Hearing Damage over 20khz?

Shadorne... Agreed... "there is no evidence that we can actually hear pure tones well above 20 KHz".

But we can detect the presence or absense of such tones. Perhaps this is because of beat frequencies as you suggest.

Listen to a 20KHz square wave and a 20 KHz sine wave. I bet you can tell them apart(if you can hear them at all. If not try a lower frequency). The only difference is the higher harmanics in the square wave.

Yes there is some interest in frequencies higher than "audible" however it appears to be the non-linear properties of the air and the way differences between high frequency tones that can make audible sounds (beat tones).

Fundamentally what we hear is still within the audible range of frequencies and there is no evidence that we can actually hear pure tones well above 20 KHz.

Shadorne... I am very familiar with Fourier analysis. (I used it a lot in my role as a test design engineer).

Evidently you have not experienced the phenomina which I described. The ongoing interest in supertweeters is further evidence that frequencies above the measured hearing range do matter.

What is your explanation of ability to sense the existance or absence of frequencies higher than measured sine wave sensitivity?

Huh? Not sure I understand you. I don't think there is evidence that we hear higher frequencies.

A square wave is made up of all odd harmonics...you hear the odd harmonics up to the point where you can no longer hear them (around 15 KHz for most people)...so you do not hear the "slope" of the square wave but within your audible hearing range you hear the harmonic content that makes up the square wave.

Shadorne... And there are woofer hairs, midrange hairs, and tweeter hairs. However, the ON/OFF mechanization can represent waveform as well as frequency.

What is your explanation of ability to sense the existance or absence of frequencies higher than measured sine wave sensitivity?

There is no evidence that the ear detects wavefront slope. The ear is like a digital device - hairs in the cochlea move and trigger nerve bundles. The on and off of the nerve bundles allows us to determine frequencies or tones. The combination of frequencies and the way they decay determines the timbre or sound.

Measurements of hearing (eg:20KHz) are based on sine waves. But lower frequency waveforms that are not sinusoidal can have wavefronts with slopes well in excess of the fundamental frequency. I believe that the ear detects wavefront slope. You may not hear a 30 KHz sine wave and yet limitation of slew rate to that corresponding to 20 KHz sine wave is audible.

I have experienced exactly this effect, except that, at my age, both frequencies are lower.

There are some that believe that having components that have a frequency response that extends beyond what is commonly accepted as the limits of human hearing has benefits. Some of those benefits are sometimes attributed to having the device not working close to limitations, and therefore working in a more comfortable, less stressful situation. Another reason suggests, that it extends the range where back reflections occur, and therefore allowing more space for dissipation of those reflections that could potentially corrupt incoming signals working within accepted hearing range.

You cant produce a 16k square wave unless you'v got three or more octaves above that. Or more accurately upper odds of the fundamental. Damn Nyquest.

Frogman is right. This is exactly why analog sounds different from digital, and live instruments often sound sweeter. I have a piano in my listening room, and play acoustic and electric guitar (for over 45 years...boy are my fingers sore...) so my reference for live sound is right here. My girlfriend's Basset Hound (currently dead...the hound, not the g/f) couldn't handle my acoustic playing (even ukulele) but could sit with me when I listened to the stereo...why? I found this to be offensive and hurtful, but I think it explains something...not sure what...but something.

Might damage your dog's ear. :)

Thanks for all of the input. I feel more at ease about the supertweeters on my KEFs with my kids around.

One thing is for sure, humans are exposed to many things today that we never were in decades or centuries past so the long term effects are difficult to predict.

Thanks again.

Actually, I'd be very surprised if most of us here could hear 16khz tones forget about 20khz.

The issue is not wether we can hear anything above 20khz, or wether this information is present in recordings; although, wether we can "hear" it or not is very much up for debate, given recent research. The real issue is how the absence of that information (above 20khz) affects audible information below 20khz.

Subharmonics, also known as undertones, are a very real part of the harmonic makeup of all music. They occur naturally as a result of the interactions (which can be quantified mathematically) between two or more fundamental frequencies, and it is an acoustical phenomenon that occurs at all frequencies ranges, including the "inaudible", above-20khz range. I remember playing flute trios in music conservatory, and being amazed by the appearence of a fourth, "phantom" flutist at certain points in a composition. At certain points in the music, due to the particular musical intervals being played, and the fact that the flute produces a relatively pure tone, a fourth tone would be generated below the lowest written tone, with every bit as much power and presence as the written tones; clearly audible to listeners as well as the players.

Why then, should it be difficult to appreciate that the removal of these harmonic interactions in the above-20khz range would have a significant effect on harmonic content in the audible range? The removal of a portion of this infinite "matrix" of harmonic interactions by the recording process would surely have an effect on perceived timbre, and spatial cues. And that is but one reason why our precious recordings will never sound quite like the real thing. I think we tend to underestimate the incredible complexity of music and acoustics, and miss the forest for the trees.

Mr Jgiacalo- I'd have thought anyone with a knowledge of musical instruments, and/or accurate music reproduction, familiar with(or, at least conscious of) the facts contained in the second site you mentioned. I guess not! Frankly- I'm glad YOU mentioned it FIRST!

Thought all responders may be interested in these related articles:

http://jn.physiology.org/content/83/6/3548.full

http://www.ocf.berkeley.edu/~ashon/audio/Ultrasonics.htm

but there are subharmonics generated below these supersonic frequencies that translate into harmonic information and/or spatial cues in the range that we DO hear.

Subharmonics in a bell is called music.

Subharmonics from an audio system is simply unwanted added distortion!

If you add a device that is only supposed to make sounds above 20KHz (and nothing else) and then you hear a difference then you must necessarily be hearing distortion from said device.

If there is audible sound between 20 and 20 KHz and it is on the recording then you will hear it - irrespective of what source (instrument) made these sounds and irrespective of whether some of these audible sounds are subharmonics of higher frequency fundamentals of certain instruments (possibly percussion?).

The whole thing about sound reproduction above 20KHz is misguided at best - at worst it is deceiving.

The only valid argument for frequencies beyond hearing capabilities is that better performance beyond human hearing capability might mean the system performs more accurately and linearly within the bandwidth of human hearing. (although this may be doubtful as resonances outside the audible bandwidth may equally be a source of distortion)

Okay, shooting from the hip... I've never heard of anyone having tinnitus at 20 hz,or even 250 hz, It'd be like a bumble bee living inside of your head. But this is where most of the wattage in our amps is used.
I think we all agree that we WANT the extended frequency in our audio systems because there's information above 20k that we don't hear, but there are subharmonics generated below these supersonic frequencies that translate into harmonic information and/or spatial cues in the range that we DO hear.
Rupert Neve, recording console designer extraordinaire has been designing audio recording equipment that is intended to reproduce up to 100k (100,000 kilohertz) and higher since the 1970's.
High frequency sound waves like this are pretty easily attenuated by walls and carpeting so unless the kids are right in the room with you it's pretty hard to imagine them
being harmed by it. I do however wonder about my dog's hearing when she sits beside me during listening sessions...

Even if the speakers can produce sound to 40Khz, there is so little music that hi up I doubt there is reason for concern. If 40Khz is causing hearing damage then the audible music would be unbearable.