2ohm Vs 4ohm

[abu]

Hi

I am running an ALPINE MRP M500 monoblock amp which is rated at '500W RMS x 1 (2 ohm @ 14.4V) and/or 300W RMS x 1 (4 ohm @ 14.4V)'

It's going to be powering a 12" ALPINE TYPE-S sub which is rated at 'Peak Power Handling: 900 Watts and/or RMS Power Handling: 300 Watts / Power Range: 50 - 300 Watts'

I'm confused about 2ohm/4ohm and all this tech stuff so just want to know what the best way is to run this sub, at 2ohm or 4ohm?

Wiring it up is no issue, it's just with the power handling I don't know which would sound/perform better. Obviously with the amp running at 4ohm it will be putting out 300rms which is perfectly matched to the subwoofer rating which is also rated at 300rms but I have heard it's better to have a more powerful amp running a less powerful subwoofer as it performs better?

Also heard that running the amp or powering the sub at a lower ohm gives better sound quality? I don't want to crank 500rms into it and blow it up if that's going to be the case if I run it at 2ohm..

Any help would be appreciated - I have included links to the full specs of the amp and sub

ALPINE MRP M500 MONOBLOCK

ALPINE SWS 1223D TYPE S SUB

Thanks in advance

[abu]

I have decieded to run the amp at 2ohm as it will probably overload or run the risk of blowing if powering the sub at 4ohm

Thanks

[Samon]

4 Ohm.

It's then perfectly matched for the sub, and has the added bonus that it will not be 'straining' the amp as much (i.e. it should run cooler). Also, you're much less likely to blow the sub accidentally. Personally I like to have my amp about 10% more powerful than my sub, and then just make sure I'm not driving it to 100%. The last thing you want it amp clipping (distortion), as that will generally exceed the thermal and/or dynamic limits of the sub, and will therefore fry a sub dam quick!

[Samon]

I have decieded to run the amp at 2ohm as it will probably overload or run the risk of blowing if powering the sub at 4ohm

Thanks

Why do you say that? 2ohm is working the amp far harder than 4ohm... and so long as it's tuned right (i.e. no clipping - so not pushing the limits of the sub) it should go practically forever.

[abu]

I looked at it in the way that the 2ohm puts out 500RMS but I will not be running anywhere near that to power the sub, probably half of that power to get adequate sound without distortion but when running the amp at 4ohm I will be running it almost to it's full potential for it to put out close to 300rms to get the sub going to its full potential

Wouldn't the amp be more loaded up running @ 2ohm 300rms than @ 4ohm 300rms?

Some other information I have just got;

Now to confuse you, If you want to run a single Type S 12"...

To run your amp with a 4Ω load: You will need SWS-1223D - dual 2Ω voice coils wired in series

To run your amp with a 2Ω load: You will need SWS-1243D - dual 4Ω voice coils wired in parallel

If you have already bought the Type S SWS-1223D, it can only be wired up as 1Ω or 4Ω, and since that amp specs are only 2Ω or 4Ω, you'll be stuck with 4Ω since the amp is not going to be 1Ω stable.

If you want 2Ω, you will need to buy the SWS-1243D Subwoofer, or another SWS-1223D and run two (but then you'll have 600w of sub for 500w of amp).

Looks like I might have to run it at 4ohm

[Samon]

Wouldn't the amp be more loaded up running @ 2ohm 300rms than @ 4ohm 300rms?

Not really... In reality it'd be about the same... but the higher the resistance the less 'load' placed on the components of the amp (which most importantly results in less heat being generated).

Well, that's not 100% true.

Current (amps) = sqrt(power(watts)/resistance(ohms)

= sqrt(300/2)

= sqrt(150)

= 12.3A

Current (amps) = sqrt(power(watts)/resistance(ohms)

= sqrt(300/4)

= sqrt(75)

= 8.66A

So as you can see, you're drawing LESS current to push the same power into higher resistance.

Now that's assuming equal efficiencies of the amplifier, which isn't actually valid, so the difference won't be that much, but it works to illustrate a point!

If you have already bought the Type S SWS-1223D, it can only be wired up as 1ohm or 4ohm, and since that amp specs are only 2ohm or 4ohm, you'll be stuck with 4 since its not going to be 1 ohm stable.

That's exactly right... the sub in question has dual 2ohm voice coils. So, if you wire them in parallel, you get:

1/R = 1/2 + 1/2

1/R = 1/1

R = 1ohm

Wiring them in series, you get:

R = 2 + 2

R = 4ohm

So that particular sub only supports 1ohm and 4ohm configurations.

Edited November 14, 2008 by Samon

[abu]

ah awesome, thanks for clarifying Sam

Not so good with this stuff, too technical for me lol

I've got the jumpers that came with the subwoofer as well as a wiring manual to run it at 1ohm, 2ohm, 4ohm, 8ohm so I will just follow that and run it at 4ohm

Just out of curiosity, is there much noticeable difference from 2ohm to 4ohm in terms of sound quality?

[Samon]

ah awesome, thanks for clarifying Sam

Not so good with this stuff, too technical for me lol

No problems!

I've got the jumpers that came with the subwoofer as well as a wiring manual to run it at 1ohm, 2ohm, 4ohm, 8ohm so I will just follow that and run it at 4ohm

You can run it at 2ohm or 8ohm??? how???? it's only got two voice coils... to get 2 or 8 ohms you'd need two subs...

Just out of curiosity, is there much noticeable difference from 2ohm to 4ohm in terms of sound quality?

In theory, none. The only difference might be that at 2ohm you would not be edging towards the limits of the amp, and so you are at less a risk of clipping out (although more at risk of overdriving your sub!). Tuned properly to avoid any clipping/distortion it should not sound any different.

[abu]

haha na can't run it at 8ohm its just got diagrams showing different setups at different ohms

ah ok no worries, thanks for the info. Should all go well at 4ohm hopefully