# Setting Gains with a DMM, speaker connected or not?



## corrado33 (Feb 27, 2011)

Yes I searched. There were a million threads but none labeled correctly.

So I finally got all of my speakers connected correctly, polarity correct, etc, and I'm ready to set my gains.

I DO NOT HAVE ACCESS TO AN OSCILLOSCOPE, so don't tell me to use one.

I have no experience with high end stereo systems, so I have NO idea what clipping sounds like, so setting it by ear is out of the question. 

So, although a lot of people don't like to do it this way, I want to set my gains with my multimeter. 

I know the equation I need to use, it's the application I can't seem to get a good answer on. I've searched the interwebs and I've found that people say to disconnect ALL of your speakers, and some say to keep the speakers you are setting connected, and disconnect the rest of them. The load is going to change with speakers connected, so the voltage will probably change as well. Correct? (I guess I could test this.)

What if I have one gain for two channels? (Typical 4 channel amp setup). Do I still run the multimeter leads across just one speaker? So I'd touch the + lead to the + speaker terminal and the - lead to the - speaker terminal for the same speaker? Essentially testing one channel at a time. 

What tone should I play for setting gains on midbass speakers? What about mids and highs?


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## cjj2d (Jun 28, 2005)

there is a good tutorial at JL's site... Car Audio Amplifiers - Car Audio Amps - JL Audio

but you do not want speakers connected when you set the gains using a DMM. you will want to play a sine wave with a frequency that is within the speaker you are setting, such as for highs something like a 4khz at 0db. 

you will need to know exactly what voltage though for the amp you are looking for or else you are shooting in the dark.


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## Slammer (Nov 14, 2010)

I have seen this tutorial on JLs site as well, and get how to do it. What I don't get, is how you get the voltage that you want to set your gain at, if you aren't running a JL amp. I have a Hertz EP5 which is running two pairs of HSK165s. Just finished my install and set them by ear, but would very much like to set it with a DMM. Any help on this would be appreciated. 
Sorry for posing another question in the thread......


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## corrado33 (Feb 27, 2011)

The equation is sqrt(rms * ohms) so rms your speakers want times the ohms you're running them at.


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## t3sn4f2 (Jan 3, 2007)

If you're on his site you might as well take a look at his thread. 

http://www.diymobileaudio.com/forum/how-articles-provided-our-members/542-tutorial-gain-setting-amplifier-power-usage.html


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## analogrocker (Aug 1, 2009)

I'm having a weird issue setting my gains on a new Soundstream Rubicon RUB5.800 amp.

My DMM is accurate from 45Hz-400Hz. I've used said DMM for setting the gains with my old Pioneer amps without issue. But I recently installed a Soundstream Rubicon RUB5.800 amp and have attempted to set the gains using the DMM method with odd results.

I usually limit the output of my amp to work with the speakers I am using. In my case I limit the output to 35 watts RMS per channel. If I want to set my gains for this, I should turn the gain dial until my DMM reads 11.8V.

So I turn the volume up on the head unit to say 3/4 of max volume and start measuring the output voltage of the amp by playing a 120Hz @ 0dB sine wave and then adjust the gain dial until I hit 11.8V. OK it's set.

Now the weird part... If I change the test tone to, say, a 250Hz @ 0dB sine wave at the same volume, the DMM will show a drastic change in voltage (i.e. 17.5V instead of 11.8V). It shows a different voltage for all different frequencies.

My question is why?? It's not my meter because I've used it on other car and home amps with consistent results using various frequencies. It's only on this Soundstream amp that the DMM shows different voltages at different frequencies.

And yes, all crossovers are off and the EQ is set to flat, as well as the balance and fader.


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## ChrisB (Jul 3, 2008)

It could be due to the fact that the amplifier is not loaded down and as a result is only seeing the impedance of your meter. I had some amplifiers that have done some strange things in dummy load situations versus a no-load condition. 

At some point in the day I am going to test a Zapco Z100s2 and will try to compare load versus no load conditions with a DMM and Oscilloscope.


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## analogrocker (Aug 1, 2009)

In that case, I wonder if hooking up a "throw away" 4-ohm speaker to one of the amp's channels and then hooking up the DMM in addition would fix the problem? I will try it later.


