"Watts" Versus "Current"

Swamp, not to take away from Dan's similar explanation, but if you read my post at the beginning of this thread, you'll realize I said the exact same thing:

Therefore, all watts are not created equal. 1 amp (of current) X 10 volts = 10 watts of power. But 10 amps X 1 volt also = 10 watts. Further, the basic W =A x V really works for direct current (DC) only. The formula is a bit more complicated for AC (as in: music signal). But leaving that aside for now, how the power is created will either be better or less good for certain kinds of speakers.

Why? Because every kind of driver generates a reactive signal BACK TO THE AMP. When the signal from the amp moves a cone back and forth, for example, the action of the cone's voicecoil in the magnetic field actually GENERATES a reverse electric current BACK to the amp! This reverse current adds to the impedance (load) the amp "sees".

What's CRITICAL (in amp selection) IMO, is HOW that (let's call it 'phantom') impedance is created. If the amp sees a capacitive type of load (an electrostatic speaker) it needs for its available watts to consist of lots of amps (current). If it sees a resistive type load (like cones, domes, ribbons and planar magnetics) it needs for its available watts to consist of lots of volts (to overcome the reverse voltage created by those kinds of drivers.)

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Ns- you bet. I've been watching this thread for a few net sessions and quite honestly had meant to mention it as well. I was mostly referring to the analogy which for non-tech types of math-phobes (I'm not one, but many are) its easier to grasp the concept that way and then on to the math and tech detail. I know I'm right about at the edge of my tech expertise w impedance. I know its the equivalence of resistance and I understand its important in matching amp and speaker. I know (or at least I think I do) that most amps operate better into higher impedance loads and that lower impedance loads will require/draw more "wattage" from an amplifier. I do get confused with input impedance and output impedance and matching source/SUT/phono stage/pre-amp/amp with respect to those parameters. And I have an advanced degree in a science (not a math oriented one, admittedly). A analogies help me make the conceptual connections that allow me to go from trying to remember "rules of thumb" to actual understanding. Then I can make judgments for myself.

Not to throw water (pun intended) on danyers' analogy but the water pressure at the hose nozzle is independent of the size of the hose (WHEN THERE IS NO FLOW), but will actually be LOWER at the end of a smaller hose because of the extra resistance to the water flow offered by the smaller hose.
The rservoir at a certain height is the Voltage and the amount of water flowing through the hose is the current and the size of the hose (pipe) can be considered the load. If the load is high, the current is actually lower.
In danyers' analogy, the reason that the water is 'thrown' further from the shorter hose is not because the pressure is higher, but because less water is being supplied at the nozzle at a higher speed thus the water can travel a further horizontal distance before falling to the ground. The trouble with using water analogies (which is commonly done for electricity) is that one must also understand the mechanics of fluid flow for the analogies to make sense. In this case the analogy is not very usefull, except to misinform.
Gs5556's reply is, by far the best analogy, because it is not an analogy but an explaination using an example.

Salut, Bob P.

Swamp, in the beginning, most of us (I know I did anyway) conceptualized 'impedance' and 'resistance' as being essentially the same thing; because they are both expressed as ohms. and we were taught (first) that ohms are a measure of resistance. Strictly speaking, that is NOT TRUE! It is IMPEDANCE that is measured in ohms, and RESISTANCE is simply ONE KIND of impedance ;-) Impedance is indeed the better term, because it refers to any condition that IMPEDES the flow of current (resistance being just one such condition.)

So, for instance, when a manufacturer specifies their speaker is "4 ohms" that's NOT what you will read if you just put an ohm meter across the speaker terminals ;-) That 4 ohm "nominal impedance" is in fact a "weighted average" of the impedance (to current flow) that the amplifier "sees" at EACH frequency across the entire spectrum. But that speaker is by no means 4 ohms across the board!

Further, when a speaker manufacturer specifies "power handling capacity" (like, 50W - 200W) they're not just saying the minimum watts you need to 'make it play', or the maximum watts before you 'fry' your speaker ;-) What they are really getting at is the RANGE of (amplifier) power ratings in which the speaker will produce the whole frequency spectrum (and without distortion.) For example, below 50 watts, some parts of the frequency spectrum (associated with hi impedance) may not reproduce at all, or only with distortion. On the other hand, driving the speaker above 200 watts, at certain (other) parts of the frequency spectrum associated with lo-impedance, you could indeed fry something (like a dome tweeter's voice coil, or burn a hole in your electrostat's diaphragm!)

Did you know that a MartinLogan panel's IMPEDANCE can drop to less than 1 ohm at 15KHz?! So if you were using a ss amp with a rated power of say 200W/ch @ 8ohms, then @ 4 ohms (following Ohm's Law) it could deliver 400W, @ 2 ohms, 800W, and @ 1 ohm, 1600W!! But at each stage, the VOLTAGE part of those bigger watts would be increasing more and more, compared to the current part. So if you were playing a LOUD 15kHz with a solid state amp into your MartinLogan, huge voltage would build up across the air gap in the panel, and pretty soon ZAP - lightening! (better known as arc-ing) and you've burned a hole in your diaphragm!

OTOH, due to the "impedance matching" capability of transformers, a tube amp won't produce this result with an electostat (unless it's a mutha of a tube amp, and your hand slipped on the volume control!) Tubes have a high internal impedance (think of a high revving 4-cyl engine) and speakers generally have a low internal impedance. Solution for getting the power to the road? A 6-speed gear box! Better known as an output transformer. If you select the correct 2, 4, 8, 16 ohm tap (gear) then you can match the amp's power (torque) to the speaker's load (incline of the hill) for maximum power transfer! (Don't ya just love physics?!) What this means (broadly generalizing ;-) is that a tube amp can supply the same watts, comprised of the same proportion of amps and volts, into any impedance. Only one solid state amplifier I know can do this, and that is McIntosh; BECAUSE they ALSO use output transformers on their SS amps, even though they don't really have to -- but it keeps THEIR clientèle from making bad amp/speaker choices ;-) I just happen to be a McIntosh "clientèle" but not because I don't know how to select an amp! ;-)
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Wow, an old thread but a topic I wanted to understand. Gs5556 really did a fantastic bit of education with his description. So I'm guessing that the JVC A-X9 amp I have, with a 390VA toroidal transformer delivers plenty of current to dip down to 4 or even 2 ohms. I finally get the idea how watts isn't the easy answer to what an amp can drive.