setting my gain with a DMM?

[smashedz28 110]

Alright, read thru the pinned topic for this, seems easy enough..but im doing something wrong.. im usin an old school volt meter but it has "ACV 200 and ACV 500" .. i set it to ACV 200 (AC volts)..the amp is a Sundown SAZ1500D running at 1 ohm so...

voltage = sqrt (1500 * 1)

voltage = 38.72 ish..

can someone verify that please...

so i pop in the 50hz test tone, loud off, bass boost off..volume to 3/4 and I stick the voltmeter to the outputs of the amp.. it tells me 2.8 and up to 5.something at full gain.. something is wrong just not sure what. appreciate any help.

[CrazyKenKid 64]

38.7 is correct!

did you unplug the sub from the amp?

also the numbers you are getting are the numbers from the h/u

if your preout voltage is 2volts then set your gain to 2volts and call it a day! if you need it louder turn it up a bit at your own risk lol!

[smashedz28 110]

yes the sub was unplugged, i believe the deck is a 4v output.. but why am i getting that voltage? If thats all i have to match whats with the 38.7 thing?

[smashedz28 110]

Bump.... Anyone help me with this?

[Adrian_D 520]

First of all you don't measure without a load.

What happens is when you wire a load the maximum voltage output drops (a lot, depending on the actual impedance) and the "settings" are not going to be worth anything.

Are you sure you are measuring the outputs right ? IE measuring across the plus and minus terminal:)

[Impious 1,476]

How does it sound to your ear? Does it sound like output is virtually non-existent, or does it sound "normal"?

[smashedz28 110]

This is how i did it.. turned the vehicle on.. unplugged the + and - wires from the sub. turned the volume up to about 3/4 with a 50hz test tone .. set the meter to ACV 200 and placed the positive and negative 'prongs' where the subwoofer was hooked to.

How does it sound to my ear.. lol.. its lovely... its going to tear my Tahoe to shreds real soon.. thing i worry about is this is my first very high powered sub, I dont think im capable to knowing when im putting the sub in danger. Nothing sounds dirty yet to my ear, just dont want to risk hurting this thing. Not sure why i got such low voltage at the amplifier. I was expecting to match it around 38.7 and i get 2.8 - 5.x volts.. something has to be wrong. Just would like to understand.

[Impious 1,476]

If the sub plays fine (output wise), I would guess it's just the measurement. Try borrowing a different DMM & compare measurements

[smashedz28 110]

The dmm I used is an older one, but seems to be good, I'll try to get my hands on another soon. Thank you.

[95Honda 486]

You've just wasted all your time. Like Adrian said, without a load it was meaningless. Also, without knowing if it is even reading true RMS, it is again meaningless using any equations. Additionally, without accurate measurement, you don't have a clue what impedance you are dealing with....

Everytime I read one of these threads it just makes me realize how much time people waste with this. Especially when you see numbers like 45.678 VRMS.... LOL...

[jcarter1885 995]

So basically this is pointless and shouldnt be stickied? Lately I havent been telling people to use a DMM to set their gains since some of you guys say it isnt right.

http://www.soundsolutionsaudio.com/forum/How-To-Set-Amplifier-Gain-t3704.html

[95Honda 486]

It is just a waste of time. Especially if you only have one sub amp and are not trying to match a ton of amps....

Here is why-

Most people have no idea what impedance they are setting the voltage gain of thier amplifier at, therefore they have no idea how much power the amplifier is actually producing...

Most people don't have true RMS voltmeters

Most people don't have a clue that the gain adjustment does nothing but set the voltage sensitivity of thier amp. They also don't have a clue that it was only put there by the manufacturer to overcome maximize S/N ratio and match HU output levels, NOT to "Keep anything bad from happening"

Set it all you want, if you are a tool, you will still find a way to overdrive your subwoofer

Clipping doesn't hurt anything....... Don't argue this unless you are willing to complete an in-depth test with accurate test equipment and publish your results as I have...

If you can't tell when your subwoofer is overdriven by ear, and are putting faith in your "setting gain with a DMM" you need to buy an amp that has drastically less power....

Many of the posts I read dealing with this on here make it painfully obvious that many people have no idea how to use test equipment accurately/correctly

Seriously, it is 99% mental masturbation with this on here.

