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Old 6th February 2007, 01:37 AM   #1
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Default audibility of ultrasonic forments

I was doing some research (shudder) and ran across this article by Dick Sequerra

www.sequerra.com/common/data/ribbons.doc

Now I've had discussions over the years as to the audibility (or not) of ultrasonic sounds harmonically related to the fundamental and their influence on the quality of the reproduced (and live) sound from a stereo or musical instrument. I'm not sure I place much credence in the argument that trumpets/pianos/sax/ whatever instruments actually produce ultrasonic harmonics that influence the quality of what is heard, (James Boyk of CalTech is a BIG proponent of this position), but that's not really the thrust of my question.

Dick Sequerra (and others I've read) make a big deal over the ability of true ribbons to reproduce freqs. out to 100 Khz and more, and that this somehow explains their superior sound qualities. While I don't dismiss that ribbons/planars sound superior, i do question the logic used ....

If, as I understand it, we can't actually HEAR the harmonically related ultrasonics, but they are important in that they induce FORMENTS (i.e., difference frequencies within the audible range) that are produced from the ultrasonic harmonics, and that these must be produced by the speaker to make an accurate reproduction of the original signal. No problem if that is taken as a measure of quality (not sure if I believe it's necessary for accurate reproduction, though).

My issue is, why do the speakers need to produce these downconverted harmonically related sounds? Shouldn't they already be recorded in the electrical signal that is captured on the medium being used (not the ultrasonics, mind you, but the forments as espoused by Sequerra et.als)? This goes to the crux of tweeter capabilities, upsampling, high bit pcm, etc. arguments wrt cd's records, etc.

I mean, if these forments are present when they're being recorded, and they are indeed within the 20 - 20Khz audible range and influence the sq, why do we need capabilities beyond 20 Khz? The info has already been "decoded" during the recording (or listening) process, as I see it.

Any thoughts? Seems all this hype about the need beyond 20 Khz is driven more by marketing departments than any fundamental science.

John L.
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Old 6th February 2007, 03:08 AM   #2
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I'm no expert, but I agree with you. From an "intuitive" standpoint I can't see any benefit from a tranducer doing something on its own, whether it's in the audible range of frequencies or on either side of it, that is not part of the input signal. In most schools of thought I know of this is called distortion!

Regarding Sequerra's paper, I read only subjective claims - he refers to no studies, measurements, data etc. to back them up. Hard for the inventor to be impartial about his invention.

As for ribbons being superior to other types of transducers, I humbly refer the reader to "Battle of the Non-Domes" at Zaph Audio.
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Old 6th February 2007, 05:29 AM   #3
bjorno is offline bjorno  Sweden
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Hi,

Chose your expert(s)

Take a look at this sample picture (1(1)) by David Griesinger:

Or read the whole story at: http://world.std.com/~griesngr/intermod.ppt

b

1(1)
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Old 6th February 2007, 02:52 PM   #4
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Default ultrasonics

I've read several of David Griesingers papers... at least he does experiments and presents data to support his work... so I tend to lend more credence to that. Plus, it makes more sense to me as well. Not that he isn't trying to earn a living too...

John L.
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Old 6th February 2007, 04:21 PM   #5
soongsc is offline soongsc  Taiwan
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I am pretty much convinced that better FR in the ultrasonic range improved the phase response in the audible range, and thus effects the shape of transient wave forms. These are audible, but may not be a great concern. Additionally, during the design of audio equipment, if this range is not accounted for during design evaluation, then adverse effects may occur. Much problems occur when the energy cannot be fully transferred to acoustic energy at the right time, and thus tends to remain somewhere in the production chain until damped out. I would not put designing to such extreme as first priority though, more accurate low end reproduction is much more appreciated by the listenters.
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Old 6th February 2007, 05:03 PM   #6
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"I am pretty much convinced that better FR in the ultrasonic range improved the phase response in the audible range, and thus effects the shape of transient wave forms."

This is interesting - and I'm sure testable - so I would be a believer if I saw a test. As for effects on the shape of transient wave forms, as long as those effects create a more accurate reproduction of the input signal, then yes there could be a benefit - as long as it's audible.

I don't care about improvements if I can't hear them.
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Old 6th February 2007, 06:51 PM   #7
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"I am pretty much convinced that better FR in the ultrasonic range improved the phase response in the audible range, and thus effects the shape of transient wave forms. These are audible, but may not be a great concern. Additionally, during the design of audio equipment, if this range is not accounted for during design evaluation, then adverse effects may occur."

I guess my real concern is at what price? If these hyper-response transducers are also hyper-expensive, how do we evaluate the cost/benefit ratio?

I've got planar drivers in my latest build that measure pretty flat beyond 50 Khz, but I'm not sure that means much (except to dogs, bats, etc.). Griesingers' point about the highly directional aspect of ultrasonic signals seems relevant, since one is unlikely to be physically located to take advantage of any enhancement such performance might provide.

