dincz

Both AC and DC current can vary but if the current alternates in direction then it's alternating current (AC).

[quote name='GregBass' timestamp='1338404576' post='1674138'] Does this mean the battery does not produce a direct voltage? [/quote] The polarity and the direction of current flow don't alternate so it's not AC - just pulsating DC.

[quote name='Mr. Foxen' timestamp='1338402459' post='1674080'] Would definitely make life easier if they didn't mention output power at all and just gave a voltage swing and min/max operating conditions. [/quote] But the operating conditions would have to include minimum load impedance so V[sup]2[/sup]/R (or V[sup]2[/sup]/Z) instead of P. Full circle no?

[quote name='Mr. Foxen' timestamp='1338397436' post='1673965'] That is for an ideal square wave, and not a clipped wave. In the real world you don't get ideal square waves because they require infinite bandwidth. Hence the suggestion of applying a real world observation, rather than demonstrating your limited understanding of the subject matter, and claiming others have seen the impossible to try and back up your claims. [/quote] Ah, 'square wave' as opposed to square wave I need to study the rules of this game. But even an imperfect square wave won't contain [i]"all the harmionics of the fundamental occuring at the same voltage swing as the fundamental" [/i]

[quote name='Mr. Foxen' timestamp='1338396166' post='1673939'] Go run a fast Fourier transform on your 'square' wave and see what harmonics you get. [/quote] I've got no way of doing that at the monent, but I'd expect to see what others have seen:

[quote name='GregBass' timestamp='1338390130' post='1673783'] "for that short period while the line is flat". If you ignore the rest of the waveform, for that short time there is DC applied across the speaker.[/quote] But you could say the same for an ac waveform. If you take a sufficiently short portion of the peak of the waveform, it would look like DC as well. It might be relevant if your notes are only a few microseconds long - but then they wouldn't be notes.

[quote name='Bill Fitzmaurice' timestamp='1338385955' post='1673665'] The difference between a sine wave and square wave is the harmonic content. A sine wave has none, a square wave has all the [size=5]odd[/size] harmionics of the fundamental [/quote]

Speakers are a can of worms. As far as amps are concerned though, the question is would you be perfectly happy if amp manufacturers didn't provide any power output information? You'd surely have to agree there are degrees of meaninglessness.

[quote name='Bill Fitzmaurice' timestamp='1338382721' post='1673594'] Since most players tend to use their amps under normal conditions that's what's pertinent. [/quote] This kind of leads us back to the point where we strayed off the track - before we got into frequency-dependent variables. I believe power output, when measured realistically and stated along with the measurement method, can be a useful guide in choosing gear. "Normal conditions" would include leaving an allowance for headroom and that's where accurate and meaningful figures come in. Of course the ultimate test is using the ears in the real world, but that's not always possible before a purchase. In any case, reliable information can help narrow down the choices before trudging around from dealer to dealer. If manufacturers stuck to some meaningful measurement standard, e.g. so-called "RMS", or EIA for continuous power and an agreed standard for peak power, then power would be a meaningful specification.

[quote name='Mr. Foxen' timestamp='1338374667' post='1673395'] He was right about resistance, but this is impedance, which he is also right about, but they are different things. I don't think you've really understood the really big fundamental differences between them and how they apply to amplifying signal. [/quote] Thanks but I can already suck eggs, having done it professionally for 30 years. Yes, of course a speaker's impedance is frequency dependent but that's not what we're talking about here. It's simply a matter of power supply impedance and power rail sag when delivering high current. It's the reason that an amplifier's maximum output power (at clipping) is NEVER doubled when you halve the load impedance. Supply rail voltage varies according to how hard the power supply is working. Test an amp into a purely resistive load and the effect can easily be seen. Use a reactive load like a loudspeaker and a fixed frequency and you'll see the same. Vary the frequency and the situation becomes more complicated but the same basic relationship still holds. Drop the load impedance and you increase the output current. The increased current results in a higher voltage drop in the power supply (and to some degree in the output devices) and the maximum available output voltage swing is now less. This really is not rocket science. It's basic Ohm's Law and there's nothing to discuss.

[quote name='Mr. Foxen' timestamp='1338337902' post='1673087'] whilst ignoring the massive flaws in the internal logic of the situation. [/quote] What flaws do you see? Was Mr. Ohm wrong?

