Quick question

Already anticipated. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Commonly done. That's why cars have as many as sixteen channel power amplifiers (as few as four is uncommon).

Den mandag den 30. juni 2014 01.07.38 UTC+2 skrev snipped-for-privacy@attt.bizz:

cars also tend to have many speakers placed all over the place

and I guess adding a few bits of silicon on a PCB is cheaper than inductors and capacitors for a speaker level cross-overs

-Lasse

[snip Google spacing]

Not only cheaper, but doesn't affect the damping. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Guess why?

Wrong again.

Den mandag den 30. juni 2014 01.55.42 UTC+2 skrev snipped-for-privacy@attt.bizz:

because the acoustics of a car is terrible ?

you can get automotive amplifier ICs for a $1, how much passive cross-over can you build for that

-Lasse

Because they (almost invariably, at least since DSPs got cheap, use active crossovers). To a lesser degree, they also use dual-voice coil speakers.

Utter bullshit. You forgot the wiring, connectors, weight, and all the rest of the costs.

pAmp with classic pole-splitting compensation.

edance fluctuations that will hurt the sound, but hurt it less if the ampli fier output Z is the same as speaker impedance (i.e. maximum power transfer ).

edance to be low, so that any variations in the impedance the >loud-speaker have minimal influence on the current through it.

of the amplifier negative, and numerically equal to the resistive part of the loudspeaker's input impedance.

power transfer" argument doesn't make sense for audio frequencies.

nce' is the energy-lost-to-sound-output component). Trust me, I've looked . So, (2) and (4) are about the same, until you hit a resonance (and one d oesn't know the speaker's resonance character when designing the amplifier) .

power output) nearly constant through frequency-dependent variance in Z_sp eaker. The 'maximum power transferred' implies d/dF (V_out * I_out) = 0 for that choice.

ative, in order to undo the wiring resistance of the speakers for enhanced low frequency drive. There actually were motion-feedback amplified speaker s made, that did that.

I thought that that was what I was suggesting - somewhat tongue-in-cheek.

In fact a serious speaker driver would control the current through the spea ker.

Provided that the speaker coil is immersed in a uniform magnetic field - wh ich is a big if - controlling the drive current directly controls the force acting on the moving diaphragm, and thus the sound output.

The one example of such an amplifier that I've worked on didn't drive a lou dspeaker, but drove the scan coils in an electron beam microfabricator to 1

8-bit accuracy at 10MHz - not that we changed the eight most significant bi ts all that often, and we did wait a millisecond or two for everything to s ettled down when we did.

The frequency compensation was tuned to match the coils we were driving - w ire tolerance introduce a +/-2% uncertainty into the coil characteristics, which we tuned out with a single trimming potentiometer.

I've forgotten the fine details, but I had to swap out the dry-reed range c hanging relays for mercury-wetted reeds. The series resistance of the dry r eeds varied enough from time to time to move our frequency compensation off dead-beat, while the mercury-wetted reeds contact resistance was a bit low er and much more stable.

--
Bill Sloman, Sydney

I think it is the bane of mostly physics types. We learn this impedance matching example which involves getting the maximum power from a battery, and then try and apply it everywhere. (Doesn't work...)

George H.

Hi Bill and others

Actually current driven dynamic speakers are way better than voltage driven speakers.

Speakers er naturelly current driven. I you drive them by voltage, the sound will be amplitude modulated by the coil heating. When the coil heats lower current for same voltage will result. Add a filter nework and you will complicate things further.

Prerequisite/requirements:

• No PA-output coupled speaker filters/network.

• Use (digital) electronic filters before PA.

• Benefit: You can use very thin speaker cables (one pair an one PA for each speaker; e.g. three pair and three PAs for a three way speaker). You do not need to deplete/drain copper mines and your wallet anymore.

How can audiophiles have overlooked this and have bought expensive BIG oxygen one-crystal copper cables which are "blessed" by some seller? OMG

-

Current-Driving of Loudspeakers Eliminating Major Distortion and Interference Effects by the Physically Correct Operation Method

Quote: "... 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. ...

**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-Driving of Loudspeakers: Eliminating Major Distortion and Interference Effects by the Physically Correct Operation Method Paperback:

October 22, 2013, Loudspeaker operation: The superiority of current drive over voltage drive:

Quote: "... The driving force (F), that sets the diaphragm in motion, is proportional to the current (I) flowing through the voice coil according to the well known formula F = BlI where the product Bl is called force factor (B = magnetic flux density; l = wire length in the magnetic field). B is the flux density that exists when the current is zero. (The current always induces its own magnetic field, which may react with adjacent iron, but the effect is not related to this equation.) ..."

February 2012, Additional thoughts on voltage, current and power drive to speakers. Article By David Berning of The David Berning Company:

Quote: "... So what really makes sense in terms of distinctions between voltage, current, and power drive to speakers? I have already implied that voltage drive is likely to over damp the speaker, while current drive is likely to under damp the speaker. Overdamping results in overly tight sound and underdamping results in loose undercontrolled bass. ..."

