4 or 8 ohm wiring question...

[SimonH]

Hi - stupid question time: is the difference in the ohm rating between a 4 ohm and 8 ohm version of a 4x10 cab simply down to their wiring order? Or are there other differences, not just series or parallel wiring? Ie can you whip out a soldering iron and convert a 4 ohm 4 x 10 cab to an 8 ohm? I'm thinking specifically of the Markbass HF cabs... Thanks!

[Dad3353]

The impedance of the cab is a function of both the individual impedances of the drivers, and the cabling method used. In the case of a 4 x 10, at 4 Ohms, I shall assume 4 drivers with identical impedances. 2 possibilities come to mind...
1 - all are 4 Ohms each, wired as 2 in series (total 8 Ohms...), the two series then cabled in parallel (total: 4 Ohms...).
2 - all are 16 ohms, cabled all in parallel (total: 4 Ohms...)
In both cases, it is not possible to rewire to give 8 Ohms.
For case 1, wiring all in series would give 16 Ohms, all in parallel gives 1 Ohm (and probably some magic smoke on 'lift-off'..!). 1 in parallel with 3 others in series gives a bastard impedance which I'm too lazy to bother with, and is not 8 Ohms.
Case 2, rewired as all series gives 64 Ohms, cabled series/parallel gives 16 Ohms.
In short: no, one cannot obtain a 8 Ohm solution with a 4 Ohm 4 x 10, assuming all drivers to have equal impedance.
Hope this helps.

(Now you know why I play drums..! )

[flyfisher]

Yep. And let's face it, given the number of times this sort of issue crops up, some cab manufacturer somewhere would have included a simple "4 or 8" ohm switch by now if it was actually possible.

[SimonH]

Merci, clear as. If every amp went to 2 ohms, we wouldn't have this problem... :-)