In fact, there are commercial implementations of just such directionality to advantage...

http://www.atcsd.com/site/content/view/34/47/

Since there most likely aren't any non-electronic instruments with step risetime waveforms, and few electronic ones anyone would want to listen to, why pay exhorbitant prices for performance not needed?

John L.
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Old 7th February 2007, 02:19 AM   #8
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by sdclc126
"I am pretty much convinced that better FR in the ultrasonic range improved the phase response in the audible range, and thus effects the shape of transient wave forms."

This is interesting - and I'm sure testable - so I would be a believer if I saw a test. As for effects on the shape of transient wave forms, as long as those effects create a more accurate reproduction of the input signal, then yes there could be a benefit - as long as it's audible.

I don't care about improvements if I can't hear them.
I quite agree that if one cannot hear the difference of extended range, then it means nothing in audio application. I have used drivers that go up to 40KHz, and it does make a difference to me. Also at a friends location, he added a supper tweeter that went so high that I could only measure the rising portion up to 48K, and he claims his system sounded like the 20KHz system I brought along until he added his super tweeter. I have also listened to various systems that have added the ELAC super tweeter. All these implementations resulted in a more precise imaging of instruments during listening.

Quote:
Originally posted by auplater
"I am pretty much convinced that better FR in the ultrasonic range improved the phase response in the audible range, and thus effects the shape of transient wave forms. These are audible, but may not be a great concern. Additionally, during the design of audio equipment, if this range is not accounted for during design evaluation, then adverse effects may occur."

I guess my real concern is at what price? If these hyper-response transducers are also hyper-expensive, how do we evaluate the cost/benefit ratio?

I've got planar drivers in my latest build that measure pretty flat beyond 50 Khz, but I'm not sure that means much (except to dogs, bats, etc.). Griesingers' point about the highly directional aspect of ultrasonic signals seems relevant, since one is unlikely to be physically located to take advantage of any enhancement such performance might provide.

In fact, there are commercial implementations of just such directionality to advantage...

http://www.atcsd.com/site/content/view/34/47/

Since there most likely aren't any non-electronic instruments with step risetime waveforms, and few electronic ones anyone would want to listen to, why pay exhorbitant prices for performance not needed?

John L.
I have used super tweeters that go to 40KHz but really do not cost much if you get them in quantities. The issue is lots of people don't care about that little difference, hence sales volume cannot get to a good size, so they have to sell them at a high price until they have volume. So it's a chicken and egg problem. So if someone want's to get 10000 per year, of super tweeters that go to 40KHz, give me a call.

The HSS thing may be good for non-hifi applications where you only need to listen to mid frequencies. Maybe just using ultrasonic harmonics to excite the audible range?
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Old 7th February 2007, 03:07 AM   #9
Geoff H is offline Geoff H  Australia
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But hang on. Where is this ultra high frequency coming from? What's the limit in the recording process? Microphones?

And on play back we're sampling at 44Khz. That means the maximum frequency/slew rate is a triangle wave at 22Khz off the CD, then a brick wall to anything higher thanks to the filter after the D to A converter.

Sure, it's nice to have a flat phase response to the limit of audibility, but then what HF components are available are locked to the clock in the D to A convert.

The advent of 4 channel explored the upper regions of vinyl, which some studios took advantage and produced some very clean recordings. But play them once with a standard cartridge and say goodbye to the top end.

Is sound on the latest HQ audio DVDs better in terms of phase and freq response? Unless we have a source, I cant see a reason for going much higher than audibility. Or am I missing something?

Then, all the top end distortion on a cd may keep the neighbours dog out, and drive mine insane.

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Old 7th February 2007, 04:48 AM   #10
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Hey Geoff -

I completely forgot about that component - if it aint recorded, it aint gonna be reproduced. Most components in the audio playback chain have a frequency response near or identical to the range of human hearing 20 - 20kHz, so even if the recording picks up the ultrasonics (assuming they actually exist), chances are slim they will make it through to your speakers.

soongsc: "I have used drivers that go up to 40KHz, and it does make a difference to me." Was it a measured difference or a perceived difference?

"Also at a friends location, he added a supper tweeter that went so high that I could only measure the rising portion up to 48K, and he claims his system sounded like the 20KHz system I brought along until he added his super tweeter." With what input signal did you measure the supertweeter - a test tone, or music? If you measure with music and it does not produce 48k, the test tone means nothing. If the tweeter makes 48k with music input you then need to test the music input signal before the tweeter and see if that same information is there - now we're getting somewhere. If that information is NOT in the music input signal, your tweeter is producing its own artifact - to my knowledge such things have never been shown to improve musical reproduction. As for your friend's claim - well he makes my point - a claim is just that.

"I have also listened to various systems that have added the ELAC super tweeter. All these implementations resulted in a more precise imaging of instruments during listening."

Imaging, to my knowledge, is not a measurable parameter of loudspeakers - please correct me if I'm wrong - I've just never seen data on it.

I don't mean to be coming down on you - I just see no science here. Again - I'm just waiting for real data.
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