Explain Speaker Impedance to me

[davewantsmoore]

36 minutes ago, Steffen said:

Customers want to mix and match components

Yes.... I don't think it's a good idea.

 

36 minutes ago, Steffen said:

Are we still talking about home stereo? Because in a home stereo setting, a $1 mobile phone speaker will sound like $1, at best.

Of course.

 

You made the point that someone would (be smart to) use "voltage drive" in an active speaker which cost < 20K.    My point is that speakers at any price point could be "current drive".     Cost has nothing to do with it.

 

Replace my comment about "TV/mobile" with "$2000 active loudspeaker"....  same difference.

 

36 minutes ago, Steffen said:

The idea of all-in-one lock-in doesn’t seem to be palatable to most people investing in a home stereo setup

Indeed....  that doesn't mean it's smart, of course.

[aussievintage]

27 minutes ago, Cloth Ears said:

off-the-shelf voltage drive is the only option.

 

6 minutes ago, davewantsmoore said:

Yes, that's right.

 

 

So where's the problem?     It's not as if the result cannot be a fantastic sounding system.

 

 

[davewantsmoore]

23 hours ago, andyr said:

This accommodates the back emf which is produced by the moving magnet coil.

?

LOL

 

This is precisely the point of why one would want to avoid voltage drive.

 

23 hours ago, andyr said:

 Pass has done some current amps, sometimes described as current source amps, but they are only suitable with specialist drivers, like Lowthers

Not really.   The work with such drivers with out any type of filter (ie. no XO filter etc, like in a typical speaker)...... but they can work with any drivers with the appropriate crossover filter (which is no different from "voltage drive")

 

 

23 hours ago, andyr said:

The benefit of SS amps is damping factor - so control over bass

Nonsense.

 

 

23 hours ago, andyr said:

You can design a SS amp to measure current for fb and such an amp is designed for balalaika amp guitars.  It is done to simulate a tube amp, particularly with a very high impedance tube like a pentode.  Such amps give a very tubey sound, delicate, but no sense of real power.

 

Yes... you don't have to design a current source amplifier to "sound different" in this way.

 

 

23 hours ago, andyr said:

In truth, most people would not like perfect current feedback because it is 'wimpy'

 

Nonsense.

 

23 hours ago, andyr said:

Current amps need to use a very stiff, low compliance voice coil/cone to sound good, to maintain mechanical control over the excursion because the amp does not have a low impedance, that is, it does not have a high DF.

 

This assume that no other method in the speaker is used to give a "flat" response.

 

It is correct to say that if a "voltage source" and a "current source" amp is the only difference in the system.... then they will have a different frequency response.   The CS will have more output around the speaker resonance, providing the "illusion" of less "control".

 

Methods must be taken in the system design to correct for this.

 

One way (a daft way) to try to do that would be to use a driver with low cms (compliance).

 

23 hours ago, andyr said:

I bolded what sprung out at me as the vital issues.  

 

In short, the bits you highlighted are basically false.

[davewantsmoore]

13 minutes ago, aussievintage said:

So where's the problem?     It's not as if the result cannot be a fantastic sounding system.

 

I'm not sure I understand?

 

Are you asking something like ....."if voltage drive can result in a fantastic sounding system, then why not just use it?"

 

If so.... "because you can do it much better... and not unsurprisingly it sounds significantly better".

[Steffen]

5 minutes ago, davewantsmoore said:

Are you asking something like ....."if voltage drive can result in a fantastic sounding system, then why not just use it?"

 

If so.... "because you can do it much better... and not unsurprisingly it sounds significantly better".

 

But then, why aren’t we seeing that? I.e. significantly better sound at a comparable price?

 

All I can see is significantly worse sound at a budget, or great sound for a price that, if I may say so, excludes the majority of HiFi lovers.

[aussievintage]

8 minutes ago, davewantsmoore said:

 

I'm not sure I understand?

 

Are you asking something like ....."if voltage drive can result in a fantastic sounding system, then why not just use it?"

 

If so.... "because you can do it much better... and not unsurprisingly it sounds significantly better".

 

 

So, you are saying current source amplifiers are (in general) always better sounding?

[sir sanders zingmore]

9 minutes ago, Steffen said:

 

But then, why aren’t we seeing that? I.e. significantly better sound at a comparable price?

 

 

 

To some extent we are seeing that - think SGRs or KIIs

 

As to why it's not more prevalent, I suspect that has less to do with actual sound quality and more to do with sales and distribution (all-in-one speakers destroy the additional margin that comes from selling amps, preamps, dacs and all the associated cabling)

[davewantsmoore]

1 minute ago, aussievintage said:

So, you are saying current source amplifiers are (in general) always better sounding?

