supposed hearing limit of 20khz is b.s., just saying

[rifftrax]

Ok, I want everyone to check this out:


Going by the logarithmic frequency graph they've got there, you can see they assume that it becomes exponentially more difficult to hear anything even (apparently) approaching 20khz. Now I actually work doing audio engineering for a company that deals with ultrasonic transducers. They are capable of rather high output levels (about 110db @ 1 meter from my measurements) at a nominal frequency of right around 25.1khz (where they are most efficient). Guess what? Pretty much EVERYONE in our office can hear these suckers when you have them angled the right way against your ear (and this is around a ft. and half away so I suppose you can add 6db per it being a point source and say that the sound is 116db at the ear). The output level and pure tone frequency (from the ultrasonic transducer) I've confirmed using a calibrated Dayton EMM-6 measurement microphone (from Spectrum labs) which was set against a Class II decibel level meter using a 1khz tone.

Myth = BUSTED

Maybe I should write a white paper because apparently "audiologists" know f**k-all lol. Also the way this describes the "preferred" method of taking the perceived sound level tests is also bullshit:
http://en.wikipedia.org/wiki/Equal-loud ... esentation

Because at frequencies over 1khz and especially approaching 20khz a frontal presentation will cause the frequencies that you are trying to record useful data from to be filtered by the lack of a direct path to the eardrum. I.E. the person has to tilt their head slightly to hear them better. In the real world, every source of sound is not going to sit directly in front of a person - people tend to actually move and turn their head (gasp!) and not face potential real-world sources of ultrasonic sound head-on all the time. So using only a frontal presentation is useless because it has nothing to do with how people in the real-world reliably interact with sound.

Anyway. Thought you all should know - what you've been taught is wrong.

[UltraJv]

Of course they can sense the pressure, yes but does it convey any information? Try a test with specific a voice message imposed on it, get the test candidates to tell you what the message was and youll fail. If you want to propose a white paper - youll have to find someone who has the test background with medical experience to back it up. Or it will just be pointless.

[whyterabbyt]

Ok, I want everyone to check this out:


Going by the logarithmic frequency graph they've got there, you can see they assume that it becomes exponentially more difficult to hear anything even (apparently) approaching 20khz. Now I actually work doing audio engineering for a company that deals with ultrasonic transducers. They are capable of rather high output levels (about 110db @ 1 meter from my measurements) at a nominal frequency of right around 25.1khz (where they are most efficient). Guess what? Pretty much EVERYONE in our office can hear these suckers when you have them angled the right way against your ear (and this is around a ft. and half away so I suppose you can add 6db per it being a point source and say that the sound is 116db at the ear). The output level and pure tone frequency (from the ultrasonic transducer) I've confirmed using a calibrated Dayton EMM-6 measurement microphone (from Spectrum labs) which was set against a Class II decibel level meter using a 1khz tone.

Myth = BUSTED

Maybe I should write a white paper because apparently "audiologists" know f**k-all lol. Also the way this describes the "preferred" method of taking the perceived sound level tests is also bullshit:
http://en.wikipedia.org/wiki/Equal-loud ... esentation

Because at frequencies over 1khz and especially approaching 20khz a frontal presentation will cause the frequencies that you are trying to record useful data from to be filtered by the lack of a direct path to the eardrum. I.E. the person has to tilt their head slightly to hear them better. In the real world, every source of sound is not going to sit directly in front of a person - people tend to actually move and turn their head (gasp!) and not face potential real-world sources of ultrasonic sound head-on all the time. So using only a frontal presentation is useless because it has nothing to do with how people in the real-world reliably interact with sound.

Anyway. Thought you all should know - what you've been taught is wrong.

I once met a guy who insisted he had a proof for Fermet's Last Theorem. He wasn't a mathematician, and in fact, upon being pressed, he admitted that he'd only barely passed O Level maths.

