Question

[Austin863 87]

According to Ohm's law I = V / R where I is current (amperes), V is volts, and R is resistance (ohm), we can derive Power (watts) = voltage * current.

As impedance (ohm) increases, current (amperage) lowers, so you end up with less power (watts).

Now you should be thinking: "But hey, my speakers are wired to 1ohm, so impedance isn't changing."

The voicecoil(s) in speakers are coils, and they have a nominal resistance measured in DC (this will be the Re value in the T/S specs of the driver), but this resistance changes when it's in an AC circuit. The reason it's not referred to resistance in an AC circuit is because it does change as it's actually a function or ratio in relation to the voltage and current.

As the voice coil heats up, impedance increases, and less current can "flow." So you could play a constant sine wave, and in the first two seconds measure 100watts, but in ten seconds, only 70watts.

Also, as frequency changes, impedance changes, and sound is composed of tons of different overlapping frequencies.

The speaker enclosure will also effect impedance in conjunction with frequency.

You may have seen graphs or models of impedance vs frequency for a specific speaker or enclosure design, they are never flat lines, nor are they exactly linear either.

So unless your playing constant sine waves all day, the impedance in the circuit for the amp's output is constantly changing, and thus the power output is constantly changing.

Don't fret about matching amp power ratings to speakers' RMS values. Just another thought to consider: You need to double power in order to increase loudness by 3dB, and that would be with an 100% efficient speaker, and depending on the frequency, 3dB isn't much of a change to the ear--if any.

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I'm sure someone else can better explain, or correct any flaws above, but hopefully you get the jist of it.

okay i understand so basically you're sub is going to see a range of different amounts of watts. i gotcha. not just a constant 1500w alright

Yes, the maximum output of the amp will be lower then it's rated 1500w because the impedance will be higher then 1ohm, and of course, music is dynamic.

Okay cool thanks for the info man. Ill keep all that stuff in mind.