Powering a sub in the trunk - how much is enough?


Founding Member
May 9, 2000
Kenmore, WA
I am looking at a 140w RMS MTX amp to push a JL 10" sub in the trunk. My question is will that be comparable to the shake you feel with the Mach 460? I don't want to have to fold the seats down to hear it.

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Like I said in one of my other posts, I had a 100W RMS MTX powering an alpine 10" in my explorer and it sounded really good. I had that same amp powering 2 Polk 12"s in my stang, and it was plenty loud enough for most people. One of my friends said it had more bass than his mach1000 system in his 02 GT.

What's the wattage rating on the JL sub? Generally you want the amp and sub wattage to be as close as possible to each other.
Just turn the gain down a little on the amp. It's actually better to have an amp that's rated higher than the sub, you just need to adjust the settings on the amp accordingly. The directions with my MTX amp said to turn the radio to your max listening level with the gain turned down, I had my volume at 27 out of 35 because that's when my factory speakers start to distort. Then, turn the gain up until it starts to distort, then back it off a little.
Ok first of all a sub will NEVER blow with too little power. Just think about that for a sec. Will a sub designed to run 500wrms blow at 1watt? I don't think so! A sub will blow when the source is underdamped, different terminology and meaning all together.

Turning the gain down does not lower the power the gain only controls the signal from the radio to the amp via the RCA cables. No matter if the gain is all the way up or down it wil still push the same amout of power @12 volts.

How do you figure? Power (watts) is a function of Volts and Amps. You up the amps and you up the power and, althought the resistance of an inductor changes with frequency, you'll basicly see the same nominal resistance, thus increase wattage through the sub.

The gain is there to balance all your levels. If the gain is at zero and the volume at 30 I might see 2 or 3 watts to the subs. Turn the gain up and the sub might see 200w.

And as far as adjusting the gain goes, you never want to max the deck then adjust the gain. Most units on the market will clip at those levels. But you still want good signal voltage to reduce noise/interference. Unless you have a reference CD and an osciliscope, you should probably keep the deck in the ballpark of 75% of max volume then adjust gains assuming you don't use deck power for your mids/highs, then you're kinda stuck.

Regarding the difference between a 10 and 12 in SQ, you will hardly notice a difference between them with comparible tunes/installs. The 12 will be more efficient, and have a lower Fs (higher cone mass) but the transient response is barely noticeable. That is more affected by your box/amp/car than anything else. I've heard 15's sound sharper and cleaner than 10's.

Anyway to answer the original question: 140watts to a 10" JL will be just fine. You'll be more than happy with it if all you want is something better than Mach460!