What? I can't hear you!

June 26, 2007 1:53 AM

Are active noise cancelling headphones safe for your hearing?

There have been a bunch of questions about which headphones are the best, but I didn't see anything about whether they're safe. (Upon googling, I found occasional comments suggesting they're not, but no citations or research.)

Are the active headphones mainly useful for improved comfort, where the sound being canceled is annoying but not loud enough to cause damage? Or are they good for protecting against noise that's loud enough to cause temporary/permanent hearing loss? Does it make sense to use both earplugs and noise-canceling headphones?

posted by spacewrench to Health & Fitness (14 answers total)

I just bought some noise cancelling headphones in order to be able to listen to music on the bus in comfort. Without noise cancellation I had to blast the music in order to hear anything over the bus noise. Hopefully, with the cancellation I'll be able to listen to music at a reasonable level.
posted by rdr at 1:56 AM on June 26, 2007

They're designed to cancel out persistent low-volume background noise, like airplane engines or the hum of a busy workplace/cafe. They're comfort devices, not ear protectors.

They're not miraculous, and they won't cancel out industrial works going two foot away from where you're sitting.

If there's a chance your hearing might be damaged, you need to wear ear protectors.

All kinds of earphones probably damage hearing to a greater or lesser degree. I'm not sure but most have volume limiters built-in, unlike the days of old, when you could play your personal stereo so loud that your ear drums tickled.
posted by humblepigeon at 2:16 AM on June 26, 2007

I got noice cancelling headphones for the same reason as rdr.

Whether or not they are safe, I don't know. But I do know that I can now listen to my music at a much, much lower volume when I'm on the bus.

That's got to be safer on my ears, and my blood pressure. :)
posted by Zarya at 2:59 AM on June 26, 2007

I don't suppose you have something in mind about /how/ they're harmful.

At worst, I can only think that they give idiots a false sense of security about what they do and people might use them in place of real hearing protection. But, when they "fail", it would be painfully obvious.

Think of sound as little walls of higher density air rolling past you. These headphones listen to the sounds around you, and when it can predict upcoming walls of sound, it emits a wall of lower-density air, and the two walls cancel out where they touch. The sound, then, gets destroyed within a very small space.

That's all they do. If you can't hear something new, then it's probably (?) not making a sound that can harm you.
posted by cmiller at 5:28 AM on June 26, 2007

Response by poster:

These headphones listen to the sounds around you, and when it can predict upcoming walls of sound, it emits a wall of lower-density air, and the two walls cancel out where they touch. The sound, then, gets destroyed within a very small space.

I understand that that's the theory, but I'm wondering if it's overly simplified. Given an initial pressure (sound) wave that's large enough to damage your hearing, it seems that the compensating pressure wave from the headphones would also be large enough to damage your hearing. I guess my concern is, perhaps the headphones cancel pulses well enough that you don't perceive any sound, but there's still enough jitter between the pulses that what you don't hear is still powerful enough to be mechanically harmful to the workings of your ear.
posted by spacewrench at 5:35 AM on June 26, 2007

Best answer: Pressure waves are sound. If a pressure wave reaches your eardrum, you'll hear it (provided it falls within the range of audible frequencies). Active noise cancellation works on the principle of wave cancellation. The incoming wave is analyzed by a mic in the headphones and an "equal enough" but inverse sound wave is generated. The peaks cancel the troughs (and vice versa), resulting in a faint murmur of the original sound wave.

If you're using headphones with the aim of protecting your hearing from damaging external sound sources, then you need to look into professional active ear protection. You won't be the coolest kid on the block wearing them, though.
posted by pmbuko at 6:02 AM on June 26, 2007

I used to sell and people asked all the time 'There's construction/blasting/industrial noise nearby. I want to block that out. Are these good for that?' The answer is no, you want something more like construction or shooter's ear guards.

There are a few shooter's guards made that are supposed to detect high sound pressure levels and 'shut down' that sound before it gets to you, but the main target for those is for shooting ranges where you might want to talk to someone and still have gunfire muted without taking the headset on and off. The only ones I've seen are expensive, and don't allow for music.
posted by pupdog at 6:19 AM on June 26, 2007

I use earplugs and noise canceling headphones together on planes so I can actually hear movie dialogue. Safety: the combination prevents my ears from ringing after travel, and also seems to help with the pressure change in my ear canals on landing (this is the earplugs, not the headphones). I think the combination of the two works better than either alone for listening to movies and books on tape on a plane.

