Amplifiers: Effects on sound if power does not double when impedance is halved? - Page 5 - AVS Forum | Home Theater Discussions And Reviews
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post #121 of 186 Old 02-09-2017, 07:48 PM
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OT: Add load pull measurements to your amplifier tests...

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #122 of 186 Old 02-09-2017, 07:53 PM
 
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Originally Posted by DonH50 View Post
OT: Add load pull measurements to your amplifier tests...
You read my mind!

I'm going to have apply some serious forethought towards devising a means to present all of this data, then on how to translate it.

Any thoughts on that?

Cheers
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post #123 of 186 Old 02-09-2017, 07:58 PM
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Well, put them into a 3-D plot, using, I dunno', a cube?

Seriously, presenting reams of data in a concise and readily-understandable format is a significant challenge. Plots, lots of plots... Hope you have Matlab or something like it! Excel does a good job as well but I am much less comfortable using it and (perhaps because of that) find it much more cumbersome.

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post #124 of 186 Old 02-09-2017, 08:49 PM
 
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Originally Posted by DonH50 View Post
Well, put them into a 3-D plot, using, I dunno', a cube?

Seriously, presenting reams of data in a concise and readily-understandable format is a significant challenge. Plots, lots of plots... Hope you have Matlab or something like it! Excel does a good job as well but I am much less comfortable using it and (perhaps because of that) find it much more cumbersome.
Hmm, I have LabVIEW with a good number of plug-ins, including Signal Express. It's adding up to look like I'll have to build a custom test suite within it.

I have just about every other major piece of audio test gear at my disposal, but none of them outside perhaps Prism Sound would serve us near as good as my LabVIEW suite.

Good call, LabVIEW it is!
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post #125 of 186 Old 02-09-2017, 09:12 PM
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Is labview an overlay that runs on top of matlab in the background? Or was that something else? Back in the day during engineering school, I used mathcad almost exclusively for everyday problems. But I did create a dynamometer and "wrote" the test software for it in a test suite overplayed on matlab. At least I think it was. I rarely used mathmatica, but I'm pretty sure this was matlab in the background. Labview sounds vaguely familiar but its been a long time. Anyway, sorry for the digression.
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post #126 of 186 Old 02-09-2017, 09:37 PM
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Originally Posted by Jady Jenkins View Post
Sure,
So you face customers often enough to know this, as in selling consumer goods.
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post #127 of 186 Old 02-09-2017, 09:41 PM
 
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Originally Posted by Bigus View Post
Is labview an overlay that runs on top of matlab in the background? Or was that something else? Back in the day during engineering school, I used mathcad almost exclusively for everyday problems. But I did create a dynamometer and "wrote" the test software for it in a test suite overplayed on matlab. At least I think it was. I rarely used mathmatica, but I'm pretty sure this was matlab in the background. Labview sounds vaguely familiar but its been a long time. Anyway, sorry for the digression.
LabVIEW is a standalone, measurement software which has many-many add-on modules, which port different types of analysis and reporting. The Full Version comes with Signal Express, which is a rather neat app, which permits the development of quick and easy visual interfaces and measurement displays.

The software, directly communicates with many frontends and as such, permits more complex analysis over that of most dedicated audio analyzers. It also permits customized reporting of the measured data. Data logging is very useful.

LabVIEW and MATLAB can exchange data and run parallel, sharing resource while running routines.

I will most definitely be using LabVIEW to improve the communication of the measurements that I capture. It's adding up to me having to create a custom test and report routine, which will save a bunch of time, post development. I need to firstly determine the actual context / scope of work.

It reads like you have a related, professional background. If I am properly inferring such, I welcome your assistance, in translating the measurements that I post, into a common, relatable language, if you will.

I can be matter of fact to a fault, which helps some, but in equal portion can leave others mostly in the dark/frustrated.

Hardly a digression, cheers.

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post #128 of 186 Old 02-09-2017, 09:49 PM
 
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Originally Posted by LFEer View Post
So you face customers often enough to know this, as in selling consumer goods.
It's obviously academic. No gear, no skill-set = no knowledge of the actual impedance and phase qualities, throughout the speaker systems pass bands, at varying drive levels...

Why make hay, about what's an obvious reality?

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post #129 of 186 Old 02-09-2017, 10:01 PM
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The Pacific Northwest is having terrible weather today. But I guess rain is what they are known for.

