JTUK Posted May 30, 2012 Share Posted May 30, 2012 oh dear.... read back a few posts and then see if you can make sense of it. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted May 30, 2012 Share Posted May 30, 2012 (edited) [quote name='dincz' timestamp='1338354523' post='1673108'] What flaws do you see? Was Mr. Ohm wrong? [/quote] 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 name='GregBass' timestamp='1338361619' post='1673133'] This cannot be true. At any specified frequency, the impedance of the speaker is fixed. That's how impedance is defined. If the voltage is constant and the impedance is fixed, then Ohm's Law tells us that the current must also be fixed, meaning that at any frequency, the power from the amp is always the same. This is clearly not the case. [/quote] We are talking maximums. You only get one maximum under a given set of criteria. You could put out full power from an amp at the top or the bottom of its frequency band, but probably wouldn't want to do the top one. Edited May 30, 2012 by Mr. Foxen Quote Link to comment Share on other sites More sharing options...
GregBass Posted May 30, 2012 Share Posted May 30, 2012 [quote name='Mr. Foxen' timestamp='1338374667' post='1673395'] We are talking maximums. You only get one maximum under a given set of criteria. You could put out full power from an amp at the top or the bottom of its frequency band, but probably wouldn't want to do the top one. [/quote] Ah - I took the quote at face value (that the voltage must be constant). That was what I disagreed with. The output voltage of an amplifier is absolutely no constant. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted May 30, 2012 Share Posted May 30, 2012 [quote name='StraightSix' timestamp='1338373740' post='1673380'] No, that is your implication. Why do you think the long-standing manufacturers/designers will have more knowledge...? [/quote] Its more important that they are current designers, and thus an understanding of how amplifiers work is really important when designing devices to play well with amplifiers. Long established ones can just keep remaking the old design and telling people its their own fault that they don't work very well with new designs. Quote Link to comment Share on other sites More sharing options...
dincz Posted May 30, 2012 Share Posted May 30, 2012 (edited) [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. Edited May 30, 2012 by dincz Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted May 30, 2012 Share Posted May 30, 2012 (edited) [quote name='dincz' timestamp='1338378349' post='1673479'] 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. [/quote] This is jsut saying that if you do a bunch of stuff that isn't applicable to the actual situation you don't get the result that you do in the actual situation. And the actual situation is more complicated. Whereas the people you are arguing with already know about the more complicated situation and are talking about it, because they deal with it in reality not in experiments where key variables have been removed. This is about learning to deal with those variables, because it is engineering and those variables are always there. Music varies in frequency, and speakers vary in impedance, those are factors that have to be considered, as soon as you don't consider them, you aren't talking about amplifying music, and thus should be posting about it in another forum. Edited May 30, 2012 by Mr. Foxen Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted May 30, 2012 Share Posted May 30, 2012 [quote name='dincz' timestamp='1338353498' post='1673105'] 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]Since most players tend to use their amps under normal conditions that's what's pertinent. [quote name='JTUK' timestamp='1338371447' post='1673334'] But to follow that on logically, you have to put their opnions and thoughts below the producers who sell volumes of the stuff. [/quote] I can't speak for Alex, but I've designed dozens of speakers for said producers, the majority of whom do not employ engineers, and are not engineers themselves, relying on independants such as myself to do their design work. [quote name='GregBass' timestamp='1338376958' post='1673451'] Ah - I took the quote at face value (that the voltage must be constant). That was what I disagreed with. The output voltage of an amplifier is absolutely no constant. [/quote]It must be a constant, otherwise the amp simply won't work. Hook up an tone generator to an amp with flat response, the amp to a speaker. Measure the voltage as you sweep across the spectrum, it will remain constant even though the speaker impedance is not. If it's not constant the amp, or generator, does not have flat response, and you'll see the same voltage fluctuation into a resistive load. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted May 30, 2012 Share Posted May 30, 2012 [quote name='Bill Fitzmaurice' timestamp='1338382721' post='1673594'] It must be a constant, otherwise the amp simply won't work. Hook up an tone generator to an amp with flat response, the amp to a speaker. Measure the voltage as you sweep across the spectrum, it will remain constant even though the speaker impedance is not. If it's not constant the amp, or generator, does not have flat response, and you'll see the same voltage fluctuation into a resistive load. [/quote] Think the guy meant it isn't constant in the sense there is no voltage when you are playing a rest etc. Its output varies massively when in use, but its output across the frequency band for a given input voltage/signal strength is constant. Bearing in mind music won't have a constant strength across the band. Quote Link to comment Share on other sites More sharing options...
GregBass Posted May 30, 2012 Share Posted May 30, 2012 [quote name='Bill Fitzmaurice' timestamp='1338382721' post='1673594'] It must be a constant, otherwise the amp simply won't work. Hook up an tone generator to an amp with flat response, the amp to a speaker. Measure the voltage as you sweep across the spectrum, it will remain constant even though the speaker impedance is not. If it's not constant the amp, or generator, does not have flat response, and you'll see the same voltage fluctuation into a resistive load. [/quote] Ah Bill - you forgot to add "under test conditions". I read your statement as meaning that under normal usage the output voltage of an amplifier is constant. If that's the case, you won't be getting no music out of it Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted May 30, 2012 Share Posted May 30, 2012 [quote name='GregBass' timestamp='1338383506' post='1673611'] I read your statement as meaning that under normal usage the output voltage of an amplifier is constant. [/quote]You misunderstood. Quote Link to comment Share on other sites More sharing options...
GregBass Posted May 30, 2012 Share Posted May 30, 2012 [quote name='Bill Fitzmaurice' timestamp='1338385013' post='1673645'] You misunderstood. [/quote] Indeed I did - sorry for any confusion Quote Link to comment Share on other sites More sharing options...
dincz Posted May 30, 2012 Share Posted May 30, 2012 (edited) [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. Edited May 30, 2012 by dincz Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted May 30, 2012 Share Posted May 30, 2012 There isn't a way of power rating speakers that isn't frequency dependent though. Sensitivity would be useful, but there isn't a standard for that as applied to cabs, you get one with speakers though, so you can sort of extrapolate onto a cab if you understand a bunch of other factors. The fact that sensitivity is the determining factor between voltage swing from the amp and spl renders watts meaningless. Quote Link to comment Share on other sites More sharing options...
dincz Posted May 30, 2012 Share Posted May 30, 2012 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 Link to comment Share on other sites More sharing options...
Mr. Foxen Posted May 30, 2012 Share Posted May 30, 2012 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 Link to comment Share on other sites More sharing options...
dincz Posted May 30, 2012 Share Posted May 30, 2012 (edited) [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? Edited May 30, 2012 by dincz Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted May 30, 2012 Share Posted May 30, 2012 Nope, nominal impedance is a fairly useful speaker spec in comparison to thermal rating. Quote Link to comment Share on other sites More sharing options...
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