measuring true rms of an amp
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=90576
Printed Date: June 18, 2024 at 11:26 AM
Topic: measuring true rms of an amp
Posted By: pimpedout92x
Subject: measuring true rms of an amp
Date Posted: February 17, 2007 at 11:32 AM
i heard you need an RMS clamp meter and a DMM to do this? does anyone locally have an RMS clamp meter that i could test mine with? its for my MA Audio 2/4 channel amps, i wanna know what they do on 12v...or is there a good clamp meter and DMM that will give me a true RMS reading that i can purchase? if so, link me to one  thanks
Replies:
Posted By: haemphyst
Date Posted: February 17, 2007 at 11:46 AM
Without seeing the waveform on a 'scope, you CAN'T. You have to be able to see the clipping - note this voltage, and figure the peak power with that number, which is the MAXIMUM power an amplifier can make, then multiply that by .707 to determine the TRUE RMS of an amplifier. You can't find the RMS power without knowing what EXACTLY the peak voltage is.
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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."
Posted By: soultinter
Date Posted: February 18, 2007 at 2:52 PM
I think that concept has a spot on their website that gives you instructions on how to measure RMS fairly acurately. conceptconcept.com go to techmaster
Posted By: haemphyst
Date Posted: February 18, 2007 at 9:27 PM
And their recommendation is COMPLETELY WRONG!!! If you were to take that same meter, and attempt to read the voltage at a wall socket, what would the meter read? 120v (which is the RMS voltage of wall current in the US) or 170v (which is RMS (120) times 1.414 - how you figure peak voltage when RMS is known). I'll tell you what it'd read - 120V. Unless you have bought a VERY expensive, VERY fast DVOM, you'll never be able to read peak AC voltages fast enough, even THEN you still wont have an accurate representation of the TRUE peak voltages... Voltmeters are notorious for "overshoot", meaning - the typically read HIGHER voltage than is actually present, in transient signals (meaning: MUSIC). It won't work...
I'll say it again... without being able to SEE the onset of clipping, you'll NEVER be able to tell what the peak output capabilities of the amplifer are, and without knowing the peak, you CAN'T figure the RMS.
I might mention, this company "Concept", has a "1200W RMS @ 1 ohm" amplifer, with 2 20A fuses in it. 40A X 14.4 = 576W in... By my math that amplifier is over 200% efficient! Where do I sign up? Even at 2 ohms, the efficiency is over 150%. Yeah, I'd trust that company...
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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."
Posted By: bellsracer
Date Posted: February 19, 2007 at 1:22 AM
haemphyst wrote:
I might mention, this company "Concept", has a "1200W RMS @ 1 ohm" amplifer, with 2 20A fuses in it. 40A X 14.4 = 576W in... By my math that amplifier is over 200% efficient! Where do I sign up? Even at 2 ohms, the efficiency is over 150%. Yeah, I'd trust that company...
No no no... their information is accurate if your vehicle operates at 30v >.<; ------------- Never send your ducks to eagle school.
The difference between ordinary and extraordinary is that little extra.
The 3Ls of life: Learn from the Past, Live for the Present, Look to the Future.
Posted By: forbidden
Date Posted: February 19, 2007 at 12:05 PM
Dave, the last Concept 1210w mono amp that I had come in had 3 x 30 amp fuses in it (I am sure that I have seen it with 3 x 40 as well though....wierd). That makes it right in the recommended power range.
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Top Secret, I can tell you but then my wife will kill me.
Posted By: haemphyst
Date Posted: February 19, 2007 at 4:43 PM
OK, I can believe that, Rob... I just happened to be swimming around their site, and the actual fuse ratings for any of the OTHER amps wasn't mentioned... I was referring to this one, in particular. Two, twenty amp fuses... right there, in black and white! ------------- 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."
Posted By: forbidden
Date Posted: February 19, 2007 at 5:37 PM
Looks like a simple typo or was carried over in the copy and paste from old to new or from model to model. Lets hope that is what it is. ------------- Top Secret, I can tell you but then my wife will kill me.
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