Bose Headsets

Scott Skylane wrote:

Not necessarily true, at all. The ANR function can be tuned to any
frequency, as desired. The Telex ANR-850's that I use in the jet are
FANTASTIC at reducing high-frequency wind noise, but are totally useless
in any propeller driven aircraft.

While there is SOME ability in digital ANR headsets like the Telex to
do some SLIGHT tuning of the ANR central frequency, it is completely
incorrect to state that it can be "tuned to any frequency, as desired".

ANR works by measuring the noise with a tiny microphone and then
injecting the inverse of the noise signal into the speakers. At low
frequencies (in the 50 - 300 Hz range, or so), the wavelength of the
sound is long enough that the sensing microphone and your ear only
need to be CLOSE to each other, but not coincident, in order for the
injected signal to approximately counteract the noise.

At high frequencies (above 1000-2000 Hz), the wavelength of the sound
starts becoming very small. This implies that for the microphone to
measure (and hence cancel) the noise that the EAR is hearing, the
microphone would have to be essentially inside the ear, or else it
would be canceling something other than what the ear perceives.

Now, that's not to say that SOME amount of ANR can be done with
digital techniques at somewhat higher frequencies than analog ANR can
do with some sophisticated algorithms, but it's hardly "any
frequency". I'd be very surprised if the "wind noise" you mention is
more than a few hundred Hz, and if, in fact, the 850's are "totally
useless" in any propeller driven aircraft, then they've got pretty
poor ANR capabilities. I've never worn them, so I can't comment on
them directly.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006

Marc J. Zeitlin wrote:

/snip/
Now, that's not to say that SOME amount of ANR can be done with digital
techniques at somewhat higher frequencies than analog ANR can do with
some sophisticated algorithms, but it's hardly "any frequency". I'd be
very surprised if the "wind noise" you mention is more than a few
hundred Hz, and if, in fact, the 850's are "totally useless" in any
propeller driven aircraft, then they've got pretty poor ANR
capabilities. I've never worn them, so I can't comment on them directly.


Mark,

Per the specs from the Telex 850 manual, they provide 12db of active
attenuation between 100 and 2000 Hz. Looking at the Lightspeed 30G
specs, their max attenuation of 36db is centered at 150 Hz, and the 12db
threshold is reached at only 400 Hz. A significant upward shift in
attenuation range for the 850's, IMHO. Looking at the design of the
relative ear pieces, I would guess the Telex microphones sit
considerably closer to the ear than the Lightspeed's.

To appease the pedants running rampant in this group, when I said ANR
could be tuned to *any* frequency, I was incorrect. What I meant to say
was that ANR can apparently be tuned to any frequency desired, within
the realm of human hearing, specifically those frequencies that are
introduced in various aircraft cockpits as "noise". This statement was
to correct a blanket assertion by Mr. Borchert that "ANR is not really
effective at high frequencies..." He is wrong. ANR can be very
effective against the high frequency noise present in some cockpits, if
the headset designer chooses.

Happy Flying!
Scott Skylane
N92054

("Scott Skylane" wrote)
To appease the pedants running rampant in this group...


I've never seen it used like that before, so I had to look it up.

ped·ant (n)

1. One who pays undue attention to book learning and formal rules.
2. One who exhibits one's learning or scholarship ostentatiously.
3. (Obsolete) A schoolmaster.


Montblack :-)

Scott,

"ANR is not really
effective at high frequencies..."


You know, looking at you own post and comparing the 36 dB reduction you
mention for a low frequency and the 12 dB reduction you quote for a
high frequency, I would say my statement still stands. Measured in dB,
there are worlds between 36 and 12.

--
Thomas Borchert (EDDH)

Thomas Borchert wrote:


You know, looking at you own post and comparing the 36 dB reduction you
mention for a low frequency and the 12 dB reduction you quote for a
high frequency, I would say my statement still stands. Measured in dB,
there are worlds between 36 and 12.

Numericaly, of course, you are correct. Subjectively, sitting in the
cockpit of a jet airliner, I say that 12 db of high frequency
attenuation is *very* effective.

Tell you what: Next time you are flying in the cockpit of a jet
aircraft, try on a pair of the 850's, and let us know what you think.

Happy Flying!
Scott Skylane
N92054

"Montblack" wrote in message
...
("Scott Skylane" wrote)
To appease the pedants running rampant in this group...


