Newsgroup: it.hobby.hi-fi.car
Titolo: Cancellazione Attiva Rumore di Fondo ???

Salve,
qualcuno sa se esistono sistemi per la cancellazione attiva del rumore
di fondo in auto da utilizzare per un impianto preesistente ????
Grazie a tutti
Mario

 di fondo in auto
si, nella fantasia dei produttori di auto e accessori...
è una tecnologia allo studio da anni ma credo che i progettisti si siano
scontrati con al necessità di avere un hardware che rilevi ed emetta un'onda
sonora contrapposta in TEMPO REALE.
senza contare che le onde contrapposte cancellerebbero(imho) anche parte
della tua musica!!!
quanto alla possibilità di sfruttare gli altoparlanti della tua attuale
autoradio...
beh...rotfl!! :-)
ciao

č una tecnologia allo studio da anni 
Certo, non č semplice ma qualche applicazione c'č.
Ad esempio la Sennheiser e la Bose producono cuffie con un sistema di
riduzione attiva del rumore di fondo.
Inoltre la stessa Bose sembra che commercializzi un sistema per auto
con DSP per la riduzione del rumore di fondo !
Di quest'ultimo per ora non ti so dire di piů. Non ho ancora avuto
modo di cercarlo.
Saluti
Mario

...

Puň darsi che sia una cosa tipo il "DOLBY" che si usa per eliminare i
fruscii nelle cassette,perň secondo me vai ad alterare anche il
suono....

Sarà una stronzata...
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
Penso proprio di si. Ma del resto se hai un signore impianto a cosa serve
eliminare un rumore di fondo? Non si dovrebbe avvertire. Se hai delle
scadenti registrazioni che vuoi un miracolo? Purtroppo non penso che per il
momento si possa rielaborare e ricostruire un suono...
Ciao

 eliminare un rumore di fondo? Non si dovrebbe avvertire.
Non credo che intendesse il rumore di fondo della catena audio,
piuttosto quello che si sente ai 150 in autostrada dentro una
scatoletta di latta koreana tipo daewoo. 

 scatoletta di latta koreana tipo daewoo.
beh,lì più che lavorare di dsp la bose dovrebbe imbottire di catrame
la macchina,allora forse può ottenere qualche risultato....


wrote:

Bravo !
Pensavo erroneamente di essere stato chiaro !
Per rumore di fondo intendo quello che si ascolta in sottofondo in
autostrada e cioè :
1) rumore di rotolamento degli pneumatici sull'asfalto
2) rumore del motore
3) rumore generato dal tubo di scarico
etc
etc
Sono allo studio sistemi elettronici che utilizzando ad esempio degli
DSP (Digital Signal Processing) rilevano mediante un microfono la
totalità dei suoni che ci sono nell'abitacolo ed in tempo reale vi
sottraggono il segnale audio proveniente dall'impianto.
Si ottiene così un segnale che corrisponde al solo rumore di fondo
(motore, pneumatici, scarico, purtroppo anche la nostra voce , etc.
etc.)
Tale segnale viene sfasato di 180° e ritrasmesso nell'abitacolo
tramite gli altoparlanti ottenendo così per cancellazione di fase, la
eliminazione del rumore di fondo.
Naturalmente questo in teoria !
Ci sono vari problemi ancora da risolvere per ottenere una soluzione
praticabile.
Che la Bose ci sia riuscita ?
Spero stavolta di essere stato più chiaro.
Mario

Che la Bose ci sia riuscita ?
Non ci credo neppure se lo vedo. Anzi.....se lo ascolto!
-- 
-------------------------------------------------------
       Marco -- Team RF -- Go fast,be loud ! 
           mar...@SPAMhifimania.net 
 
http://www.hifimania.net
      Only Focus Tuning Club Member N°106

 Anzi.....se lo ascolto!
Se esistesse... Sai che pizza!!
Ogni volta che devi parlare con qualcuno in macchina lo devi spegnere 
altrimenti il passeggero (che ti stà a 10 cm).... ehehe.. Non ti sente!! 
ahah Non trovi?