One amp? It's easy. Turn the F'n gain all the way up, especially if you have a variable subwoofer output on your HU. If you don't have a variable subwoofer output, you may not have to turn it up all the way, maybe just set it near the nominal pre-out voltage of the HU. Listen to music and don't overdrive your sub. That's it. It takes 5 minutes and no test equipment. If you can't handle this, you are out of your league as far as your equipment goes...

[Impious 1,476]

I've never been a real advocate of the DMM method.

Is it accurate? No, not really. From the get-go, the formula, you're making assumptions that will render the entire exercise futile. That "4ohm" driver will hardly ever present a "4ohm" load to the amplifier, and you're assuming that the manufacturer's rated power is accurate. Then you have the "meaurement" factor, the accuracy of the measurement itself as 95Honda pointed out. Beyond that you also have the issue of gain structure; most people use 0db which gives a gain ratio of 1:1 and also provides the lowest average output from the amplifier with a non-0db source (such as music). Richard Clark and others advocated a -10db test tone for a ~ 3:1 gain structure, which increases the average output from the amplifier when used with non-0db sources (such as music) at the risk of clipping the musical peaks (they argue that since peaks are transient and dynamic as well as the masking tones in music, any distortion from clipping won't be audible and the increased power won't damaging).

But, it helps get someone newer or unsure within the ballpark. Given most people's perception that "louder is better" and/or inability to identify driver strain, they may not be able to make an educated adjustment by ear alone which potentially increases the possibility of damaging equipment. Once they are in the ballpark they can make further minor adjustment by ear with music to dial it in. It's not a perfect method, but neither is setting it by ear. Unfortunately many people do buy equipment beyond their experience (I actually can't help but laugh at the number of people who are asking about 3kw amplifiers, then ask how to set the gain or where to set the bass boost).

Clipping doesn't hurt anything....... Don't argue this unless you are willing to complete an in-depth test with accurate test equipment and publish your results as I have...

I know you are aware that the issue isn't clipping itself, but the potential increase in average power as a result of clipping that can potentially be damaging to the drivers. The shape of the waveform doesn't matter (normalized power in your test), but the increase in power from a hard-clipped amplifier (normalized voltage in your test) can be damaging to the drivers. The latter being applicable to the discussion of the thread, which does make it a potential hazard.

To quote your test;

Normalized voltage (AKA amp at full clipping). This shouldn't have been much of a surprise to anyone knowing that a square wave with the same Pk-Pk voltage as a sine will have almost double the power. As you can see on the spreadsheet and graphs, power handling severely dropped when the square wave was applied in this test. Time to failure was cut by a factor of 4 for most drivers.

[smashedz28 110]

lol...95, your real smart bro.. but in no way possible have i wasted any time whatsover. i came here to find an answer, its something i didnt understand. All i needed was someone to come in here and shoot me an intelligent answer i could understand. Maybe i dont know how to use my voltmeter correctly.. maybe you should use some of your knowledge and write up one of those guides? Even though you seem to talk with the 'im smarter than you attitude" ill take what you have said and learn from it. appreciate the post.

[Don Ganso 13]

Perhaps some of this info should be added as a disclaimer in the "How to set your gains with a DMM" sticky.

[95Honda 486]

Most of the time when someone farts around with a DMM trying "set thier gain" they have wasted time... Lol..

Then, if they think they have done it right, most of the time they have just given themselves a false sense of security and thier next thread is "My FI Q stopped working, how do I get my money back???"

I am not trying to come off ass a smartass, it is just hard not to sound that way when you read this everyday on car audio forums for 10 years......

There doesn't need to be an article on this. The gain control sets the voltage gain of the amplifier. That's it. If you need more info, google "Amplifier Voltage Gain" there will be plenty of information there....

To be honest, these days at least, you don't even need a gain adjustment (as far as the sub amps are concerned) 99% of the time. It is just one more thing in the signal chain to foul up someone......

And if you are so running the ragged edge of power handling that if you ever so slightly drive your amplifier into clipping and this single event causes the slight increase in power to fry your sub, you have other problems and shouldn't blame this on snything but yourself...