Amp gain and RMS question.

[Cubed]

Here's the formula you'll need ...Sqrt(Power*Resistance) = Voltage

(i.e. If you bridge a 4 ohm subwoofer to your amplifier that is rated to produce 100 RMS @ 4 ohms in bridged mode, you would want Sqrt(4*100) = 20 volts).

My amp is rated 450 x 1 RMS at 4 ohm, however this is at .5% THD into 13.8v. Question is I have always heard when talking about power ratings it should be at or less then .1% THD. So if my amp is rated at .5% THD then they are blowing smoke up my butt about the 450 x 1. So how can I find out what the true power rating of my amp is to properly set my gains? Would an oscilloscope work or is there some way to use a DMM to find this out. By the above formula I should adjust my gain so that the dmm reading would be 42.43. It did not come with a birth sheet, also the amp is an Aura RPM2300.

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[thch 10+ year member]

the amp may be incapable of ratings below 0.5% or the lower ratings might be associated with very low power ratings or odd resistances.

a handheld oscope almost certainly won't be able to detect 0.5% clipping. visually, anything less then 1% will be hard to see. I forget excatly what is visible on a real oscope that has more then 6 bit effective resolution. IIRC 1% was around the limit of visibility. that was on a real oscope though.

adding a bandstop network can improve resolution dramatically, and would be invaluable in trying to make detections of less then 1% distortion.

techinically a DMM could work with the bandstop, but i'm not optimistic you'll detect less then 1% distortion still.

i really wouldn't worry about that too much from a practical standpoint. its more important if you are trying to impress people your selling an amp to. other feilds of audio often give ratings at 1% THD and 10% THD. this makes sense because people will tolerate the higher distortion in hopes of more power.