ahah Non trovi?
Vero! Non ci avevo pensato. Tanto il problema non si pone: non
comprerò mai qualcosa marchiata BOSE


 praticabile.
Un segnale sfasato di 180° cancella il suo simmetrico, questo è vero ma
deve essere emesso ESATTAMENTE in fase, il rumore di fondo proviene da
tutta la macchina, NON da un punto preciso, x questo motivo il sistema che
hao detto tu non funziona al 100%


 ahah Non trovi?
1) a volumi medi, il passeggero al mio fianco non mi sente in ogni caso
2) a volumi medi, non lo senti nemmeno il rumore della strada e del motore
saluti, e tenete alto quel volume !!!
ciauz
tot 


Salve,
1) in certi casi durante lunghi viaggi ( 13 ore ) mi succede che
desideri riposare l'udito e spegnere l'impianto per ascoltare il
Silenzio !
2) ho il problema di mia moglie che ha problemi alle orecchie (acufeni
cioe' ronzii alle orecchie ) per cui non posso esagerare ne' col
volume ne' con ascolti troppo prolungati.
Comunque, ho avuto solo critiche !
Evidentemente un dispositivo come quello che cerco non e' ancora stato
messo a punto da nessuno ?
Grazie comunque.
Mario

Affinchč possiate chiarirvi le idee date un'occhiata ai seguenti
links :
http://www.sennheiser.com/sennheiser/icm_eng.nsf/resources/Noisegard_eng.pdf/$File/Noisegard_eng.pdf
http://www.sennheiser.com/sennheiser/icm_eng.nsf/root/products_headphones_streetwear_pxseries
Sennheiser PXC 250
25 of 26 people found the following review helpful: 
 Middle of the line, August 31, 2003 
 Reviewer: tbradley_tx from Texas, USA  
I bought these Sennheiser's after reading a recent CNET review that
rated them "best" in this price range at both noise cancelation and
overall sound quality. I have now tried them both in my office area
and also on a very long flight to Europe. Overall, I have been pleased
with the sound quality - but only when the "noise cancel" mode is ON.
If it is not ON then the bass is very much lacking. I also had a
chance to do a direct compare of these Sennheisers to the original
Bose version while on my flight. The Bose win hands down. No contest.
Even with the Bose's noise cancel feature OFF the Bose cut out more
noise than the Sennheiser's do while ON. I also compared them to a
friend's set of Aiwa noise cancel headphones - the Awia's were also
better at noise canceling than these Sennheisers but not as
comfortable to wear on my head.
On a positive note, I will say that I could sleep with the
Sennheiser's on my head where it was a bit difficult to do this the
Bose version on my head due to the bulky nature of the Bose. The
Sennheiser's also fold up nicely and fit into the carrying bag quite
easily with minimal over all space in my carry on bag.
To summarize: If you want the best of breed noise canceling headphones
keep looking and comparing with the Bose. If you want some decent
headphones that cut maybe 1/4 - 1/3 noise, take up little space in
your bag, and are reasonable comfortable then these Sennheiser's will
do. 
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 Customer Reviews 
 
 Dreamy addition for this music fiend, December 31, 2003 
 Reviewer: An electronics fan from Honolulu, HI United States  
Twice as good for less than half the price of the Bose noise reduction
headphones. Fit nicely and feel great but mostly they really block out
most of the ambient noise. I really love everything about this
headphone. Also, note that it comes with a 2 year warrenty, better
than most other headphones. 
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 very disappointing design, December 30, 2003 
 Reviewer: William Russell (see more about me) from Springfield, VA
USA  
While the noise reduction circuitry works fine, it is of little use
considering the flawed design. The ear pads fit ON instead of over and
around the ears. This not only lets in background noise but also gets
pretty uncomfortable after awhile since you have to have them as tight
as possible to get any noise reduction at all. Until Sennheiser has
the sense to use a more sensible design, stick with the cushioned sets
that go over the ear for comfort and keeping out more noise. 
          Was this review helpful to you?     
 