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post #130 of 186 Old 02-09-2017, 10:13 PM
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Originally Posted by Fjodor2000 View Post
For many amplifiers the power output does not double when the loudspeaker impedance is halved...
Now what I wonder is whether that only comes into play at loud listening volume? [and elsewhere asking why buy a huge Levinson amp etc]
Well, if we consider
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Originally Posted by Bill Fitzmaurice View Post
The voltage output of an amp is constant into any load impedance.
I wonder if that is ABSOLUTELY so, under dynamic conditions with real music. I'm trying unsuccessfully to remember if I tested anything like that with non-resistive impedances. However, I tested various amps over time where with the same input, changing the resistive load from say 8 to 4 to 2 ohms would result in a very slightly different output voltage. I'm making this up, but say from 2.704 to 2.603. Small. Significant? I think nobody has really researched this enough to state definitively. It's just a fraction of a decibel, but amplifiers are NOT perfect linear things, they incorporate physical devices and limited power supplies and there could be some small dynamic nonlinearities going on.

Some believe all amps sound the same below clipping, others feel they sound different. I personally have never heard a comparison whose conditions were controlled enough-especially as regards level matching-to make any kind of definitive statement.
--> I'd love it if someone set up such in LA!

On the other hand, at high levels I don't think many people would argue that all amplifiers sound the same when they clip. They certainly don't all behave the same on the bench. And I suspect that especially with today's largely inefficient speakers and less-than-Levinson receiver power amp sections, clipping happens more than we might think.
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post #131 of 186 Old 02-09-2017, 11:29 PM
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Originally Posted by head_unit View Post
Some believe all amps sound the same below clipping, others feel they sound different. I personally have never heard a comparison whose conditions were controlled enough-especially as regards level matching-to make any kind of definitive statement..
I've conducted a test of a Mark Levinson grade power amp [their companion line called Proceed, but Mark Levinson publically announced this very amp was to be rebadged as Mark Levinson without any modification other than cosmetics, not too long after I conducted the test] to settle a small bet with an audiophile friend of mine who insisted under his specific gear, wiring, professional listening room, and music requirements he could hear a difference compared to a Yamaha integrated amp (a stereo receiver without a tuner section) which was a fraction of the price, weight, and power. He lost the bet.

Of course testing just one audio professional who had undergone training and referred to himself as an expert listener proves nothing in the big picture. I would have had to test everyone on the planet who insists they can tell a difference to even begin to draw some conclusions, but somehow I don't see that as happening any time soon.

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Originally Posted by head_unit View Post
. . .And I suspect that especially with today's largely inefficient speakers and less-than-Levinson receiver power amp sections, clipping happens more than we might think.
There is no controversy as to if amps differ in power. They often do.

The Sonus Faber speakers he selected for the test were said to have a sensitivity of 87dB/1W/1m and an 8 ohm nominal impedance, by the way. The inexpensive Yamaha didn't have any trouble driving them at the levels he wanted but since it had a much lower power rating [100w/ch vs. 250w/ch, both into 8 ohms] I'm sure if the test was one of maximum clean output it clearly would have clipped much sooner, had we cranked things up to very loud levels.
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post #132 of 186 Old 02-10-2017, 06:37 AM
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Originally Posted by Jady Jenkins View Post
Hmm, I have LabVIEW with a good number of plug-ins, including Signal Express. It's adding up to look like I'll have to build a custom test suite within it.

I have just about every other major piece of audio test gear at my disposal, but none of them outside perhaps Prism Sound would serve us near as good as my LabVIEW suite.

Good call, LabVIEW it is!
I used VEE a lot in a previous workplace where we had about an equal number of LabVIEW and VEE proponents. In my case I did not know either well at the beginning but the equipment I needed to drive was HP (Agilent, Keysight) and LabVIEW did not have drivers for it yet whilst VEE did. I liked having a graphical interface that made it easier to set up and run the tests, though it took me a bit to get program flow and looping under control (no pun intended). I used Mathcad and/or Matlab to crunch the data. The next place I worked used Matlab for everything, with the Matlab Instrument Control Toolbox. It was nice having everything under one program. These days I am using Python scripts with some C++ functions to drive various test equipment, and Excel or Matlab to crunch the data.

My current workplace does not have any audio-range test equipment, one thing I miss. But OTOH my work hours are such that I am too tired to play after work anyway, barely have the energy to practice for an hour so before I pay bills, catch up on emails, and fall into bed. Testing does give me extra time to post during the day, however, while the tests are running (a mixed blessing).
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post #133 of 186 Old 02-10-2017, 09:13 AM
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Originally Posted by Jady Jenkins View Post
Current is prime in the production and utilization of energy.

Without the presence of coulombs, their can be no electrical energy produced.

Voltage-Electricity cannot exist without the presence of Current in a circuit.
Agreed.

