Regarding supertweeters

in my ears theres no doubt the supertweeters are worth the money(from what ive heard in some systems). but,- theyre supposed to take over for the standard tweeter where it cant go higher. what if the cd player and amplifier cant produce the over 20000hrtz "normal" range? ive only seen some cd players do this, where it says from 15-100000hrtz or so. my cd player and amp says 20-20000. does that mean a supertweeter will not do any good in my system?

Your own conclusions will be better than mine.
I believe in supertweeters, because I know, from personal experience, that auditory ability exists well above the frequency at which you can detect the pure sine wave that is used for testing.

However, I think you may be on to a point about CDs, and their 20KHz limitation. Some LPs can go a bit higher, but there is some argument about how high, and it certainly varies a lot between different LPs. If there is no signal at 30KHz, a supertweeter good to 50KHz is just an expensive paperweight. Probably the best application for a supertweeter (apart from some very exceptional vinyl systems) would be a SACD or DVDA system, where there is no doubt about the ability to have signal above 20KHz. Of course, the recording equipment must be good enough to include this signal.
Hifimannen, in order for the supertweet to contribute (musical) supersonic sound this content (sound) must be on the storage medium in the first place. It rarely is, as Eldartford notes.

Further, no cdp plays over 20k. What is there is often spurious hi frequency noise (unless you throw a sine at it).

Even further, if yr amp specifies 20kHz then its amplitude response will be much reduced beyond that --limiting the usefulness of a supertweet.

To make things worse, our ears' sensitivity typically goes down as the frequencies go up over 3kHz (i.e. to our ears, a louder signal at say 10kHz will sound as loud as a soft signal at 3kHz).

Ultimately, a supertweet usually functions as a "supratweet", intensifying (i.e.playing in conjunction with the nromal tweet) ordinary audio frequency signals over 13kHz or so -- thereby creating the effect of "spaceousness".
thank u! a little more clear on this now. Gregm, if the supertweeter helps the standard tweeter from as u say 13kHz or so,- will it not be very difficult to calibrate the two tweeters to eachother so the frequenses dont "crash"? maybe a stupid question, i dont know much about it. also, the Tannoy s.tweeters can be set to where they are supposed to "take over". from what i understood u are supposed to set them exactly where the standard cant follow anymore, but of course..u can set it to boost the standard as u say. but - as i understand u guys, if i dont get a cd player that can play above 20000, and do not have an amp. playing above 20000, theres no need for a supertweeter. other than helping out in the standard 20-20000 with ordinary cd's. lack of either that special cd player or amp. will also ruin the point..
also.. the reading on the back of most amps and cd players that say 20-20000.. isnt that meant just to say that either the cdp. or amp. give strong signals in 20-20K? it doesnt mean nothing under or above those figures are let through?
heh.. am i being difficult?
The wavelength of 20KHz sound is 0.66 inch. Therefore there is no need to carefully align the supertweeter and the tweeter for phasing reasons. Slight changes of listener position will affect the relative phasing of multiple drivers, so there is no "right" position. Perhaps the best approach is to aim the supertweeter at the wall behind the speaker, and many designs that include supertweeters do this.
I'll admit I haven't investigated this subject from auditioning, but I'm skeptical about the trend for a few reasons:

>I know I can't hear anything above 20Khz, nor very much for maybe a 1/4 of an octave below that too. This doesn't mean that nobody can, but among audiophiles, who mostly tend to be middle-aged males, I don't think this limitation is uncommon.

>Even with LP's or hi-rez digital media, most of what's up above 20KHz is likely to consist of a high percentage of noise in my view.

>Most of the so-called supertweeter designs I've seen are dynamic domes with diameters on the order of 3/4". Therefore, by the time they're actually reproducing frequencies much above the range of standard tweeters, they will have become highly directional (beaming in their dispersive nature), as attested to by Eldartford's stat about the wavelength at 20KHz already being less than 3/4". Combined with the high degree of absorption at these frequencies likely to be encountered in the home listening environment, unless they're aimed right at the listener's ears, supertweeters won't contribute much to a speaker's power response as perceived at the listening position.

>My hunch is that what most people must hear with supertweeters is reinforcement of a speaker's 10-20KHz octave power response, since all of them seem to roll-in well within the regular tweeter's nominal passband. This may not be a bad thing, since many standard tweeters are rolling-off their power responses (becoming directional) in that range, but hearing such an effect hardly qualifies as proof of the ultrasonic rationale used to market supertweeters.

>I think the primary reason why extended ultrasonic response in a tweeter ("super" or not) should be viewed as desirable is because it implies A) more linear power response within the conventional audioband, and B) that the inevitable resonant peak is moved out farther beyond the audioband, where it's less likely to be excited by MC cartridges or hi-rez digital media (something which might cause audible intermodulation distortion back down into the audioband).
will it not be very difficult to calibrate the two tweeters to eachother so the frequenses dont "crash"?
As you correctly note it is VERY difficult to correctly align the two drivers. Eldartford hints as to why this is so (a fraction of an inch & you're off many degrees in phase... etc). Unlike he, I would like to have the top part of my spkr playing as "correctly" a possible, so would welcome a 1st order crossing for the supertweet (which makes the story even more complicated).

Zaikes: while you can't "hear" you may "perceive". However your point is very valid IMO. OTOH, it's not necessary to have supertweets beaming -- their 15+% dispersion is often OK. Again, however, your point about in room absorption is valid for most rooms.
Also, as you note & I have experienced (mentioned in my 1st post), there is reinforcement in the upper AF octave and that's what attracts users...

Ultimately, as you note, it's good to have extended HF response for exactly the reasons you mentioned -- rather than hoping for actual musical content in the 50kHz region!