 The first and last Noise-Canceling HP for me, December 28, 2003 
 Reviewer: daniela from Boston, MA United States  
I bought these headphones after reading a few online reviews for this
product, but without trying them first.
The sound quality was not impressive (considering the price), they
sound very weak when the noise canceling was off, and when it is on
you could hear a very load hiss.
This means that in a quiet environment you must suffer the hiss if you
want to hear the bass load and clear.
I had a personal problem with them which was a painful pressure on the
drum-skin similar to scuba-diving( before equalizing ) after using
them for a few hours.
I ask friends to try them and they experience only a mild pressure so
it must be me( and I guess you will experience the some pressure with
every noise-canceling headphones )
I also didn't like the noise canceling device in the middle of the
headphone cable - very heavy and cumbersome, but again this is
probably the case with every noise canceling HP.
I'm sending them back 
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 Good for the money, December 19, 2003 
 Reviewer: Gregory Glockner (see more about me) from San Francisco, CA
USA  
With the PXC-250, I really enjoy listening to MP3's or in-flight audio
while traveling in a noisy plane or train. The PXC-250 are very
comfortable. But the PXC-250 do not compare at all to the quality of
the HD-600 for quiet listening. The HD-600 are much more dynamic and
refined. Also, I find that the PXC-250 introduce a bit of white noise
in order to mask the background noise. That's OK for noisy
environments like trains and planes, but it is silly for regular
listening. On the other hand, the HD-600 are large and impractical for
travel. So I am glad that I own both the Sennheiser PXC-250 for travel
and the Sennheiser HD-600 for home. 
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6 of 6 people found the following review helpful: 
 Great alternative to the $300 Bose, December 4, 2003 
 Reviewer: An electronics fan from Littleton, CO United States  
Bought these instead of the Bose QC2 (cuz I'm cheap). I was astounded
at what a difference these made over regular headphones on my last
airplane flight. Greatly reduced the background jet noise to play
DVD's on my laptop or to listen to music using the planes headphone
jack. I am VERY pleased with my purchase and will spend the $175 bucks
I saved on other toys 
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9 of 9 people found the following review helpful: 
 Does what I bought them for, November 29, 2003 
 Reviewer: clearskiesfollowingwinds (see more about me) from Bethesda,
MD USA  
I bought these headphones for a flight from Washington, D.C. nonstop
to Tokyo. That's 13.5 hours. I wore them almost the entire way and
felt no discomfort from having worn them for hours on end. I even wore
them when I didn't have them attached to anything, just to reduce the
noise from the sound of the engines. Sound is very good, especially
with the noise reduction on. You never heard movies or music sound so
good on a plane. I assume this would be true for trains and buses, as
well. No, they don't sound as good as my high-end Sennheiser
headphones since a) the PXC250 is not closed, and b) they are smaller
than the higher end headphones so that they travel well. I bought
these for a purpose other than listening to music in my home (although
I do occasionally since they are so convenient to use and the sound is
very decent).
I tried the Bose and they were not for me. Twice the price, larger,
and less comfortable.
At this price, especially, I'm very satisfied. They work well at both
reducing ambient noise, are very comfortable, and produce an enjoyable
sound. Highly recommended. 
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9 of 10 people found the following review helpful: 
 Maybe these are it., November 23, 2003 
 Reviewer: An electronics fan from San Diego, CA United States  
I've been through at least a dozen different types and styles of
headphones and earbuds. I think these Sennheisers might finally be the
ones I've settled on. I work in radio, and have been spoiled by high
quality headphones. I can't stand ear buds, even though they tend to
sound the best. After an hour I want to rip them out of my ears. I've
tried over the head and behind the neck styles, and they just don't
have the richness in frequency response I want unless you hold them
tight to your head with your hands.
The Sennheisers sound very, very good and are comfortable to wear.
They're a little larger than I'd like for travel, but I really can't
give up quality sound. One word of negativity; they only sound good
when the noise cancelling circuit is turned on. Yes they still work
without it, but they lose a great deal of sound quality. I don't have
enough experience with them yet to know how long the batteries will
last, but on longer trips to Europe I'll carry spares just in case.
These come with a nice carry case and a couple of adapters to use with
home systems and the Delta Airlines double plug. Pricey yes, but I've