 

Yes..... in general.   There is systemic distortion that is part of "voltage drive" which can be avoided.   If we look at a moving coil loudspeakers electrical properties while it is moving ....... it becomes obvious that using the coil as a "voltage to current converter" to recover the music signal, is a crazy-bad idea.

 

But like many/most things this is an "all else being equal" type of thing.    Without dramatically changing the speaker design, then a VS vs a CS amplifier will sound strikingly different as the speaker won't have the same frequency response.

 

Depending on the speaker, switching to a CS amp (without changing anything) might sound better or worse, if you "like" the  specific change in the frequency response.  Typical modern multiway speakers have an electrical impedance rise at low frequencies, sometimes high frequencies, and at the crossover points .... so the FR could get quite lumpy.

 

 

It's not all roses of course .... not everything can be magically fixed  (the electrical impedance of the driver still fluctuates) .... but by taking control of the signal (the current) via feedback, it can be a marked improvement.

[Steffen]

I reckon that if we see a broad adoption of integrated active solutions then this will not be by transitioning from controlling voltage to controlling current. I think we’ll skip right over that and go to controlling membrane position.

 

This has been done for decades, to a certain extent and with varying success. Designing an automatic controller to keep the instantaneous position of the membrane linked to the instantaneous amplitude of the input signal is almost trivial, but the implementation isn’t. With high-speed digital processing and sufficient power and bandwidth this will eventually be possible.

 

Until then, we’ll have to concern ourselves with things like speaker impedance

 

[Steffen]

39 minutes ago, sir sanders zingmore said:

 

To some extent we are seeing that - think SGRs or KIIs

 

 

Sure, if money is no object. But can you take a typical, say, $3k+$6k amp+speaker combination, and replace it with a current control setup that costs the same but sounds better? No. One that sounds the same but costs less? No.

 

In other words, the prevailing voltage control approach is not daft, it is simply the most cost effective approach in the price regions that are of interest to the majority of customers.

 

 

Edited April 9, 2021 by Steffen
clarity

[sir sanders zingmore]

 

 

5 minutes ago, davewantsmoore said:

There is systemic distortion that is part of "voltage drive" which can be avoided.   If we look at a moving coil loudspeakers electrical properties while it is moving ....... it becomes obvious that using the coil as a "voltage to current converter" to recover the music signal, is a crazy-bad idea.

 

 

"crazy-bad" implies an awful impact on the sound quality, is it really that bad in practice?

If you have a voltage drive amp that can respond to the changing electrical properties of moving speakers, why wouldn't this be "good enough"?

 

Or put another way, what improvements does current drive provide to the sound that ultimately comes out of the speaker (is it lower distortion, flatter FR etc?) 

[davewantsmoore]

28 minutes ago, Steffen said:

But then, why aren’t we seeing that? I.e. significantly better sound at a comparable price?

 

That's a complex question.....  but point was only that such an amplifier costs no more or less to build.... and uses the same speaker drivers, etc .... so there is no need for it to cost more  (aside from business 101 = sell product for as much $ as the market will bear).

 

28 minutes ago, Steffen said:

significantly worse sound at a budget

I'm not sure why you say that.

[sir sanders zingmore]

4 minutes ago, Steffen said:

 

Sure, if money is no object. But can you take a typical, say, $3k+$6k amp+speaker combination, and replace it with a current control setup that costs the same but sounds better? No. One that sounds the same but costs less? No.

 

In other words, the current voltage control approach is not daft, it is simply the most cost effective approach in the price regions that are of interest to the majority of customers.

 

I guess it's a chicken and egg thing, we are seeing current drive coming in at the expensive end and also at the very cheap non-audiophile end, perhaps the tech will trickle down/up to the middle of that range.

 

Having said that, there are still precious few current-drive systems at the high end. I still reckon a big reason for that is the lack of profit margins and tweak-ability

[aussievintage]

13 minutes ago, davewantsmoore said:

Without dramatically changing the speaker design, then a VS vs a CS amplifier will sound strikingly different

 

13 minutes ago, davewantsmoore said:

Depending on the speaker, switching to a CS amp (without changing anything) might sound better or worse,

 

14 minutes ago, davewantsmoore said:

It's not all roses of course .... not everything can be magically fixed  (the electrical impedance of the driver still fluctuates) .... but by taking control of the signal (the current) via feedback, it can be a marked improvement.

 

I am seeing it as -  the best of the best comparison between the two types would lean towards the current drive.  Other than that, it is pretty much a case of maybe.

 

Combos of voltage drive amps and speakers that are known to work well, always seems to me to be the best bet.  Of course that would be true for current drive, but they a much less common and much less well known.

 

[davewantsmoore]

4 minutes ago, sir sanders zingmore said:

"crazy-bad" implies an awful impact on the sound quality, is it really that bad in practice?

