Speakers for High Frequency Sound

You make good points, Jay. Please understand, though, that after 40 years of almost every person I've met (and I've worked with electronic techs, too) telling me that they don't hear anything at the same time that I hear a screaching loud sound, it is difficult for me to accept that now everyone hears this sound.

Excerpt from encyclopedia entry: "George Gleason has often been compared to Sir George Martin, due to both being named 'George'; and further, due to both men's surnames ending in the letter 'n' " :D

Neil Henderson

LOL Thanks G

Much less likely than when you post and say "My TV produces a really high-pitched sound", and a whole bunch of people who work daily with video and audio tell you that they, too, hear the high-pitched sound, and tell you the exact frequency, and tell you the precise explanation for what generates the sound, and their explanation in no way fails to describe what you're hearing, that they're all talking about a different sound.

If you want to do the experiment for experiment's sake, you should do it. It's not a bad entry into the world of audio measurement, and a curious itch is one you should always scratch. But it's pointless to keep saying "Yeah, but it sounds higher", ignoring that pitch discrimination at the edges is practically nonexistent, and coming up with theoretical possibilities as to how it could possibly be higher, and how if it were you could possibly theoretically hear it without simultaneously noticing the very obvious pitch an octave or two lower that we're all talking about.

A much better way to measure it is with a small-diaphragm measuring microphone, a preamp (most cheap ones will work) and a frequency counter. Or do what the guy a few dozen posts back suggested: look at an oscilloscope. Trying to match frequencies with an oscillator is less accurate than either of those methods. And when you're done, odds are overwhelmingly in favor of your result being equal to the horizontal sweep frequency of your TV system, wherever you are.

Make an appointment with a neurologist, or visit a friendly dept. of neurology at your local medical school and ask someone how this works. It might take graduate-level courses to understand the answers, which would probably be the best use of the thousand bucks if that's what you want to spend it on. Me, I'd buy season tickets for the symphony, if they weren't locked out.

Peace, Paul

Some people can. Folks who have had certain kinds of cataract surgery no longer filter out UV, and their retinas are sensitive, so they can see things other people can't. Not much real harm, and most of the time they wear glasses with UV filters in them. I'm told that during World War II people who'd had that kind of surgery were used by British spy services; they'd hang out on ships off the coast of occupied Europe, and spies would flash signals to them using flashlights that emitted only UV. They could see it, others couldn't. (I've always wondered whether the story was urban legend, since the slightest fog or haze would cut the UV level drastically, and the North Sea and English Channel are always well-supplied with both.)

"Fog in Channel -- continent isolated!"

Peace, Paul

Ribbon HF drivers can easily do that contact SLS loudspeakers they can sell you a unit for about 100$ that will go to 40K george

I read in sci.electronics.design that snipped-for-privacy@aol.com wrote (in ) about 'Speakers for High Frequency Sound', on Sat, 12 Feb 2005:

Both 0% and 100%. The horizontal scan frequency of around 15.75 kHz is 'one frequency', but the waveform you hear is not sinusoidal; it is quite rich in harmonics. Probably, the odd-order harmonics predominate. Maybe I can measure it for you (on a British TV), but not tonight, Josephine.

I did a quick Google search, and found that there are a lot of things in a computer that would operate at 30.72 kHz.

"A bi-directional horizontal scanner must have a scanning frequency of

Also, several computer switching power supplies operate at 30.72 kHz.

The bearings in the hard drive produce a wide spectrum of noise, especially on the high end. When their pitch drops down enough for it to bother most people, it means the bearings are about to go out (from my experience, that's true of your car's alternator as it is of your computer's hard drive, and they both sound the same when they go bad).

"George Gleason"

Toss up between Cocker, aka world's highest paid spastic and Leon Russell for the No 1 wanker honours.

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

Very likely, but the sweep will be the loudest one. It will also produce harmonics of the sweep (which you won't be able to hear) and some other noises (especially modern TV sets which tend to have switching supplies running at their own frequencies, rather than scan-derived supply voltages for everything like older sets).

The Bruel and Kjaer 2804 microphone power supply whistles very audibly around 18 KHz from the little switcher in there. Potting the transformer in RTV helps a little bit. But it drives me up the wall since the supply is normally close enough to the mikes that the sound gets picked up.

--scott

Lots of electronic techs are deaf too. TV sweep is not subtle at all.

I had a noise on a Nagra III recorder once, and I couldn't tell if it was brush noise (not to worry about) or bearing noise (to worry about). I took it to the US service operation and nobody there could hear it.

A couple decades later, it's still making that sound, and it still is annoying.

--scott

I've had some luck with a sound level meter hooked to a scope. Have to get one with selectable weighting, cause the standard A weighting used for industrial noise study etc. rolls off too fast. I can get enough signal for tracing well above the normal frequency range and well below the level that can produce a meter reading.

Another interesting toy is an ultrasonic frequency translator. Used for leak detection and bearing noise detection. Mine's made by GoPro, whoever they are. There's a LOT of high frequency stuff coming out of my TV that I can't hear.

FWIW, I've never been able to correlate ultrasonic bearing noise coming out of a hard drive with failure. Ideas? mike

I've measured several samples, they do what the charts show.

It's just a matter of speaking to the *right* people. This whole topic is well-known and been around *forever* I think the first time I read about it was in a copy of Popular Electronics in the late 1950s.

Electronic techs and recording engineers aren't the same thing. The folks who hang out on this newsgroup are people whose job (paid or unpaid) it is to listen very carefully to things. And we notice the high-pitched squealing. I noticed it for the first time when I was nine, and we got our first (B&W) television set. I don't hear it as much any more, because my hearing isn't as sensitive as it used to be up there.

Is it possible you're hearing something other than the 15xxx Hz horizontal sweep frequency? Yes. But it's not particularly likely, because THE HORIZONTAL SWEEP FREQUENCY IS THERE. Known to be there, to a greater or lesser degree, on damn near every television set made. There's a chance that you're hearing other things, that you can hear >20kHz better than most people, but the overwhelming *likelihood* is that you're hearing the horizontal sweep frequency.

(If I had to guess, I'd say you have some sort of resonance going on in your hearing apparatus that makes it unusually sensitive to tones at or near that frequency, and that's why it's so easily audible, and why it's so annoying.)

So...Let's say you find out it's the horizontal sweep frequency, or something else up there, after spending money for an oscillator, amplifier and speaker, or whatever test gear you decide to use, then what? Knowing the exact frequency you're hearing plus-or-minus a Hz won't make it any less annoying. If I were spending money, rather than chase after numbers that would satisfy my intellectual curiosity but not ease my discomfort, I'd put the bucks into getting a set of really good, custom-fitted earplugs.

Peace, Paul

There is a recent paper on the subject in Sound and Vibration. Basically if you plot the spectrum, you'll see one big peak at the rotational frequency and a bunch of sidebands. When the sidebands get bigger and bigger and farther from the fundamental peak, the drive is starting to fail.

--scott

If you get a full test done, you'll see that the high end response drops off slowly enough that you can't really say there is a limit. You can say "My hearing is down 30 dB at 16 KC" which is pretty dramatic a drop, but even so you might still hear something at 16 KC if it is loud enough.

Now, the question of course, is how many different mechanisms are involved in that top end corner. And it's certainly more than just one or two.

--scott