[quote name='Mr. Foxen' timestamp='1338322884' post='1672848'] Speakers aren't a resistive load. And you need to have a scope or other means of determining when you are at max clean output, or it doesn't tell you anything relevant. [/quote] No they aren't purely resistive and yes you do need a scope or distortion analyser or similar. No disagreement there.

[quote name='Bill Fitzmaurice' timestamp='1338334423' post='1673073'] Explain then why a speaker doesn't reproduce every note at a different level, when this is what a typical speaker's low frequency impedance looks like: [/quote] We're talking at cross purposes here. You're talking about an amp's behaviour under normal operating conditions. I'm talking about maximum available output voltage swing i.e. at clipping.

[quote name='Bill Fitzmaurice' timestamp='1338317666' post='1672711'] Within the operating load ranges actually presented by speakers amps must deliver a constant voltage, otherwise they simply won't work. [/quote] Connect an 8ohm load, measure the maximum output voltage swing and then repeat with a 4ohm load. It'll be different on every single amplifier. Not even debatable, just a demonstrable as well as theoretical fact.

[quote name='Mr. Foxen' timestamp='1338318423' post='1672731'] How exactly do you measure voltage across an open circuit? [/quote] If you want to nitpick, then it's true that a multimeter across the output terminals is not an open circuit, but a megohm or so is near enough.

[quote name='Bill Fitzmaurice' timestamp='1338310418' post='1672549'] Amps deliver the same voltage swing irrespective of load impedance. [/quote] On this I have to say that's absolutely untrue. Every amp I've ever bench-tested could deliver a higher voltage swing into an open circuit than with a load connected. The power rail voltage and maximum available output voltage swing reduce as you drop the load impedance. No surprises there, just Ohm's Law and real-world imperfect power supplies.

[quote name='51m0n' timestamp='1338296724' post='1672272'] Well there you have it, Watts [i]alone [/i]doesnt come close to falling under that description, its a small part of a far more complex situation. [/quote] I think we've reached agreement, i.e. not that power is meaningless, but power alone is meaningless.

[quote name='Bill Fitzmaurice' timestamp='1338296685' post='1672271'] if the amp can deliver that voltage swing [b][i](to a specified load)[/i][/b] you'll get full output. [/quote]

[quote name='51m0n' timestamp='1338286656' post='1672031'] Enough real world volume for your gig is everything[/quote] I don't think anyone's arguing with that - at least I hope not. The point is that if meaningful and accurate figures are available, and if they are interpreted by someone who understands what they really mean, then it's possible to predict which amp is going to match your needs - in terms of output power anyway - before handing over any money. Tone is another thing. Clinical, warm or fluffy are not meaningful specifications.

[quote name='Mr. Foxen' timestamp='1338281810' post='1671935'] Didn't specify anything. Output watt ratings are pretty much meaningless anyway, so it is fully valid to be able to have a rating above the consumption, because amplifier output isn't like mains output. [/quote] I agree that power figures are meaningless - IF the measurement method is not stated. If a manufacturer provides figures for both continuous output power AND peak power for a SPECIFIED duration, then they are very meaningful. Provided they are interpreted along with other relevant info. There seem to be only two points of view around here: 1. Power is everything 2. Power is meaningless

[quote name='Mr. Foxen' timestamp='1338280900' post='1671925'] Power demands in music aren't constant, and capacitors are cheap. [/quote] Why? Because he didn't mention instantaneous power. As written it amounts to perpetual motion.

[quote name='paul_5' timestamp='1338247690' post='1671738'] the 'slower' bit is the response of the valve when the attack of the bass signal hits it - we're talking milliseconds here. That is a scientific fact. [/quote] And if we're talking nanoseconds, you'll find that valves were/are used at radio-frequencies. Clearly a bollockesque over-generalisation. Edit: I see someone beat me to it.

[quote name='Happy Jack' timestamp='1338226750' post='1671162'] But we're talking about amps ... [/quote] Current is measured in amps

[quote name='JamieMillsBass' timestamp='1337948450' post='1667856'] Its jumping about between notes like crazy with seemingly no noise whatsoever coming from the guitar. [/quote] Do you mean with the strings damped the tuner still jumps around?

The two drivers are delivering different content thanks to the crossover so phasing isn't relevant. The coaxial tweeter will influence the dispersion of the larger driver though.