC capabilities are
suffiient that there results a welcome reduction in the amount of such
"drumming" heard.

I presume this is because they cannot
have the damping material that is fitted in standard ear muffs.
I've done
these manikin tests only on ANR headphones, and of course the amplification
changes to attenuation when the ANR is switched on. I've not had the
chance to investigate this amplification further, but there is a real effect
present as I could hear it when I wore the headphones myself. At a guess I
would say it could be a resonance of the mass of the shell assembly and the
springiness of the enclosed air and seals, but I haven't measured the mass
or tried to do any calculations. Anyone else?

IMHO, it is not productive to try to remove this via damping. One such
measure is to increase the clamping force of the headband. All this does
is reduce the time to where a headache results. In this day and age, the
effort is ptter spent in improving the ANC low frequency attenuation
capaility.

An example - with Sennheiser Noiseguard headphones, in the 125 Hz 1/3 octave
band, the amplification with ANR off was around 10 dB (rather variable
between different trials when the headphones were re-fitted to the manikin),
and the attenuation with ANR on was about 17 dB, so the ANR is certainly
doing something, but the net effect is not much better than a good pair of
passive muffs. If the effective attenuation is really 27 dB, that is way
above what muffs could do by themselves.

That agrees with my experiences.

Incidentally, the crossover frequency between active and passive attenuation
was about 500 Hz on those headphones. The 500 or 630 Hz band seems fairly
typical.

Affirmative. And when speech sound is introduced via a secondary
speaker in the earcup volume, whatever below 600Hz is cancelled is of no
consequence since speech intelligibilty contribution is greatest above
1kHz, peaking at 2kHz. It's a win-win situation. It accounts for the
universal acceptance of ANC technology by pilots and other militar
personnel.

A word of advice:

The subsequent universal ANC acceptance by commerce and industry is
right around the corner. This is a good time for any of you to get into
the ANC marketing (headsets, NOT fixed equipment) business.


Angelo Campanella

www.campanellaacoustics.com

 

[Tony]

Quite so. I've known and experienced that for decades. It's not touted
commercially because it undermines a huge amount of lore (that earmuffs
are the 'answer'). (snip)
IMHO, it is not productive to try to remove this via damping. One such
measure is to increase the clamping force of the headband. All this does
is reduce the time to where a headache results.

Yet many passive muffs do have useful attenuation in the 125 Hz band,
without excessive headband force. I think there is a difference between
active and passive in this resonance. There are a couple of factors I can
think of, acting in different directions on the resonance frequency: the
transducer has mass, and it takes up space. It is also a resonant system
itself but I don't think this is a controlling factor as the transducer
resonance will probably be higher. I did a brief test that showed there was
no significant difference in attenuation whether the transducer was open or
short circuit.

 

[Angelo Campanella]

Yet many passive muffs do have useful attenuation in the 125 Hz band,
without excessive headband force.

The problem is that ther are many headphone systems that resonate so.

Consider that earmuff sustems, often headphones, must be worn where it
is also noisy; the aim of the headphone being to improve the hearing
capability in such noisy environments.

I think there is a difference between
active and passive in this resonance.

Consider also that in hte headphone design, it is often reasonable to
enhance low frequency sound (modern music listening). A poor noise
isolation results. This is not to say that they are "improper" noise
reduction devices, since it was not the original intent of the design to
be so, or if it were, the design is indeed "poor". ANC applied there
reamarkably improves matters. I think this has been the r\drift of
recent comments.

There are a couple of factors I can
think of, acting in different directions on the resonance frequency: the
transducer has mass, and it takes up space.

The mass is defineiteely a problem since it shifts the resonance to
lower frequencies.

It is also a resonant system
itself but I don't think this is a controlling factor as the transducer
resonance will probably be higher. I did a brief test that showed there was
no significant difference in attenuation whether the transducer was open or
short circuit.

Agreed, the transducer being activated, or not, presents a minor
effect. It is the physical mass added to the headphone, combined perhaps
with a lightweight earcup for comfort, that presesents a mechanically
resonant system.

My experiences come from some early aircraft cabin headsets, with boom
mic (making the unit special, if not necessary for flight), that makes
this resonance amplification a nuisance.

If one wants the advantage of a head-mounted boom mic and earphones for
better speech clarity, they have had to put up with the nuisance of the
bass resonance.

My final solution in this special case was to buy earcup ANC modules
from Headsets, Inc in Amarillo TX, and fit them into my old boom mic
headset (with co-pilot intercom integrated). Now I have all four
functions in one unit; earphones, boom mic, ANC and intercom. The ANC is
moderate but quite comfortable. Can't buy this system anywhere.

Angelo Campanella

 

[glenn P]

I think perhaps the "amplification" at certain frequencies is a function of
the enclosure's mechanical resonant frequency.

 

[Angelo Campanella]

I think perhaps the "amplification" at certain frequencies is a function of
the enclosure's mechanical resonant frequency.

Yes, but be aware of two tpes of "mechanical" resonance:

1- The bending resonances of the earcup material. In noise-reducing
earmuffs, this is hardly ever a problem since the materils and shapes
are specifically chosen so as to be stiff or to have very much damping.
In common earphones, this also not be a problem since sound quality
would suffer if any ringing resonances were in a manufactured product.


2-Cup air/clamp-spring resonance, where the earcups are the mass and the
clamp spring in combination with the spring caused by the enclosed air
volume between the ear & head and enclosed by the cup. This is the
resonance I believe to be most prominent in any earmuff (aka earphone,
headset, etc.). It is usually active in the 100 Hz range but can be at a
much lower or higher frequency. In the best of situations, theactual
sound atenuation afforded at this frequewncy is but a few decibels.
Under the wordst conditions, this could actually be resonant
amplification of several dB.

In practice, the higher frequencies are passively attenuated by the
material of the earcup, as planned, and the sound level at lower
frequency range remains. The resulting overall timbre of sounds heard is
that of a very boomy and dull soundscape.

When virtually and ANC system is instlled in any earcup, the quality of
the net sound heard immediately improves, being very much less in
amplitude over the effective ANC frequency range, which often extends to
100 Hz and less because the speaker need drive only the tiny volume of a
few cubic inches. It is not extremey quiet unless the ANC system is very
good.

But any speech sound introduced, say by an auxiliary loudspeaker will he
heard and understood with ease. True, some speech sounds will be
actively attenuated by the ANC system. But human speech has such a wide
diversity of frequency components, and especially at high freuencies, 2
kHz and above, where earcup ANC cannot work because of min/speaker/ear
spacings, that the surviving speech is "crystal clear".

Hence we see Communicatons headsets to be invading the aircraft and
industrail markets, and with good cause.

Angelo Campanella