You always hear comments that an audio amp is simply a "voltage source" for the speaker and the speaker itself being connected in parallel with this source. When in reality, the speaker simply completes a series pathway in this case AC . I like to use this schematic:

http://www.hafler.com/pdf/archive/MA..._P1000_man.pdf

why ? because the schematic drawing clearly illustrate this current pathway i.e note the speaker terminals, power supply and semi conductor output topology.
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post #134 of 186 Old 02-10-2017, 12:07 PM
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Quote:
Originally Posted by Jady Jenkins View Post
Edit: Caveat being a customer wouldn't have a clue what the impedance and phase responses are...
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Originally Posted by LFEer View Post
Has that been your observation?
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Originally Posted by Jady Jenkins View Post
Sure,
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It's obviously academic.
It went from observation of customers to being academic. When did it cross over?
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post #135 of 186 Old 02-10-2017, 01:18 PM
 
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Originally Posted by LFEer View Post
It went from observation of customers to being academic. When did it cross over?
It has always been academic, audio reproduction is academic. Your question(s) requires an engineering perspective, therefore the responses are based on the academic realities, which govern an audio products design and manufacturing, regards of when you personally caught on to them being so.

In very plain English I have simplified things for you.

If a consumer doesn't have the gear or the skill-sets to make the measurements in question, at varying amplitudes, then they don't actually know what the impedance and phase qualities are throughout the band passes. 1 - 2 - 3 a very linear, academic progression.

If you cannot come to terms with this reality, fine, but there is no need to continually bagger me about it.

I think we are done with this circular discussion.
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post #136 of 186 Old 02-10-2017, 02:33 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post
Current does vary with frequency, and by dint of that so does power delivery, but speakers respond to voltage, not current.
This is an example of what I posted (#133) earlier.

IIRC, Bill Fitzmaurice is a speaker designer, and I understand what his is attempting explain, but in reality it's the other way around.

1)The power amp output being a relatively high current (AC) source

2) and the speaker excursion is a product of the alternation current be delivered.

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post #137 of 186 Old 02-10-2017, 02:46 PM
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Quote:
Originally Posted by Tomas2 View Post
This is an example of what I posted (#133) earlier.

IIRC, Bill Fitzmaurice is a speaker designer, and I understand what his is attempting explain, but in reality it's the other way around.

1)The power amp output being a relatively high current (AC) source

2) and the speaker excursion is a product of the alternation current be delivered.
Bill is right. If two would be the case then you would getting different voltages for different speaker designs. This is obvious not the case.
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post #138 of 186 Old 02-10-2017, 02:55 PM
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Bill is right. If two would be the case then you would getting different voltages for different speaker designs. This is obvious not the case.
Please take some time and parse the Hafler .pdf (schematic) I provided in post #133 . The speaker completes a series circuit.

Speakers excursion is without a doubt a product AC current.

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post #139 of 186 Old 02-10-2017, 03:38 PM
 
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Originally Posted by Tomas2 View Post
speaker excursion is a product of the alternation current be delivered.
Load up your favorite speaker modeling software, be it anything from WinISD to HornResp to AkAbak. Model any driver. Enter whatever current value you wish to see the resulting excursion.
Of course, you can't, because there's no entry field for current, only for voltage, or with some programs power, which they reference to the nominal driver impedance to arrive at a voltage figure.
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post #140 of 186 Old 02-10-2017, 03:48 PM
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The Pacific Northwest is having terrible weather today. But I guess rain is what they are known for.
Is that where his store is?
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post #141 of 186 Old 02-10-2017, 03:56 PM
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Per your request, I searched pages and pages of your postings and found zero effort on your part to understand anything.
It was a suggestion, not a request. You cannot possibly have finished going through that much info overnight. It will take you at least 6 months to digest the useful audio info on this forum. Yes, there is that much. A lot of that have been posted by those who professionally design electronics, acoustic treatments and edit music albums you use. The sooner you start, the sooner you will be properly informed.
See you in August.
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post #142 of 186 Old 02-10-2017, 04:03 PM
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^^^

move on

please take the high road in every post:do not respond to or quote a problematic post: report it
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post #143 of 186 Old 02-10-2017, 04:09 PM
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So I guess there is no dumb question? can modeling software give you the best answer for all types of music?

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post #144 of 186 Old 02-10-2017, 04:26 PM
 
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So I guess there is no dumb question? can modeling software give you the best answer for all types of music?
Short answer, no... its only as good as the input data, and the source of that data, and the conditions in which it was acquired/sampled needs to be fully disclosed. Then they are of some objective value, but not absolute value.

Voltage like wattage is a product based on the presence of current in a circuit. All circuits possess one or all three of the following electrical impedances Inductance, Capacitance, Resistances - LCR; which produce EMF - Voltage, which in turn produces Watts, VAR's or VA's...

The Power that Bill suggests is based upon a Voltage, is also and more so, based on Current, by a factor of two to one: P=IxIxR or Voltage x Current...

There can be no Voltage, without the presence of Current. It is impossible. Current is the prime mover, in Power, or actual work. If something moves, it is firstly because of the presence of sufficient Current to act upon it.

