Question about Gain setting

[spoonraker 10+ year member]

don't worry, this isn't the standard "how do you set your gains" question. I've already read up on the DMM method of properly setting your gains, I understand the math, and have done it on my own setup...but here's my question.

On my current setup it was easy, I had 1000W @ 1 Ohm and my sub was exactly 1000W RMS....but on my new setup I'm running a 1200W amp to a 1000W sub....so when I go to do the math, do I use 1200 as my power or 1000?

In other words, for figuring out the proper voltage of a 1200W amp hooked to a 1000W RMS sub, would I use sqrt(1200) or sqrt(1000)?

Click to read more...

 

[rlcowboy 10+ year member]

Most of us that have been in car audio for a-lot yrs can set gains by ear but the ONLY TRUE CORRECT WAY to set your gain properly is with a sine-wave test tone CD,like the Auto Sound 2000, and an AC Volt meter. I know some folks say you can use the dif. formulas out there but it's NOT the correct way to do it! Thats not my opinion it's just a plane simple fact! There r so many drivers on the market today that there is no way u can use those formulas that some folks have come up with to set ur gains properly. Now I'm not saying that u coul'nt use a formula and probably get it sounding pretty good cause I'm sure u could but if u are interested in setting ur gain the absolute correct way then u need to get the sine-wave test tone CD and a basic $15 AC Volt Meter. When u set it this way u will be able to turn ur audio system up to full volume with NO distortion at all. Now also I am assuming that u would want your drivers to be properly balanced with ur front stage and rear stage and not one of those folks that "CLAIM" to have a killer audio system but in fact all they have is some 2000 watt 18" sub that will rattle all the windows in his town and the ONLY NOISE the SO-CALLED system will make is something that sounds like boom,lol. I mean why not just get an air horn or jack hammer, I mean they both makes loud noise that anoy others too,lol. Well to me just having some big driver that goes boom and shakes ur car is far from a nice system. You can get the sine-wave test tone CD through Crutchfield or ebay, thats the Auto Sound 2000. Or u can borrow mine. There othe sine-wave test tone CD's out there, it's just the Auto Sound one is the one I personaly use & recomend. Like I said if u want u can borrow mine if u leave a few thousand dollars cash with me as a deposit,lol. Here is a link to JL's page that will explain it in detail for ya. Good Lc

http://mobile.jlaudio.com/products_amps_pages.php?page_id=30

 

[phyphoestilic 5,000+ posts]

seems to me u answered ur own question. The sub can take only 1,000 rms. So doesnt it make sense to only feed it 1,000?

 

[spoonraker 10+ year member]

I don't think you quite understand what I'm asking....

Basically here is how I understand you set gain :

1. Disconnect speakers from amp, turn head unit volume to ~85% maximum, turn amp gain all the way down

2. Calculate your target AC voltage. This number comes from the following formula : Voltage = sqrt(Power * Resistance)

3. While playing a test tone, connect an AC voltmeter to the amplifier speaker outputs, turn the gain up until you reach the desired voltage

4. Turn everything off, plug everything in, play the system at a moderate volume, and determine if anything needs to be turned down. Nothing should be turned up, only turn down the drivers that are overpowering.

That all makes perfect sense to me, but my question is about step 2.

When using the formula Votage = sqrt(Power * Resistance) are you supposed to use the Power your amplifier is rated at, or the power your subwoofer is rated at? My best guess is that you are supposed to use the amplifier power, since this formula is designed to determine maximum AC voltage without a clipped signal.

 

[phyphoestilic 5,000+ posts]

well if u do it that way then u'll be sending 1,200 watts to the subwoofer right? So it could potentially overpower the subwoofer. So it only makes sense to set it at 1,000 cuse thats what ur subwoofer can take. //content.invisioncic.com/y282845/emoticons/eyebrow.gif.fe2c18d8720fe8c7eaed347b21ea05a5.gif

 

[spoonraker 10+ year member]

So the gain actually does change the power outputted by the amp? I wasn't sure exactly what the gain did, I just knew it wasn't volume knob.

 

[shovelhd 10+ year member]

The amp gain control changes the signal level to the output section of the amp where the power is made.