I've never seen it used like that before, so I had to look it up.

ped·ant (n)

1. One who pays undue attention to book learning and formal rules.
2. One who exhibits one's learning or scholarship ostentatiously.
3. (Obsolete) A schoolmaster.

Then there's the manager who wanted to have someone fired for being
"pedantic", confusing it with the word "pedophile". (Somewhere on the Scott
Adams/Dilbert website)

Jon Kraus wrote:
Maybe I need to get over my first-impression that I got from the
Lightspeed threads we have had here from a few years back... I got
scared from the stories of folks having to send their Lightspeeds back
many times because they were made cheaply and broke easily... People
always raved about LS's customer service but I thought that they sure
did have to use that customer service a lot.

My Lightspeed back 2 or 3 times. It seems the whole problem was a bad
battery box system. My 30-3G has not had a problem since the last time
it came back and the newest one has not since the factory since
manufacture. Once fixed, it was a great headset. I don't think I'd
worry about the past problems any more if I didn't want to spend money
on a Bose.

Mike

Jon Kraus wrote:
No Jack... You have a 3 way partnership and I'm only in a 2 person one
(so I pay more)... So you should have way way way more money than me...

Ah...but you see, you can afford a 2-way partnership, I can only afford
a 3-way partnership...so you have more money you can spend on aviation.

Plus I thought that everyone that lived in California was rich... Am I
mistaken? :-)

Um...yes. :-)



--
Jack Allison
PP-ASEL-Instrument Airplane
Arrow N2104T

"When once you have tasted flight, you will forever walk the Earth
with your eyes turned skyward, for there you have been, and there
you will always long to return"
- Leonardo Da Vinci

(Remove the obvious from address to reply via e-mail)

"Marc J. Zeitlin" wrote:
At high frequencies (above 1000-2000 Hz), the wavelength of the sound
starts becoming very small.

The wavelength at ~2000 Hz is still about ~6 inches.

This implies that for the microphone to
measure (and hence cancel) the noise that the EAR is hearing, the
microphone would have to be essentially inside the ear, or else it
would be canceling something other than what the ear perceives.

Two limiting factors would seem to be the distance between the external
microphone and the headphone, and the frequency response of the feedback
electronics. If your feedback response is slow, it might actually pay to
design it so the external microphone is farther away from the headphone.

Since sound approaches from all directions, and the microphone and
headphone must accomplish their tasks in only a one to two-dimensional
space, a three-dimensional "cone of silence" device is best. Fortunately
such a device was invented back in the 1960s; here's some pictures:

http://www.oneeyedman.net/cone_of_silence.jpg
http://www.hojohnlee.com/weblog/wp-c...of-silence.jpg

I have a Bose X, a Telex ANR 50D, and a Lightspeed 30 3g in the 310.
I use the Bose, it's more comfortable and the frequency response suits me
better. I don't know about customer service because I have never had to
send the Bose back, but I have only had them about 2.5 years. I have had
to return the Telex but not the Lightspeed. I am going to get a second Bose
for my wife, she likes it better too!

Mark Manes
N28409
WC5I


"Jon Kraus" wrote in message
.. .
Maybe I need to get over my first-impression that I got from the
Lightspeed threads we have had here from a few years back... I got scared
from the stories of folks having to send their Lightspeeds back many times
because they were made cheaply and broke easily... People always raved
about LS's customer service but I thought that they sure did have to use
that customer service a lot.

I haven't been flying that long (5+ years) so my headset experience isn't
extensive but the one time I did have to send my DC 10XL's back for a ANR
module that went bad, my experience with DC's customer service was very
good...

I know that the Bose headsets are very expensive, but the few times I have
used mine I am very impressed. I agree that the passive NR isn't as good
as my DC's but so what... I will never use just the passive part (I always
have batteries iin my flight bag)... The ANR on the Bose is superior to my
DC's IMHO. And the comfort is better too...

Jon

Thomas Borchert wrote:

Mike,


I
thought my Lightspeed 30-3g's were quieter and as comfortable. The low
profile was what made me keep and give them a fair chance.



I agree. I was quite disappointed when I compared an LS Thirty 3G
directly with the Bose at the Bose sound test station at a trade show. I
expected, well, a 400-$-wow effect. Didn't get it. They were about the
same in ANR quietness. The lower profile of the Bose is neat, no doubt.
However, the passive NR is very low.

In all, for my wallet, they're not 400 $ better than the Lightspeeds. But
each to his own.