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***How to set the gains with a multimeter.***

Old 09-24-2006, 07:17 PM
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Lightbulb ***How to set the gains with a multimeter.***

Alright, I suppose you guys could call this a help tutorial but I am actually just trying to find out if the following is pointless or not.

I read this sticky on another forum, I want to know if it really works because this is what I have been using to set my gains and it seems like it is better than just setting the gains by ear. This is how it is done:



Quoted from fullsizechevy.com,

"Most audio equipment dies for one simple reason. Most people push their equipment beyond its limits. Whether it is the amplifier, subwoofer or full range speakers, clipping is the number one cause of failure. To prevent clipping, use this tutorial.

To figure out what voltage you should set the gains to, multiply the RMS power of the amplifiers output by the impedance of the speaker, then find the square root of that number. If you are using an amplifier that has an RMS rating of more than your speaker(s) can handle/rated for, then use the RMS rating of the speaker (instead of the RMS of the amplifier) to determine the voltage to set your amp to. This is also referred to as gaining down.

Gain Setting Equation
Voltage of the output = sqrt(RMS Power X impedance of the speaker)
Example
Say the amp provides 100WRMS into a 4 ohm speaker:

Voltage = sqrt(100W X 4 ohms)
Voltage = sqrt(400W*ohms)
Voltage = 20V

Again, that was only an example, use the ratings of your amp to figure that out.

Setting the Gain(s)
To set the gain(s), you need two things:
1. A DMM (digital multi-meter) that is capable of measuring AC voltage (needs to be able to measure up to a range of 200V).
2. A test tone CD to use to set the gains at the correct setting.
Now, to set the gain(s):
1. Start the vehicle, and pop the test tone CD in the head unit.
2. DO NOT hook up the sub(s) or speaker(s) to the amplifier while doing this, just leave the outputs unused at this time.
3.Now, time to set up the head unit.
a. If the loudest you listen to your music at on a regular basis is 22/35 with bass @ +3 and treble @ 0 with MX (or any other sound processor) on, use those settings. NEVER turn the headunit above 3/4 of the maximum volume.
b. Remember to have the car turned on.
c. If you want to use bass boost on a sub amp, set it prior to setting the gains on the amp and use the center frequency of the bass boost (45 Hz for most amps) as your test tone.
d. Please remember that if you have a subwoofer volume control on the headunit, set it to full before you set the gains on the sub amp.
3. Take the leads from the DMM and but them on the outputs from the amp.
4. Set the gain so that the outputs of the amplifier equal the voltage you found above. This is a MUST.
Here is JL Audio tutorial on their site:
http://www.jlaudio.com/tutorials/Input_Sen...ensitivity.html

And here is 20-80Hz test tones:
http://www.ronelmm.com/tones/

For test tones higher than 80Hz, download this program and you can create your own:
Adobe Audition Trial Version

It is best to use 50 Hz tone for a sub amp (unless you have bass boost, use the frequency that is boosted as the tone), and a 1kHz tone for a full-range amp.

This is a good way to set the gains, but if you have access to an oscilloscope, by all means use it. Then you can set the gains to their absolute maximum as you can see when the amplifier clips.

If you are wondering what exactly clipping is, and what it looks like, read this:
http://www.bcae1.com/2ltlpwr.htm

If you have any questions about this, post up, I’ll try my best to answer them.

Also, remember a sub can only handle what it can, if you set the amp to its RMS you have to remember that the sub can handle only so much. It is box dependant, but it is best if you are not experienced to follow the manufacturers recommendations.

Enjoy, and remember to thump responsibly!"




Let me know what you guys think cuz it is a big convieniance for me and I feel better about turning my H.U. to 3/4 volume. Thanx guys.

Last edited by Lspade69; 09-24-2006 at 07:22 PM.
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Old 09-24-2006, 09:48 PM
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that post is only useful if you're using a decent, true RMS multimeter, not a cheapo DMM.

if you're going to use a cheap DMM, only use a 60 Hz test tone, since that's all that will be accurate.
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Old 09-24-2006, 10:03 PM
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So how do i know if I have a dmm or an rms meter? Its my dad's meter that he used on the farm equipment but I am guessing it is a cheapo. Are rms meters hard to find???? Thanx for the tip about 60hz's. I will remember to use that tone next time.
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Old 09-24-2006, 11:47 PM
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what is the name on it ?
is it a Fluke ?
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Old 09-25-2006, 12:02 AM
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I've posted somewhere before about setting your gains with a meter, but that is a very good detailed instruction. I like it!
Not all Fluke DMM's are true RMS. The fluke 70, is not. The fluke 80 is.
I have a meter that i know is only accurate up to 400hz, but that works, except for my tweeters.
I also like what the article said about clipping, more speakers are blown by distortion at low power than overpowering.
I made the mistake of lending my test cd to a guy at work. Now he doesn't work there. Now i need a new cd.
I can probably download something, but who knows if the levels are calibrated.
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Old 09-25-2006, 01:51 AM
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whoever wrote that is fairly cluesless

for starters the speakers/subs should not be disconnected

I recommend a search on the subject at carsound.com if you want to know the correct procedure..... also a true RMS meter is probably going to set you back at least $100...

Last edited by Haunz; 09-25-2006 at 01:54 AM.
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Old 09-25-2006, 03:32 PM
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Originally Posted by Haunz
also a true RMS meter is probably going to set you back at least $100...
Ouch, I can feel my wallet's pain just thinking about it.

I suppose I will start searching around then on carsound, thanx.

EDIT: Do you guys know if the Fluke 10 is rms??? I am guessing not cuz my dad said he only paid like $80 or something around that price range for it.

Last edited by Lspade69; 09-25-2006 at 03:36 PM.
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Old 09-25-2006, 10:47 PM
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Stereo System Test & Analysis Tones by Nino B. as mentioned above is a great site if youre looking for test tones. The great thing about it, is you can play indivdual tones not just a sine sweep...and as a bonus, he states on the site "feel free to download, burn and distribute" ...
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Old 09-26-2006, 01:05 AM
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trust me man testing speakers the speakers aint really worth your time... first you need the dmm then you at least need to know the actual impedance of your speaker if not have an rms current clamp....

.... now that I think about it for 2 more seconds the best advice IMO is to hook up a 10 ohm non inductive resistor.... a 10w will work, just drop it in some oil or -distilled- water to keep it cool... now set the levels with your cheap dmm using a 60hz tone (where its accurate)...

that should be a decen't approximation...

Last edited by Haunz; 09-26-2006 at 01:28 AM.
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Old 09-26-2006, 01:38 PM
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Originally Posted by Haunz
trust me man testing speakers the speakers aint really worth your time... first you need the dmm then you at least need to know the actual impedance of your speaker if not have an rms current clamp....

.... now that I think about it for 2 more seconds the best advice IMO is to hook up a 10 ohm non inductive resistor.... a 10w will work, just drop it in some oil or -distilled- water to keep it cool... now set the levels with your cheap dmm using a 60hz tone (where its accurate)...

that should be a decen't approximation...

thanx haunz I will do that next time
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