already spent more than double what these cost trying to find
something good. I think these could be the ones.
The battery compartment is a little bulky, but can clip onto your
belt. The cord could be a little more substantial, but there is a two
year warranty should it break. The headphones adjust to your head very
nicely, and the ear pads are thick and comfy. These don't totally
enclose the ear, rather they sit on the outside. Not the smallest or
easiest to carry around, but if you want high quality sound without
the discomfort of ear buds, these are the way to go. The noise
cancellation is decent, but the sound quality with the noise reduction
circuit engaged is the prize. 
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7 of 8 people found the following review helpful: 
 Good for the Price, November 6, 2003 
  Reviewer: gobirds2 (see more about me) from New England  
I got what I paid for. They sound great, cut out outside noise
effectively, are lightweight and can be folded up and kept in compact
places. 
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15 of 16 people found the following review helpful: 
 An Oasis of Tranquility Amid the Noise of the City, November 4, 2003 
  Reviewer: weirdears (see more about me) from Chicago, IL United
States  
I am looking forward with dread to four months of apartment
renovations starting soon and I was looking for ways to keep my sanity
during all the racket and mayhem. The idea of Noise Canceling
headphones seemed just the ticket to help me keep from losing my mind.
I tried the Bose, the Sony, and the Sennheiser in a comparative
listening bout. Overall, I liked the Bose a little better than the
Sennheiser, but not enough to justify the increased price. Both blew
away the Sony, which just doesn't sound that good and conducts too
much movement noise up into the headphones. The Sennheiser are closed
ear headphones, very lightweight and comfortable to wear unless you
are exercising, where they tend to get a bit too hot. The snug fit of
the earphones helps block out sound, even without the noise-canceling
feature. But with the feature the amount of noise that is reduced or
effectively canceled is remarkable. Most of the daily rumble of
Manhattan is removed from your listening experience, though louder and
sharper sounds still can be heard. The actual sound in the headphones
is excellent, very clear, with a focused treble and a distortion free
bass response. I tested the phones using a variety of music,
orchestral, jazz, rock, and organ music. For my money, organ is the
most difficult of instruments for headphones, as the rich bass
frequencies almost always lead to distortion. Happily, the Sennsheimer
phones were able to reproduce the massive sounds of Messiaen without
mishap!
As a final test I took my headphones on a street run last night. I
picked out the quietest CD that I have, Morton Feldman's Rothko
Chapel, which never really gets above a whisper. Walking through
Lincoln Center, which was crowded with concertgoers, I barely heard a
thing. Walking down the street, there was an eerie sense of calm. I
could hear car horns, and some other ambient noise, which I was glad
of, since it could be dangerous otherwise, but the quiet and clarity
of the Feldman was remarkable. The final test was a Subway ride. While
I can't say that the Subway ride was noise free, the headphones did a
wonderful job of blocking all but the loudest noises. I didn't even
miss notes when the express train rumbled through my station.
The design is a bit of a negative. As has been said, the battery pack
is a bit bulky, though not so much as to really bother me. And the
headphones do fold up nicely, making them a good compact option for
travel. But the wires tangle easily, unlike the Bose. Hopefully, in
future models, Sennheiser will find a way to improve this feature. 
Overall, I am extremely pleased with the performance of this product,
and at the price point, it can't be beat. 
I've now tried out the various Sonys (NC5, NC10, NC11, & NC20), the
Bose (QC2) and the Sennheiser PXC250 and the Sennheiser is ultimately
the best for air travel. I started out with the Sony NC10 thinking an
in-ear model would not only cancel noise but also just plain seal it
out. I didn't realize how uncomfortable they would be on a long-haul
flight. I switched to the over-the-ear closed NC20, but those were too
bulky for true portability. I switched back to the in-ear NC11
thinking they would be more comfortable than the NC10's but the NC11
seemed to actually be much worse at noise cancellation. What happened,
Sony?
A friend then suggested the Bose QC2 and they were pretty good both at
noise cancellation and suppression. But they were too big and bulky
for frequent or light travel. I then tried out the Sony NC5 but found
they were poor both in noise cancellation and in general sound
quality. I finally ended up trying the Sennheiser PXC250 and found
that they sounded and cancelled noise as well as, if not better than,
the Bose and were much smaller to carry. They don't seal out sound
