Question about setting gains with DMM

[gamehawk55 10+ year member]

Hey everyone.

So I'm getting a set of Sundown SA-8v2 D2's in tomorrow so today I wanted to check what kind of AC voltage the sub channel on my amp would push out to make sure I could get the amount of wattage to the subs that I want.

My amp is an Audison LrX 5.1K and is listed at 1150W @2ohms on the tech sheet. So I used the equation sqrt(watts x ohms) to find that I needed to see 47.95v on the DMM to be aprox. 1150W.

I will explain my current setup a bit to give a little more info on this.

I'm running a Kenwood DDX419 Head unit (4v Preout), but I'm not running my speakers off the amp so I can only turn up the HU to about 15-20/35 to get to my max listening volume so would definitely not be putting out 4v from the preout. I am also running a Cache Line Driver to help boost the voltage a bit but still definitely needs a lot of extra gain to hit the proper voltage. So now when I go on with this story you will know why my gain is going so high haha.

So anyways with no speaker hooked to the sub terminal on the amp I ran a 60hz test tone at volume 17/35 and managed to hit the 47.9v (1150W) at about 3/4 gain. Now onto my final question.

I'm pretty sure this amp is underrated on the sub channel because I was able to get 66.6v(number of the beast haha) before the amp went into protection. Now what I want to know is if it would be safe to go higher than the 47.9v or will that most likely be clipping the amp? Or is there no real way to tell without actually putting a load on the amp and using a scope or something like the SMD Distortion Detector?

And actually with a proper 2ohm load on the amp will it require more gain to hit the RMS voltage or less gain? I'm not sure how the resistance will affect the AC Voltage. How much resistance is going to the amp with no speaker attached? Zero Ohms?

Click to read more...

 

[Tenacious]

I guess I missed the point, but why is your max listening volume only about 20? I usually listen to music with my Kenwood HU between 22-25/35 and up to 28/35 if I want some extra volume.

 

[gamehawk55 10+ year member]

I guess I missed the point, but why is your max listening volume only about 20? I usually listen to music with my Kenwood HU between 22-25/35 and up to 28/35 if I want some extra volume.

Because I have a Pontiac G6 with the monsoon system. So the stock speakers aren't only being powered by the HU they are also being pushed louder by the Monsoon amp which cannot be adjusted. That's why my max volume is 15-20

 

[gamehawk55 10+ year member]

It still sounds good just needs a hell of a lot more gain on the amp to push it to the proper levels because of the lower volume on the HU

 

[gamehawk55 10+ year member]

I guess I missed the point, but why is your max listening volume only about 20? I usually listen to music with my Kenwood HU between 22-25/35 and up to 28/35 if I want some extra volume.

Did you have any more input on the situation?

 

[Tenacious]

Did you have any more input on the situation?

I'd keep the gain where you have it unless you can use an O-scope. I've heard that it's safe to use up to about 3db of bass boost on max recommended gain though, due to music not being quite the same as a sine wave. Like I said, your best bet would be to locate a O-scope or DD-1

 

[gamehawk55 10+ year member]

Wouldn't increasing the gain a hair to like 50v be better than using the bass boost? because the bass boost on my amp says its for a 50hz boost. Also on a side note when I adjust the X-over on my amps sub channel it seems to make the sub louder. Even if I'm playing a 50hz tone and I adjust the X-over from 85hz to 100hz the sub gets louder. Is that normal? Cuz in my mind it shouldn't because the X-over is already way higher than the frequency being played. Or am I a little mistaken on how a X-over actually works?

 

[The Squeakquel 10+ year member]

I'd keep the gain where you have it unless you can use an O-scope. I've heard that it's safe to use up to about 3db of bass boost on max recommended gain though, due to music not being quite the same as a sine wave. Like I said, your best bet would be to locate a O-scope or DD-1

Neither of those are necessary or useful for setting a gain. The SMD DD-1 is an even worse idea. All you really need is your ear and common sense.

 

[The Squeakquel 10+ year member]

Wouldn't increasing the gain a hair to like 50v be better than using the bass boost? because the bass boost on my amp says its for a 50hz boost.

Don't increase the bass boost.

If you're at ~48V right now, adjusting the voltage to 50V isn't going to make a damn bit of audible difference.

My guess would be that you used a 0db test tone to set the gain with a DMM.....which is what's causing your problem of anemic output with music. If using the DMM gives you the warm-fuzzy feeling inside, use a -6db test tone instead. If you are comfortable, best thing to do is just set it by ear and listen for stress from the subwoofer.

Also on a side note when I adjust the X-over on my amps sub channel it seems to make the sub louder. Even if I'm playing a 50hz tone and I adjust the X-over from 85hz to 100hz the sub gets louder. Is that normal? Cuz in my mind it shouldn't because the X-over is already way higher than the frequency being played. Or am I a little mistaken on how a X-over actually works?

Crossover Slope Basics

 

[gamehawk55 10+ year member]

Neither of those are necessary or useful for setting a gain. The SMD DD-1 is an even worse idea. All you really need is your ear and common sense.

