STAHL - 'Acebass' Synthesis of Loudspeaker Mechanical Parameters by Electrical Means

[forr]

GI
>Is it available? Can it be DIY'd?

Yes.
See US patent n° 5,206,912 by Masao Noro
at Patents Free On Line.

It consists in the inclusion of an op-amp ahead of the power amp. with an overall feedback about 26 dB around the whole and a local feedback of around 20 dB (network applied to the - input made a 10 kOhm and 1 kOhm) and around the op-amp. In parallel with the 10 kOhm resistor, there is a capacitor of 6 nF which limits the open loop bandwidth to 2.65 kHz -3 dB/o to maintain stability As the system is only going to work at low very low frequencies only, this is sufficient and most power amps should work ok.
The patent is not limited to this clever tip.

As always when dealing with negative resistance, include overcurrent protection at the output of your power amp. A polyswitch or two 12V car lamps were recommanded by Ian Hegglun for such experiences ("Speaker Feedback", Electronics World, may 1996, p378-382) to protect the voice-coil of your loudspeaker to be burnt. I suggest you start with low cost units to see how spectacular the results can be.

~~~~~~~~ Forr

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[consort_ee_um]

As Hegglunds article points out this idea has been re-invented every 10 years from the golden age of hi-fi in the early 1950's
I am surprised that nobody has mentioned the Audiopro subwoofers that were the result of Stahl's work. Stahl took the negative resistance idea a stage further and electronically tweaked the compliance and moving mass.
Also surprised that nobody has mentioned the key reason for using negative resistance, that is to match the Qts (more correctly the Qes) of a particular drive unit you like to a cabinet size that you might have already.
Rod Elliott has an article on this:
http://sound.westhost.com/articles/cscaling.htm
but he does not mention that you can reduce the Qts of a driver by negative resistance. This has the beneficial effect of damping the bass response

[Svante]

I wrote a short text on AC-bass in the tech docs of Basta!

[forr]

consort_ee_um

Find below what Elliot has written about negative impedance amplifiers.

http://sound.westhost.com/z-effects.htm

He used to have a much larger article on the subject, which seems not to be anymore on his site, and was not keen on the technique. I think that he never undertood how to use it. Commercially they are at least two huge successes using it, Audio-Pro (sorry, not mentionned probably because not DIY) and Yamaha (sorry, mentionned because it's a well known company...) .

Note that positive feedback and negative resistance may probably beknown before negative feedback.

~~~~~~ Forr

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[consort_ee_um]

Yes, Rod does not like the technique but it works for me
See Gainclone with negative output impedance
Scroll down to Moamps posting for my humble contribution

[phase_accurate]

I once built such a thingie. The result was quite astaounding. With today's wide availability of specialized subwoofer drivers I wouldn't use it anymore.
AFAIK not even Sonab (the owner of the trademark AudioPro) uses it anymore.
I have both articles (i.e. Stahl and Normandin) on photocopy and I copied them from the Journal ond not convention preprints. I can have a look when they appeared if someone is interested.


Regards

Charles

[Mobster]

Originally posted by phase_accurate
AFAIK not even Sonab (the owner of the trademark AudioPro) uses it anymore.

But all AudioPro subwoofers are still using AceBass (I've got one of those in my second system). I don't think Sonab (brand) never used this technology.

[phase_accurate]

But all AudioPro subwoofers are still using AceBass

Wasn't aware of that ?

Regards

Charles

[mike.e]

phase_accurateYes its true check out audiopro.com ,little 8" subs n things with acebass

[phase_accurate]

Yes I have seen it in the meantime !
I just haven't seen those a while a go ehan I visited the website and thought they didn't use the principle anymore.
I also mixed up Sonab and AudioPro.

Are you still interested in the papers BTW ?

Regards

Charles