Quiet = A, Fidelity = C, Average = B
938730
What I think some of the less satisfied reviewers here may be missing is a proper seal in the ear canal.  These phones are NOT earbuds.  The key is for them fit like earPLUGS.  The earmold should go in more deeply than you think.  If properly fitted they'll provide ample bass (but see below) and good noise reduction, and they won't slip or fall out.  However, Audio-Technica's instruction booklet tells you essentially nothing about how to fit them.

First, make sure you're using the correct unit for each ear.  The letters L and R are printed on the ear side of the phones, but they're almost impossible to read.  Hold one of the phones in front of you, the silicone earmold pointing to the left (as if you were about to put it in your right ear).  The earmold should be pointing upward at about a 45 degree angle.  The wire exiting from the phone should be running away from you.  No?  Grab the other phone.

With your left hand, pull up gently on the top of your right ear.  With your right hand, push the earmold *upward* into your ear canal with a slight twisting and rocking motion.  Repeat with the left ear, of course.

Much of the ambient noise should be gone, before you even switch on the dongle.  If you still hear lots of noise, or if the phones fall out just by the weight of the cord, you haven't inserted them right.  If necessary, try different earmold sizes.  In many cases you may need a SMALLER earmold, not a larger one, so the earmold goes deeply enough into the ear canal.  Also try adding a drop of K-Y Jelly or similar skin-safe lubricant to the silicone earmold.  You snicker!  I'm not joking.  It works.

The cord shouldn't hang down from your ears.  The wires should exit forward and slightly upward.  Loop the wires over the top of your ears and bring the wires together behind your head, not under your chin.  The sliding bit of plastic on the phone wires snugs up the wires, to keep them in place over your ears.  Bring the cord forward over one shoulder, and clip the dongle to your collar or pocket.  This will eliminate the thudding noise that dangling wires transmit to your ears when they hit something.

How do these phones work?  I'm not sure the ANC reduces noise by 20dB - I'd estimate it at something closer to 12dB - but it's still quite a substantial difference.  The pure isolation phones (without ANC) such as the Shures and Etymotics are great if you want to shut out the world entirely.  The ATH-ANC3s don't isolate quite as completely, so conversation is still possible (if a bit awkward).  Just hit the mute button.

Sound quality:  Warm and fat, with a sizable mid-bass peak.  The high end is a bit pinched and not too clean.  Instruments lack a sense of air around them.  Stereo imaging isn't what it could be.  There is some audible hiss when the ANC is on, but it's minimal, and far less objectionable than the background noise it's eliminating.

I'd characterize the ATH-ANC3's as a rock- or pop-oriented sound.  Classical music lovers might want to consider the Shure or Etymotic isolators - but remember, they cost 3-4 times as much.  For many folks, these phones will sound just fine and will almost certainly trounce the $1.50 cheapies that came with their mp3 players.

Build quality: I don't see too much to gripe about.  The dongle feels reasonably sturdy, though the clip looks flimsy.  These phones are made in China, unlike earlier (and more expensive) Audio Technica products that were made in Japan.  Be aware that they may not have passed through the kind of quality control that the name would suggest.  But also remember what you're paying for them.

Bottom line is that these phones provide significant relief from noise while still allowing conversation.  The sound is acceptable if not stellar.  I don't think I'd pay A-T's MSRP for them, but at anything under seventy bucks or so, they're a more than respectable value, especially if most of your listening is rock, jazz, or pop music.
3475572
A great example of how music should be recorded.  In my opinion recorded music should have fidelity, but also a sense of life, dynamic range and ambience.
2280551
Small fan, noisy in a quiet environment. Good for one or two people up close (less than 4 feet away). This product looks better when you compare it to other 12v fans then it does when comparing it to same size A/C fans. I am happy. Using a wind meter I measured 6MPH air coming out of the grill.
1942613
I have 2 of these fans, one runs at 1150rpm, and the other at 1180rpm, averagely.  They are quiet, but seem to blow a little less air than the so-darn-noisy 120mm back fan I pulled out of my Sonata Antec III Quiet case.  Because of that, I decided to put one in the back & one in the front.  I'm ok with them after 2 weeks of use, so they're keepers.

My main use of PC is for computer recording, so the quietness of the PC is critical.
1526572
I'm a fifty-ish woman who got an IPod for Christmas and suddenly realized I needed to upgrade my computer speakers. Certainly not a techie or audiophile! A friend recommended Klipsch so this is what I bought. They're pretty easy to set up--the instructions are clear--and I think they sound great! To get what amounts to a new sound system at this price seems like a good deal to me.

At first I heard no trace of the dreaded hiss or hum--and my ears are pretty sharp. But after a few days I realized that when the computer is completely shut down I could hear the barest trace of a hiss coming from the speakers. But when the computer is on the slight noise is completely drowned out by the normal hum of the computer and monitor. And when the computer is completely shut off I'm usually not close enough to hear the hiss at all.

How one figures out in advance if it's going to bother you or not I don't know. But for me these speakers are a 5 so far.
2608411
This headphone provides a moderate amount of noise isolation. It is okay for drowning out office din. Does not do much for server room noise (by extension airplanes / trains / buses etc.). Hence returned it.
2716691
I brought this from the information in the listing, although you shouldn't.