How do you figure that an O-scope or SMD DD-1 be useless? They are supposed to be the best ways to set your gain because you can actually SEE when you're at your max amount of gain. It's not like a have to worry about overpowering these subs because they will take 1000W daily each no problem and my amp puts out nowhere near 2000W so I just need to find the absolute max that I can set the gains for this amp. And as for using my ear to listen for distortion, either I can't hear it or my old JL 10W7 was just too worn out that it was just distorting all the time because I couldn't hear any audible difference in the speaker as I turned up the gain. Either that or I couldn't turn up the gain far enough to clip it, because that sub was old and in the last year started making a "pop" when it hit hard or excurted to a certain point. Which I thought was the sub being pushed too far but since I could never hear and audible difference in the tone that's what I figure maybe the gain wasn't high enough to clip it.

 

[The Squeakquel 10+ year member]

I'm pretty sure this amp is underrated on the sub channel because I was able to get 66.6v(number of the beast haha) before the amp went into protection.

That measurement has nothing to do with the amp being underrated. Your measurement doesn't include distortion, which is important when trying to compare to "rated" power which is rated at a specific distortion level. Every amplifier on the market is capable of producing more power than it's rated for, but the distortion increases to a significant amount at those levels. We also don't even know if that measurement with the DMM was RMS or peak, and that makes a huge difference.

It also depends on how badly you were clipping the amplifier. Worst case scenario if you drove the amplifier to the point of producing a true square wave it would "appear" to have 2x the output since Vrms = Vpeak for a square wave. Point is, with knowing nothing but the voltage it's impossible to determine whether or not the amplifier is "underrated" as the results are in no way comparable to the rated power figure and generally aren't really useful at all.

Now what I want to know is if it would be safe to go higher than the 47.9v or will that most likely be clipping the amp?

If you were using a 0db test tone then yes it's safe to go over 47.9V since music is almost never at a level of 0db. What is "safe" depends on many factors, and it's not something a DMM is going to be able to help you with. Which is why I said earlier to simply set it by ear. Even if you, for example, undershoot power by 20% by setting it by ear, the difference is not going to be audible.

Or is there no real way to tell without actually putting a load on the amp and using a scope or something like the SMD Distortion Detector?

You don't need a scope, DMM or DD-1 to set a gain. Just your ear and common sense.

And actually with a proper 2ohm load on the amp will it require more gain to hit the RMS voltage or less gain?

In an ideal world the gain would be set exactly the same. All the gain is doing is adjusting the required input voltage to reach the target output voltage.

 

[The Squeakquel 10+ year member]

How do you figure that an O-scope or SMD DD-1 be useless? They are supposed to be the best ways to set your gain because you can actually SEE when you're at your max amount of gain.

Pretty simple to understand why they are useless. Any o-scope the average user has access to is not going to have enough resolution to be able to visually identify exactly the point of distortion/clipping, typically you are going to be well over 1% THD before the waveform is visually identifiable as no longer being a pure sine wave. I haven't seen an independent verification of the DD-1's level of accuracy. Beyond that having a detailed level of accuracy for setting a gain is completely unnecessary. As I pointed out before rather large variances in power are not going to be audible, so even if you undershot the power output by a good margin you are not going to hear a difference. And due to the nature of music you would have to overshoot the gain by a ridiculous margin before you ran into problems on the high side of things. Going over by a reasonable amount isn't going to be instantaneously damaging to the subwoofer and a small increase in distortion is again not going to be audible.

Beyond that we have the issue of proper system adjustment that is not accounted for by either of those methods. You might have an amplifier capable of overpowering the subwoofer even if the gain was set "perfectly". Now, this might not apply to your situation, but it will in others. Along with that you have the issue of proper level matching the subwoofer to the rest of the system, which is again not accounted for in either of those methods.

These along with other issues I have probably forgot to mention make both an o-scope and the DD-1 completely unnecessary and not useful for setting the gain. If someone told you either of those methods are "the best".....I would stop taking that person's advice. All you need is your ear and common sense. Really, it's that simple.

I just need to find the absolute max that I can set the gains for this amp.

I already gave you another method to use if you are absolutely oblivious to driver stress....use the DMM with a test tone recorded at a lower level, such as -6db.

 

[splwj47 10+ year member]

How do you figure that an O-scope or SMD DD-1 be useless? They are supposed to be the best ways to set your gain because you can actually SEE when you're at your max amount of gain. It's not like a have to worry about overpowering these subs because they will take 1000W daily each no problem and my amp puts out nowhere near 2000W so I just need to find the absolute max that I can set the gains for this amp. And as for using my ear to listen for distortion, either I can't hear it or my old JL 10W7 was just too worn out that it was just distorting all the time because I couldn't hear any audible difference in the speaker as I turned up the gain. Either that or I couldn't turn up the gain far enough to clip it, because that sub was old and in the last year started making a "pop" when it hit hard or excurted to a certain point. Which I thought was the sub being pushed too far but since I could never hear and audible difference in the tone that's what I figure maybe the gain wasn't high enough to clip it.

where you from man?

 

[Tenacious]

FYI, setting a 3 to 6db bass boost on a gain set with a DMM with a 0db sine wave would be the same as setting the gain with a -3 or -6db sine wave.

 

[gamehawk55 10+ year member]

where you from man?

BC, Canada