# 4 ohm amp into a 2 ohm sub?



## nick650 (Feb 7, 2011)

I have a JL 12w6v2's and a Zed Leviathan amp

I plan to have two channel bridged into 4 Ohm to give me roughly 580 RMS.

My sub woofer can handle 800RMS but it is rated at either 2 or 8 Ohm. 

I plan to run my sub at 2 ohms and give it 580 RMS at 4 ohms. Is this a bad idea?

Thanks


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## dragonrage (Feb 14, 2007)

Some amps will run with a lower impedance than rated as long as you don't go above the current that it can put out. Some will go right into protection. For those that don't, if you go above the current limit, some will then go into protection, and some will be damaged. I don't recommend it unless you really know what you're doing.

Either way, you're not going to get 580W.

@ 2 ohms, we use the formula P=I^2*R. I is the current - we'll use the maximum current, since it could change at any time with the signal. The current would thus need to increase by a factor of sqrt(2) to compensate for R halving. This isn't going to happen, either because the amp is current-limited or because it doesn't have the heatsinking. Either way, if it were capable of doing this, it would be rated for 2 ohms. So we're halving R while either not increasing I, or not increasing it by sqrt(2). You will thus get at least 290W but less than 580W - and that's assuming the amp doesn't go into protection.

At 8 ohms, we use the formula P=V^2/R because we are going to run out of voltage, not current. Voltage will either stay the same or go up by a factor less than sqrt(2), but resistance will double. You're most likely going to get 290W, and your amp will run cooler at full tilt with 8 ohms than it would with 4 ohms.

I can't give you the EXACT figures here because that varies depending on the amp design. But what I can tell you for SURE is that one of these is safe (8 ohms) and one may not be (2 ohms).

I'd use 8 ohms.


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## brandinooooo (Jan 9, 2011)

I dont know if you understand exactly how ohms work. dragonrage^^ is explaining it well.

You dont pick what ohm your speaker plays at. If you wire your sub to 2 ohms its likely that your amp will be putting substantially more wattage than at 4 ohms. 

e.g. i have a alpine mp500. its 300 bridged at 4 ohm. 500 bridged at 2 ohm.




Oh and by the way, your amp is not stable at 2 ohms bridged. Lowest its stable is 4. So like dragonrage said, go with 8 ohms.


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## nick650 (Feb 7, 2011)

??????????????????????

I know about Ohms law and sorts but i don't get what your poking at lol.

All I know is when you bridge an amp, it is two 2 Ohms to make a 4 ohm load.

So far what I got out of what your are saying this is a bad idea and I should just run one channel to the sub.


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## brandinooooo (Jan 9, 2011)

You can but you wouldnt be getting a lot of power. Which model amp do you have exactly?
3, 4, 5, or 6 channel?


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## 08Raider (Jun 17, 2010)

nick650 said:


> ??????????????????????
> 
> I know about Ohms law and sorts but i don't get what your poking at lol.
> 
> ...



Wrong.....

Bridging your amp does not determine the load. 
*The wiring of the speaker or speakers determines the load*. Amps have ratings based on the current they can draw without overheating, based on the resistance of the load. 

Your amp will draw its maximum "safe" current at 4ohms when bridged.
Meaning if you could wire your speakers to 4ohms, then that would be it's optimal max current(or power) without pushing past it's limits. Any load lower than 4ohms when your amp is bridged means that the amp will try to draw more power than it is designed to. and that could cause it to overheat and run unstable, or even fry it's insides.


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## ZAKOH (Nov 26, 2010)

nick650 said:


> I have a JL 12w6v2's and a Zed Leviathan amp
> 
> I plan to have two channel bridged into 4 Ohm to give me roughly 580 RMS.
> 
> ...


If you connect a 2 ohm subwoofer to your amplifier then the amplifier will see a 2ohm load. This may be dangerous for your amplifier because the bridged channel is rated for 4ohm load. 

Another thing you can do is wire the subwoofer for 8 ohm load. The problem with this is that power output of the amplifier will drop by half. If your subwoofer is efficient enough to run off 290watts RMS, then that's not an issue, and amp will be running cooler. However, something is telling me that an average subwoofer that's rated for 800watts just won't be very happy running on 300watt RMS power. I would recommend you to either trade your subwoofer or buy a 2ohm stable mono amplifier for it.


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## Earzbleed (Feb 10, 2013)

08Raider said:


> Wrong.....
> 
> Bridging your amp does not determine the load.
> *The wiring of the speaker or speakers determines the load*. Amps have ratings based on the current they can draw without overheating, based on the resistance of the load.
> ...


 Mate! That's the clearest explanation aimed at noobs that I've read. I'm looking at changing my sub and was wondering about ohms and stuff and you cleared it up perfectly for me. Thanks


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## Oliver (Jun 25, 2007)

nick650 said:


> I have a JL 12w6v2's and a Zed Leviathan amp
> 
> I plan to have two channel bridged into 4 Ohm to give me roughly 580 RMS.
> 
> ...


:laugh::laugh::laugh::laugh:


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## Chaos (Oct 27, 2005)

~2 yr old thread FTW!


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## Oliver (Jun 25, 2007)

It is still being done every day by people who have and haven't read here 

Hey watch me have to buy a new amplifier, battery and speaker -* nuttin to dis car audio stuffs *:laugh:


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## ZAKOH (Nov 26, 2010)

No offense to anyone. It's certainly easy to reply to a very old discussion thread. It's a flaw of the discussion forum.

I really wish this web site had this one feature..


Once nothing has been posted in a thread outside of "member reviews" or "member build logs" forums, the thread gets locked for good. I am kind of tired of seeing 3 year old "help me decide with components" or "help me choose tweeters" suddenly being replied to.


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## Oliver (Jun 25, 2007)

ZAKOH,

Only defense you have is your memory.


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## minbari (Mar 3, 2011)

nick650 said:


> I have a JL 12w6v2's and a Zed Leviathan amp
> 
> I plan to have two channel bridged into 4 Ohm to give me roughly 580 RMS.
> 
> ...


this is a fundamental failure to understand electronics. it doesnt work that way. if you run the sub to 2 ohms, then you are running the amplifier at 2ohm bridged. your amplifier will get very hot and be damaged. 

just run it stereo. 1 coil off each channel.


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## Oliver (Jun 25, 2007)

Chaos said:


> *~2 yr old thread* FTW!





minbari said:


> this is a fundamental failure to understand electronics. it doesnt work that way. if you run the sub to 2 ohms, then you are running the amplifier at 2ohm bridged. your amplifier will get very hot and be damaged.
> 
> just run it stereo. 1 coil off each channel.


*Great advice for all future cheapskates who don't want to spend money then turn around and spend more money and then turn around and spend more money

*:laugh::laugh:


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