Hear Here

Most Audiophiles have a pretty fair idea of how the human hearing system works, but there are always new readers who take "obvious" things for granted. I myself also recently learned a few of the finer points while perusing websites on the subject. Our hearing system, from the visible outer ear to the hairs in the inner ear that sends the signals to the brain that we interpret as sound, is exceptionally complex. Less complex, perhaps, than our eyes, but amazingly sophisticated nonetheless.

The outer ear (or pinna) is clearly visible. At its bottom, the ear lobe, by all accounts, has no effect on our hearing. But it has sprouted some fanciful and looney-tunes theories. But the most prominent part of the outer ear, the pinna with its intricate folds, is a key player in directing sound waves into the ear canal. The pinna best captures sound originating from in front, but offers enough sensitivity to sound from behind to sense the approach of a saber-toothed tiger.

How far your pinnae stick out from the sides of your head does affect how well you perceive sound coming from the rear. Pinnae that stick out a bit further than usual (Alfred E. Neuman style, like mine) are a little more sensitive toward the front and a bit less so to the rear. While this may somewhat affect how well you perceive Dolby Atmos, or surround sound in general, I suspect the difference is subtle. But it's logical to assume that protruding ears do somewhat affect your perception of sound, as anyone who has cupped their hands behind their ears can attest. It would be interesting to survey a large group of critical listeners to evaluate this, but I'm unaware if such a study has ever been done.

While the pinnae are generally fixed and immobile for most humans, there are some folks who can move them slightly, though often only after practice and effort. It's likely that one or two of you reading this screed can do so, to the amusement (or horror) of friends and family. Cats and some dogs, however, can do this easily when they have need to identify what's creeping up behind them. Some cats can actually rotate their ears by 180 degrees!

The pinnae direct the sound waves into the ear canal. Without the effect of the pinnae, our hearing would be very different, as Van Gogh likely found out (luckily he was a painter and not a composer). The ear canal directs sound vibrations from the outside toward the eardrum (tympanic membrane) at its far end. Ear wax helps keep dust and other contaminants away from the ear drum. A little ear wax is inevitable and even desirable, but too much can affect your hearing. How much it accumulates varies from person to person.

As my father once taught me, never stick anything in your own ear smaller than your elbow, and certainly not the ever-popular Q-tip. That sort of implement can puncture an eardrum. While the latter can usually heal itself, that takes time and might somewhat alter your hearing. In my annual physical, or any other time I visit my doctor, I always ask him to check for excessive ear wax and, if necessary, clear it out. If you suspect a possibly serious problem beforehand, seek out an ear specialist who may be more comfortable or practiced in doing this than a GP.

The vibrations on the eardrum are transferred to three tiny bones in the middle ear (the hammer, anvil, and stirrup — the smallest bones in the human body). The far end of these bones connects to the inner ear, where the vibrations excite tiny and very sensitive hairs in a circular organ called the cochlea. These hairs generate the signals that our brain then interprets as sound.

To answer that old chestnut, if a tree falls in the forest, it will generate air vibrations but there'll be, technically speaking, no "sound" at all unless a living being with ears is there to hear it as such. If an other-world alien happens by, what he, she, or it "hears" will depend on their auditory system. And in space, with no atmosphere to produce those vibrations, no one can hear you scream. Every outer-space sci-fi show, replete with explosions and rocket engines, is wrong, though this can be excused as dramatic license (and without it millions of viewers would think that their TV sound has suddenly shut down).

Most readers are aware that human hearing, at best, extends from 20Hz to 20,000 Hz. Below 20Hz or so we can feel vibrations, though the extent to which we can actually hear subsonic frequencies appears to be highly variable. Play back a pure 10Hz frequency (assuming your subwoofer can do so!) and you're just as likely to be hearing your sub's 20Hz and/or 30Hz) harmonic distortion instead of a pure 10Hz. At the top end, only 2-year-olds are likely to hear above 15,000 Hz, and possibly only 12,000 Hz. One might argue here with the current audiophile love for high-res audio (sources mastered to well above 20,000 Hz) but that's a very long and touchy subject well beyond the scope of this discussion. In any event, our ears are most sensitive to the range between 2,000 and 3,000Hz — likely another evolutionary adaptation to help us avoid that saber-toothed tiger.

Probably because our visual system is so well developed, many animals have far more sensitive hearing than we humans do. Some animals can hear well above 20,000 Hz. Dogs in particular. When I was a lad we had a black cocker spaniel. Even with floppy, hairy ears covering his ear canals, he'd howl loudly on specific television ads, with his nose lifted toward the sky. We never knew why; it certainly wasn't the 5-inch full-range speaker in our CRT TV. Maybe he just didn't like the product.