like the in-the-ear or over-the-ear models, but they were much more
comfortable after a long-haul flight than any others I had tried. And
they're half the price of the Bose.
Short of buying a pair of the Etymotic ear-canal headphones with
custom-molded earpieces, the Sennheiser is probably the best way to
reduce airplane sounds right now. 
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24 of 25 people found the following review helpful: 
 Worthwhile, but not Bose, October 5, 2003 
 Reviewer: pdm1881 (see more about me) from Roslindale, MA United
States  
Went to Tweeter, looking for the Bose QC2. Turns out, Bose only sells
their premium items directly - QC2, Wave, etc. Tweeter had the PXC250.
The sales guy did not want to open them for me to try, so I bought
with 30-day return. Not content with them, I went to a Bose Kiosk in a
mall and bought the QC2's, also on a 30-day return. The Kiosk was
under an escalator, and the mall was busy - the headphones cut down
that background substantially - a test similar to an airplane, I
believe. 
Over the next week, I did a few tests, mostly with a TV at moderate
volume in the next room (my major interest other than travel). Both
the Sennheiser and the Bose have their advantages, but both the sound
quality and noise dampening are clearly better with the Bose. I took
the Sennheiser back, and am keeping the Bose.
A year ago or so, I tried a $50 Aiwa pair - hiss and not much
cancellation - took them back also. I suspect that anything less than
the Sennheiser PXC250 is not worth considering. If small size and
price are important, and TV noise is not, the Sennheiser may be a
better value than the Bose. For me, the Bose is one star better than
the Sennheiser, but not perfect.
Because you won't find the Bose QC2 on Amazon, I give a point-by-point
comparison:
Bose QC2: $300
folds flat into semi-hard case about twice the size
around the ear - better sound, but can get warm
no external wand, wire detaches
1 AAA in headphone, claimed 35-hr
excellent sound
no sound (music) when switched off
TV reduced without music, hardly heard with music
Sennheiser PXC250: $150 (less at Amazon)
folds flat into soft case about half the size
on the ear - inferior sound, but cooler
2 AAA in external wand (wire is captive?)
sound OK, but weak/no bass
diminished sound (music) when switched off
TV not reduced much without music, still intruded a little over music 
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10 of 10 people found the following review helpful: 
 Still one of the best. But far from perfect!, September 27, 2003 
  Reviewer: MartyHansen (see more about me) from Los Angeles, CA USA  
I bought these Sennheiser PXC 250 noise-reducing headphones as a
replacement for my trusty HDC 451's, which were excellent. For
straight noise reduction, the PXC 250 is definitely better. But as a
wear-it-everywhere set of headphones to improve one's overall quality
of life, the PXC 250 still leaves something to be desired. (For this
latter usage, the HDC 451 might still be a wiser choice.) Here's a
rundown of the PXC 250's pros and cons.
On the positive side, noise reduction for the PXC 250 is up 50% versus
the HDC 451, going from 10 dB to 15 dB of noise suppression. Quietness
is further enhanced by the 250's on-the-ear, cup-style listening
units. The earphones also twist to lie flat, and the headband folds in
two places to make the PXC 250 even smaller for stowing. The 250 even
comes with its own black carrying case, which has a zippered pocket on
the outside which is perfect for hiding the included ź" audio and
two-pronged airline adapter plugs.
On the downside, the battery carrying case (which also houses the
electronics) has grown significantly - even though the battery size
has been reduced from two (2) AA's to a pair of AAA's. The batteries
are held in-line, rather than side-by-side. So the case for the PXC is
about as long and thick as a short cigar, whereas the compartment for
the HDC 451 is about the size of a box of Tic Tac mints.
The most bothersome feature of the PXC 250, though, are the dual wires
emerging from the earphones (one for each side), which are probably
required since the headband now breaks in two places. The wires,
besides being more numerous, are also fairly thin -- which causes them
to get tangled much more often when storing and unstoring them (as
compared to the HDC 451 which has a single, thicker wire).
Lastly, the increased quietness of the PXC 250's enclosed ear cups,
although superior for blocking noise, are no longer an "open air"
style - which makes hearing ambient sounds and other people's voices
more difficult. The PXC 250 is thus best suited to indoor (or
stationary) music listening only, and are perhaps a little too
insulating for using outdoors (or while moving or interacting with
others).
In short, if enjoying music indoors (or on a plane) is your objective,
the PXC 250 is definitely the way to go. If, on the other hand, you'd
like to bring sanity to a noisy world by wearing your headphones
