help me figure out this ohm rating

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ad0lescnts

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ok,
I have a Mesa 400+ and i want to connect two cabinets: one 4 ohm and one 8 ohm. do i connect both of the speakers into my two ohm outputs? or do i connect the 8 ohm cab into the 8ohm output, and the 4 ohm cab into the 4 ohm output?

I read somewhere that the combined ohm rating for combining a 4 ohm cab and an 8 ohm cab would be 2.667 ohms, so i'm leaning towards connecting both cabs to the 2 ohm speaker outs.

Confirm this for me!! thanks ( :

T
 
A 4 ohm and a 8 ohm cabinet connected in parallel equils 2.66 ohms. Connected in series they're 12 ohms.
 
Last edited:
Track Rat said:
A 4 ohm and a 6 ohm cabinet connected in parallel equils 2.66 ohms. Connected in series they're 12 ohms.
Click to expand...

That is COMPLETE and UTHER BULLSHIT!

Here's the right version: a 4 ohm and a 8 ohm cabinet connected in parallel equils 2.67 ohms. Connected in series they're 12 ohms.
 
It's not hard...
1/((1/X)+(1/Y))

1/4=.25
1/8=.125
.25+.125=.325
1/.325=2.667

(I used a calculator, btw... ;) But the formula is very simple)
 
Don't listen to these other guys, they don't know what the hell they're talking about....





The correct answer is 12 ohms.
 
ok,
but if my cabinet has 2 two ohm speaker outs, then does that mean it's splitting the signal or is it sending two different ones? parallel or what??

so now it's just a matter of how this amp is set up! i have no idea...

¡¿what do i plug where!?

Thanks a lot
T
 
I believe that the speakers connected to different output jacks from the amp (you said cab, but I assume you meant amp) run in parallel. Anyway, it would be a strange piece of design if they were running in series. So connect the two cabs (4- and 8-ohm) to two 2-ohm outputs. There'll be an impedance mismatch, as you'll be connecting 2-2/3 ohms to outputs that want 2 ohms, but I think the world can survive that. Generally, being mismatched on the high side is better than low, though with tube amps (as opposed to transistors) what actually happens in the real world is more muddy. At least to me.

Actually, the whole question of impedance matching in this situation is a bit tricky. Generally, the actual impedance of speakers varies with frequency, and may be quite different from the rated impedance at various frequencies. Maybe not an issue in typical home-stereo use, but since you're talking about a bass amp, it's safe to say that this isn't typical home-stereo use. Bottom line is that that connecting two 4-ohm speakers to the 2-ohm outputs probably wouldn't result in as perfect a match as they'd like you to think either.
 
awesome. thanks a lot!

i dont really understand all this stuff, but how would it be different for a home stereo? you mean that a stereo has 2 separate amps? and why wouldnt two 4 ohm cabs work as perfect?

well thanks again!

T
 
ad0lescnts said:
... you mean that a stereo has 2 separate amps?
Click to expand...


Yes -- a stereo amplifies two signals separately: one for the L channel, one for the R. So long as you're only connecting one speaker to each channel, everything's relatively simple. In the unlikely event you start connecting two speakers to the left (or right) channel, you need to start worrying.

and why wouldnt two 4 ohm cabs work as perfect?
Click to expand...


Because they're not actually 4-ohm cabs. Generally, in actual practice, impedance varies with frequency. The signal produced by a bass amp is anything but typical, in terms of predominant frequency. Also -- it is my understanding that the rated impedances that manufacturers put on their speakers is, at best, an approximation anyway.
 
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