One thing all audio fans should take to heart is protecting the ears you have. I always bring ear plugs when I expect to be anywhere that loud sound is likely to be present and out of my control. That means to loud movies in theaters equipped to maximize loud soundtracks, such as IMAX and Dolby Cinema. In such a situation you can usually anticipate when the loud bits are likely to come, so you don't have to wear the plugs throughout the movie. Rock concerts can be far worse and some of the biggest offenders. I once attended a Blue Man Group concert during a CES in Las Vegas; if I hadn't had my ear plugs with me I would have walked out.

Headphones can be a real concern as their isolation from others gives you free rein to crank them up. Loud audio playback at home over loudspeakers is rarely an issue as you can turn the level down yourself if you sense a problem. But loud headphone listening at home can be tempting even when you're alone.

There's one piece of advice I've taken to heart from an Air Force briefing many years ago. Your eyes keep you from looking at the sun (or any other extremely bright light that might damage your vision) for more than an instant because of the discomfort or even pain involved. But hearing is different. The threshold of damage from loud sound comes before the threshold of pain, so you could be damaging your hearing without experiencing discomfort.

If your ears are ringing after a rock concert, of course, you know you've overdone it. You might recover in a day or two, but subliminal damage might still be there, though as yet imperceptible. Do it frequently and the damage can build up over time with a more serious end result. There are also OSHA limits as to how long you can be exposed to continuous loud sound, without protection, before experiencing potential and possibly permanent hearing damage. I find the published OSHA levels a bit generous, though: 90dBA for 8 hours or 105dBA for 1 hour, for example. Note that those levels are dBA, which is largely confined to above 100Hz. OSHA's safe limits for impulse noise, on a rifle range for instance, are far lower. The moral of the story, of course, is to not take your hearing for granted.

mtrot's picture

With my high frequency hearing loss, I am often at a loss(pun intended) for understanding song lyrics or movie dialog. However, my ears do lie fairly flush with the side of my head and, if I pull my ears forward even a little bit, it makes a massive difference. It's as if I've gone back into my younger days! I may figure out a way to put something behind my ears just enough to bring them forward just a bit when listening!

mround's picture

I notice an effect, also, with the headrest on my computer chair, which noticeably enhances mid-highs from the (old Altec 85 bookshelf) speakers. Interesting. At the low end, I don't have a good enough subwoofer, but if you do you might want to look up something recorded at the Sydney (Australia) Town Hall's organ. One of only a couple of pipe organs with an actual, full-size 64' stop, speaking as low as 8 hz. In most of the recordings, all I've heard was buzzes and rattles from both the organ (in the recording) and from my own system (anything loose, as well as the too-small woofer trying to destroy itself) - as the story notes, I'm hearing harmonics and mechanicals, not the actual note, which can only really be felt.

mround's picture

>Even with floppy, hairy ears covering his ear canals, he'd howl loudly
>on specific television ads, with his nose lifted toward the sky. We
>never knew why; it certainly wasn't the 5-inch full-range speaker in
>our CRT TV. Maybe he just didn't like the product

The dog might have been reacting to slightly enhanced horizontal sync whine from the TV. At one time I could hear that too (it's been a long time...). From an online lookup: "Note that the deflection frequency - just over 15 kHz for NTSC and PAL - is on the border of audible for adults but will likely be loud to younger people possibly to the point of being terribly annoying - or worse. If you are over 40 (men more so than women), you may not be able to hear the fundamental at all (at least you can look forward to silence in the future!). So, even sending the TV back for repair may be hopeless if the technician cannot hear what you are complaining about! "

Lack of flyback transformers and CRTs in TVs these days might be a blessing!

RatherBeFishing's picture

Good article, but don't let OSHA's noise exposure limits fool you. Tom was being polite describing them as "generous". They are very poor when it comes to preventing hearing loss. In general industry, workers legally don't have to wear hearing protection until exposed over an 8-hour time-weighted average of 90 dBA (unless they already have hearing loss, in which case it is 85 dBA). That's insane. In a typical working population, you could expect about 12% or more of the workers to develop permanent hearing loss at that level. I suspect higher. Noise induced hearing loss caused by chronic noise exposure begins aroung 81 or 82 dBA. Remember, decibels are logarithmic with a 3 dB doubling rate, so that represents a vast difference from the allowable limit. (Impulse or impact noise is a different animal with different standards.) So yeah, wear your ear plugs. If you have to raise your voice substantially to talk with someone, you probably should be wearing plugs. And make sure to insert them correctly. Otherwise, you're just fooling yourself.

Related to that, the loudest concert I ever attended was Mountain in 1974 during my junior year at college. They had speakers stacked to the top of the curtain on both sides and behind. That was before I knew what I know now and before a 42 year career in industrial health and safety. My ears were ringing so hard the NEXT Day at DINNER that I hardly could hear. (Temporary threshold shift) Got smart after that!

sara167's picture

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