everywhere, then the older HDC 451 is probably a smarter choice.
I'd like to suggest to the company (Sennheiser) that they also
consider offering a behind-the-neck style so that outdoor users (like
yours truly) can enjoy the benefits of superior noise reduction -
while wearing a hat! And there's definitely something to be learned
from the new Bose QuietComfort 2's (which are unfortunately bigger and
much more expensive) which incorporate the electronics into the
headphones themselves. This design allows the audio cord to be
completely detached - which takes everyday noise suppression to a
whole new level of convenience. 
To conclude, I've tried a variety of affordably priced noise-reducing
headphones and earphones from Sony, Aiwa and others. From my own
experiences, the Sennheiser PXC 250 and HDC 451 are definitely the
best! And I certainly wouldn't want to live life without them! 
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3 of 3 people found the following review helpful: 
 light weight, great for air travel, September 25, 2003 
 Reviewer: airtraveler from Cypress, TX United States  
I travel by air every two weeks and this headset's active
noise-cancellation is every effective. I now can truly enjoy listening
to my MP3 music without the intrusion of ambience noise even when I
get to seat close to the jet engine. It also came with adapter which
allows connection to the plane's audio system for watching movies or
listening to music. The sound quality is excellent, deep bass and
clear trebles. And size is very compact compare to other
noise-canceling headphones. The price is also reasonable. The only
thing that I didn't like about this headphone is the wand, which
houses the battery compartment and the noise-cancellation circuitry,
because sometimes it gets in the way. 
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 Happy with the purchase, August 14, 2003 
 Reviewer: Keith K Robinson from Fort Lauderdale, FL United States  
I travel a fair amount and wanted headphones I could use to reduce the
loud airplane engine noises and improve the sound of the airplane
movie or music I was playing. I've traveled with them twice and am
pretty impressed with the sound. When you turn on the noise canceling
it definitely cuts down on the airplane noise. Unfortunately they
don't block out people talking near by which would often be a benefit.
They fold up and can be put into a small case. They seem pretty sturdy
and are very comfortable to wear. The battery case for the noise
cancellation part is a bit bulky but clips to your shirt so it's not
too bothersome.
I bought these headphones because I've heard Sennheiser make good
products and because they were a lot cheaper than the Bose noise
canceling headphones. Although I've never tried the Bose ones, I'm
pretty happy with my purchase. 
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2 of 2 people found the following review helpful: 
 Mostly good, with some annoyances, August 8, 2003 
 Reviewer: steve_hollasch from Redmond, WA USA  
These are fairly nice headphones, with a lot of plusses. I found them
to be very comfortable, and sound quite good (I'm not an audiophile,
though, so I'll defer to others.) The compact design is very nice, and
includes a nice carrying case (a heavy-duty nylon weave), a regular
phono jack adapter, and an airplane jack adapter. I'm very impressed
with all of the above.
On the minus side, I don't think they're worth the price I paid --
they seem quite a bit pricier than other models.
On the very minus side, the battery compartment latch broke
immediately -- it has a flimsy, tiny plastic latch that seems doomed
to failure at some point. One of the most annoying things is that if
you have the battery compartment attached to your body (as they
designed for and recommend), you've got about a meter (one yard) of
cord to work with. You'll have to sit on your desk or stand in front
of your stereo to use them. A very poor corner to cut, in my opinion.
I subsequently ordered an extension cord, but chafe at having to do
so.
Regarding the noise cancellation, I found it to be quite good. Noise
cancellation is typical of other units (e.g. aircraft headsets) -- it
cuts ambient noise about 10dB in the lower frequencies. This helps
quite a bit (and I expect would be particularly nice on airplane
trips), but customers who expected dramatic silence were expecting way
too much. Even foam earplus can only attenuate about 30dB (though
arguably do much better at higher frequencies).
All in all, I'm happy with these headphones, but annoyed with the
price, the flimsy battery compartment, and the ridicuously short cord.
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 Great sound quality, compact size, and cheaper than Bose!, August 2,
2003 
 Reviewer: bkusf from San Francisco, CA United States  
I've been only using them for 3 weeks now and love them. Good bass
response and the noise cancellation is pretty good. Not as good as the
Bose, but the compact size, price, and comfort makes up for it. 
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3 of 5 people found the following review helpful: 