 

Circa 20dB of non-linear distortion....    but it depends a lot on the amplifier and drivers in question.

 

On one hand there are things much more audible (eg. linear distortion).... and NLD can be quite benign when below certain levels.

 

... but I think we find that this type of voltage-drive distortion is more audible than expected as it is not constant (ie. it's related to cone velocity) ..... kinda insidious in a way, like "jitter".

 

 

4 minutes ago, sir sanders zingmore said:

Or put another way, what improvements does current drive provide to the sound that ultimately comes out of the speaker (is it lower distortion, flatter FR etc?) 

 

It's lower non-linear distortion.

 

It's also lower linear distortion due to temperature effects (ie. frequency response doesn't change due to changes in VC resistance) .... but for hifi this is usually a corner case.

[davewantsmoore]

5 minutes ago, sir sanders zingmore said:

 

I guess it's a chicken and egg thing, we are seeing current drive coming in at the expensive end and also at the very cheap non-audiophile end, perhaps the tech will trickle down/up to the middle of that range.

 

Maybe... as was already mentioned.   Not while we have people mixing and matching systems.... and loudspeaker designers who want to make a speaker which can be driven by any amplifier (for many reasons, either they may not understand the issue, or they may think it's what the "market wants", or both, etc).

 

5 minutes ago, sir sanders zingmore said:

I still reckon a big reason for that is the lack of profit margins and tweak-ability

 

Yes.... and many players in the high-end are exclusively either amplifier OR speaker manufacturers.

[Playitloud]

JkSpinner,

I did Electronic Engineering years ago. One crazy thing that has stayed within my head's old grey matter is that for amplifiers, maximum power output is achieved when input impedance & output impedance are equal. Meaning if they are not you will either have losses or risk overdriving your speakers. Bit like having odd sized wheels on your car, they'll still turn but not always efficiently. I may get shouted down but that's the simple way that I've always looked at it.

Regards,

Alan...

[andyr]

Sorry, Alan ... can you explain that a bit further - as what I read doesn't make much sense!  

 

You said:

 

9 minutes ago, Playitloud said:

 

I did Electronic Engineering years ago. One crazy thing that has stayed within my head's old grey matter is that for amplifiers, maximum power output is achieved when input impedance & output impedance are equal.

 

 

But the input impedance (Zin) of a power amp will be anywhere from 10K (rare) through 33K/47K (common) to 100K (typical of a tube amp).

 

Whereas the output impedance (Zout) of a power amp will typically be much less than an ohm.

 

Andy

 

 

 

 

[aussievintage]

23 minutes ago, Playitloud said:

maximum power output is achieved when input impedance & output impedance are equal.

 

You are thinking of the maximum power transfer theorem.  It doesn't apply here,  and even if did, it would be referring to the output impedance of the amp, and the (input) impedance of the speaker.

 

Modern amps have a very low output impedance and drive the higher impedances of modern speakers (4, 8, 16 ohms)

[Playitloud]

Well, I knew I'd probably light up the tech gurus & others.

 

Yes, I was inferring to the Amp's (working) output impedance & input impedance of the speakers. Whilst the exact science (static resistance of the Amp's output stage) & calc's may not directly apply, due to varying frequencies etc, most manufacturers will still quote a range within which their amplifiers will more happily match the speakers; thus providing greatest efficiencies. That is all I meant, my sincere apologies to the electronic purests!

 

Head down,

Alan...

[almikel]

 

On 03/05/2021 at 4:40 PM, Playitloud said:

Whilst the exact science (static resistance of the Amp's output stage) & calc's may not directly apply, due to varying frequencies etc, most manufacturers will still quote a range within which their amplifiers will more happily match the speakers; thus providing greatest efficiencies.

As @aussievintage says, the maximum power transfer theorem does not apply.

Solid state amps typically have an output impedance orders of magnitude lower than speakers, valve amps usually have a higher output impedance than solid state amps, but still much lower than speakers.

The "range" of speaker impedance an amp can drive is about the amps' current delivery while maintaining voltage...which of course relates to the amp's output impedance, but "matching" an amp's output impedance to a speaker's input impedance is not something desirable with typical amps/speakers (eg amps that try to be constant voltage sources) 

 

Maybe with current drive speakers and amps/EQ set up to drive them "maximum power transfer" would be a thing?

 

Mike

 

 

Edited May 7, 2021 by almikel

[Steffen]

On 03/05/2021 at 4:01 PM, Playitloud said:

One crazy thing that has stayed within my head's old grey matter is that for amplifiers, maximum power output is achieved when input impedance & output impedance are equal.

 

There is no shame in misunderstanding or misinterpreting the maximum power transfer theorem, since James Prescott Joule himself did so

 

It is all explained (along with the common misconceptions) here:

https://en.wikipedia.org/wiki/Maximum_power_transfer_theorem