STAHL - 'Acebass' Synthesis of Loudspeaker Mechanical Parameters by Electrical Means - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th September 2005, 02:22 AM   #1
mike.e is offline mike.e  New Zealand
diyAudio Member
 
mike.e's Avatar
 
Join Date: Sep 2004
Location: NZ
Send a message via ICQ to mike.e Send a message via MSN to mike.e
Default STAHL - 'Acebass' Synthesis of Loudspeaker Mechanical Parameters by Electrical Means

: A new Method for Controlling Low-Frequency Loudspeaker Behaviour

$ 20 for non AES members.
Worth buying? Does it present a practical evaluation circuit?

I can see the merit for high Qes drivers forced electronicalyl to be low Qes,but is there some disadvantage apart from complexity?

Ive seen the experimental schematic as available in HIGH PERFORMANCE LOUDSPEAKERS edited by MARTIN COLLOMS.

Seems interesting to adjust amplifier output impedence to negate Loudspeaker Re,but then also adjust CMS etc(directly or indirectly?)

Im interested in both servo and this issue wrt transient response and resonance of bass units.

http://www.aes.org/publications/prep...nts_search.cfm

Mike.e

Quote:
ACE-Bass is a really effective alternative to MFB.

http://www.diyaudio.com/forums/showt...363#post360363

I've built a few sub boxes over the past 10 years using ACE-Bass, from twin 6.5" to quad 10", with 3db points as low as 20Hz.

The degree of control the electronics has over the cone is quite staggering. If you try to manipulate the cone with the system on, it actually feels heavier, stiffer, more damped, with a lower Fs (assuming you choose to increase all of these terms).

You just have to listen to one of those little Yamaha subs to realise that for such a small driver, being driven hard in a small box, the LF extension is quite impressive. Applying the technology to less compromised drivers running a much larger headroom results in very impressive performance, especially if dual subs are arranged in push-pull fomat.

If you look at Stahl's original AES paper on the technology, he prints some fine examples of measured improvement in performance and range extension, comparable to the best commercial MFB systems.

No messing around with accellerometers, and the system works great with a vented box, giving plenty of efficiency down low (if you choose that avenue).

For the DIYer, I think it would be much harder to get better performance from a MFB system compared to an ACE-Bass system design with the same effort.
http://www.1388.com/articles/tech_Ace-Bass/
Quote:
Synthesis of Loudspeaker Mechanical Parameters by Electrical Means: A new Method for Controlling Low-Frequency Loudspeaker Behaviour
A method for extending bass response and lowering distortion in louspeaker systems, which differs from both equalized and servo or feedback systems, is described. It can be seen as an extension of the technique to increase loudspeaker damping by giving the driving amplifier a negative output resistance. However, this method also controls the moving mass and compliance. Very good results, such as flat frequency response down to 20 Hz and excellent distortion data, have been achieved with moderately sized bass-reflex enclosures.
Preprint Number: 1381 Convention: 61 (October 1978)
Author: Stahl, Karl Erik
E-lib Location: (CD aes9) /pp7680/pp7811/1483.pdf
downloadable electronic version PDF (642 KB) $5.00 AES Member | $20.00 Non-Member
hard copy $5.00 AES Member | $20.00 Non-Member
  Reply With Quote
Old 16th September 2005, 06:54 AM   #2
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
This article was also in the Journal (maybe even in a nicer form than the preprint) where I copied it from.
Is there any Library around where you can get the JAES ? I can find out what year and issue.

Regards

Charle


BTW: The patents are also quite explicit.
  Reply With Quote
Old 16th September 2005, 02:27 PM   #3
forr is offline forr  France
diyAudio Member
 
forr's Avatar
 
Join Date: Dec 2004
Location: Next door
The AES papers are horrendously expensive. For a little more than $ 20, you can get the full AES anthologies from AudioXpress, that's a lot of good reading.

The Stahl idea is described in a patent you can find at Free Patents On Line. The AES paper is not very different. Have a look to other patents using similar ideas, too (Barbetta, Hahne, Nagi, Saville, Walker, Massao, Yamaha...)

The Stahl patent is in fact partly based on Voigt ideas which are anterior to Black's (negative feedback) and Rice and Kellog's (electrondynamic loudspeaker) patents.

I agree with all Mile.E. wrote


Stahl's basic idea is as genious as simple.
An amplifer and the loudspeaker connected to it must be considered a whole, not as two separate entities. This is evident when one considers that loudspeakers parameters are electro-mechanical parameters.

In Stahl and similar embodiments, the electronics circuit can be considered as having two imbricated parts. A first one is an amplifer with a standard negative feedback loop and a with second feedback loop, positive, which cancels the Re of the loudspeakers by the effect of negative impedance. Then we can consider we have a direct access to the Les, Res and Ces of the loudspeaker. Voltage directly applied to this impedance defines the cone velocity.

A second loop around the amplifier and using op-amps at its input defines its own complex impedance which comes in parallel with the loudspeaker one
(remember : a perfect voltage amplifier has zero output impedance, it can be considered as a short circuit generating voltage) . Then the electro-mechanical parameters of the whole system can be modified at will, in certain limits of course.

Some details to look after :
- the resistor sensing the current to generate the negative impedance should have the same temperature sensitivity as the voice coil. It seems this has been very well engineered by Yamaha.
- just as in motion feedback systems, an important problem is the inductance of the voice coil, Le, and its cancellation : its value is not constant with frequency and with the position inside the gap.


Negative resistance of amplifiers is obtained by positive feedback. It is very easy to obtain it, without using an additionnal op-amp, by bootstraping with adequate resistors the input of the amplifier with the voltage accross the sensing resistor (overcurrent precautions are mandatory).

