I'll keep this short and sweet. I have a RF 400W 2 channel amp for my interior speakers (BA SC85's) but ended up wanting little more low end. So I picked up a amp off CL and had a 10" JL sub.

Amp: MTX 400W mono amp (400W @ 2 Ohm; 200W @ 4 Ohm)
Sub: 10" JL 125W RMS 8 Ohm

after doing research I found out that a 8 Ohm sub is useless, unless I get another 8 Ohm and put them in parallel but I don't want 2 subs...

what would my amp be running at and what would my sub be seeing? I know it is bad to run an amp at a lower Ohm rating than the spec....but I'd be running at a higher Ohm than the amp is rated at.

I would assume the amp would go into the 200W @ 4 Ohm setup and the sub would be seeing 100W?? would this damage the amp at all?

thanks guys
Dean

 

Chances are your amplifier will output 100 watts or there about at 8 ohms. Generally, 8 ohm subwoofers have a higher sensitivity than their 4 or 2 ohm counterparts, therefore less power isn't always a bad thing.

EDIT: You may need to watch your amp carefully if it is a class D amplifier. Some of the class D amplifiers I owned in the past DID NOT like 8 ohm loads and would heat up like you wouldn't believe.

 

that's what I was thinking. I just wanted some more opinions. I'll keep an eye out for another 10" 4 Ohm sub rated arounf 200W to be paired perfectly with the amp.

thanks oldschool

 

When I ran a to low ohm load on my amp it got really hot and after about 10 minutes it shutdown on me.

 

Amps usually get hot at 2 ohms if they are not made for it, most amps are fine at 4 ohms.

 

right, but I'm going in the opposite direction...I would be running an 8 Ohm load off a nominal 2 or 4 Ohm rated amp.

from what i have gathered I will not damage anything, but I would not get as good of sound out of the 8 Ohm, and would be better off just finding a 200W min sub with a 4 Ohm impedence, hook it up and be done with it.

local car audio place will let me hook up my amp and go there and run a new boston acoustic G1 rated at 200W 4 Ohm sub in a premade box they sell just to see the kind of bass i could expect. if I like it, I will search for a cheaper sub, if i want more, I'll have to upgrade to a 12" or find a 10" 400W 2 Ohm sub.

 

Devon...when you see this:

I had my eye on this sub but not the box:
Kenwood KFC-W2512 300W rms 4 Ohm
http://nh.craigslist.org/ele/1703780998.html

but I would only be running 200W to a 300W sub.....so it woul barely move. Not to mention I found it online free shipping NEW for $55 lol

 

I just thought:

I'll be putting ~200W at 4 Ohm to my sub...I SHOULD look for a sub which puts 200W between the RMS and Peak of the sub correct?

If I run a 300W RMS sub with 200W....it will barely move, but if I run a 150W RMS, 400W Peak(random numbers) sub with 200W I would be better off.

or should I just keep it to looking for a 200W RMS sub to be supplied with 200W?

 

OK, let's start back at the beginning here, and go from there.

A) What types of music will you be listening to the MOST, and at what volume level? i.e. rock music cranked through the roof, or rap etc etc.

B) Does the Amplifier you are going to use have a built in adjustable cross over, or does it have a specific frequency output range listed on it anywhere?
This will also help us determine the proper type and size of subwoofer.

C) Are you running a factory head unit? If not, does the aftermarket head unit have subwoofer outputs with an adjustable crossover or cutoff filter?

D) If you build the box yourself, how many cubic feet of space do you have available for the box to take up in the trunk?

Now, as far as some of the other things your had discussed already..

The power rating of your subwoofer will sound optimal as long as the amp puts out approximately 2/3 of the rms rated power of the sub. For example, if your amp is rated at 400w RMS @ 2 ohms, you can run a subwoofer rated between 400-600w RMS @ 2 ohms and it will still perform well.

Now, you mentioned a 4 ohm sub....dont bother, get your self a DVC 4 ohm sub. That's Dual Voice Coil. Each coil is rated at 4 ohms, you then wire them in parallel and the observed load on the amp is now 2 ohms. This way, you can still run just one sub, and still use all of the amps power to your advantage.

To elaborate on the questions I asked you...

Here is an example, say you are a rock guy, and like it loud! (i know i do!)

You could mount a single 10 inch woofer in a sealed box about 1.5^3ft and this would add a nice little punch to your music.

Or, you could run two 10's, in a sealed-sperated chamber box, about 1^3ft. each chamber stuffed with polyfill to save space, and have more of a noticeable punch, and still not take up a terrible amount of trunk space.

Or, you can run a single 12" woofer, with about the same space as the two 10's, and have the punch, AND some deeper bass for the double kick drum hits to feel in your chest...

I would recommend nothing more than that, as you mention saving space, and anything more would require ALOT of space.

 

I really wont be able to tell the difference between 50 or so watts. It takes 10 times the power to get double the volume.