vitocorleone

If lacking the proper tools to measure, here's an equation I came across by searching the Net (specifically, from www.talkaudio.co.uk)

Thoughts? Analysis on what this means for amp shoppers? Obviously, by this equation, the bigger your max current draw (fuse), the better.

elduderino

Most Class AB amps are closer to 50% efficient.

And I don't think that I'd assume that the fuse on the amp is relevant - at least on the cheap crap.

That is, if the fuse is too small, this equation will tell you, but if it's too big, then this won't.

BTW, Vito, looks like the Audison 60x4 fits under the seat too...

bhjazz

This also doesn't take into consideration the resistance ratings. Theoretically, an amplifier should double it's output when changing from, say, 8 ohm to 4 ohm, but it rarely happens...even on high-end home gear. If we get too far into this equation, it is difficult to explain 1000 watt amplifiers!

Also, yeah, don't get too hung up on the fuse thing. They are there just for safety and major overages.

biker

Of course all of these equations go out the window in 42V hybrids.

elduderino

Actually, this isn't accurate. Many amps do claim to double power into half the load... and many of those that say they do, dont ...but it is NOT a theoretical expectation of all amps. It's only "supposed to" if the manual/brochure says it is. The power supply is of course the limiting factor...

I remember when car amps that claimed this were a novelty. The first Alpine amps that were rated to do that were the 3523 and 3525, in the late 80's... the Alpine 3519 actually put out LESS power into 2 Ohms...(its replacement, the 3521, increased by 5 watts - woo).

The JL Slash amps, for instance, measure the DCR of the speaker circuit at power up and set the power supply rails to make rated power into the measured load, over a very wide range.

Bass Mechanic

doing calculations from the power side of the amp tells you nothing about its output. all amplifiers have different power supplies. they are all different as to their efficiency. if you measure the current at the supply end of the amp will tell you how many watts it generates both in heat and output but it tells you nothing of the output unless you know the efficiency.
if you want to find the actual watts of an amp run a test signal into a known load and measure it with a true RMS DVM meter. if you want to get more exact use a scope and see where it clips.

jpswanberg

Typically specialists firms underrate their equipment (especially if it is meant to be competed with). Check with ME and Car Audio to see if thgey have tested the amps. Specialists will typically rate their amps at the lowest resistance and then half the power as they go up (meaning that since no amp is perfect, you get more than the rated power at higher resistances). A couple of personal examples: 1) MTX 4300X: rated power 37.5 W X 4 into 4 ohms, actual power: 106 W X 4 into 4 ohms, 168 W X 4 into 2 ohms, 2) JL Audio 500/1 rated power: 500 W into 1.5 to 4 Ohms, actual power: 604 W into 1.5 to 4 Ohms, 3) JL Audio 300/4, rated power: 75 W X 4 into 1.5 to 4 Ohms; actual power: 103 W X 4 into 1.5 to 4 Ohms. Stay with a respected specialist who has experience. Personally, I can recommend Rockford Fosgate, MTX, and JL Audio.

elduderino

Hi, JP, welcome.

I used to have that same expectation of manufacturers, but I don't any more. Too many are starting to stretch things the other way.

Just curious, have you recent experience with Rockford? I haven't used their stuff in a long time, and I know they're hemorraging red ink at present...

Where did you get your data? (Don't get me wrong, I'm happy to find out my 300/4 is pulling into 3 digits even before I narrow my bandwidth with the internal crossovers, I'm just curious...)

You in the industry?

jpswanberg

hey, my amps came with a "certificate" which said what my amps were tested at. No, I'm not in the industry (but I wish I was). According to the store I bought them at, JL tests each amp individually, not in batches. I remember an article a few years ago in Car Audio, who tested the 300/4 as well, and they came up with numbers in the lower 100 watts per channel as well (I can't remember the specific numbers, though). Robert Zeff did the review and liked the amp. I haven't used RF in a few years either, but I was pleased with their performance then, and from looking at their literature, they seem to use the same features now. I was under the impression that they just bought MB Quart recently, so maybe they expanded a little quickly? But that is just an uninformed guess on my part.