Using a 2-ohm sub with a 4-ohm stable amp

[leousm]

First of all, hello everyone //content.invisioncic.com/y282845/emoticons/cool.gif.3bcaf8f141236c00f8044d07150e34f7.gif

I have an MTX TA3404 amp (100x4 RMS @ 4-ohms, 200x2 RMS bridged @ 4-ohms) with which I want to use the front channels to power a pair of components (in stereo) and the rear channels to power a sub (in bridged mode).

The sub is a Kicker CompVR 12" with dual 4-ohm voicecoils (wired in parallel for a 2-ohm load). Now, I'd like to run this sub off the bridged rear channels, but the amp specifications allow for only 4-ohms.

My question is: Can I still use the 2-ohm sub, but set the amp to a lower gain?

The way I see it, I could set the gain using a digital multimeter so that the voltage across the bridged speaker outputs is 20.00 volts and thus produce 200 watts @ 2-ohms, instead of the 28.28 volts at the manufacturer specified 4-ohms to produce 200 watts.

Would this be at all feasible? If so, are there any drawbacks to this?

Basically, I just want to do as much as possible with the stuff I already have, without buying a new sub or amp. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Thanks in advance

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[FredS3251 10+ year member]

Well its been done before had a couple kids aroud my area with the same issue...its not the smartest thing to be doing due to the damage you could bring to ur amp. I had to set the gains much lower so the amp wouldnt go into protect. I would suggest a second amp to save all the hassel. Im sure the amp will perform ok on lower gain setting, but I have also seen a amp not run at all due to wrong load.

 

[1LOWCHIEF 10+ year member]

This may be the stupidest comment in the world right here but : couldn't you just run one channel per coil of the sub? Why wire your sub to 2 ohms, bridge your amp to a single channel and then do all your adjustments to only output 200 watts when you state that the amp does 100 watts per channel RMS at 4ohm? Use 2 channels for your components and then the other two channels to your sub?

Actually, i just looked up your amp and here are the specs I found :

* Thunder 4-channel high-performance car amplifier featuring patented class A/B output* 50 watts RMS x 4 at 4 ohms (100 watts x 4 at 2 ohms)

* 200 watts RMS x 2 bridged output at 4 ohms

* Xtant Technology Cooling (XTC) - Thermal-regulated turbo-charged fan intercooler

* PrizmEFX accent lighting effects - Customizable to match your vehicle's interior

* Semi-unregulated MOSFET power supply

* Overload and thermal protection

* StreetWires connection terminals

* Electronic crossover at 85 Hz, 12 dB/octave Hi pass (front channel), defeatable

* Electronic crossover at 85 Hz, selectable 12 dB Hi/24 dB Low (rear channel), defeatable

* Dual mono output, selectable

* Input (RCA connection): Low-level, hi-level w/Smart Engage

* Input sensitivity: 100mV-1V/1V-10V switchable

* Input select 2/4 channel

* CEA-2006 Compliant

* Dimensions: 12-11/16" L x 9-5/8" W x 2-1/2" H

your 100 watt RMS is at 2 ohms per channel so listening to me up there would only get you 50 watts per coil.. but you knew that and that's why your asking about bridging the last 2 channels into the subto get 100 watts per coil.

Perhaps my comment is the stupidest comment in the world... lol

 

[p8ntballweird]

I'm probably abou tto pick that same amp up for my 2 10' MTX 6000s. My problem is however that I don't know the OHM of the subs, and I dont' have access to one of those machines that tells you. Should I just go ahead and buy the amp and hope for the best? How would I hook up the amp channel wise or w/e?

 

[mil81 10+ year member]

It also depends on the amp. Some amps are horribly under rated when it comes to impedence levels. I had a small, old school, kicker 2 channel amp. I ran a dual 4 Ohm sub at 2 Ohms, and bridged the amp. It was definately not rated for that, and kept blowing fuses. Once I jumped up 10 Amps in the fuse size it ran like that for years.

That said, it was a dumb thing to do. I got the amp for cheap, and didn't really care if it died, but the point is, it didn't die.

 

[leousm]

Well, I e-mailed MTX about this and this is what they said:

you can not use the 2-ohm sub set to a lower gain.your voltage calculations are correct; however, it is the current dissipation of the output transistors that will increase by about ten times when the output load is dropped to 2 ohms and the gain is turned down to the voltage specified.

the safe way to connect this woofer to this amp is at 8 ohms.

So I guess what dictates whether or not an amp is stable at a given impedance is its amperage rating. This is why mil81 was able to run his amp at a lower impedance by bumping up the fuse. This however isn't as simple as changing fuses as the output transistors will handle up to a certain amount of current before you see some smoke. //content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif

Well I guess I'm putting my sub on eBay and getting a dual 2-ohm. Why settle for 100 watts when I can get 200 //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif

Thanks for the input guys.

 

[leousm]

I'm probably abou tto pick that same amp up for my 2 10' MTX 6000s. My problem is however that I don't know the OHM of the subs, and I dont' have access to one of those machines that tells you. Should I just go ahead and buy the amp and hope for the best? How would I hook up the amp channel wise or w/e?

I recommend picking up a digital multimeter, they run about $15 at Walmart or an auto parts store. With it you can just measure the resistance across its terminals.

Otherwise, I'm sure your subs have a part # stamped somewhere on them. You can check here and find all the specifics on them:

http://www.mtx.com/caraudio/archive/archiveSubwoofers.cfm