For just music, I think the noise canceling headphones alone work the best. If I have regular headphones on, my ears ring like crazy after flying b/c I have to turn the volume up high. If I have noise canceling headphones on and listen to music, my ears ring as much as they would have if I had not listened to music, but no more.

I find the noise cancelation works best for constant low frequency noises, but the earplugs can block high frequency sporadic noises, like babies crying. If it makes a difference, I have the Bose quiet comfort 3 and smushy foam earplugs.
posted by Eringatang at 6:49 AM on June 26, 2007

I guess my concern is, perhaps the headphones cancel pulses well enough that you don't perceive any sound, but there's still enough jitter between the pulses that what you don't hear is still powerful enough to be mechanically harmful to the workings of your ear.

Thinking of it as canceling pulses isn't really correct, the process is analogue.

Anyway, I think what you are asking is.. Could the noise canceling headphones produce sound that you can't hear, but is nonetheless harmful to hearing?

The answer to the first part of that question is, not likely. The transducers (speakers) in the headphones aren't very good at reproducing inaudible frequencies, so any signal they produce outside the audible range will be of very low intensity.


The more general question, can ultrasonic 'sound' damage hearing, doesn't appear to have an answer - What Sounds Can Damage Hearing?:

Sounds must also be specified in terms of frequency or bandwidth, roughly like the span of keys on a piano. The range of audible frequencies extends from about 20 Hz, below the lowest notes on a piano, to at least 16,000 or 20,000 Hz, well above the highest notes on a piccolo. Most environmental noises include a wide band of frequencies and, by convention, are measured through the "A" filter in the sound-level meter and thus are designated in dB(A) units. It is not clear what effect, if any, sound outside the frequency range covered in dB(A) measurements may have on hearing. At this time, it is not known whether ultrasonic vibration will damage hearing.

posted by Chuckles at 7:20 AM on June 26, 2007

Given an initial pressure (sound) wave that's large enough to damage your hearing, it seems that the compensating pressure wave from the headphones would also be large enough to damage your hearing

There's some shaky science going on around here.

1 - 1 = 0

Alternatively, you throw an apple at me and I immediately throw one back, hitting yours out of the air.
posted by humblepigeon at 8:52 AM on June 26, 2007

The reason this question initially made sense to me is that I was thinking of white noise generators instead of noise canceling. I think that a white noise generator that could cover up the loudness of an airplane engine (or whatever) would probably damage your hearing, because it has to be loud enough to drown out the troublesome sound. But, like others have said, the point of the noise-canceling feature is that it kills the sound waves before they get to your eardrum. It really does make sounds quieter, rather than drowning them out with something louder.
posted by Inconceivable! at 9:11 AM on June 26, 2007

1 - 1 = 0

That is the basic principal, sure, but it is a lot more complicated..

Obviously, the two signals can't be exactly identical. But, to keep them as close as possible, there must be something non-linear going on. So, there will be sound leaking through, and some of that will be harmonics of the noise being canceled. The question is, can any of that be harmful.

Well, probably not.. Within the audible range of frequencies, you would be able to hear any harmful signal. Outside the audible range, the headphones can't generate much pressure. So, even if ultra-sonic pressure can be harmful (an unanswered question), it is likely that the level of ultra-sonic pressure produced, if any, will be very low.
posted by Chuckles at 9:41 AM on June 26, 2007

Best answer: Just pick up a pair of sound blocking headphones, like those made by Shure. They go in your ear and act like ear plugs to block the sounds mechanically. Therefore, the volume needed to be heard coming from your sound source doesn't have to be cranked up.

Plus, they produce awesome sound. I have a pair of their older low end models (2c or something like that) and they give my good Sennheiser closed-air studio style headphones a run for their money in sound quality.
posted by jeversol at 11:44 AM on June 26, 2007

Best answer: Seconding jeversol to get a set of in-ear headphones. High end ones will include a variety of tips, some which look just like a pair of ear plugs that will do a fantastic job of cutting out ambient sound so you can listen at low volume levels.
Here's some info from Shure's website.
posted by metaname at 12:31 PM on June 26, 2007