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## ChrisB (Jul 3, 2008)

As promised, here is some testing:

Here is a Zapco Z100S2 in a no load condition:









with the volume on the head unit:









Here it is again with 4 ohm dummy loads:









Note the volume on the Head unit this time:









NOW, here is what happens if I go to the unloaded volume level of 30 with an actual load condition:


















In a no load condition, you'd be thinking, ZOMG, this 50x2 amplifier is underrated and gives me 83 watts RMS per channel.

Toss a 4 ohm dummy load on it and you'll be saying, crap, it makes rated power at 53 watts per channel.

Now, go back to volume 30 while loaded down and you'll see visual signs of clipping. 

FINALLY, with all of that typed, do you see why there are some who argue against using a DMM alone to set one's gain?


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## analogrocker (Aug 1, 2009)

analogrocker said:


> In that case, I wonder if hooking up a "throw away" 4-ohm speaker to one of the amp's channels and then hooking up the DMM in addition would fix the problem? I will try it later.


Well, I tried loading the amp by connecting two "junker" 4-ohm speakers to the front left & right channels but the DMM is still showing varying voltage on different frequencies. I don't know what's going on. I am abandoning the "Set Your Gains with a DMM" method for this amp. It's not reliable at all.


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## SirLaughsALot (May 18, 2011)

analogrocker said:


> DMM is still showing varying voltage on different frequencies.


You should be running a high quality test tone (1 khz for speakers, 50 hz for subwoofers) to insure that the voltage stays the same. Mine when calibrated this way does not fluctuate at all.

I also have done this without a dummy load, which I believe is NOT the best way to do it..


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## ChrisB (Jul 3, 2008)

SirLaughsALot said:


> You should be running a high quality test tone (1 khz for speakers, 50 hz for subwoofers) to insure that the voltage stays the same. Mine when calibrated this way does not fluctuate at all.
> 
> I also have done this without a dummy load, which I believe is NOT the best way to do it..


It also depends on the quality of the meter. Many of your $5 to $15 meters are only accurate around the household AC frequency of 60 Hz. Anything above and below that, expect results to vary greatly!


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## analogrocker (Aug 1, 2009)

SirLaughsALot said:


> You should be running a high quality test tone (1 khz for speakers, 50 hz for subwoofers)


I can't use a 50 Hz tone for this task because I am using a LOC. All passive LOCs usually roll off around 80 Hz or so. That's why I use a sine wave of 120 Hz or more.

Either way, I'm pretty certain that it's not my meter that's the problem. It works fine on other amps. But I do plan on getting a Fluke True RMS meter soon. I will give it another try then and see what happens.


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## djkomplex (Feb 18, 2012)

I was reading somewhere about speakers being "reactive" loads so their resistance changes... connect a DMM to a speaker, set it to Ohms and move the speaker with your hand and you can watch the value change. Before I owned a oscilloscope I would set my gains with the speakers connected and playing either a 40hz or 1kHz test tone. Unless your playing 0db test tones you should be fine with a little overpower on your speakers. I actually use a 5db gain overlap now as when I tuned the system using a 0db and then kept a oscilloscope hooked up while playing normal music; the output never reached even half of what the amp could put out. So if your setting your gains with a DMM, using a 0db test tone, you will be fine.


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## RC Audio (Mar 12, 2012)

djkomplex said:


> I was reading somewhere about speakers being "reactive" loads so their resistance changes... connect a DMM to a speaker, set it to Ohms and move the speaker with your hand and you can watch the value change. Before I owned a oscilloscope I would set my gains with the speakers connected and playing either a 40hz or 1kHz test tone. Unless your playing 0db test tones you should be fine with a little overpower on your speakers. *I actually use a 5db gain overlap* now as when I tuned the system using a 0db and then kept a oscilloscope hooked up while playing normal music; the output never reached even half of what the amp could put out. So if your setting your gains with a DMM, using a 0db test tone, you will be fine.


I just got an oscilloscope and I have set gains for three amplifiers so far just using the clipping point shown on the scoped. I know real music is far different than a sine wave which has a steady voltage so you can do "gain overlap". My question is what exactly is gain overlap and how do you do it?


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## djkomplex (Feb 18, 2012)

if you want 5 db of gain overlap, get a 40Hz tone recorded at -5db and proceed like a normal gain setting with the oscope.


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