 First it indicates 10" Blade diameter, it is not it barely is 7".  They provide words like "soothing white noise" and "quiet" neither are accurate. "White noise" is more often termed as a low whooo... or Haaaa or Sooooo type sound when adequate distance given the size of the fan.  This fan from about 5ft away presents a moderate loaded vrmmm or zrnnnn, while high it has your attention with more a rrrummmmm.

Second, Quiet is a subjective term and is left to ones opinion, if I have to place a quantitative measurement in decibels (dBA) to me it's 50-55 dBA on the low setting at 5ft distance.  The fan is in window of a small bathroom off the bedroom, at 10ft away at night, ceiling fan (low), this fan (on low) easily over powers and is more than audible. If the sound it produce was truly more a white noise tone it might less pronounced, perhaps "soothing" but it isn't.

Interestingly I had a little Holmes desktop style fan hung up their for a while now (looks to have the same exact 7" blade shape). Honestly it at low speed (similar rpm's) offers a slightly quieter sound and is providing a slightly lower tone. I was making due with that one, after the one I had for like 8 years had the bearing wear to the point it would rattle.  When summer showed and nights got warmer I thought this box fan (with supposed 10" blade) would move more air and be even quieter and why it ordered it.  Interestingly this does seem to move more air, it might have more to do with the shape of the enclosure. If it had a 10 blade and they had slightly lower rpm's at both settings it might supply a better noise profile and still provide ample air flow.

Now a month old; it run not that much as the A/C been on, so hardly 2-3 nights a week to where there's starting  some dust build up on the blades.  It still the same sound, although you can hear a slight unbalance now when close.
2423384
Easy to install, great noise, not obnoxious sound, perfect size!
4942161
These headphones are known for their accuracy: what the recording engineer meant you to hear is what you should hear. If a track has accentuated bass, you should hear accentuated bass. If a track is filled with nuances, you should hear the nuances. In my experience, the AKGs deliver exactly that. I bought them for my home studio mainly for mixing the tracks I compose and record, and they have been superlative for that purpose. The only reason I rated them four  instead of five stars is their comfort level. After three or four hours in the studio, Ive noticed that the earpieces impart noticeable pressure, not painful but slightly annoying. Not a show-stopper by any means, but worth noting.
3744803
Very quiet.  It was packaged very well to protect it during shipping.  Met my expectations.
1881935
Slightly more clarity and dynamic range than the standard A&M CD. Probably due to the 24bit mastering.
This short review is of the SACD release and not the standard CD as amazon does mix it's reviews.
4009379
I picked this up to use in a friends recording studio and man has it meet my expectations! not only on the high end side, and yes we get loud. But just as importantly we use it for ambient noise and reducing sound in the recording studio. We now know what changes we need to make to keep lowering the ambient noise. This is a great product.
287798
I purchased three, and two of the three are awesome!  Even at their loudest, they are relatively quiet, the middle setting is about equivalent to a white noise system, and the quietest mode, is very quiet.  I like to sleep with this one on.  Our rooms are technically too big for this machine, which states on the box it is "Certified for Small Rooms (Up to 85 sq. ft)".  One is about 144, the other about 120, and the third about 200 square feet.  Despite its certification, it has noticeably improved the air quality in each room it is in.

As for the third one...  it was LOUD.  It sounded off balance straight out of the box, and after a night of running, it was screaming (literally making a squealing noise).  If I had only gotten one of these, I would have thought this product was awful!  Not sure how many come off the line like that, but you get one, exchange it!  Amazon had a new one to my door before I even had the old one ready to ship.

This product, on whole, seems great, although I only received them four days ago.  I may return later to update on long term use.
3789949
I've have a Quiet Comfort 2, the predecessor model to the Quiet Comfort 15, for about 4 years now. I've used it almost every day, either as regular headphones for music or simply for the noise canceling while studying.

However, my one complaint is that the QC2 does not block every type of background noise, especially low frequency stuff like footsteps on the ceiling above or base coming through the wall. This is particularly distressing for me as I live in an apartment with noisy neighbors and the murmuring babble of their TV often comes through the floor.

Well, I just got the updated QC 15 model today in the hopes that the updated noise canceling technology was in fact significantly improved. And remarkably, they don't just reduce the bleed through noise from my neighbors' TVs, they COMPLETELY block any hint of such noise. I'm wearing them now as I type this in blissful quiet. This is a far better result than I could have hoped for, and to me the $300 is well worth the improvement.

So if you're wondering if there is a noticeable improvement in the noise canceling, I for one am happily convinced that there is.
947157
Major issue with non-noise.  If you are watching a movie for example and there is a quiet scene, the sound will turn off.  When the sound comes back on it's not a seamless transition.  Basically unusable unless you are watching something with constant noise such as a football game.
1877081
Excellent, performs as advertised, great for a small room, quiet, noticed the difference within 30 minutes.
4284406
What can I say, automatic  lowering seat and quiet, auto lowering seat and quiet ,auto lowering and quiet ,automatic lowering  seat and quiet