Despite a small group of people with University-level maths trying to point it out to him, he couldn't actually accept that if he picked three random numbers and put them into the equation (a**n + a**n = c**n) and got the expected result, then that didn't, in and of itself, constitute mathematical proof'of the equation. As far as he was concerned, he was the first person ever to try putting some numbers in, and 'proving' that the Theorem held.

Oh, and some transducer systems can produce subharmonics. Its even a known artefact of ultrasonic cleaners.

Thought you should know.

[rifftrax]

Of course they can sense the pressure, yes but does it convey any information?

It's a pure sine tone, what the hell is it supposed to convey? Other pure tones at other frequencies? Gosh, I'm pretty sure that would be called a harmonic actually. Testing for hearing bandwidth has nothing to do with testing for whether I can tell someone was toasting a cheese sandwich which a Sunbeam on setting "6" while wearing flannel pajamas by listening to an audio clip. We're not talking about timbre here. TOTALLY DIFFERENT.

Try a test with specific a voice message imposed on it, get the test candidates to tell you what they heard and youll fail.

I can go in the office and do that today, I'll just have someone talk loudly to me while activating the ultrasonic speaker. Oh wait this has already happened. And yes I can still hear it extremely clearly.

If you want to propose a white paper - youll have to find someone who has the test background with medical experience to back it up. Or it will just be another load of crap like youve just posted.

Wait, I'm sorry. Was what I posted a load of crap because you've managed to propose completely useless arguments that in no way actually stand against my testing experience? Or was it a load of crap because you didn't want to take the time to formulate a half-decent argument.

Look bro. I can hear 25.1khz @ 116db. This shit really isn't up for debate. I wasn't trying to prove anything more than that (maybe you should re-read what I wrote and think about this).

[BertKoor]

Are you really doubting established and proven concepts?

Some thoughts:

* Have you checked / confirmed the transducer only emits the 25kHz freq? It could be a sub-harmonic frequency of 12kHz (already f*cking high pitched and perceivable by most 40+ persons) is either emitted or created through acoustic reflection & cancellation.

* Audiologists do hearing tests using headphones, aimed directly into the ear channel. So your "directional" myth is thus BUSTED! as well.

* Anyone with a headphone and an audio interface supporting 96kHz can do such hearing tests. It will show a sudden drop in the highest perceivable frequency, and this frequency depends mainly on the subject's age. Young persons will perceive the 19kHz or so emitted by CRTs, while older persons won't at all. I'm now 45 years old and I can't hear a thing above 14 or 15 kHz.

[UltraJv]

Of course they can sense the pressure, yes but does it convey any information?

It's a pure sine tone, what the hell is it supposed to convey? Other pure tones at other frequencies? Gosh, I'm pretty sure that would be called a harmonic actually. Testing for hearing bandwidth has nothing to do with testing for whether I can tell someone was toasting a cheese sandwich which a Sunbeam on setting "6" while wearing flannel pajamas by listening to an audio clip. We're not talking about timbre here. TOTALLY DIFFERENT.

Try a test with specific a voice message imposed on it, get the test candidates to tell you what they heard and youll fail.

I can go in the office and do that today, I'll just have someone talk loudly to me while activating the ultrasonic speaker. Oh wait this has already happened. And yes I can still hear it extremely clearly.

If you want to propose a white paper - youll have to find someone who has the test background with medical experience to back it up. Or it will just be another load of crap like youve just posted.

Wait, I'm sorry. Was what I posted a load of crap because you've managed to propose completely useless arguments that in no way actually stand against my testing experience? Or was it a load of crap because you didn't want to take the time to formulate a half-decent argument.

Look bro. I can hear 25.1khz @ 116db. This shit really isn't up for debate. I wasn't trying to prove anything more than that (maybe you should re-read what I wrote and think about this).

