Thread: Tutorial: Setting Subwoofer Amp With Multimeter

[QUOTE=SlowNA06;653175]This tutorial explains the process I used to tune a subwoofer amp piggybacked on a stock 2004 Monsoon system with a digital multimeter.

It varies slightly from other tutorials you may find in that I am not approximating and being as specific as I can. As near as I can tell, this is almost as good as using an oscilloscope, and WAY better than tuning by ear. What I am doing, basically, is ensuring that the amp's signal can not clip, no matter how loud, raunchy, or dagnasty evil the music. For free. Seriously, if you don't already have a multimeter, you have a friend that does and unlike your buddy with the o-scope, he's not going to charge you. And if you don't have any friends, well, pick one up cheap.

Lol.... nice write-up. This is a basic skill needed by all. However, this is NOT going to guarantee that the amp can not/ will not clip... nothing does. Music is dynamic... some songs are recorded clipped. While this will help them not clip their subs to death, nothing prevents clipping. It is also, as you said, a mostly free method suitable for the average consumer looking for a little more muscle. If, however, you know someone serious enough about audio to invest a significant amount of money in an o-scope that will let you view the waves of your signal, monitoring for flat spots (clipping), you should take advantage of the chance for the peace of mind.

Edit: It is also worth mentioning that the max wattage box should be completed with the rms of the amp. Amplifiers that advertise "max wattage" ratings do NOT do that amount RMS, and attempting to extract that amount of power out of the amplifier will result in... yup... a clipped signal.

Edit again: Excuse me, I seem to have missed this... bass boost clips the signal! It should NOT be used at all... however, I will let people do their own research to come to this conclusion. If you like the way that your system performs using this feature, so be it. This is what brought up the o-scope comment in the first place. However, this is a useful write up, and I thank you for posting it. For one that is more in-depth, including setting subsonic filters, and choosing which dB levels of test tones to use according to musical tastes and experience, as opposed to a generic number, please refer to http://www.caraudioclassifieds.org/f...correctly.html .

Lol... one last thing... setting sub-sonic filters is MUCH more involved than choosing "what sounds good to you." With a ported enclosure, the SSF will help to filter out frequencies that are too far below tuning. Playing too far below tuning causes what is known as unloading, which is a loss of cone control due to insufficient pressure behind the cone to stabilize it. This results in catastrophic failure of your subwoofer more often than not. This is a good basic tutorial, but please supplement it with links to more specific information.

Originally Posted by Fatboy501

this is NOT going to guarantee that the amp can not/ will not clip... nothing does.

I agree with this. I will emphasize this in the tutorial.

Originally Posted by Fatboy501

If, however, you know someone serious enough about audio to invest a significant amount of money in an o-scope that will let you view the waves of your signal, monitoring for flat spots (clipping), you should take advantage of the chance for the peace of mind.

Absolutely. There is no better tool for this than an o-scope, let alone a mere multimeter.

Originally Posted by Fatboy501

the max wattage box should be completed with the rms of the amp. Amplifiers that advertise "max wattage" ratings do NOT do that amount RMS

Here's where I thought I had done this correctly. I wired my sub so that the amp would operate at 1 Ohm, which my amp's manual says will result in 1000W. If I have done this wrong, please help me to correct it.

Originally Posted by Fatboy501

bass boost clips the signal! It should NOT be used at all... however, I will let people do their own research to come to this conclusion. If you like the way that your system performs using this feature, so be it. This is what brought up the o-scope comment in the first place.

Again, I wish I had an o-scope to check this.
Bass boost is maxed when setting gain, so that no matter how high the bass boost is, it should avoid clipping. It is not to be left at max. I use the slightest touch of bass boost, perhaps a 5* turn of the knob. Without it, my sub sounds like farts on a pillow.

Originally Posted by Fatboy501

setting sub-sonic filters is MUCH more involved than choosing "what sounds good to you."

I will look into this.

Originally Posted by Fatboy501

Playing too far below tuning causes what is known as unloading, which is a loss of cone control due to insufficient pressure behind the cone to stabilize it.

This especially interests me. I suspect that this event manifests in a couple of tracks I have listened to, however very seldom.

Originally Posted by Fatboy501

This is a good basic tutorial, but please supplement it with links to more specific information.

I suppose I will have to find some. Everything I read on this was incredibly vague, which is part of my motivation for this tutorial.

Thank you for your input, it has given me much to consider. I am sadly the most experienced tuner among my friends now (they all, as well as local shops "tune by ear," which I have found to be consistently horrific/painful as well as destructive), so I need to rely on the advice of guys like you to learn more. Please be as free as you like with your advice here - I am far more student than teacher.