# cab wiring question need help

Discussion in 'Amps and Cabs [BG]' started by Jebthebassist, Apr 19, 2005.

1. ### Jebthebassist

Dec 8, 2004
I have a question about running some cabs. Lets say I have 2 210 4 ohm cabs and i have a 115 8 ohm cab. now according to ohms law i would have an 8 ohm load.
A1 x A2 x A3
-------------
A1 + A2 + A3

So even though the 210 cabs are 4 ohms would I be able to run these 3 cabs out of my amp in mono bridged mode putting 800 watts out @ 8 ohms? Or would I just screw my transformers or would my speakers just put out low volume?

2. ### Eric Moesle

Sep 21, 2001
Columbus OH
No no no!!!!! Stop!!!!!

You can only do this if you use special cables resulting in a series/parallel situation, where the two 4 ohm cabs are run in series, then are paralled with the 8 ohm cab.

Running this cabs together in ANY fashion with regular cables will fry your transformer almost immediately!

3. ### Mudbass

No, your impedance would be 1.6 Ohms which would cook just about any amp around.

4. ### jp1994

Nov 18, 2004
Western Massachusetts
this doesn't sound right...

the 2 4 ohm cabs would give you 2 ohms.
plus the 8 ohm cab would be 1.6 ohms?

am I wrong?

5. ### BassIan

Apr 27, 2003
Cupertino, California
That formula you used is only applicable for two impedances/resistances. It is derived from the more general parallel resistance formula being as follows:

1/R = 1/R1 + 1/R2 + 1/R3 +.....

However, you can think of your 2 4 ohm cabinets as 1 2 ohm cabinet (that is their parallel impedance), and use your formula for the 2 ohm "virtual" cabinet and the 8 ohm 1x15. Either way, you should get 1.6 ohms as your final impedance.

This would absolutely cook your amp, since that equates to 0.8 ohms on each channel (since you're bridging). It would try to push too much current through the output devices and overheat. Hopefully the amp would go into some protective mode, but it's *better not to do that*.

6. ### Jebthebassist

Dec 8, 2004
Thanks guys. I didn't think it would work but I thought I'd ask. Don't worry I dont have the cabs to do this and haven't done it. But I want to buy 220 cabs @ 4ohms and I was just wondering if I could ever add on too it and what ohm cab I would need. Thanks for your help. Also if you have any suggestions I would like that