All software relies on us providing at least two knowns, and the rest is extrapolated, when calculating primary transfer function relating to EMF.

I hope this helps you out.

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post #145 of 186 Old 02-10-2017, 04:27 PM
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http://www.edn.com/design/consumer/4...-voltage-drive

“The most remarkable thing here regarding loudspeakers is that the voltage between the ends of the wire does not appear anywhere in these equations. That is, the speaker driver in the end obeys only current, not caring what the voltage across the terminals happens to be.”

This equation:

"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."
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Quote:
Originally Posted by Tomas2 View Post
http://www.edn.com/design/consumer/4...-voltage-drive

“The most remarkable thing here regarding loudspeakers is that the voltage between the ends of the wire does not appear anywhere in these equations. That is, the speaker driver in the end obeys only current, not caring what the voltage across the terminals happens to be.”

This equation:

"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."
You are correct.

Then Qes is derived based on BL as expressed here: 2pi x Fs x Mms x Re over BL squared

I am head out for the evening, I'll check back in tomorrow. However, in my books, please note that you are on the right track!

Understanding subwoofer driver frequency ratings
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post #147 of 186 Old 02-10-2017, 07:24 PM
 
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Quote:
Originally Posted by Tomas2 View Post
http://www.edn.com/design/consumer/4...-voltage-drive
“The most remarkable thing here regarding loudspeakers is that the voltage between the ends of the wire does not appear anywhere in these equations. That is, the speaker driver in the end obeys only current, not caring what the voltage across the terminals happens to be.”
This equation:

"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."
Are you aware that the subject in question, current drive, is a theoretical exercise and does not exist in mass marketed products? Go back and read it again, and note that well before any of the passages that you quoted there's this one: Today, practically all available audio amplifier and loudspeaker equipment works on the voltage drive principle without significant exceptions.
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post #148 of 186 Old 02-10-2017, 08:16 PM
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Quote:
Originally Posted by LFEer View Post
So you face customers often enough to know this, as in selling consumer goods.
He might not but I did for well over 20 years on a retail sales floor dealing with the general public 6 days a week 10 to 12 hours a day and the overwhelming majority didn't know even the basic differences between horsepower and torque or where the curb weight of a vehicle differed from the GVW or how to figure a vehicles payload capacity into it's trailering capacity as to not exceed the vehicles GCWR (so as not to find themselves with their feet trying to do a Barney Rubble act because their brake pads glazed over from the heat produced from trying to stop a highly overloaded vehicle.) The occasional GM rep or engineer from the tech sector knew most of the times but even then you would be surprised how many degreed people tried to buy an underpowered V6 pickup truck to tow their travel trailer with a tow bar and another car behind it😱. Some even bought 2 wheel drive pickup trucks thinking they were actually 4 wheel drive and came back weeks later after sticking their truck in the mud only to find out their error😕 so yes it's very plausible.
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post #149 of 186 Old 02-11-2017, 07:54 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post
Are you aware that the subject in question, current drive, is a theoretical exercise and does not exist in mass marketed products?
Hi Bill,

This was the reason I provided the schematic, as example for transconductance (current drive) amplification. This patent design by Jim Strickland here:

http://www.hafler.com/pdf/archive/MA..._P1000_man.pdf

Transconductance is nothing new. I became interested in all this after noting the apparently superior sounding performance of the little Hafler P1000 which happened to be in most of my post production edit suites.

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

"the first article offering "current drive" being approximately some 30+ years ago Current drive of speakers was actually quite common back in the day of pentode output stages with no feedback."

"This is interesting, and may explain a significant difference I heard in a demonstration of different kinds of opamp-based headphone drivers. One opamp system was a traditional voltage system, the other a 'transconductance' system"


From Wiki:
For vacuum tubes, transconductance is defined as the change in the plate(anode)/cathode current divided by the corresponding change in the grid/cathode voltage, with a constant plate(anode)/cathode voltage

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post #150 of 186 Old 02-11-2017, 09:16 AM
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A lot of this is semantic wrangling.

"Transconductance" simply means that the output conductance is controlled by the input voltage.

Conductance = 1/Resistance; the unit is, unsurprisingly, the mho ("ohm" spelled backwards). This is a basic property of MOSFET devices. When used in a conventional audio power amplifier circuit, however, the unit becomes a voltage source due to significant amounts of negative voltage feedback.

Speakers respond to current, as that is what activates the electromagnetic transduction. Current, however, doesn't exist in a vacuum. When produced by a power amplifier, which is a constant-voltage source, current becomes the dependent variable (y-axis) which, for a given output voltage, is a function of the complex transducer impedance (x-axis), itself a function of frequency and other complex variables.
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