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Comment by Anechoic | Hacker News Reader

Agree one-hundred percent about the room (although the prescription isn't always as simple as "get a thicker rug" etc).

The other issue regarding high-frequency sound reproduction is that in most cases, the loudspeaker won't be outputting much beyond 22-25 kHz (assuming very good quality loudspeakers, cheap consumer grade units might struggle to hit a -6 dB point at 18 kHz) and even for the speakers that have usable output at that range, the directivity at those frequencies will be so narrow that your head will have to be locked in the perfect "sweet spot" to hear anything.

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  > Agree one-hundred percent about the room

With a username like yours, I'm not surprised. :-)

  > although the prescription isn't always as
  > simple as "get a thicker rug" etc

A prescription is only as good as the likelihood that it will be heeded by the patient. A rug is an easy win; acoustic ceiling tiles and bass traps are a bit harder...

I might sound/be stupid for asking, but what's the actual physical response from something at 22 kHz+? I have a hard time picking up a pure sine > 17 kHz. I doubt I'd get any aural response from anything at 22 kHz, so what's the deal?

The deal is just that you're getting older. Your ears just don't work as well as a 12year old's. Neither do anybody else's your age (within the bounds of typical human variation - probably well over 95% of use _never_ heard 22kHz, not matter _how_ "young" our ears were).

I was once in a small, treated room working with some rather large PA speakers. I was curious how far my hearing range actually extended, and did something very unwise: I played a 20kHz tone and very briefly ramped the volume up and down. I definitely heard it, but I also induced quite a lot of pain. I learned two lessons: 1. my threshold of hearing at 20kHz is near or above the threshold of pain, and 2. don't do that ever again.

heh, your story reminded me of the bar scene in Good Will Hunting:

WILL: The sad thing is, in about 50 years you might start doin' some thinkin' on your own and by then you'll realize there are only two certainties in life.

CLARK: Yeah? What're those?

WILL: One, don't do that. Two -- you dropped a hundred and fifty grand on an education you coulda' picked up for a dollar fifty in late charges at the Public Library.

Yeah I get that I'm getting older. It's just, what's the point of having a stereo that gives perfect playback at 22 kHz if you can't hear it? I'm guessing there must be something since people buy gear like that, or is just a case of deranged audiophiles?

You might not hear a pure 22kHz sine but any sound from, say, a harpsichord will have much off these highs, and some think it is a part off the sound, that one feel without actually hearing it. I'm not endorsing this view, sound islike wine tasting, a lot of hand waving and few solid ground.

There's blind wine tasting, if you want the real deal. Without the hand waving.

...of course I mean audible. Or spectral? Not aural, anyway. English is not my first language. Sorry.

That's really good actually, I'm not even sure I know the difference between aural and audible. (<- also, that sentence is a run-on and not good English haha)

I don't really know much about this, but wouldn't the 22kHz sounds potentially create beats in the lower frequencies?

Acoustic "beat tones" aren't "real" tones— you hear them because of non-linearies in the ear-brain system, but you have to hear the initial tones first. (Well, unless you're talking >>130dB SPL levels where the air starts becoming non-linear, but then lower frequency recording would capture it fine)

If you could hear subharmonic beats from ultrasonics then it would be _very_ easy to demonstrate, alas.

Curious, what does non-linear mean in this context?

IIRC, linearity is when you put a sound wave frequency into the medium (air) a some point, you can predict the frequency of the sound wave at some other place using a linear function - meaning that there is no distortion. Non-linear is when the physics of the medium starts screwing with that function.

I believe that it means that the superposition principle (http://en.wikipedia.org/wiki/Superposition_principle) doesn't hold: the net response at a point is not just the weighted sum of the individual responses.

so without very high power sounds and the nonlinearity business the whole "Sound from Ultrasound" wouldn't work? Huh, I guess all this time I misunderstood it.

for those curious http://en.wikipedia.org/wiki/Sound_from_ultrasound

Well, what I can think of is that of course you need to sample at > 2*max frequency if you do uniform sampling to avoid aliasing (by Nyquist), but that's not the same as playback.

Yes, there will be inter-modulations from higher frequencies. There are also from the audible spectrum but if the amp is linear enough they will be low.

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