# Combining an 8ohm and 4ohm cab... an idea for discussion

Discussion in 'Amps and Cabs [BG]' started by KJung, Apr 13, 2005.

1. ### KJung

Here's an idea that I've thought about (based on a recent 8ohm/4ohm cab thread)...

Given that many heads now can comfortably run at 2ohms (iAmp800, EA350 and 650 and some of the Acoustic Image models), to get the ultimate large/medium/small room rig you could purchase a 4ohm 410 cab and an 8ohm 210 cab (for example an Epifani410UL at 4ohms and a 210UL at 8ohms). With the iAmp800, for example, for small gigs, the 210 at 8ohms would 'pull' about 500 watts from the amp and be a great sounding small rig. For moderate to large size gigs, the 4ohm 410 would pull 800 watts for from the amp and put out a lot of sound. For the largest of gigs, combining the 410 and 210 would result in 2.66 ohms (and here's the point I want to make sure I have right), the iAmp would put out about 900 watts or so, and each of the 6 10" speakers would draw the same wattage... resulting in a 'virtual' 2ohm (approximately) 610 cab. so, you would be optimizing the power of the amp and size of the rig to the three types of gigs with one amp and two cabinets.

Is my math correct and does this make sense?

2. ### Mudbass

Of course running both cabs probably means you won't hear the 2x10 cab because it has half the speakers of the 4x10 and would be getting 50% less power than the 4x10.

3. ### KJung

By my calculations, each speaker would be drawing the same power, so adding the 210 at 8ohms to the 410 at 4 ohms should be virtually identical to have a 610 cab... yes the 410 will be louder, but only because it has another pair of speakers... think of it as 'three pairs of 10's, each getting the same power... comments?

4. ### MuzikMan

This is my way of thinking about it too. Sounds like a great idea to me.

5. ### Mudbass

It doesn't work that way. When you mount identical drivers on the same baffle and feed them the same audio signal they couple together sonically and cease to behave as individual speakers. You have to figure each cab as an idividual speaker. The 2x10 cab has twice the resistance of the 4x10 so it gets half as much power and therefore won't be nearly as loud as the 4x10.

6. ### Petebass

Dec 22, 2002
QLD Australia
Your math is correct. Each driver gets 150w. And because they're 6 identical drivers, it should be ok. Anyone else thinking of doing this should be aware that mixing different drivers with different sensitivities my run into trouble. This is definitely on of those case-by-case ideas.

7. ### KJung

Great point.... you would have to use the same 'brand' of 410 and 210 so that they would match up. Thanks.

8. ### ErnieD

Nov 25, 2004
Atascocita,TX.
I just asked on the Is Avatar the best 2x12 cab thread this same question. I was asking about pairing a 4ohm 2x12 cab with my 8 ohm SWR Goli III 4x10. My GBE 600 goes to 2 ohms, see a problem here. Reason was to use either cab as a stand alone, I have the Goli III and use it frequently as stand alone. I was thinking I want the Ava 2x12 to replace my 2nd cab SWR SOB 1x15, to then use the 2x12 as stand alone that is why I was considering a 4 ohm cab. Any thoughts here, not all 10's anymore?

9. ### Petebass

Dec 22, 2002
QLD Australia
It gets complicated when you start mixing different model drivers. It gets especially difficult when you mix different size speakers, because equal wattage to each speaker becomes irrelevent. Instead it becomes a case of equal SPL per cab.

It can be done, but you should do the math first.

As you know the 4ohm cabs get twice the power of the 8 ohm (400W to the 4 ohm, 200W to the 8 ohm). So your 4x10 would have to be significantly more efficient than the 2x12 to produce a similar amount of volume from both cabs.

The 4x10 has a sensitivity rating of 105dB. The 2x12 would be 100dB given it uses 2 Delta 12lf's. Using the formula

SPL = 10(Log Watts)+Sensitivity.

The 8 ohm 4x10 = 10(Log200)+105 = 128dB SPL.
The 4 ohm 2*12 = 10(Log400)+100 = 126dB SPL.

So by my calcs, it could just work. The 4x10 looks like producing 2dB more than the 2x12 even though it's getting half as much power. Of course this is all at 1K which is where sensitivity is measured. Who knows what the real life blend will sound like for bass. But it's worth a try.

10. ### Crockettnj

Sep 2, 2005
North NJ
Nostalgia-laden bump for what I think is a great "plan" on the part of the OP.

11. ### KJung

I do like this idea, although I've become the 'voice of 4ohm minimum' solid state rigs for most other applications and combinations