Current Source Amplifiers and Sensitive / Full-Range Drivers by Nelson Pass:

Quote: "... Most of the examples we will examine do not require true current source amplifiers, only amplifiers of quite high output impedances. Most of these cases will be happy with an output impedance of approximately 47 ohms or so and prefer 47 ohms loaded in parallel with the output of a current source. That being the case, you can build a Thevenin Equivalent of such a current source by placing a large resistor (here later referred to as R0) in series with the output of a high wattage voltage source amplifier and get similar results. ..."

Effects Of Source Impedance on Loudspeakers:

Quote: "... Does this mean that current drive can (or should) not be used? Of course not - current drive can do some useful things for loudspeakers, but none of these things are magic, and none will reduce the loudspeaker's distortion by any useful amount or create sound that is otherwise unattainable.

This article was originally prompted by a reader who did some simulations of a loudspeaker having no voice coil resistance. Of course, this is not possible, but driving with negative impedance can theoretically accomplish the same thing. ... Negative Impedance Drive at -3 Ohms ... The performance of this combination is completely unacceptable in every sense of the term. This combination could never be used in practice, for any reason. There is a vicious attack, with the signal doing something at a frequency completely unrelated to the input signal - unrelated in any way that I can determine, at least.

Considerable ringing is apparent (again at an unrelated frequency) when the signal is removed. This is highly visible and audible, and the sound of the attack and decay is grossly inferior to any other combination. The others (using positive impedance) have some character, but it is related to the signal, and makes some sort of musical sense. ... Overall, this exercise has simply proven that which has already been proven by so many before me ...

• Voltage drive is the best choice in the vast majority of cases

• Moderate values of positive impedance (current drive) can be useful - if the enclosure is particularly well damped

• Negative impedance is generally loathsome, and should be avoided ..."

Current driving:

Quote: "... The system, if current-driven, has a much better impulse response: impulse is narrow, is more linear and, above all, has a shorter decay. The woofer get faster (it seems like a tweeter); all this with damping factor zero. ...

**Conclusion 1: the current driving allows extraordinary musical performances due to his behaviour in time domain.**

Conclusion 2: the current driving allows higher results respect to voltage driving, because it is possible to use also impedance variations to model total response; complexity increases, but performances too. ..."

Glenn

Not good.

You can not, because the speakers impedance varies with speaker coil temperature (power history dependent for each speaker...)

To complicate matters: Do you want to the match "funny" (power history dependent...) voice coils or the acoustic impedance?

Might be the best - if used with a electronic filter before the PAs. One PA per speaker.

You can not, because the speakers impedance varies with speaker coil temperature (power history dependent for each speaker...)

To complicate matters: Do you want to the match "funny" (power history dependent...) voice coils or the acoustic impedance?

Not good - "funny" responses - see former separate reply.

Glenn

Low amp impedance (good damping factor) has been the historical goal, which is why even tube amps usually had negative feedback from the output voltage.

Low electrical drive impedance makes the voice coil a low mechanical impedance, which translates to stiff position control of the cone. Hi-Z drive lets all the speak bits resonate at will. Some people like the sound of boomy resonances.

A small negative amp impedance is probably ideal, to null out the ohmic part of the wiring and the voice coil. That would further reduce the mechanical impedance of the voice coil.

But it's just audio. I doesn't matter.

We've designed power supplies with negative output resistances, to improve regulation at the end of a cable.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

...

...

...

Hi John

Do you agree with this?:

October 22, 2013, Loudspeaker operation: The superiority of current drive over voltage drive:

Quote: "... The driving force (F), that sets the diaphragm in motion, is proportional to the current (I) flowing through the voice coil according to the well known formula F = BlI where the product Bl is called force factor (B = magnetic flux density; l = wire length in the magnetic field). B is the flux density that exists when the current is zero. (The current always induces its own magnetic field, which may react with adjacent iron, but the effect is not related to this equation.) ..."

-

Of cause the (many-way) speaker(s) has to be adjusted for good (time domain) impulse reponse - and frequency response - after applying current-drive of each speaker individually.

The current driven speaker has lower IM distortion and way better impulse response, which our ears among others uses for directionality of the original music.

Glenn

Sure, if you want frequency response all over the place.

Kevin Aylward B.Sc.

- SuperSpice

More:

October 22, 2013, Loudspeaker operation: The superiority of current drive over voltage drive:

Quote: "... This force, then, determines the acceleration (A) of the diaphragm, which in the main operation area (the mass-controlled region) is got from the Newtonian law F = mA. The radiated pressure, in turn, follows the instantaneous acceleration and not the instantaneous displacement, as many mistakenly imagine. ... There cannot be found any scientifically valid reasons that justify the adoption of voltage as the control quantity - it is only due to the historical legacy originated almost a century ago, most likely by cheapness and simplicity; the quality and physical soundness of operation have not been considerations in this choice. Engineers are also more accustomed to identifying electrical signals as voltages rather than currents. ..."

Glenn

Current makes the voice coil create force. Voltage makes it create position. What happens next is up to the cone and the enclosure. Typically, hi-Z drive boosts acoustic resonances.

