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In Reply to: RE: Why More Power? posted by Norman M on July 13, 2015 at 09:58:26
Power is volts times amps. period. Given impedance, and watts, it is a simple ohms law calculation to determine voltage and current.
Now, amplifiers DO have peak current capability. My Parasounds have some factory rating of amps output. Since my hearing is till pretty good, I'm not concerning with that measure. In fact, I doubt there is any agreement among manufacturers about HOW to specify that value. It turns into more mis-information than I'd care to deal with.
Those high currents are at a very low voltage, anyway. That doesn't do me much good though it may indicate a robust power supply.
It is ALSO true that music is NOT rms in nature. By this I mean it is very dynamic and the demand upon the amp is always changing. To this end, I look at rise time and slew rate. It is also a good idea to have some idea of 10khz square wave response.
Taken as a whole, a more complete characterization of an amp gives you a better chance of picking one simply by going with the 'on paper' results.
What you are 'up against' is an amp MAY have good output into 8 ohms but simply FAIL to get it done with lower impedance loads.
8 ohm power may be less than the ideal way to buy an amp for maggies. I'd like to know 4 ohm power as well.
I'm not very concerned with the amps ability to charge a battery or work into highly capacitive or inductive (reactive) loads since panels are a generally reasonable load in those regards.
I had a Rotel RB1070 of 125 or 135 x2 @8 which was utterly incapable of making my Panels work right. NO factory 4 ohm rating, but rather a 'bridged' rating of 330 or so at 8 ohms, which IMPLIES a 4 ohm rating of 165x2. Maybe I just didn't like the sound? I sold it within MONTHS. My bad.
The rule of thumb most Maggie owners go by is the 'double up' rule where a true voltage source amp should (or could?) double up power as impedance 'halves'
I'm not fully on board with THAT either, since you could have an amp with some huge power output which Doesn't double down as impedance halves yet still provide enough juice for your panels.
Here is a link to a 'power cube' measuring scheme. Each amp is tested for voltage output at various impedances and at various PHASE ANGLES. I suspect ANY amp which passes this test with good results should power your panels. The quality of sound, is still up to YOU, however.
Too much is never enough
Follow Ups:
"Power is volts times amps. period. Given impedance, and watts, it is a simple ohms law calculation to determine voltage and current."Uh, no. Power is volts times amps ONLY if the phase angle is zero......as in DC circuits.
It gets a little more complicated in AC circuits.
You're on the right track though. :)The AP testing scenario is a good one because it measures power at various phase angles and dynamic conditions.
Dave.
Edits: 07/20/15
Did I fail to mention Power Factor?
Beyond the scope of necessary answer trying to explain THAT, though when I linked the Power Cube measureing system, you'll get some of that information.
Too much is never enough
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