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  #21  
Old 11th January 2006, 01:19 PM
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Default Re: Super Tweeters

Don't forget that second order is 12dB per octave, so the contribution from the super tweeter is still highly audible at half the crossover frequency and still making a contribution at a quarter of the crossover frequency.

That is it is only a contribution if still phase coherent with the treble unit. If not, and this is quite likely, there will be peaks and dips in the response due to interference between the drivers.

Why do I say quite likely? Because the interdriver spacing is unlikely to offer a phase coherent array, no matter how much you make the crossover minimal phase.

And people wonder why super tweeters make a difference!
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  #22  
Old 11th January 2006, 01:26 PM
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Default Re: Super Tweeters

Quote:
Originally Posted by Global
An experiment!

Feed your 'supertweeted' system with a sine wave and then a square wave from a signal generator. Try 1KHz, 5KHz, 10KHz.

I think you will find you can tell the difference at 5 and 10 KHz even although the first harmonic of the square wave does not occur until 15 and 30 KHz respectively and you could not hear these frequencies in isolation.

I imagine that ears have some kind of undocumented 'accellerometer' function making the wave-shape significant.

But I could be just conning myself of course!.

Mark
Hi Mark

I've just noticed your idea, sorry not to comment earlier.

A 10kHz sine wave is quite a nice signal for an amplifier. A 10kHz square wave is a horrid signal for an amplifier. Assuming that your amplifier is not 100% perfect, i.e. it is bandwidth limited by feedback and perhaps oddities like output transformers, then it will produce some distortion components when fed by the square wave that it wouldn't when fed by the sine wave.

Could these be what you are hearing?

The ear, of course, has all sorts of undocumented features that we can only guess at. In principle it is a mechanical amplifier that is bandwidth and amplitude controlled by the gain lever of the bones of the inner ear under muscular tension. The cochlea converts the mechanical vibration into frequency selective nerve impulses through what seems to be a simple frequency filter to provide a form of fourier analysis. How the brain interprets these impulses is far more complex and IMO the brain, using its own filtering techniques, is able to decode far more information than you would believe is fed to it from such a crude mechanical amplifier and frequency analyser.

One thing the brain is VERY good at is pattern recognition. Give it part of a pattern and it will fill in the rest. But it has to be trained. So, if you go to a concert and 'learn' the harmonics of an instrument you can recognise it from hi-fi playback even though the harmonic structure may be slightly distorted or some harmonics may even be missing. For example many of us think we can hear the fundamental of a bass guitar at 44Hz even though our speakers are well down by that frequency. A strong second harmonic will help you 'hear' thunderous bass. The same can happen at high frequencies. There's a lot to explore here, but I would rather tackle the very real problems that amplifiers and speakers have before following a tangent that has minimal results.

In the Mission Pilastro we co-developed with DST a treble unit with a bandwidth of 3kHz - 56kHz. We didn't do it because of the extended response, though this was undoubtedly useful in marketing terms, but instead to reduce distortion within the audible bandwidth. I could go on, but I won't because this will make its way into a Hi-Fi World article on speakers in due course.

Last edited by petercom; 11th January 2006 at 01:49 PM.
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  #23  
Old 11th January 2006, 05:19 PM
Lord.
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Default Re: Super Tweeters

Peter (All),

This is a piece of research that has been referred to in similar discussions elsewhere:
Inaudible High-Frequency Sounds Affect Brain Activity: Hypersonic Effect.

Last edited by Lord.; 11th January 2006 at 06:39 PM.
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  #24  
Old 11th January 2006, 06:19 PM
Global Global is offline
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Default Re: Super Tweeters

Hi Peter

My post for this evening was going to be along the lines of "I wonder if tweeter dome breakup modes when trying to reproduce 30 KHz could output audible sound"?

Probably - and the amp too!

Mark
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  #25  
Old 12th January 2006, 04:02 AM
Chris Chris is offline
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Default Re: Super Tweeters

So how about a diy super tweeter?

Chris...
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  #26  
Old 12th January 2006, 08:11 AM
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Default Re: Super Tweeters

Put it on the wish list!
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  #27  
Old 12th January 2006, 08:59 AM
kgb144
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Default Re: Super Tweeters

Guys,

The phenomenon of augmented frequencies can be easily and regularly demonstrated by any competent singers. I sing in an a capella close harmony group and we normally perform in four voices; tenor, lead, baritone and bass. When a four part chord is accurately locked overtones and undertones can be produced, i.e. only four voices but five or six notes can be discerned. With overtones these are normally higher than the available voice range and with undertones these are normally lower than the available voice range. This is not a myth and we hear these fairly regularly during rehearsal.

It is the reinforcement of compatible frequencies that will enable supertweeters to augment bass and mid-band frequencies. I hope this helps.

Kind regards,

ft
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  #28  
Old 12th January 2006, 09:39 AM
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Default Re: Super Tweeters

Hmmm, I still don't get it, perhaps I'm missing something or can't see the wood for the trees. In FT's example, if FT's harmony group are recorded in a studio with a mike that has limited bandwidth, processed / mastered etc through all the studio layers and then bandwidth limited again for production on CD with a brick wall filter at 22.05KHz, when that CD is played back through a domestic hi-fi system the super tweeter is not going to be fed with anything above 22.05Khz, higher music correlated frequencies are simply not in the signal.

Now its possible that as FT says under and overtones are created in the room from the fundamental but I'm pretty sure the super tweeter is not producing them.
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  #29  
Old 12th January 2006, 10:08 AM
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Default Re: Super Tweeters

Here's a suggested explanation which seems reasonably logical:-
http://www.st-and.demon.co.uk/AudioM...coherence.html
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  #30  
Old 12th January 2006, 10:59 AM
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Default Re: Super Tweeters

Thanks John,

Which is the same more or less as Peter said in post #19. The enhancement or addition of a second tweeter in the audible frequency range is going to be heard even with CD. However, with CD there is still no output above 22.05KHz plus there are amplifier bandwidth considerations meaning these things may be just expensive tweeters (fashion fad?) and you could probably get similar 'enhancements' by using a standard tweeter with similar filters?
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