Amp testing/comparison

Hi there, I'm Leif, and I'm new here. :) I'm currently building a system, and I'm trying to figure out which amp to use for my front speakers (Alphasonik components in kickpods). I have three amps laying around. Sony Xplod XM-7547 - a 4 channel amp, 4x75w or 2x300w bridged at 14.4 volts/4 ohms, according to the manual. Fused at 100 amps. Alpine MRV-1507 - a 2 channel amp, 2x225w at 14.4 volts/4 ohms according to the manual. Fused at 80 amps. Alpine MRV-F407 - a 4 channel amp, 4x60w or 2x160w at 14.4 volts/4 ohms according to the manual. I've learned not to put that much weight on specs, so I decided to test them to see which one would put out the most power. I hooked them up to my (running) car, and two Alpine Type-R 12 inch woofers (yielding two 4 ohm loads). I also connected an Oscilloscope in parallel with one of the woofers - so that I could actually look at the waveform and see when they clip. Then I played both deep, bassy music (Ying & Yang twins - Salt Shaker) and very peaky bass (Alicia Keys - If I ain't got you). I tested each amp in turn separately, and turned up the gain on the amp until I saw clear clipping on the scope. I was quite unpleasantly surprised when I noticed that ALL THREE AMPS CLIP AT VIRTUALLY THE SAME LEVEL. I.e., all three amps are outputting the same power - regardless of the specs! So, my question is.. Is it really supposed to be that way? I mean, the MRV-F407 is half the size of the other two. I suppose maybe the MRV-1507 would produce more power into a lower impedance load, but.. What's going on? Did I do something wrong, or is this normal? And, if I want more power than this into my front speakers, which amp should I get instead? ///Leif

What was the power output at the highest level?Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Alpine is pretty honest with their specs, sony is not. There is no need to find the maximum power output. This rating really has nothing to do with sound quality. Pick the amp that has the continuous power rating closest to your speakers continuous power rating (besides the sony).

To clarify, power output is a term so commonly misused that I don't even know how I would measure it. Clipping voltage however (at a given load) is more of an irrefutable measurement, and really tells how loud an amplifier can play without distortion. So, I didn't actually measure absolute power - I instead compared the three amps (with very differently specced output powers) and noticed that they clipped at the same voltage, thus all producing the same power. Customsuburb, the two alpine amps with different specs had equal maximum output power at 4 ohms. Let's assume that my speakers can handle infinite power (just to take that out of the equation), and that the amps sound identical (which they do), then it comes down to which amp has the highest power output. ///Leif

So, let me ask again.  What was the power output?Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Stevdart, I just said I don't know how exactly to measure it. Or to be precise, I don't know how to translate the voltage reading I got into watts. Could you tell me how to do it? ///Leif

Oh sure, I thought you would just give the voltage reading.  Use P = Esquared / R, where you square the voltage reading and divide by the ohm load to find power in watts.  You showed the amp ratings but I couldn't tell which of the Alpine amps is rated closer to what you found.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Stevdart, I believe I was getting around 12 volts peak to peak, which would equal close to 150 watts. (24*24=576, 576/4 = 144). I suppose this makes a lot of sense, because unless they put a switching power supply in to get the input voltage above 12, a bridged amp would only give you -12 to +12 volts. So, with these measurements, the smallest and cheapest amp (the Alpine MRV-F407) had the truest specs. ///Leif

In order to judge the power output comparison of the three amps, you would have to read AC volts at the speaker terminals that the load is connected to.  Use a digital multimeter.  Here is a link to a good tutorial for measuring power output, although it's not done at the car.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Indeed, except I wasn't trying to measure power outage in watts, I was comparing three amps, and they all came out very close to one another. So I guess it comes down to living with it as is, or getting another Alpine MRV-1507 amp (since it can be bridged, but will then only drive one speaker).. Of course, that'd be 900w RMS per speaker or so - might be a little much for a set of 6.5" components, even if they are alphasonik's :). I guess I'll just go for the smallest of the amps (space is always a consideration). Unless someone else has a different take on it, of course :). ///Leif