Here is the deal. I have an Alpine MRV-F450 amp which drives an Infinity Kappa Perfect 10.1D woofer. This is a dual voice coil sub, with two 4 Ohm coils, so it can be hooked up as either an 8 Ohm or a 2 Ohm.

The trouble is that I made a mistake - although the amp is 2 Ohm stable on the four stereo channels, I misread the specs and thought it can also handle 2 Ohm on the fifth channel. However it appears that's not the case and the mono channel must have at least 4 Ohm impedance, according to Web sources.

What can I do in this situation? Obviously, getting rid of the dual voice coil woofer and buying a single coil, 4 Ohm one is the cleanest but also the most expensive fix.

What if I hook up the woofer as a 8 Ohm, so the coils are in series? Or maybe just hook up a 2 Ohm resistor in series to the 2-Ohm setup to make the overall impedance 4 Ohms? Would I lose a lot of the power this way? Which of these two ways would be better to minimize the loss?

Bear with me since I don't have too much experience with this stuff, so I'm probably asking something stupid...

I appreciate the input - thanks folks.

 

Hooking up a resistor to would just waste half your power. Your options are to hook the sub up as an 8 ohm sub and get 1/2 the power from the amp or buy another sub.

You could also just run the amp at 2 ohms mono. Since it is a brand name amp, if you provide adequate cooling, maybe an external fan, it will likely take it, although it will shorten the life of the amp. When I was younger and just threw together whatever I could get for free I hooked many amps up as a 2 ohm mono configuration that weren't rated for it. I had one amp blow out one channel after about a years worth of use. All of the other ones were still going when I got rid of them. But you are of course taking your chances. I'm sure your amp has a thermal protection switch to turn the amp off if it gets to hot.

 

To be safe no matter what, if you are going to keep this sub, wire it in series to 8 ohms. It would however be best to purchase a different sub, the 4 ohm version.

 

you could always just not hook up one voice coil. (i know i'm smart, you don't have to tell me)

 

If you do end up buying another infinity sub, let me know because I may be able to help you.

 

Why, do you have a Kappa Perfect 10.1 for sale for cheap?

 

I just might have a brand new one under my bed.

 

Sent you a PM...

 

This is easy. Buy a SECOND sub running the voice coils for each in a series and then parallel connections between the subs and the amp!

 

Yeah, except then I'd have to buy another sub box too plus probably a new amp as well, because the current one only has 200W RMS on the mono channel and even the one sub is for 350W RMS... it'd seriously underpower the TWO subs.
Too much weight and too much money.

 

Man this must be the shittiest manual. It covers 3 different amplifiers in 3 different languages and nothing is really clear.

http://cartoys.com/cartoy/pdfs/mrvf540_manual.pdf

Wow Tamas, all I have to say is that you are on your own on this one. After reading the manual it really doesn't say whether you can use a 2 ohm sub or not. I think they might have pre-bridged two channels to create channel 5 so 4 ohms is the limit. Regardless even if it doesn't overheat running at 2 ohms - you will be cutting the dampening ratio in half which isn't the best thing in terms of sound quality.

I would run it at 8 ohms. You will still get probably 150 Watts out of it that way.

If you want a real amp, I would try the JL e6450. I have one and it kicks ***. Even if you run your sub 8ohms it will still put out 200 Watts into channels 5 and 6 bridged.

Good luck. I can't think of an easy answer. I tell you what though, I have never liked Alpine amps.

-Mr. Wigggles

 

Yeah, it's not too good - actually, part of the reason why I misunderstood the parameters was exactly this. It wasn't clear and I assumed something - but it was wrong.

Yes, I figured I'll try that first before buying a new sub and see how it goes that way. I'm not looking for crazy boom anyway, just good deep bass that complements the music. If the sub will do that with 8 Ohms then I should be OK.
I called Infinity and the guy said I should not compensate the lost power by turning up the bass EQ or gain on the amp because that might make it start clipping and that'll destroy the sub. I wonder if using the amp with normal volume (speak: not turning up the head unit to 30+ or something) plus increasing the gain a little would be OK...

So far I'm OK with this Alpine... works fine for me.

 

You can't destroy the sub with 150 Watts no matter what you tried. It simply wouldn't hurt anything - it will just start "sounding" distorted but not harmful to your sub.

Yes, If you run 8 ohms you will more than likely run with considerably more gain on the Sub channel.

And running your head unit at 30 with the gain turned down on the amp is the same as running your head unit at 20 with the gain turned up on your amp. It six one way and a half dozen the other way. All that really matter is that you don't give the amp way too much signal or way too little signal.

-Mr. Wigggles

 

^^^^ adds to the alpine comment. The only Alpine amps that I have ever liked were the old 3552 - 3558 series that were all made in Japan. The new stuff, I'm feeling kinda squemish about but if it what you have let's get it to work as best it can. Don't open up that gain control too high Tamas, we don't want to see a clipped signal going to that sub. A clipped signal will cook most (not all subs) in no time flat.

 

Yes you can, It is just as bad to under power a speaker as it is to over power it. Now, 150 watts is not under powering it. But, lets say, 50 watts on the hand could destroy the sub just as 500 wats could. You need to look and see what the min and max rms power handling for the sub is.

 

You can over / under power a sub all day long provided you do / do not do the following.

1) allow the sub to cool.
2) allow the sub to cool.
3) allow the sub to cool.
4) do not feed it a clipped signal on a continuous basis without allowing the sub to cool.
5) ensure the gain is set properly to keep the speaker from seeing a clipped signal.

The last one is much more predominant in the industry as people usually have too small a amp to power too big a sub, they set the gain way too high and expect it to just lay waste because that's what the salesperson said it would do. Not the case at all. Too small of an amp + too high of a gain = clipped signal and sss (smelly speaker syndrome).