gain setting for .5 ohm?? Dont wanna blow this new amp!!

[dB-r 10+ year member]

You can buy $50 clamps at Lowes, they work good enough.

Formula that I know is this:

AC Volts x AC Amps = power output in watts

AC Volts / AC Amps = Impedance

So:

50VAC x 50A = 2500 watts

50VAC / 50A = 1 ohm

Typical impedance rise from .5 might be higher than 1 ohm, at tuning frequency, it will be closest to 1 ohm, but will go much higher as you get away from tuning frequency so it's a blind test if you ask me... Like I said $50 clamps at Lowes if I remember right... Maybe even less than that, like $45. You can use the DMM you already have to check the AC Volts coming out of the amp and use the clamp to get the AC Amps.

You can't measure the output power with a scope, or the impedance, but you CAN tell if the signal is clipped or dirty in anyway with a scope, but that would be way more of an advanced set of testing on an install than most people will ever do. A cheap DMM and Clamp will get you started, and check, DMM's are like $10 at Autozone or Oreilly's and cheap clamp is $40-$50 at lowes and you can test all day and know alot about your setup for under $100. It's worth it. And yes, some scopes are cheaper than some RMS Clamp meters. I use Fluke here, but they are not True RMS, don't really need to be either, save your money, buy the standard stuff it will read nearly identical to the high dollar "true" rms stuff. I have had bad luck with cheap DMM's reading incorrect volts though, so beware on the $10 DMM's, maybe buy a $40 DMM along with your $40-$50 clamp meter so you can at least get decent readings. IMO WAAAY better than relying on a "guess" as to what you impedance is by just using a DMM.

 

[Johnny Law.Lulz 5,000+ posts]

Im wired to .5 But expect to rise to 1ohm so Ill set it for that, Close enough for a budget daily setup with no money for anyhting other than this dmm
But Id love some clarification on the formulas, as Im unsure which is correct

There is almost no way in hell you will have only .5 ohm of imp rise. It pisses me off when people dont talk about this and try to help newer people with imp rise. They buy an amp that does 1500 @ 1 ohm for their 1500 watt sub and then wonder why its not getting too loud. You need overhead to battle imp rise. Your Imp rise is the least around the freq your box is tuned to. If your box is tuned to 30 hz, then whenever a 30hz note plays, thats when youll get closest to yolur nominal ohm setting. You can battle imp rise with a smaller box, but too small and itll sound like shit. A larger box will make the imp rise greater but itll also take less power as effiency is increased as size increases.

 

[quins90lac 10+ year member]

I just set by ear. but if you want to be picky about it Ohms Law Calculator . The answer is 27.38 but your going to be pulling 54.77 amps

 

[skmfkr 5,000+ posts]

You can buy $50 clamps at Lowes, they work good enough.

do you know the brand or model to look for? i got a $20 one from harbor freight, but its not a true rms clamp so i dont get the correct results, we were getting like 5k when i tested my rd 3250 lol

 

[bubbagumper6 5,000+ posts]

You can't set gains with a DMM. Impedance rise..... Why DMM Gain setting tutorial? it just drives me crazy. If your subwoofer is wired at 1 ohm once it starts moving it goes to anywhere from 2-9 ohms changes with frequency so how can you possible get anywhere close with a DMM to whatever power level you want if the numbers are going to be WAAAY off... Sorry for ranting, this crap drives me crazy. BUY A CLAMP METER AND A DMM, THEN set your gains so you KNOW what actual power is going to the woofer. You cannot possibly even get close without a clamp and a DMM....

It may not be the best way to do it, but it's the easiest/simplest/cheapest way for noobs to set their gains and KNOW they aren't clipping. I mean, if you set your gain using 1 ohm as your reference point, and imp rise causes it to really be 2 ohms, it's not like your going to destroy anything, your just not going to be getting full power. Most noobs will read what you said and say "Screw it, I'm not spending $100 on equipment I'm only going to use once, I'll just put the gain at 3/4 and be done." and that is certainly worse than setting it with a $5 DMM.

And to the OP, my formula is correct, check this link

http://www.thesuicidaleggroll.com/gain.htm

 

[snoopdan 5,000+ posts]

You can't set gains with a DMM. Impedance rise..... Why DMM Gain setting tutorial? it just drives me crazy. If your subwoofer is wired at 1 ohm once it starts moving it goes to anywhere from 2-9 ohms changes with frequency so how can you possible get anywhere close with a DMM to whatever power level you want if the numbers are going to be WAAAY off... Sorry for ranting, this crap drives me crazy. BUY A CLAMP METER AND A DMM, THEN set your gains so you KNOW what actual power is going to the woofer. You cannot possibly even get close without a clamp and a DMM....

This is why you buy subs with 4" coils //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif Then, you just don't care what you set it to!

 

[CoilBurner]

I guess i just go by what the chart says for 1 ohm then, for 1500rms

Ill try later

 

[Databyter 10+ year member]

The formula for the voltage measuring method is The square root of this product - (RMS to Channel X ImpedanceOHMS) So it should look like what the first poster said 1500x.5 = 750. Square of 750 = 27.4

If using a DMM set it for AC and at a range capable of several hundred volts for best results.

If your going to be using a wired sub remote volume set it on high, if your going to use a bass boost set the boost to what you will use before doing the gain adjustment.

Regarding Clamp meters etc, you're over-thinking it. A DMM is the laymans standard way to test it if your NOT doing it by ear, but using factory recommended voltages at average tones for channel.

I'm pretty sure that the guys who make the Amps know if this is a decent method for those who don't have scopes. I know the JL audio Amp I just bought, and the other I am about to both recommend using this method. Although they don't show the math, just the values, when you actually do the math you end up very very close to the charts.

And any scope worth buying will be well over a thousand dollars, and can check just about anything you mentioned, as well as the wave form itself.

Databyter