[ETM]

This is to announce the release of the book:

CURRENT-DRIVING OF LOUDSPEAKERS:
Remedy to the Fundamental Fallacy of Sound Reproduction Technology
by Esa Meriläinen





Softcover, 342 pages, available at http://www.amazon.com/Current-Driving-Loudspeakers-Fundamental-Reproduction-Technology/dp/1448695325/ref=sr_1_1?ie=UTF8&s=books&qid=1254919079&sr=1-1

Introduction:

Why have the basic laws of electrodynamics been disregarded in the design of loudspeaker operations? A frank exposure of the flaws of voltage drive and a thorough, groundbreaking guide to the physically reasonable way of operating electrodynamic loudspeakers - current-drive. The author argues that the sound quality of virtually all existing speaker systems has been severely impaired by the manifoldly indefinite electromotive forces induced in the voice coil (arising from both motion and inductance), that corrupt the flow of current; and what's dramatic - the measurable evidence is plain and overwhelming! These inherent EMFs in themselves can never be suppressed by any kind of amplifier, but their detrimental effect on current and hence on sonic performance can be eliminated by adequate source impedance. Thus, the secret of valve amplifiers also becomes apparent. Written for all from the academic community to lay hobbyists. Besides new concepts for amplifier and speaker design and demonstrative projects, the book also features novel ideas for modelling, filter design, measurements, and protection; and a useful tutorial on analogue linear systems. For more details, visit www.current-drive.info.

From the back cover:

Is it indeed possible that all audio power amplifiers of the world operate and have operated since their inception - on an all wrong principle? Is it also possible that the sonic aberration caused by this gross technical mistake has substantially impaired our experience with loudspeaker-produced sound, with implications even on the musical evolution of our civilization?

According to laws of physics, electric current is that which in a speaker driver effects diaphragm acceleration, which in turn produces sound pressure. Yet all power amplifiers strive, often tooth and nail, to control the voltage at the loudspeaker terminals, which only indirectly affects the current flowing in the voice coil.

Current-controlling loudspeakers is nevertheless not an all-new concept. Some of the benefits it brings, like decreasing of harmonic distortion and expanding of frequency range, have been known at least by specialists. However, there prevails great ignorance about the many grave interference mechanisms that traditional voltage drive inevitably creates and that are fully or partially eliminable by correctly operating current-drive. Also, current-drive does not necessitate active speakers any more than voltage drive does, but amazing improvement in sound quality is achievable by simple means. Based on properties of linear systems and investigation, many other flawed conceptions prevalent in the field of audio technology are also pointed out.

When writing this, virtually no full-range audio equipment operating on the current-principle has yet been seen on the market. One reason may be that controlling the resonance of the bass driver under current-drive has been considered difficult. To resolve this, new handy techniques and circuits are introduced, so that technical obstacles for the extensive utilization of the current-principle are cleared away. Also, it is shown that so-called electrical damping, that pertains to voltage drive, is in reality totally inoperative outside the fundamental resonance region.

The book has been written out with easy-to-understand language for both professionals and interested laymen, so the novel amplifier and loudspeaker realization concepts are made available to all. An ordinary circuit simulator can be used also for predicting the acoustic response, without need for special software. In the appendices is provided valuable basic knowledge about analogue systems.
_____________

Questions and feedback are welcome either here or through my website.

Esa M,  the author

[ETM]

Why such a silence when some essential truths about the operation of our basic necessities are being disclosed?

[Niteshade]

I must say- this is very intriguing.

[planet10]

Cool. I'll see if someone can get it for me for xmas. Available anywhere besides amazon?

Many of the loudspeakers i build prefer amps that at least tend towards preferring current drive.

We have a prototype variable transconductance amplifier that lets us dial in the output impedance. Every speaker seems to prefer a specific setting. Firstwatt F2 clone also in the queue.

dave

[Niteshade]

I should have asked if you would have like to talk about this in the Lab circle yesterday. Your concept is very interesting and a little controversial (a good recipe for lively discussions). Anything about feedback usually is.

Why such a silence when some essential truths about the operation of our basic necessities are being disclosed?

[ETM]

We have a prototype variable transconductance amplifier that lets us dial in the output impedance. Every speaker seems to prefer a specific setting.

Interesting. The observations that speakers seem to prefer different impedance settings, instead of the maximum impedance, are generally due to the frequency response that changes in accordance with the speaker's impedance curve. For such a comparison to be fair, the responses should be equalized in each case which is not an easy task.

I should have asked if you would have like to talk about this in the Lab circle yesterday. Your concept is very interesting and a little controversial (a good recipe for lively discussions). Anything about feedback usually is.

Yes, I would like to talk where I can, but I'm rather slow in writing, and advertising is allowed only here.  I intend to open some topics as soon as my time allows. (You are also welcome to do so.) I have also addressed the seeming controversies in the book quite thoroughly.

[JoshK]

So the idea is that a high output Z from the amp is good, i.e. a low dampening factor. That is quite interesting.

[ETM]

That's the main point, but it's not only the amp but also other impedances seen by each driver in the passive circuitry that count.

Thus, ideal current-drive has to be compromised somewhat when using passive crossovers and/or response shaping, but exactly the same also holds true if one strives for voltage drive.

[turkey]

Why such a silence when some essential truths about the operation of our basic necessities are being disclosed?

The title of the thread promises secrets will be revealed. So are you a proponent of tube amplifiers, or do you point out a fatal flaw with them?

[Occam]

So the idea is that a high output Z from the amp is good, i.e. a low dampening factor. That is quite interesting.

aka 'hard' amps, with output Z of the amp matching that of the LS. Quite common at the movieolas of the 30s-40s typically with a WE91a driving.