I have a test background. You havnt got a leg to stand on. What youve done is just fool yourself. I know its not up for discussion with you, youve made your mind up despite the evidence. I will just sit and watch the show

[rifftrax]

I once met a guy who insisted he had a proof for Fermet's Last Theorem. He wasn't a mathematician, and in fact, upon being pressed, he admitted that he'd only barely passed O Level maths.

Despite a small group of people with University-level maths trying to point it out to him, he couldn't actually accept that if he picked three random numbers and put them into the equation (a**n + a**n = c**n) and got the expected result, then that didn't, in and of itself, constitute mathematical proof'of the equation. As far as he was concerned, he was the first person ever to try putting some numbers in, and 'proving' that the Theorem held.

That's pretty cute. What does this have to do with the fact that if you were to come to my work I could prove without a shadow of a doubt that you too could likely hear 25.1khz? Oh, nothing... that's right. Anyway.

Oh, and some transducer systems can produce subharmonics. Its even a known artefact of ultrasonic cleaners.

You're totally right, and those subharmonics would have clearly shown up on the spectrograms I was running. So, actually - no, you have a totally moot point in this instance. Doesn't apply here.

Thought you should know.

Thanks, that was super helpful of you. I actually know how to use the equipment at my test bench though.

I have a test background. You havnt got a leg to stand on. I know its not up for discussion with you, youve made your mind up despite the evidence:-)

You've already made up your mind too. When was the last time you tested an ultrasonic transducer at 25khz? Seriously, I'd like to know.

[BertKoor]

those subharmonics would have clearly shown up on the spectrograms I was running.

Not if they are caused by reflections within the hearing channel

[rifftrax]

Are you really doubting established and proven concepts?

Yes, I sure as hell am actually. Wouldn't you if you had the actual experience I described above?

Have you checked / confirmed the transducer only emits the 25kHz freq? It could be a sub-harmonic frequency of 12kHz (already f*cking high pitched and perceivable by most 40+ persons) is either emitted or created through acoustic reflection & cancellation.

Duh, yes I have as I mentioned above. There are NO SUBHARMONICS. How do I make this clear? Let's see. ZERO ZIP ZILCH NADA. Subharmonics = not there in the slightest (ok I lied there is a very low-level emission at 100hz).

Audiologists do hearing tests using headphones, aimed directly into the ear channel. So your "directional" myth is thus BUSTED! as well.

See the wiki article on equal-loudness contours. Obviously I used the word "preferred". Did anyone read what I wrote? Jesus come'on guys.

Anyone with a headphone and an audio interface supporting 96kHz can do such hearing tests. It will show a sudden drop in the highest perceivable frequency, and this frequency depends mainly on the subject's age. Young persons will perceive the 19kHz or so emitted by CRTs, while older persons won't at all. I'm now 45 years old and I can't hear a thing above 14 or 15 kHz.

I'm pretty sure zero headphones are able to produce a 116db 25khz signal. Hence the more reliable testing method of actually using a high-power ultrasonic transducer.

[Meffy]

Oh, and some transducer systems can produce subharmonics. Its even a known artefact of ultrasonic cleaners.

You're totally right, and those subharmonics would have clearly shown up on the spectrograms I was running. So, actually - no, you have a totally moot point in this instance. Doesn't apply here.

Unless the subharmonics are generated in the auditory apparatus instead of the ultrasound generator.

I work with ultrasonic transducers in medical applications. This comes up. When investigating the system containing a transducer and an ear, you can't ignore the effects of the ear itself and what it comes mounted in (a head).

[edit] BTW, when I was a schoolchild I was tested and could hear reliably up to about 23.5 kHz, intermittently maybe past 24 kHz. Nothing new there. It's perfectly well known, just part of the natural variability of people. With age my ears' high-end frequency response has decreased, which is a good thing because the high-pitched sound from video flyback transformers used to drive me up the wall.

[rifftrax]

those subharmonics would have clearly shown up on the spectrograms I was running.

Not if they are caused by reflections within the hearing channel

What? On a spectrogram? What are you talking about?

