I need some help figuring out how much power amps really put out. I know theres an equation for it.
It would be a great ARTICLE for any golds who felt into it.
Here is the senerio.
You see an amplifier on EBAY and say WOW checkout that RMS rating but than you see only a couple fuses?
Would someone be kind enough to write this?
Replies (5)
uochronos on 02/17/2004 21:25:29
basicaly amps X volts = watts(A x V = W) .... if you see a amp thats 1200watts RMS and it only has 60amps of fuses then you would need around 20volts to get the RMS value now not many amp companies are that shady as long as its 12-14.5 volts that the amp is wanting then the rms rating should be pretty accurate.
ttocs on 02/17/2004 22:04:54
except for the fact that amplifiers are generally very inefficient. If you knew the efficiency rating you would have a descent idea, but they are different for different amp...
uochronos on 02/17/2004 22:24:55
ah i wasnt even thinking about that wow i feel a little dumb.
swez on 02/18/2004 09:25:29
Yep, this is a bit more complex subject than it seems at first blush.
Class D amplifiers are generally 80-90% efficiency
Class A/B amplifiers are 50-60% efficiency
Class T or Digital amps are close to 90% efficiency
As mentioned earlier, to find the true output of an amplifier, we need to know the actual input voltage, current draw and efficiency rating. We can roughly determine the peak power of an amp, then with a little math... (Ohm's Law) we can estimate the RMS power of same.
Let's run some numbers on a popular Class D amp: JBL BP600.1
Voltage Source: 12.9 volts/specs (assumed)
Peak current draw: 57 amperes/specs (2 x 30A. fuses)
Class D Circuitry (eff % > 0.8)
RMS Ratings: 300 RMS @ 4 ohms, 600 RMS @ 1-2 ohms
The Math: (Ohm's Law)
Volts x Amps = Watts (this is peak or max rating #)
12.9 x 57 = 735.3 watts (peak draw)
RMS/735.3 = .816 eff. rating
RMS power = peak watts x eff. %
735.3 x .82 = 600 RMS @ 1-2 ohms (300 RMS @ 4 ohms)
OK, that the scoop. I did fudge a bit to determine the efficiency rating number. But we do know that the minimum output specs for this amp are 600 RMS into a 1-2 ohm load. We also know that this Class D amp is above 80% eff.
To really dial this in perfectly, we would need a regulated power supply, a fixed load resistor, a calibrated input signal (1-4 volts AC) source, a voltmeter and an ammeter to measure voltage and amps at the load resistor. Having all this test gear, we can then make a precise output measurment of a given amp.
Hope that helps,
Swez
Relax_The_Mind on 02/18/2004 15:36:35
If you break it down further to a theoretical level. According to amplifier circuits in an "Ideal" state... theoretically, cascaded transistor based amps are only but 2-5% efficient mostly due to imperfections and impurities in silicon and other transistor materials.
Most of the loss in energy from the primary power source to the subs is given off in the form of ...you know this one... HEAT!!!
If you own an amp you know at some times you can almost swear you can cook an egg on them.
my 2¢
¤¯RTM¯¤
It would be a great ARTICLE for any golds who felt into it.
Here is the senerio.
You see an amplifier on EBAY and say WOW checkout that RMS rating but than you see only a couple fuses?
Would someone be kind enough to write this?
Replies (5)
uochronos on 02/17/2004 21:25:29
basicaly amps X volts = watts(A x V = W) .... if you see a amp thats 1200watts RMS and it only has 60amps of fuses then you would need around 20volts to get the RMS value now not many amp companies are that shady as long as its 12-14.5 volts that the amp is wanting then the rms rating should be pretty accurate.
ttocs on 02/17/2004 22:04:54
except for the fact that amplifiers are generally very inefficient. If you knew the efficiency rating you would have a descent idea, but they are different for different amp...
uochronos on 02/17/2004 22:24:55
ah i wasnt even thinking about that wow i feel a little dumb.
swez on 02/18/2004 09:25:29
Yep, this is a bit more complex subject than it seems at first blush.
Class D amplifiers are generally 80-90% efficiency
Class A/B amplifiers are 50-60% efficiency
Class T or Digital amps are close to 90% efficiency
As mentioned earlier, to find the true output of an amplifier, we need to know the actual input voltage, current draw and efficiency rating. We can roughly determine the peak power of an amp, then with a little math... (Ohm's Law) we can estimate the RMS power of same.
Let's run some numbers on a popular Class D amp: JBL BP600.1
Voltage Source: 12.9 volts/specs (assumed)
Peak current draw: 57 amperes/specs (2 x 30A. fuses)
Class D Circuitry (eff % > 0.8)
RMS Ratings: 300 RMS @ 4 ohms, 600 RMS @ 1-2 ohms
The Math: (Ohm's Law)
Volts x Amps = Watts (this is peak or max rating #)
12.9 x 57 = 735.3 watts (peak draw)
RMS/735.3 = .816 eff. rating
RMS power = peak watts x eff. %
735.3 x .82 = 600 RMS @ 1-2 ohms (300 RMS @ 4 ohms)
OK, that the scoop. I did fudge a bit to determine the efficiency rating number. But we do know that the minimum output specs for this amp are 600 RMS into a 1-2 ohm load. We also know that this Class D amp is above 80% eff.
To really dial this in perfectly, we would need a regulated power supply, a fixed load resistor, a calibrated input signal (1-4 volts AC) source, a voltmeter and an ammeter to measure voltage and amps at the load resistor. Having all this test gear, we can then make a precise output measurment of a given amp.
Hope that helps,
Swez
Relax_The_Mind on 02/18/2004 15:36:35
If you break it down further to a theoretical level. According to amplifier circuits in an "Ideal" state... theoretically, cascaded transistor based amps are only but 2-5% efficient mostly due to imperfections and impurities in silicon and other transistor materials.
Most of the loss in energy from the primary power source to the subs is given off in the form of ...you know this one... HEAT!!!
If you own an amp you know at some times you can almost swear you can cook an egg on them.
my 2¢
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