low voltage readings off amp outputs
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=127039
Printed Date: May 02, 2024 at 7:14 AM
Topic: low voltage readings off amp outputs
Posted By: irishdrunk
Subject: low voltage readings off amp outputs
Date Posted: April 20, 2011 at 11:38 PM
So I decided I wanted to check my gain match with a multimeter to reinforce what my ears thought :)
2 Alpine Type R DVC 4Ohm subwoofers, wired Series/Parallel for 4Ohm load. Wired inside the enclosure to a single terminal, which reads 4.1Ohm DC...my first thought after my initial results was "Oh crap are they wired to 1 Ohm!!!!)
So....40Hz Sine Wave 0db (off the Audiosound 2000 disc)
Head unit a tad under 3/4 volume...I get a reading of around 34 volts AC....??? That is with the gain almost 3/4 of the way up as well...set to the .01-1.0v side (the other side is 1v-8v)
I am rounding voltages to whole numbers for sake of topic btw.
I should be getting around 69 Volts....
Anyone know what is up here? It seems like If I crank up any higher there is audible distortion, and strain.
Replies:
Posted By: irishdrunk
Date Posted: April 20, 2011 at 11:40 PM
For reference
2000 Honda Civic Si
ida-x305s Head unit with PXA-H100 Imprint Module
PDX-M12 Amplifier
Posted By: j.reed
Date Posted: April 21, 2011 at 12:03 AM
IMP rise and voltage drop. ------------- 
Posted By: oldspark
Date Posted: April 21, 2011 at 1:05 AM
I presume the MX12 is a "1200W" amplifier which is 600W RMS, hence 49V not 69V.
You are measuring 290W RMS or ~300W which is ~3/4 of full volume.
Posted By: smalltime80
Date Posted: April 22, 2011 at 10:03 AM
The PDX-M12 is a 1200W RMS @ 2 and 4 Ohm monoblock amp. It's the newest model offered by Alpine. Very new and very solid. I'm not totally up on the voltage drop though. Just trying to clarify the model for further discussion.
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Nick C.
Posted By: oldspark
Date Posted: April 22, 2011 at 11:14 AM
Ah - Alpine.... they probably would quote RMS.
1200WRMS into 4R means 69V yes.
But I know not the amps specs.
But I muse at the thought that it could be fed with 2 cables at under 10A each instead of 100A....
(Sorry - that's my dig at "modern" hi-output car amp designs.)
Posted By: lspker
Date Posted: April 24, 2011 at 9:02 PM
does your meter read peak or rms value, most read rms which would be .707 of peak
not all deck and gain pots are linear, what voltage is your deck putting out
Posted By: oldspark
Date Posted: April 24, 2011 at 10:09 PM
Rarely will a meter read peak.
Most read average which is then scaled to read as if RMS (ie, assumes bandwidth limited sinewave - ie, not square, triangle or distorted...).
True-RMS read true-RMS (allegedly).
And almost all volume adjustments will ne non-linear - ie, log pots generally used (so that double the rotation is double the volume and 4x the power etc).
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