Interesting tome. A rigorous mathematical analysis of this could lead to interesting insights.

[TONEPUB]

So when will your awesome line of speakers that will destroy everything on the market
be available for purchase?

Considering everyone else that's made speakers for the last 100 years is wrong, you
should be a very rich man soon.

Will you be showing at CES this year?

[ETM]

Sorry about this delay in responding. I was on a visit.

The title of the thread promises secrets will be revealed. So are you a proponent of tube amplifiers, or do you point out a fatal flaw with them?

No, I'm not advocating nor speaking against tubes or any special devices. What I am implying here is that the difference in perceived sound quality between tube and solid state amps (often in favor of tubes) has a very understandable technical explanation, that is related to the output impedance of the amplifier and how this impedance is able to keep down the detrimental EMF-derived current components that form a very considerable part of the total current in conventional designs at all frequencies. Tube amplifiers usually exhibit output impedances of several ohms, which is already enough to attenuate these EMF currents somewhat and bring about a noticeable difference.

So when will your awesome line of speakers that will destroy everything on the market
be available for purchase?

I'm not a businessman, and currently I don't have plans or resources to come forth with a commercial product line. Instead, I'd rather see some existing or emerging manufactures take advantage of the huge opportunities that the concept offers and possibly also of my circuit ideas. If there seems to be no response within a few years, then I may have to find some partners to begin some production.

[HAL]

I just received the book and will be reading it over my holiday week off.  Very interesting concept.

[planet10]

My copy should arrive just after the new year.

dave

[planet10]

So when will your awesome line of speakers that will destroy everything on the market
be available for purchase?

Considering everyone else that's made speakers for the last 100 years is wrong, you
should be a very rich man soon.

Jeff,

You are sounding a bit sarcastic

As mentioned earlier in the thread, it was common practise at one time... the trend towards high damping factor amplifiers really started with the conjunction of the acoustic suspension loudspeaker & the solid state amplifier. This is the big right turn that almost the whole industry took (some say wrong turn). So 100 years is not accurate. The AR1 started shipping in 1954 (same year i was hatched) so something like 50 years is more accurate. Recent trends are eating away at the end of that.

ETM's stuff isn't new, it is topical and reinforcement for a growing trend.

Talk to a Western Electric engineer, and the right way was to have the amps output impedance was equal to the loudspeaker.  A long chat with one of the last of these engineers (from an introduction by Lynn Olsen) some 10 years ago got me onto the path of designing loudspeakers that like high output impedance amplifiers.

Along the way encouragment from the work of Thorsten Loesch & Nelson Pass didn't hurt.

This is a very valid approach, but is very much a systems one. Amp, speakers (and the cable connecting them) have to be considered as one (as it should be).

You should get someone to build you a set of Fonken with the full zoot drivers... you might be surprised. You would have to pull out some high output impedance amplifiers thou.

dave

[MaxCast]

I have removed a couple of posts as this is a for sale ad and not a discussion thread.
Perhaps Mr. Esa M would like to start a discussion thread here
http://www.audiocircle.com/index.php?board=122.0
or anyone, a specific topic in the Lab.
http://www.audiocircle.com/index.php?board=20.0

Thanks,

[AmpDesigner333]

I experimented with this a bit in the late 80s.  There are practical concerns for such a design, such as stability.  The topic also came up a few years ago when I was discussing electrostatic speakers with a friend.  The idea is that an electrostatic transducer is closer to pure voltage-to-displacement action than cones, for example.  Unfortunately, the voltages are quite high.  During this discussion, the issues with current drive came up, most importantly, the crossover.  Better to try this with an amp per transducer.  By the way, voltage to current circuits are not trival in nature.  Just my 2 cents...

[ETM]

In general, loudspeakers have to be designed for current-drive use to get the full benefit, existing gear is seldom suitable as such.

By using output impedances of the same magnitude than the speaker impedance (as in some speciality designs), remarkable improvements can surely be gained, as the EMF interference currents are about halved, but this is not yet current-drive though a few steps toward it has been taken.

In current-drive design, the goal is to keep the impedance seen by the drive unit as high as possible. Also, with infinite output impedance, there is not necessarily need to "match" amps with speakers any more than there is such need in voltage drive. The contact resistances and other series impedances of the speaker connectors, cabling and possible switches and fuses can also be virtually forgotten.

There are practical concerns for such a design, such as stability.

True, but by using a compensation network at the output, the feedback and load seen by the amplifier can be made nearly resistive at high frequencies, so stability issues can be managed, and such networks are commonly employed in voltage amplifiers too.

[AmpDesigner333]

In general, loudspeakers have to be designed for current-drive use to get the full benefit, existing gear is seldom suitable as such.

By using output impedances of the same magnitude than the speaker impedance (as in some speciality designs), remarkable improvements can surely be gained, as the EMF interference currents are about halved, but this is not yet current-drive though a few steps toward it has been taken.

In current-drive design, the goal is to keep the impedance seen by the drive unit as high as possible. Also, with infinite output impedance, there is not necessarily need to "match" amps with speakers any more than there is such need in voltage drive. The contact resistances and other series impedances of the speaker connectors, cabling and possible switches and fuses can also be virtually forgotten.

There are practical concerns for such a design, such as stability.

True, but by using a compensation network at the output, the feedback and load seen by the amplifier can be made nearly resistive at high frequencies, so stability issues can be managed, and such networks are commonly employed in voltage amplifiers too.

The technical issues seem to mushroom with this, but still, it's not rocket science.  Do you have some plots you can share?  Something like a microphone-recorded-speaker waveform comparing voltage drive versus a current drive?  Thanks.

[AmpDesigner333]

...infinite output impedance...

Can you explain the phrase above a little more?