Let's say your head unit starts to distort at 28/35, so you'll want to set the gains with the HU at 26/35. Let's also say that at 26/35 with a 500Hz 0dB tone, your HU output is .75 volts. Finally, let's say that your amp makes full rated RMS power with a 1V input voltage. Turning up your amp gain control makes up the .25V difference by boosting the input voltage that your HU can't put out cleanly. It's not a volume control, it's a voltage gain control, and it should be used sparingly.

As others have said, set the amp gains to match what you feel your speakers can handle.

 

[PatFitz9 10+ year member]

you use whatever number you want to send to the sub(s). if you have a one billion watt amp and a 1000 watt sub it's the same calculation as a 1000 watt amp.

 

[Immacomputer 10+ year member]

Most of us that have been in car audio for a-lot yrs can set gains by ear but the ONLY TRUE CORRECT WAY to set your gain properly is with a sine-wave test tone CD,like the Auto Sound 2000, and an AC Volt meter. I know some folks say you can use the dif. formulas out there but it's NOT the correct way to do it! Thats not my opinion it's just a plane simple fact! There r so many drivers on the market today that there is no way u can use those formulas that some folks have come up with to set ur gains properly. Now I'm not saying that u coul'nt use a formula and probably get it sounding pretty good cause I'm sure u could but if u are interested in setting ur gain the absolute correct way then u need to get the sine-wave test tone CD and a basic $15 AC Volt Meter. When u set it this way u will be able to turn ur audio system up to full volume with NO distortion at all. Now also I am assuming that u would want your drivers to be properly balanced with ur front stage and rear stage and not one of those folks that "CLAIM" to have a killer audio system but in fact all they have is some 2000 watt 18" sub that will rattle all the windows in his town and the ONLY NOISE the SO-CALLED system will make is something that sounds like boom,lol. I mean why not just get an air horn or jack hammer, I mean they both makes loud noise that anoy others too,lol. Well to me just having some big driver that goes boom and shakes ur car is far from a nice system. You can get the sine-wave test tone CD through Crutchfield or ebay, thats the Auto Sound 2000. Or u can borrow mine. There othe sine-wave test tone CD's out there, it's just the Auto Sound one is the one I personaly use & recomend. Like I said if u want u can borrow mine if u leave a few thousand dollars cash with me as a deposit,lol. Here is a link to JL's page that will explain it in detail for ya. Good Lc http://mobile.jlaudio.com/products_amps_pages.php?page_id=30

You are an idiot. Did you read his post? Did you read JL's link? Do you have a **** clue what you're talking about? I already answered that last question though.

The BEST way to set your gains is to use a nice scope, your eyes, and your ears, not this terrible DMM method.

 

[spoonraker 10+ year member]

I wish I had an oscope...

I've also heard some people can hear distortion, but since I've had nothing but cheap **** up until this point I doubt my ears can tell when something doesn't sound right lol

 

[PatFitz9 10+ year member]

thats my problem with setting it by ear, different people hear differently.

 

[spoonraker 10+ year member]

Obviously an oscilloscope is the way to make 100% sure no clipping is occuring, but is there anything wrong with the DMM method? I see so many people talking **** about the DMM method saying it a scope is way better, just use your ear, blah blah blah, but can somebody explain to me what is actually wrong with the DMM method? As far as I can tell, if you do it correctly, there is no way that it could be wrong...

 

[Immacomputer 10+ year member]

1) I don't trust any DMM that cost less than $100 and isn't a true RMS meter from a nice name brand. I have seen many DMMs tell me all sorts of crazy numbers, especially with AC.

2) I don't trust amp manufacturers to correctly label their amps. I don't care if they're underrated or overrated.

3) When you attach a load to the amp, your calculated gain setting may change and give you even less power than you set it for.

4) I don't trust DMMs.

5) I don't trust manufacturers (and yes, that includes all forum boner manufacturers as well).

 

[spoonraker 10+ year member]

Well I have an Autotek amp, and I've never heard a bad word said about Autotek. It will do what it's rated and probably a bit more from what I've heard.

And I'm assuming my multimeter is accurate, it's actually my dad's from when he was an engineer for texas instruments

 

[Immacomputer 10+ year member]

I don't assume anything, even if the amp and DMM were made by Jesus himself.