I have a strange point of view about negative resistance amplifiers. From the amplifier input, there is positive feedback, yes. But viewed from the impedance of the loudspeaker, it can be considered a negative feedback : the current through it decreases as its impedance increases. Then I tend to consider Stahl system as a kind of motion feedback system, disagreeing with his comment who said it is not. This is not an important question.

By controling the impedance of the amplifier, you can much extend the possibilities of a given loudspeaker or adjust it more adequately to your needs. Because it deals with the essential parameters of loudspeakers, I think it is a more interesting area to investigate than the endless discussion about the sound of amplifiers and the supposed horrible effects of feedback.


~~~~~~ Forr

  Reply With Quote
Old 16th September 2005, 07:39 PM   #4
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
I agree that the AC-bass technique is a very nice piece of engineering. I work at the department where Sthl made his master thesis, but that was before my time there. Recently there has been a few DIY projects on swedish audio fora, building ACE subwoofers. The guy I share office with has even tried a DSP implementation of ACE, which is pretty cool. The parameters (Mms, Cms etc) can be modified in real time with a slider on the computer screen.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  Reply With Quote
Old 16th September 2005, 08:12 PM   #5
forr is offline forr  France
diyAudio Member
 
forr's Avatar
 
Join Date: Dec 2004
Location: Next door
Hi Svante

"The guy I share office with has even tried a DSP implementation of ACE, which is pretty cool. The parameters (Mms, Cms etc) can be modified in real time with a slider on the computer screen."

This could be a very useful tool to study psychoacoustics : for example, with a closed box, what are the just noticeable difference for Qtb, resonance frequency fb, etc..

I just had a look at your simulation tools. Great !

~~~~~~~~ Forr

  Reply With Quote
Old 16th September 2005, 10:13 PM   #6
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
Forr, thanks!

Indeed it could be used for psychoacoustics tests, but I wonder if it wouldn't be easier to just calculate the response difference and simulate that. But definitely, having two of these systems would be great to compare different design parameters perceptually.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  Reply With Quote
Old 17th September 2005, 05:15 AM   #7
mike.e is offline mike.e  New Zealand
diyAudio Member
 
mike.e's Avatar
 
Join Date: Sep 2004
Location: NZ
Send a message via ICQ to mike.e Send a message via MSN to mike.e
Quote:
Originally posted by phase_accurate
This article was also in the Journal (maybe even in a nicer form than the preprint) where I copied it from.
Is there any Library around where you can get the JAES ? I can find out what year and issue.

Regards

Charle


BTW: The patents are also quite explicit.
ahh http://www.freepatentsonline.com/4118600.html !


Its not actually in the AES papers that I can see,we have 1978-1997 at UNI,I checked 78 and 79,not there in the articles anyway. Is that where I find the patent number?

Quote:
Recently there has been a few DIY projects on swedish audio fora, building ACE subwoofers. The guy I share office with has even tried a DSP implementation of ACE, which is pretty cool. The parameters (Mms, Cms etc) can be modified in real time with a slider on the computer screen.
Thats quite cool,it would certainly have its uses.
  Reply With Quote
Old 17th September 2005, 08:21 AM   #8
Svante is offline Svante  Sweden
diyAudio Member
 
Svante's Avatar
 
Join Date: Feb 2004
Location: Stockholm
Quote:
Originally posted by Svante
Forr, thanks!

Indeed it could be used for psychoacoustics tests, but I wonder if it wouldn't be easier to just calculate the response difference and simulate that. But definitely, having two of these systems would be great to compare different design parameters perceptually.
Silly me, of course you need only one system, since you can change the parameters so easily.
__________________
Simulate loudspeakers: Basta!
Simulate the baffle step: The Edge
  Reply With Quote
Old 17th September 2005, 02:22 PM   #9
forr is offline forr  France
diyAudio Member
 
forr's Avatar
 
Join Date: Dec 2004
Location: Next door
"Synthesis of loudspeaker mechancical parameters by electrical means : a new method for controlling low-frequency loudspeaker behaviour"
by Karl Erik Stahl
The paper was presented at the 61st Convention of the AES, 1978 November 3-6; revised 1981 April 9.
Patents "ACE-bass method" :
USA 4,118,600
Sweden 7603585-6
The paper can be found in the AES anthology, volume 2, "Loudpseakers", pages 241 to 250.


Another interesting AES paper, explicitly based on Stahl's ideas :
"Extended low-frequency performance of existing loudspeaker systems" by R. Normandin which can be read in the AES Anthology, volume 3, "Loudspeakers" p61-65. The final embodiment needs two op-amps, a power amp, less than ten resistors and one capacitor.


Yamaha has patented a method where almost any kind of power ampilfier can be used, for example, one which the user already owns.


One of the most fascinating aspects of Stahl's ideas is that it can be applied to any kind of load : closed, bass-reflex, transmision line, etc...


~~~~~~~~ Forr


  Reply With Quote
Old 17th September 2005, 11:23 PM   #10
qi is offline qi
diyAudio Member
 
Join Date: Oct 2003
Location: .
Quote:
Yamaha has patented a method where almost any kind of power ampilfier can be used, for example, one which the user already owns.
Is it available?
Can it be DIY'd?

This is really cool shBLEEP
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
"Dainty" loudspeaker parameters. ashok Multi-Way 24 26th December 2012 05:48 PM
Audio Synthesis DAX 2 at 24/96 Sandor Digital Line Level 8 16th October 2011 12:45 AM
Loudspeaker electrical damping zebra100 Multi-Way 1 7th July 2009 09:48 PM
< Synthesis Speakers > Terry Lukiwski Multi-Way 1 29th November 2003 11:47 PM


New To Site? Need Help?

All times are GMT. The time now is 09:44 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2