testing amp wattage

Again, RF is in the LEAD with misleading information... to whit:

Rockford Fosgate wrote: N O T I C E The method described in this document is not designed to determine the actual "rated," "peak," or "dynamic" output power of an amplifier. It is specifically written for the "do it yourself" car audio fanatic as a troubleshooting method designed to verify power output of a properly working amplifier. This document recommends using test equipment and measurement procedures that are fairly easy to work with, versus professionals who use oscilloscopes, specific voltage measurements, distortion limits and signal-to-noise parameters to accurately test and measure the actual output power of amplifiers per CEA-2006 guidelines.

Right there on the TOP of the page! Had you read both of my previous posts, you'll see WHY this method WILL NOT WORK. Also, NO meter will be accurate at 1K, so, yet again, RF is spewing crap. (I hate that company - sometimes they are as bad as Audiobling)It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

haemphyst wrote: Because the numbers regarding input vs. output calculations are suggestions. They are in NO way concrete, as EVERY manufacturer's efficiency will be a little bit different, based on topology, output devices chosen, power supply driver transistors, quality of the traces or bussbars internally, how MUCH Class A (in percentage) will the amplifier run... ALL of those things will have an effect on it's output - the "theoretical" output. If mfr A says this is a 500 watt amplifier, but it is only 50% efficient, it will have +/- X rail voltage, right? This rail voltage will be limited by the input fuse. If mfr B also makes a 500 watt amplifier, but it it 60% efficient, the output rails will be the same, (they HAVE to be, right) but the input fuse can be smaller because more power is tranferred to the output buss. It's just that mfr A chose a topology slightly less efficient than mfr B - maybe a different switching frequency, maybe a smaller toroid, larger filter caps... MANY things can affect efficiency, and since nobody advertises efficiency numbers, you'll have to use a number "that's close enough for government work", right? Since REAL output is based ON THE RAIL VOLTAGE AVAILABLE, you have to know that voltage, right? Meters won't get it, because you can be into a 10 or 15% clipped situation, before the meter even registers a difference in the voltage.

Does anyone know how to get the actual efficiency # on a class D amp or is it just around a standard percentage say 85%? I called my manufacturer and they didn't know. Is there some other calculation to get this figure?

Step 1: You must know the RMS output power, first. Figure it however you need to. Step 2: Once you know that, than you can easily figure the efficiency, as calculating the input power is easily done. DC current at DC voltage, equals input power. Step 3: Output power divided by input power equals efficiency. That formula will give you overall amplifier efficiency, including DC-DC conversion, and output stages all figured in. Obviously, you need to figure your input power AT THE SAME OUTPUT POWER that you discovered in step 1.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Do you know which amp brands have the highest efficiency? I calculated 62.5 on my Kendwood 9152.  So CEA on this puppy says 900rms and in all actuality it's 540rms. Is that legal for CEA compliancy?

No, you're using the wrong numbers. If the amp is 900 watts RMS, and it has a claimed 62.5%, then the INPUT side would be 1440 watts. 1440 watts, divided by 14.4 volts SHOULD be meaning 100A worth of fusing on the power cable. If you are not seeing 100A of fusing or MORE, then either the efficiency has been stretched, or the real output power has been, or a possible combination of both. That's all there is to it.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Ok bare with me here as I'm new to all the tech stuff. Kenwood 9152 900rms / 60a fuse / 14.4 is the voltage rating, what do you come up with and what calc do you use?

gk_thin wrote: http://www.rockfordfosgate.com/scripts/rightnow.cfg/php.exe/enduser/popup_adp.php?p_sid=VrNE2Fwi&p_lva=311&p_admin=&p_li=&p_faqid=468&p_created=1119555993 Here is a link for the do-it-yourselfer to estimate the output wattage of an amplifier.

That tests the output voltage. :/

'94 Ford Explorer / Kenwood KVT-815DVD / RF Power T1682C 6x8 (all doors) / RF Power T10001 / 12" Kicker L5 (x4) / Optima Yellow Top Battery

Yeah I need the voltage meter to work with that option.