Speakers for High Frequency Sound

"John Woodgate"

** I just did some tests with a condenser mic ( AKG CK2 omni + pre-amp ) on my PC - when viewing the output from a 60 dB gain mic pre on a scope I immediately saw a high frequency sound buried in the LF room noise. Then I added a parallel LC filter ( broadly resonant at 40 kHz) across the preamp output and that cleaned it up allowing a frequency counter to lock on.

I thought it must be from the monitor until I saw the frequency was 30.723 kHz - while the monitor runs at 48.4 kHz.

Switched off the monitor - no change.

I found the tone was stronger near the ventilation slots on the PC case but strongest if the mic was placed on the open CD rom drawer and pointed into the box. The frequency is very steady while the SPL is critical on the

*exact* mic position - ie there are standing waves galore. I reckon it is coming from either the main PSU or the HDD.

The sound would be around 50 dB SPL when on the CD rom drawer - and no, I cannot hear it.

................. Phil

** Hey - learn to quote properly !!!!!!

** Got zero to do with what is inside a standard PC case. ** " I reckon it is coming from either the main PSU or the HDD. " ** But not this one.

................ Phil

.............. Phil

Does this mean that any single person doesn't have a strict HF hearing limit? If you have any links or info on that, I'd certainly be interested..

D'oh, you apparently meant that the highest audible frequency varies with the intensity of the sound, but there is always an upper limit to human hearing and that limit is individual.

Thanks, Arny. I'll look at what Vifa has to offer.

Earthworks' founder David E Blackmer using a study of the human hearing mechanism

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dale

Well, its just not just one number.

Isn't that what the Fletcher Munson curves show?

I think this paragraph summarizes pretty well:

"TO FULLY MEET the requirements of human auditory perception I believe that a sound system must cover the frequency range of about 15Hz to at least

40kHz (some say 80kHz or more) with over 120dB dynamic range to properly handle transient peaks and with a transient time accuracy of a few microseconds at high frequencies and 1°-2° phase accuracy down to 30Hz. This standard is beyond the capabilities of present day systems but it is most important that we understand the degradation of perceived sound quality that results from the compromises being made in the sound delivery systems now in use. The transducers are the most obvious problem areas, but the storage systems and all the electronics and interconnections are important as well."

He's says that this is part of his belief system, and I think he's telling it like it is. Thing is, the paper really doesn't provide evidence that supports his stated belief.

I read in sci.electronics.design that dale wrote (in ) about 'Speakers for High Frequency Sound', on Mon, 14 Feb 2005:

Having described how the system works, he just states his opinion that a bandwidth wider than 20 kHz is necessary. I, too, did experiments with tweeters, when I could hear properly. The response above 20 kHz matters IF there is any signal up there. The point is that there is **amplitude non-linearity** in any transducer, so that spectrum components above 20 kHz intermodulate to produce difference-frequency signals which are quite audible.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

"Arny Krueger" wrote

Though widely quoted as gospel, I was under the impression F&M have been discredited. ISTR that F&M were also responsible for the (also bogus) finding that anything less than 3% distortion is inaudible.

From rane.com:

"In the '30s, researchers Fletcher and Munson first accurately measured and published a set of curves showing the human's ear's sensitivity to pure tone loudness verses frequency ("Loudness, its Definition Measurement and Calculation," J. Acoust. Soc. Am., vol. 5, p 82, Oct. 1933). They conclusively demonstrated that human hearing is extremely dependent upon loudness. The curves show the ear most sensitive to pure tones in the 3 kHz to 4 kHz area. This means sounds above and below 3-4 kHz must be louder in order to be heard just as loud. For this reason, the Fletcher-Munson curves are referred to as "equal loudness contours." They represent a family of curves from "just heard," (0 dB SPL) all the way to "harmfully loud" (130 dB SPL), usually plotted in 10 dB loudness increments.

D. W. Robinson and R. S. Dadson revised the curves in their paper, "A Redetermination of the Equal-Loudness Relations for Pure Tones," Brit. J. Appl. Phys., vol. 7, pp. 156-181, May 1956. These curves supersede the original Fletcher-Munson curves for all modern work with pure tones. Robinson & Dadson curves are the basis for ISO: "Normal Equal-Loudness Level Contours," ISO

226:1987 -- the current standard.

Users of either of these curves must clearly understand that they are valid only for pure tones in a free field, as discussed in the following by Holman & Kampmann. This specifically means they do NOT apply to noise band analysis or diffused random noise for instance, i.e., they have little relevance to the real audio world. A good overview is T. Holman and F. Kampmann, "Loudness Compensation: Use and Abuse," J. Audio Eng. Soc., vol. 26, no. 7/8, pp. 526-536, July/August 1978.

For real audio use, the Steven's curves are more applicable: S. S. Stevens, "Perceived Level of Noise by Mark VII and Decibels (E)," J. Acoust. Soc. Am., vol. 51, pp. 575-601, 1972. [Used to create ISO 532:1975 and ASA S3.4-1980] See Holman & Kampmann above for discussion. "

-- Nicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

I think that orthodox wisdom is that F&M are accurate and representative as far as they go.

I don't know how you made that leap. My diving board isn't that springy, it seems.

Obviously you're way behind on your reading, as I've made many posts in the recent and distant past about putting the F&M numbers into context. If you take them simplistically, they are usually very optimistic about what might be heard in most real world contexts, if for no other reason that they ignore masking.

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telling

that

here are the texts he gives as reference found at bottom of paper

An Introduction to the Physiology of Hearing, 2nd edition James O. Pickles, Academic Press 1988 ISBN 0-12-554753-6 or ISBN 0-12-554754-4 pbk.

Spacial Hearing, revised edition Jen Blauert, MIT Press 1997 ISBN 0-262-02413-6

Experiments in Hearing, Georg von Békésy Acoustical Society of America ISBN 0-88318-630-6

Hearing, Gulick et al Oxford University Press1989 ISBN 0-19-50307-3

dale

"Nicholas O. Lindan"

** Neat how you eliminated the context so you could change it to your hobby horse. ** Think there is a decimal point missing.

** The only on topic bit.

** Seems to apply to folk with headphones on OK.

Audiology relies on it.

** I note this is your totally whacko opinion and not a quote as you are trying to pretend.

The threshold SPLs and frequency limits of human hearing are ENORMOUSLY important to "real audio world ". It is hardly possible to design a piece of audio equipment or an audio system without taking them into account.

............ Phil

Ignoring the mumble concerning construction of the ear, nerves, etc--it is known that one can easily detect *phase* differences that could be interpreted as a 100KHz+ frequency. Easily described using "first principles" as "where is that damn tiger that might be stalking me".

Your guess is way out - what you're hearing is the line frequency which on European PAL TVs is about 15 kHz. I could hear it until my mid to late twenties; now at age 32 I can't hear it at all. However, that might be because new TV's aren't as noisy :-)

I'd be VERY surprised if you could hear anything at all above 20 kHz.

David.

Piezo tweeters will generally go to above 20KHz. I've worked a lot with ultrasonics - way above audible range - you 'hear' it from time to time due to subfrequencies generated by mechanical nonlinearities around the transducers, at a much lower frequency.