 Mediocre quality for the price., July 17, 2003 
 Reviewer: hapybrian (see more about me) from Irvine, CA United States
I have other studio headphones for home use that cost less than
these, and provide very high quality, with good frequency
response. So, I expected a lot from these headphones. Maybe the
noise reduction technology is expensive, but I am still not happy
with Sennheiser. I bought them to reduce sound in my office, and
while sound is reduced, it's nowhere near what I was expecting.
There's a noisy computer under my desk, and its high-pitched
whine is reduced--some. Mostly, I found LOW-pitched sounds to be
quieted more than high. And when co-workers hold an impromptu
meeting outside my door--forget about it; the headphones reduce
an awful din to an annoying din.
I now wish I had saved my money and just used my old studio head
phones--I could have bought some CD's to mask the sound instead.
As for claims like "I couldn't even hear the phone ring", I find
it highly unlikely. 
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4 of 4 people found the following review helpful: 
 Great for planes, July 3, 2003 
 Reviewer: An electronics fan from Monument, CO United States  
I travel quite a bit and have been looking for headphones that would
work for overseas travel. The open air headphones just let in too much
noise and the closed headphones are too heavy to wear for 8 hours.
These are a nice compromise. Feather light, but pretty good mechanical
isolation. They sound great. 
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10 of 11 people found the following review helpful: 
 I'd recommend them..., June 27, 2003 
 Reviewer: steve02 (see more about me) from McLean, VA United States  
The Basics
Constructed of solid metal/plastic components, comfortable vinyl
padding, folds up into a relatively small and flat profile, and fits
great in the quality padded case that's included. The noise-canceling
circuitry is contained in a separate plastic container as long and
wide as a thick cigar -- not bulky at all to handle especially with
the belt clip. The power switch is pushed up/down and has enough
resistance where I don't see how it could be unintentionally turned on
as a previous reviewer commented. It is powered by 2 AAA batteries
(documentation doesn't state how long the power would last with
continuous use) and will conveniently continue to function even when
the batteries drain (albeit without the noise cancelation). The
adapters/connections are NOT gold plated which is rather disappointing
for a product of this price. Not that it matters to me, but these
headphones are not "silver" colored as stated and shown in the product
title and picture; they are black and gun metal gray and don't appear
obnoxiously showy. The standard two year warranty is definitely an
advantage over other headphone manufacturer offerings. I've never
owned/used noise-canceling headphones before and therefore will be
comparing them to the Sennheiser HD-280 cans I purchased at the same
time. 
Audio Quality
The audio reproduction of the 250s is inferior to the 280s, which I'll
admit is an unfair comparison as the latter are semi-professional
studio headphones. With the noise canceling circuitry turned off the
audio sounds shallow and tinny because the padding causes the
headphones to sit somewhat far from the eardrums. If you push the
headphones against your head you'll notice the audio quality and bass
response improves. When the circuitry is turned on the tinnyness
disappears, but audio seems a little over-boosted particularly the
bass. Mid and high range is more accurately produced. For its size,
design and intended purpose these headphones have acceptable audio
quality.
Noise Cancellation
The 280s definitely blocked out surrounding ambient noise better
because of its closed design that fit around the whole ear unlike the
250s that just rest on top of the ear. When the noise cancellation is
turned on, it does a great job of blocking out fan/air conditioning
droning as well as other low-pitched noise but the circuitry produces
a higher pitched hissing in return (comparable to an audio cassette
tape without Dolby Noise Reduction technology). I suppose this is the
effect of one noise canceling out the other, fortunately it isn't that
noticeable while listening to music at moderate levels. Don't expect
these to isolate you from noisy coworkers or screaming babies on an
airplane; you'll still be able to hear outside conversation especially
when women talk because of their higher pitched voices.
Conclusion
Although the HD-280 has a foldable design, they are still rather bulky
and heavy to transport while traveling. If an acceptable compromise,
I'd have to recommend them for its better sound isolation, audio
quality and lower price. However I'm keeping the PXC-250 as they're
very convenient to tote around, allow me to hear others when being
addressed at work and have acceptable audio quality for what its
worth. 
_____________________________________________________
Saluti
Mario