I think speakars are usually designed assuming low-Z drive.

But it's just audio. It doesn't matter. Whatever you do, you'll probably like the way it sounds.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation

Just guessing but current drive need not automatically mean high source imp edance always? I guess some of these current drive scenarios might involve current sense feedback instead of voltage feedback. i.e. a fairly conventio nal amplifier is used but where feedback is taken from a low value sense re sistor in the speaker ground wire instead of output voltage feedback via a divider. The amplifier is then servoing speaker current to faithfully follo w the input. Should then still have plenty of muscle to damp speaker resona nces when they occur ??

But quality audio is a mystery to me so I am willing to be corrected.

piglet

Just found this:

The Mystery of the Current Mode Amplifier:

"The Linear Current Loudspeaker":

Quote: "... Oh dear! The Red line is the Voltage amp, the Green line is Unity Coupling amp and the bottom two Blue and Violet represents what Current amps would do.

So that is clearly not acceptable. But let us now look at what the different non-Voltage amplifiers do to the electrical phase. This is rather interesting: ... This is quite credible.

Here is the modeled impedance and phase plot: ... Now for the impedance and phase plot, the actual measured result: ... This is simply stunning. Right now I have a smile on my face. Again, if I may repeat, I do not know of anybody else who has achieved such a result and I have been doing speakers for more than fourty years. BTW, the electrical phase plot, there is no point showing it as it just gets flatter, flatter and flattest. At 33 Ohm it is ruler flat.

I will do the ultimate test a little later using one thousand Ohm. ... The Linear Current Loudspeaker finally puts the nail into the ?damping factor? coffin. I read a review of an amplifier in the latest Hi-Fi World where it was extolled for having a damping factor of over 200. If that is so good, then what happens when we have a damping factor that is negative.

The problem I see here is that some people design amplifiers and others design speakers. Never shall the twain meet. The number of designers who does both is rather smallish. You have to see both sides of the coin. Who promotes damping factor? Mostly amplifier makers. What speaker manufacturer talks about the need for amplifiers with high damping factor? I search my memory bank and I can?t think of any. ... Will that become a trend? Time to start one.

Yet the following rules are as non-violable as laws of nature; they will stand the test of time:

Fact one: Voltage amplifiers, specifically of the Solid State kind, with significant feedback to supposedly bolster damping factor, do not have a desirable high level of immunity.

Fact Two: Classic Single-Ended Triodes so beloved by many have high level of immunity because they are Unity Coupling (got that phrase from Lynn Olson) and not Voltage amplifiers. Not just because they are Single-Ended. Similarly, a properly designed Push-Pull Triode does likewise.

Fact Three: It does not take a lot of intelligence to come to the conclusion that the speaker must be designed to suit the kind of amplifier used. But a speaker with linear load characteristics incorporating critical localised damping will have the edge when driven by non-Voltage amps.

The Linear Current Speaker goes much further than even what Pass has done and demolishes the reliance on the damping factor myth, and does so effectively. It will work with any amplifier. But it will work even better with non-Voltage amps as the localised critical damping will do its job without being short-circuited by the low output impedance of a Voltage amplifier. Speakers with localised damping will work better with non-Voltage amps. It will work with amps with more than 100 Ohm output impedance. ... This is a speaker that does not require any damping factor!!!

Damping factor from the amplifier is completely mute. But the amplifier?s immunity to the speaker?s reactance is enormous. And you can hear that. ... So I indeed got in touch with him and also got some computer print-outs from him that showed results from different box sizes. He asserted that the driver was over-damped for use in small sealed enclosures and recommended adding a series resistor as tabulated in his print-outs. I was truly taken aback by that. Who would recommend adding a series resistor between the amplifier and speaker? I argued the point with him and even blurted out at some point, what will happen to the amplifier?s damping factor? He would have none of it. It was irrelevant as far as he was concerned.

It took me a long time to realize that he was right. It was the alignment of the speaker, the actual final configuration of the speaker that matters. Get that right and all?s fine.

BTW, the gentleman with whom I had that argument was none other than Richard H. Small. Maybe that name ring a bell? When you look up the specs of any speaker you find the Thiele-Small parameters. Yes, it was that Small I was arguing against, the silly fool I was. ..."

Glenn

On 30/06/14 18.46, John Larkin wrote: ...

...

Please remember that from a "4 ohm" loudspeaker 3.99 ohm is from the voice coil resistance and 0.01 ohm (assuming 1% efficiency; 92dB/1W/1m) is from the acoustic impedance.

The acoustic impedance is of cause hugely changed around a loudspeakers own resonances and the speaker cabinet resonances.

Whetheryou use current driven or voltage driven you have to dampening them mechanically and electronically.

-

Electrodynamic loudspeakers sucks, when evaluating their efficiency:

Loudspeaker efficiency versus sensitivity:

Quote: "... You will get a shock if you know how inefficient the conversion of the electrical power Pe of the amplifier to the emitted (acoustical) sound power Pac of the speaker really is. The efficiency is only around 2 percent. ..."

Glenn