What are the ohm considerations when running a 2x10 & 4x10 cab together?

[Jarrett]

Should you run:

8ohm 2x10 + 4ohm 4x10
4ohm 2x10 + 8ohm 4x10
4ohm 2x10 + 4ohm 4x10

And why?

[billfitzmaurice]

The 2x10 should be twice the impedance of the 4x10 for equal power distribution to the six drivers.

[James Judson]

No, because most amps work reliably at 4 ohm and all the combinations you listed are less than 4 ohms. If you have an amp that goes down to 2 ohms then your set, any combination you listed will work.

[walterw]

bill's point is that while all those combos will "work", unless the little cab is twice the impedance of the big cab, it will get too much of the amp's power while the big cab gets too little.

if you have an 8Ω 4x10, you'd want a 16Ω 2x10 to get equal power to all 6 10s. (in practice this means finding a 4Ω 2x10 and rewiring it from parallel to series).

of course, a stereo amp renders this unnecessary, as each cab would get its own amp side and could be adjusted relative to each other.

[Jarrett]

Let's say I have a 2ohm capable (BX500) amp running mono

So you are saying I'd want the 8ohm 2x10 paired with the 4ohm 4x10? Why is that?

[KJung]

Originally Posted by Jarrett

Let's say I have a 2ohm capable (BX500) amp running mono

So you are saying I'd want the 8ohm 2x10 paired with the 4ohm 4x10? Why is that?

Yes. That combination would result in 2.67ohm nominal impedance, and each driver would get the same power (i.e., the 8ohm 210 with half the drivers of your 4ohm 410 will get half the power).

So, basically, you have created a 2.67ohm modular 610. The downside is you have to have a head capable of 2ohm or so operation. The upside is that you have a 'three use' modular system that automatically adjusts power for the speaker size... 210 8ohm, smallest cab, lowest power for small gigs, 410/4ohm, single large cab/high power for most gigs, 210(8ohm)/410(4ohm) most drivers, highest power for your biggest, loudest gigs.


Think about it this way (regarding the different impedances of the cabs), you wouldn't want two of the six drivers in a 610 to each get twice the power versus the other 4 drivers. Same thing with the 210/410 (assuming the cabs use the same drivers).

Edit: This doesn't mean that other combinations (8/8ohms or 4/4ohms) won't work... just doesn't make as much sense.

[mikeddd]

Assuming a stereo amp, how would you ensure each cab was putting out what it was supposed to put out? I.E. setting the individual channel gains on the amp would be arbitrary due to the diff sensitivities of the cabs. Would you use a db meter?

[KJung]

Originally Posted by mikeddd

Assuming a stereo amp, how would you ensure each cab was putting out what it was supposed to put out? I.E. setting the individual channel gains on the amp would be arbitrary due to the diff sensitivities of the cabs. Would you use a db meter?

Having a stereo power amp with a 'balance' control or separate channel volume controls makes this issue a moot point. You can just use your ears.... nothing that complicated IMO.

[billfitzmaurice]

Originally Posted by Jarrett

Let's say I have a 2ohm capable (BX500) amp running mono

So you are saying I'd want the 8ohm 2x10 paired with the 4ohm 4x10? Why is that?

Once again, but this time with feeling: So that all six drivers receive equal power.