This is a spectrogram:

http://en.wikipedia.org/wiki/Spectrogram

You get those by using data from a microphone.

If you're saying that somehow a 25.1khz wave can bounce around in my ear-hole and somehow 'produce' a sub-harmonic then I'm really interested to hear the theory behind that.

[Meffy]

This shit really isn't up for debate.

If it's not, then the thread should be locked. If you want the thread open there will be debate, debunking, and related debris.

[rifftrax]

Unless the subharmonics are generated in the auditory apparatus instead of the ultrasound generator.

The non-linear effects I know about in relation to ultrasonic sound comes from typical wave propagation in a free-field through air due to the slight difference of pressure created by the wave trough vs. wave front (which creates slowly decaying frequency over distance)... not due to a reflection. Those serve as the basis for technology like the audio spotlight.

I work with ultrasonic transducers in medical applications. This comes up. When investigating the system containing a transducer and an ear, you can't ignore the effects of the ear itself and what it comes mounted in (a head).

The creation of a sub-harmonic due to surface reflection is something I have never heard of. Do you have a reference?

[edit] BTW, when I was a schoolchild I was tested and could hear reliably up to about 23.5 kHz, intermittently maybe past 24 kHz. Nothing new there. It's perfectly well known, just part of the natural variability of people. With age my ears' high-end frequency response has decreased, which is a good thing because the high-pitched sound from video flyback transformers used to drive me up the wall.

Tell everyone else in this thread that. LOL. Thanks for backing me up though. Finally a voice of reason.

This shit really isn't up for debate.

If it's not, then the thread should be locked. If you want the thread open there will be debate, debunking, and related debris.

I mean that particular part, that I can hear 25.1khz. Everything else people can debate all they want. Well even then I guess someone is welcome to come prove me wrong... just not sure how they would do that.

It's just funny to me that given the total knee-jerk responses early in this thread that pretty much 99% of people everywhere (Meffy appears to be part of the 1%) don't realize that people (and remember, I'm 26... I'm not a teenager) of a variety of ages can hear well beyond 20khz with no problem. And yes, of course the ear is a non-linear system so at some point there will always be a type of distortion and extra harmonic content creating added to the original wave by the time it hits your brain. I'm not so sure about sub-harmonic content.

[BertKoor]

Are you really doubting established and proven concepts?

Wouldn't you if you had the actual experience I described above?

I'd investigate the phenomena indeed, and think of possible causes. Like I just did in my first post, and I just read some confirmation of their likeliness. Plus the unlikeliness that you have ruled it out completely and systematically, since you're too eager to see confirmation of your own theory.

Anyone with a headphone and an audio interface supporting 96kHz can do such hearing tests.

I'm pretty sure zero headphones are able to produce a 116db 25khz signal.

I'm not. And I lied a bit too: an interface with only 44.1kHz abilities suffices as well.

What's interesting though is the level you need, and plot the lower threshold of perceivability. Example with fictive (and wrong) data:
* 14 kHz: 10 dB
* 15 kHz: 40 dB
* 16 kHz: 60 dB
* 17 kHz: 90 dB
* 18 kHz: beyond scale of transducer
* 20 kHz: beyond scale
* 22 kHz: beyond scale
* 25 kHz: 115 dB
* 28 kHz: 100 dB
* 33 kHz: beyond scale

I'd like to see such a graph... You have the means, you have the theory to defend, so the ball is at your side

[Meffy]

Reference? You have the kind of internets that come with a Google, yes? :-} If you're really interested you can find the studies. They're hardly secret. The research that led to an actual, working product that I worked on has been around at least since the early 1970s.

I don't recall saying anything about "surface reflection." You extrapolated that. For more info, read up -- same as I did about fifteen years ago when I started on that project I mentioned. [edit: Ghawds above and below, it's been almost eighteen years. My, how the fun times when you're flying haves.]