The importance and effect to and above 20kHz...

The Boyk paper makes no such speculation and it is, frankly, old news. As for the speculation (it was not a finding or otherwise demonstrated) in the referenced paper that the saccule might be a transducer for such high frequencies, it is hard to entertain such a speculation given the biophysics of the saccule. It is, rather, much better at extreme low frequencies, not high frequencies.

The Oohashi, et al., paper has been discussed in many forums and it is highly intriguing but far from convincing on several levels of experimental design and analysis.

Kal

"Good point. Not many people are aware that we can't even hear proper waveforms above 4 KHz....the ear's nerve bundles fire too slowly! In order to hear above 4 KHz the brain relies on two things; beat frequencies and differences in timing of what arrives at one ear versus the other." That's not correct. While it is true that the afferent axons cannot fire more than about 1KHz (Volley Principle) and they can convey up to 4KHz by firing as phase-locked groups, frequencies above 4KHz are coded by labelled lines under the Place Principle. In the latter, it is not the frequency but the place of the receptor cell on the basilar membrane that codes for frequency.

Interaural timing differences are important for localization of sounds.

Kal

Here is an interesting paper that addresses the existence of seemingly inaudible music frequencies above 20kHz and discusses the potential effects of these frequencies on the listener:

http://www.cco.caltech.edu/%7Eboyk/spectra/spectra.htm

The paper raises the possibility that ultrasonic frequencies may be perceived in a different manner through a different part of the inner ear. I have no technical knowledge in this area, so I leave this to others to debate.

Having heard two different speaker systems with treble extension significantly above 20kHz, I have personally experienced a greater sense of hall ambience and air from these speakers than I have ever heard through speakers that use more conventional tweeters. The dimensions of the recording venue - and, particularly, the height of the ceilings in the venue - were more apparent than I have otherwise ever heard from an audio system. It has been my running hypothesis that the additional treble extension produces this enhanced sense of space, but this is just my own subjective impression.

For example, 20hkz and a 22khz interacting together would create a 2khz beat freq. Whether or not there is enough energy in this signal that could affect the hearing would be difficuilt to say

Good point. Not many people are aware that we can't even hear proper waveforms above 4 KHz....the ear's nerve bundles fire too slowly! In order to hear above 4 KHz the brain relies on two things; beat frequencies and differences in timing of what arrives at one ear versus the other.

However, very low signal amplitude because the basilar membrane does not vibrate enough to transfer energy to the inner ear at higher frequencies impies that you can't even hear beat frequencies for signals with frequency content higher than 20 Khz (or 15 Khz for most of the older folks).

While we can't hear above 20khz, any sound content above 20khz could interact with other sounds and the resultant interaction create sound that are the difference between the 2. For example, 20hkz and a 22khz interacting together would create a 2khz beat freq. Whether or not there is enough energy in this signal that could affect the hearing would be difficuilt to say.

So then...I guess my next question would be...how important is it to build a system around the >20kHz factor, so to speak?

If there are any benefits, be it small or great, are these added benefits substantial enough to warrant building a speaker around them? For instance, 99.5% of todays electronics are capable of transmitting signals above 20kHz, most about 50kHz. This covers the CD Player, Pre/Pro, Amp and even cable sections; which leaves the weakest link...the speakers. Some claim but few produce over 22kHz. Even fewer over 25kHz to 30kHz. Mind you, >20kHz is inaudible, but it adds the "air" to the recording. Is this the only benefit and should a system be built around it?

I am not aware of any evidence that frequencies beyond audibility (around 15 KHz for most of us) have any relevance at all. The basilar membrane is a band limited device and can't resonate enough above 20 KHz to generate any neural discharges to the brain.

It's not important to me at all in my right ear, I can't hear the crickets in that ear anyway but if a system goes to 20khz and past it's a good indicator that the audible high frequency performance will be good. Systems that only claim 15 khz usually sound rolled off on the top end.

Thanx, Russ

It has been demonstrated that the quality of sound in supersonic frequencies has an effect on the sound in the audible regions. High frequency sounds affect detail such as soundstage "air" and dimensionality. One would intuitively think that supersonic frequencies shouldn't have an effect on audibility, especially linearity since the second harmonic of 20kHz is 40kHz, but again, this has been proven out in listening tests. Also, if there is too much high-frequency content in a system, it could lead to instability in power amps. Some early digital noise-shaping systems caused high-frequency oscillations in some power amps.