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. I can't speak to the quality of super cheap ones, but I've seen digital multimeters go for $3-$250. By my eastimation, $35 or cheaper ought to do you. I honestly don't know much about the things. You should probably read some reviews or something. I borrowed a $23 Craftsman DMM and it worked flawlessly.
Alright, that's out of the way. You got your buddy's digital multimeter now? Well, come back to the tutorial when you have it. Okay.
Just so the bases are covered:
1. Digital Multimeter
2. CD with a 50Hz 0dB track - Google will get you one if you don't have it.
3. A CD or three with bangin' tunes
You need to figure out what voltage to set your amp to. I went to this site and entered in my specs. Every amp and sub is different, and the specs are different depending on how you wire the sub. Read your manuals to figure it all out. I used the listed ratings because I have no idea what the amp's actual ratings are. Here's my input and output: (1000 amp max Watts, 1 sub, 2 voice coils, 2 Ohms/voice coil = 31.6V)
Write down your recommended voltage.
So, you see this end?
There's your gain, bass boost, low pass, and sub sonic adjustment knobs.
- Set gain to the minimum.
- Set bass boost to maximum dB.
- Set low pass to 50Hz.
- Set subsonic to 50Hz
Pop your test tone CD in the head unit.
I set my boost levels to ones that sound good. On the stock Monsoon system, I found that a little bit of bass boost brings the midbass up to the point that it plays well with your sub's bass. It is important to set these before wetting your amp. The light increase to mid boost brightens lyrics and guitars. The same on treble brightens snares and has the unfortunate effect on the monsoon system of bringing hi-hats slightly too loud. That sucks; can't have everything. You want volume as high as you can get it without hearing distortion from your other speakers. And of course, fade to the rear a bit less than half way. Your taste, or even speaker wear may disagree with my settings. Just for reference, here's what I use:
Now, check out this end:
- Stick the multimeter probes in the appropriate speaker wire holes.
- Turn on the multimeter and set it to 200VAC.
- Get your engine running. The grounds change when the engine is running, so this is important. It wastes some gas, but will get more accurate results.
- Make sure your volume is down.
- Play your 50Hz 0dB track and loop/repeat it.
- Slowly turn the volume up to your desired max.
- Slowly turn up the gain until the multimeter reads the recommended voltage or slightly less. Never more. This will probably be somewhat short of halfway to the max on the knob, depending on the amp. You will never change this, except to lower it in the case that your sub winds up being too loud for the rest of your speakers.
- Turn down the volume and eject your CD.
- Turn bass boost to minimum.
- Plug in your sub, put it in the place you like in your trunk, and sit in the front seat. With your amp. If your wires aren't long enough you're stingy. And you'll have to hack it from the back seat. Sucks to be you.
- Pop in a CD and turn up the volume again. Make sure you're playing juicy tracks.
- Adjust low pass and sub sonic to levels that sound good to you. Sorry kids, no math here. Just good ol' fashioned ears.
- Turn on your headlights.
- Now, if you're fortunate enough to have a voltmeter, keep an eye on it for the next set. If you have a 5-button DIC, switch to battery voltage.
- Now that your gain, low pass, and subsonic are set, the last thing is to turn up bass boost. Make sure you use a very high quality, high volume recording. I put "Happiness (Troubled Troubled Faces)" by Pretty Lights from the Taking Up Your Precious Time album on repeat to tune bass boost.
- If voltage dips on a bass hit, your bass boost is too high. If your lights dim, your bass boost is too high.
Keep in mind that I'm just some guy that kind of figured this out from whatever info I could find on the web and hours of playing with the system. I'm sure some pros think I'm an idiot for not using the method they've been winning competitions with. But it worked for me so I hope it works for someone else.
I just spent forever writing this. I have no idea if it's coherent, so I'll come back and edit it later.
