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Coytee

Tweeter question...

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Long long ago, I had a question that I put to a physics teacher in college.  (he had stated he was into music)

 

I stopped by his office and posed the following.  I'm sure I don't know enough to ask it intelligently

 

If you have a system capable of playing for example, 20-20K (insert any value you want, the absolute values are not important)

 

If you could swap the 20 Khz for a theoretical tweeter capable of say, 50K, I understand that the common man wouldn't hear it.

 

Here's what I'm wondering, if you swap a 50Khz tweeter for the 20Khz tweeter, the higher driver can move faster.  

 

Since it can move faster, it should be able to articulate or color in more accurately, the inner detail compared to the lessor tweeter.

 

He said "Richard, what you are asking, is a POWER question" and got onto some answer that flew right over my head.  I said back, no....I THINK I'm asking a frequency question....

 

He reiterated that I was asking a power question, repeated his answer and I walked out shrugging my shoulders.

 

 

So, would a tweeter capable of higher frequencies, yet, limited to the same range as the 20Khz tweeter, be able to play the inner detail better because it's a quicker driver?

 

(if possible, the question is presumed with all things equal)

 

 

 

 

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I don't see any benefit in getting a tweeter to 50 kHz.  It's like a car that can go 500 mph and the usable terrain won't let you go past 150 mph.   The extra is a waste and will not make it operated better at 150 mph.

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Maybe the question is whether the 50k tweeter has better transient response than the 20k tweeter.

 

My guess is that it would, but I'll guess that our eardrum and middle ear are still the limitation.

 

OTOH, in practice it could be that the 20k tweeter is getting weak even at 10k and so maybe the 50k tweeter is doing better down there.  Maybe.  Maybe.

 

WMcD

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I would rather see someone make a cluster of tweeters to faithfully reproduce a standard cymbal hit in your living room. So you would roughly need about 20 inches of tweeter diaphragms to match the output of the cymbal. Now you have something that can give the subs a run for their money. Then take it up to 50K capability.

JJK

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Maybe the question is whether the 50k tweeter has better transient response than the 20k tweeter.

 

I have no idea, but wouldn't the quality of transient response be a result of things like diaphragm material, voice coil size and weight, gap size, magnet weight, etc., rather than how high it goes?  Or are they (all?) co-variates?

 

As to whether we can benefit from being able to actually hear or reproduce sound above 20K, I doubt it.  Audyssey claims that most movie soundtracks sound better with the treble rolled off (-2 dB @ 10K, and -6 dB @ 20K).

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A typical cymbal crash has a ton of energy around 200hz.

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So, would a tweeter capable of higher frequencies, yet, limited to the same range as the 20Khz tweeter, be able to play the inner detail better because it's a quicker driver? (if possible, the question is presumed with all things equal)

 

This is the rationale used by the makers of these type of "super-tweeters" (as they are apparently known in Japan and elsewhere) to sell more of their extremely high priced devices.  So if you are making an argument to buy one, understand that there are some other issues to deal with to actually use them:

 

1) Crossover frequency--most of these super-tweeters require you to cross over at something like 8-10 kHz.  A rule of thumb is that you need to be within 1/10th of a wavelength with the midrange or "regular tweeter" at the crossover frequency in terms of phase/time alignment.  If using 10 kHz as the crossover and the 1/10th rule of thumb, your looking at something like 1/8th of an inch (0.135") alignment requirements.  If you are able to align that at some point in the room--a sitting position, perhaps--by the time that you simply stand up, you're probably now out of phase by more than 1/10th of a wavelength, and probably approaching 180 degrees (0.7 inches).  That's a good reason to have the supertweeter integrated into a dual diaphragm full range HF driver, like a BMS 4592ND, etc.

 

2) You said nothing about the polars of said super tweeter.  All the devices that I've seen are of the "bullet super-tweeter" variety, which means that they have extremely poor polar coverage.  YMMV.

 

3) CDs and phonograph records don't do much above 16-18 kHz, as I've found using Audacity to remaster recordings.  In fact, I've found that the loss of subwoofer frequencies (below 32 Hz, etc.) to be much more objectionable.  I'd worry about faithfully restoring that octave (15-30 Hz) before I'd worry about anything above 20 kHz.  (SACDs and DSD formatted digital downloads are actually worse than red-book CDs in the highest octave--and not a lot of people know about that issue.)  The only formats that I see that can exceed the 20 kHz limit in terms of fidelity are DVD-As and digital music files running 24/96 PCM.  Using higher sampling rates of 24/192 actually create their own problems.  However, typical recording microphones have issues capturing those frequencies and most record corporations do an extremely poor job of transferring those frequencies unmolested to the consumer.

 

4) As we age (I know--it sucks), we begin to not be able to hear those frequencies, and if you're male, it's much worse than if you're female in terms of HF hearing loss - about an order of magnitude.  Right now, I'd bet that you're having trouble hearing much above 11 kHz.  Bummer. If fluorescent lights and older tube-type televisions still drive you nuts, then you're hearing 16 kHz (actually very high SPL at 16 kHz, at that). 

 

 

To answer your question: what you're describing is mass roll-off in the tweeter, leading to phase shifting as the frequency increases.  The problem is that humans cannot hear absolute phase, only relative phase (i.e., tweeter vs. midrange in their crossover band, etc.).  So with all that work and money to get something that is radiating acoustic frequencies above 20 kHz, all you're probably doing is ruining your dog's or cat's hearing.  Certainly, any young people (below 25 years of age) will probably be cringing while you're smiling...and you're not really hearing but perhaps feeling those high frequencies between 10-20 kHz, assuming that you've got a player and recordings that consistently take you that high, cleanly.  Remember that the recording, mixing and mastering engineers, plus the digital disc or vinyl pressing plants faithfully follow through without attenuating--all these entities have to not mess it up in order for you to hear those extreme high frequencies as they might have occurred in real life.

 

If you were going to fix the above issues first, and fix all of them well, then you might begin to be worried about a super tweeter.  I'd call the notion of needing a super tweeter as the real-world analog of "liberal world-gestalt thinking", in other words, thinking that you're solving a system-level issue, but really just making it worse.  ;)

 

Thanks for asking that question, Richard. :emotion-21:

 

Chris

Edited by Chris A

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A typical cymbal crash has a ton of energy around 200hz.

 

That's very interesting. I still wonder if anyone has tried using about 20 tweeters on one channel to see what you get out of it.

JJK

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It was the realism (to my ears) of cymbal crashes that astonished me with the performance of the CT-125 tweeter. IMO it is a head and shoulders improvement over the K-77 and i also preferred the CT-125 over Beyma. 

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" I still wonder if anyone has tried using about 20 tweeters on one channel to see what you get out of it."

 

Richard Burwen did, see the 20,000 watt home hi-fi.

 

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