 messo a punto da nessuno ?
No è come ti ho spiegato non potrà mia essere messo a punto.
Se vuoi abbassare il rumore della macchina insonorizza con pannelli
insonorizzanti (non fogli bituminosi ma pannelli apposta x abbassare il
rumore) tutto il fondo della macchina, 4/5db li riesci a guadagnare!


 rumore) tutto il fondo della macchina, 4/5db li riesci a guadagnare!
ma, imho ti compri una macchina come si deve e non una scatoletta. Sono 
stato su un audio e anche su un alfa, modelli abbastanza costosi, e dentro 
e' il silenzio. Poi appena abbassi il finestrino senti il motore che sembra 
un aereo (i diesel... che casinisti :D ).
Cercare di annullare i rumori dell'auto con dispositivi che lavorino in 
controfase e' IMPOSSIBILE. Troppe riflessioni. Dovresti far vibrare tutta la 
carrozzeria in controfase e non solo qualche ap da 16cm...
Sto thread mi ricorda molto l'articolo uscito su una rivista di caraudio per 
il primo aprile :D
Narrava la storia di un "proiettore di immagini sonore" che creava 
l'immagine sul cruscotto lavorando su due emettitori che lavorando sulla 
fase ricreavano un suono in un determinato punto dello spazio :D
saluti
totem 

> stato su un audio e anche su un alfa, modelli abbastanza costosi,
volevo dire audi... lol. L'alfa era una 166 2500 o 3000 turbodiesel e l'audi 
era una a4 anche se non ricordo il modello esatto. Entrambe erano veramente 
mooolto silenziose.
ciauz 


Ricordi la mia 2400TD ?
minkia se era silenziosa...
E pure quella di Marco.... io sono stato su una uguale identica stesso 
motore (1.8 T benizina)
E' una camera sottovuoto :-) Silenzio assoluto. La mia a confronto č un 
trattore agricolo! Di quelli vecchi addirittura :-DDDD
CLA