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Old 30th January 2014, 08:01 AM   #1
Bonsai is offline Bonsai  Taiwan
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Default Current drive for Loudspeakers

In this thread we will discuss current vs voltage drive of loudspeakers in an open and friendly way.

Here is the EDN article to kick the discussion off.

http://www.edn.com/design/consumer/4...-voltage-drive

I've put it here under solid state since we want to discuss not only the transducer and acoustical aspects, but also the amplifier and sensing requirements.


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Old 30th January 2014, 08:43 AM   #3
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It is a fashion topic now. Someone has realized that F = bli.
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Old 30th January 2014, 11:16 AM   #4
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Quote:
Originally Posted by Bonsai View Post
In this thread we will discuss current vs voltage drive of loudspeakers in an open and friendly way.

Here is the EDN article to kick the discussion off.

Loudspeaker operation: The superiority of current drive over voltage drive | EDN

I've put it here under solid state since we want to discuss not only the transducer and acoustical aspects, but also the amplifier and sensing requirements.


What about filters? It is all good-looking stuff when you use one speaker. How about calculate a filter for multi-way speaker? I bet all programs that are available for us assume Rout of amplifier to be zero or almost zero.

Last edited by Devilsdance7775; 30th January 2014 at 11:21 AM.
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Old 30th January 2014, 11:26 AM   #5
Bonsai is offline Bonsai  Taiwan
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You are probably right.

If this current drive is to ever take off, it will mean a that speakers have to be characterized differently (or at least additional parameters will have to be provided).

I think this technique will probably also require some feedback mechanism - perhaps an extra winding on the voice coil for example. Ideally you want to control accurately the instantaneous position of the diaphragm. Difficult in practice, but not insurmountable. Don't know how this would work at HF though.

A technique probably suited to a DSP approach.
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Old 30th January 2014, 11:33 AM   #6
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I see no other chance than active crossovers + DSP. Otherwise this current drive concept brings much more troubles than benefits. A new bubble.
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Old 30th January 2014, 11:44 AM   #7
Bonsai is offline Bonsai  Taiwan
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Perhaps, but I expect that it is a technique that can only now be explored and a reasonably economical solution developed

Sensor + A/D + DSP + class D

Mount the whole thing inside the speaker behind the magnet assembly.
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Old 30th January 2014, 07:05 PM   #8
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Default some thoughts on Merilainen and current drive

I stand back in amazement at how many people, including knowledgeable engineers, are so dismissive of the work of Esa Merilainen. It is really obvious that they 'know about' this, but have never experienced it or worked with it. From my perspective, this argument reminds me of the story of the parade of circus elephants where everyone in the parade is holding the tail of the elephant in front of him: bitching about the smell and the view, but afraid to let go. So everyone in the parade criticizes the elephant goes of in a different direction, and achieves significantly different results.

Esa's work deserves some serious consideration and experimentation before all these judgements are given forth. The list of experts picking at his article in EDN is just amazing. I think he has delivered some of the most constructive, new thinking in a very long time. His comprehensive analysis of the problems that occur with voltage drive is very complete. Many of these problems are either greatly reduced with current drive, or disappear altogether. Have you actually read his book? Or do you just know that current drive can't work? Have you actually experimented with it and done some listening tests? Based on the most of the published comments the answer is obviously NO.

PMA: At the risk of offending, I think that problems of inductance, and especially resonances CANNOT be 'fixed' with a DSP. Chopping holes in the audio program just adds insult to injury. It does simply not fix the resonance problem(s), any more than the elaborate 1/3 octave filters of yesteryear did. Those who believe you can deal with resonances with a DSP have a very poor understanding of what resonance is and how it works, but then the audio business has always been very long of selling 'band-aids' to fix its perceived problems.

As far as it being a fashion topic: F=Bli ... I don't see a term for voltage anywhere in that formula! Maybe in fact, it is a direction worthy of serious exploration. I find it to be some of the most promising and exciting work I've done in a long time.

Loudspeakers are one of the nastiest, reactive loads you can place on an amplifier. And nearly every amplifier made today has global feedback right on its output ... so all the load caused foibles are introduced back into the amplifier ... which is my opinion, functions as an active distortion generator as a result. I'm convinced that this is the major cause of active distortion in music playback today. Lowering source impedance, and fancy speaker wires do not correct phase shifts and other problems in the loudspeaker.
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Old 30th January 2014, 07:28 PM   #9
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Originally Posted by LdSpkrPro View Post
The list of experts picking at his article in EDN is just amazing. I think he has delivered some of the most constructive, new thinking in a very long time.
There was very little new in there that hadn't been covered thoroughly by Mills and Hawksford.

My first exposure to the concept was from Nelson Pass. It looked interesting and I spent some time playing with it. I came away convinced that you could make it work well if you could design a driver from the ground up. Better than voltage drive? Maybe not.
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Old 30th January 2014, 07:36 PM   #10
jcx is online now jcx  United States
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Default it really isn't 1980 anymore

and even then this was quickly shot down
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...And nearly every amplifier made today has global feedback right on its output ... so all the load caused foibles are introduced back into the amplifier ... which is my opinion, functions as an active distortion generator as a result...
wrong - no one with actual engineering understanding of audio power amps, feedback theory, global feedback is going to talk about the issues this way

this is straight out of the 1970's-80's - repeated "theories" put forth to build egotistical Audio Guru's names, then analysis, peer reviewed replies, with hardware tests, real measurements showing the "theory" is vapor - effects in the noise with "conventional engineering" practice
you can search the AES eLibray for “interface distortion” or interface IMD as a directly relevant example of buzzword invention, self promotion, over issues covered by engineering textbooks for decades preceding

I suggest as long as you're into books try Cordell, Self's latest editions, anything on feedback by Putzeys

Last edited by jcx; 30th January 2014 at 07:39 PM.
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