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Old 08-30-2012, 09:20 PM   #1
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Speaker RMS question.

I wanna build a custom sub enclosure for the back of my jeep and I'm gonna put in 2 Polk audio MM1240's there "12. There 425 RMS and my amp puts out 500 RMS. If I turn the gain down a lot will it save the sub or should I just find a different sub?

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Old 08-30-2012, 09:21 PM   #2
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You should probably get a bigger amp. Under powering speakers will damage them a lot more than over powering, plus most amps don't put put what they advertise

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Old 08-30-2012, 09:34 PM   #3
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X2 on a bigger amp. Also whats the impedance of the speakers? I'm assuming they are 4 ohms when wired together you'll be at 2 ohms. Is this a 2 channel amp or a mono? You'll want a mono amp thats 2 ohm stable at least 600 watts rms preferably 800. Basicly in jeep terms you've got 37" tires on a 4 cylinder jeep with a clogged fuel filter if you run that set up.
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Old 08-30-2012, 09:58 PM   #4
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What kind of amp do you have, 2 channel or mono block? A 500 RMS 2 channel amp is probably going to be under powered for a pair of Polk MM1240's. Though some 2 channel amps can be bridged down to 1 x 2 ohm. If you can bridge your amp down to 1 x 2 ohm and wire the subs in parallel (2 x 4 ohm wired in parallel = 2 ohm load) you may be able to get away with it. For your set up though I'd really go with a good 1,000 watt 1 x 2 ohm mono block and wire them in parallel. MTX used to make a killer mono at a great price, it's been a while since i've been in the business though. Can never go wrong with alpine, I used to run 2 Polk Momo 10's off an Alpine mono, damn I miss that system.
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Old 08-31-2012, 12:14 AM   #5
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"Under-powering" speakers does not damage them. However, turning up the volume on a low-power amplifier past signal distortion will be bad for them. I can't recommend an amp/speaker combination, but I can say that a 1,000 watt amplifier (or 500x2 channel) will draw more than 70 amps from the Jeep's electrical system, at peak. That's a lot. Make sure you run some big cable to that amplifier.
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Old 08-31-2012, 07:51 AM   #6
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Don't go smaller than 4AWG with that much power. If it really taxes the electrical system you can wire in a 1 farad capacitor. It's cheaper than a high output alternator.
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Old 08-31-2012, 08:52 AM   #7
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The amp I have is an Alpine PDX amp. It's 4 channels + a mono for the sub. So if I I hook up 2 subs to 500 RMS does that mean each sub get 250 RMS? I'm confused.
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Old 08-31-2012, 09:16 AM   #8
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Let's lay out the basics....

Your amp's mono block puts out 500w RMS and is stable at at 2 or 4 ohms (pretty cool).
Your subs are single voice coil, 4 ohm, 425 rms

Running both of those subs to the amp, the amp will see a 2 ohm load.
Your subs are each going to see 250w.

The best solution for you, with the amp you have and the subs you're looking at, is to run ONE sub.

If it were me, I would buy ONE JL Audio 12w3v3.
....actually if it were me, I would buy a 10w3v3, but we're not talking me.


edit - I will say this....in my opinion and experience, one 500w sub sounds better than two 250w subs. If you are really looking at 500w subs, a 250w sub will not satisfy you. Running two of them only pushes more air; it doesn't make them sound better than they are.
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Old 08-31-2012, 10:15 PM   #9
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That's a nice amp. I agree, you'd probably be better off running only one of the 12's, probably sound better.

Tomorrow's project is wiring up an Infinity Kappa 4, Kappa 6.5 components and Kappa 4x6's. Thinking about adding a 10" Alpine Type R and 600 RMS Alpine mono block.
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Old 09-01-2012, 10:52 AM   #10
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Quote:
Originally Posted by TXST8tj View Post
edit - I will say this....in my opinion and experience, one 500w sub sounds better than two 250w subs. If you are really looking at 500w subs, a 250w sub will not satisfy you. Running two of them only pushes more air; it doesn't make them sound better than they are.
+1. I'll take a higher quality sub with more watts than 2 cheaper ones with less watts. All 10 or 12" subs are not even close to the same. I had 2 cheap jl 12s and 300w. My friend has 1000w and one 12w7. Not even remotely close to the same volume or quality of bass output (but also costs way more). I see no need to ever need to run dual subs unless there is a space requirement and you cant fit the deep subs. Then I'd run the JL 13 something that is only ~2" thick and doesn't need much box space. I even thought about making an overhead box for one of those in my jeep

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