On February 6, 2018 at 15:21, highfigh said...
Speakers are presented with voltage. What happens after this is up to the speaker's resistance/impedance. If the impedance is extremely high, not much current will flow but the power is still only determined through calculation and it's neither constant, nor is it due to anything more than the fact that a connection between the amp and speaker has been made.
It makes little sense to ignore all the things that need to be in place so that when one connects the amp to the speaker, power flows. You're describing the action of a system. Saying "not due to anything more" ignores all sorts of assumptions about what is in front of you, including but not limited to whether there's a line level signal of the proper voltage, and even whether the damn power amp is plugged in!
Everything I said above may be seen as trivial, but it's true: without ALL things in place, no power will flow.
Also, "the power is still only determined through calculation" if you mean knowing the quantity of watts so you can write it down. That is a bit of a philosophical statement, the idea being not to confuse the actual power with the number we give to it. (A parallel example is thinking that the number "3" IS three. It's only a symbol that represents three, just as a measured power level represents the power, but is not the power.)
The actual determiners of actual power in any given situation are... you've heard it already: the speakers connected to the power amp, the line voltage level (whether 120V power or audio), volume control setting, load impedance, etc. Those things are far more determinative of power than a calculation. A calculation only describes what already is.
On February 10, 2018 at 03:24, g007 said...
james_aa
This is very interesting question. It seems simple to answer, on the surface, but when you get into it, not so simple. In fact it can get quite complex. I will throw out some tidbits and let you guys run with it.
That's fair. We've already gone a few miles as it is.
3. The load is an AC Load, so it has AC Resistance (will hit on this later), Inductance and Capacitance. because of its reactive components, it has the ability to STORE energy and RELEASE (back EMF of the speaker) energy.
Isn't AC resistance the combination of resistance, and reactive components?
4. DC Resistance implicitly indicates 0Hz operation!
I love the blank look thrown my way when I tell someone, quite on purpose, that DC is 0 Hz. Or that for transistors to work, they must first encounter the first half of a very long 0 Hz-ish waveform, that is, the application of battery power.
5. When you talk about any AC Load you MUST specify the frequency. Once you know the frequency the reactive terms have meaning. You can calculate the magnitude of each one and then vector sum them together to get the net reactive impedance, either inductive or capacitive. You then vector sum the AC Resistance with the resulting reactive component to realize the impedance vector Z at the frequency of interest. You then can compute the Phase angle and determine the true power and apparent power.
These paragraphs are in the wrong order. It's not appropriate to bring in a new term, AC resistance, without definition, especially since it has next to nothing to do with audible signals. You should defined it first, so we could know we could ignore the difference between AC resistance and DC resistance.
6. AC Resistance takes into account the Skin Effect present in all non-zero frequency wire situations. It is a calculation that is always done by power transmission engineers AND especially RF engineers and/or anyone who is subject to its effects. The best analogy I can come up with to describe this Skin Effect is the water pipe analogy.
The rest of this was just mental play since skin effect is negligible at the frequencies we've been talking about, that is, audible-by-humans audio.
