mixing speaker ohms

[sebtones]

ive done a bit of research regarding my question but im really keen to hear what you guys think. i have a cab w/ 4 celestion g12t 75's(16ohm) and i have an opportunity to trade 2 of them for vintage 30's(8ohm) an therein lies my problem, is there a way to wire the cab to accept 2 16ohm speakers and 2 8ohm speakers? maybe if i wired the two 16 ohms in series as if it was one 8 ohm speaker? am i better off holding out for 16ohm v30's(its a really good trade though so i'm keen for it to happen). thanks.

[martin manning]

It's not clear to me what impedance you want or need out of the combination, but if you have Excel you should be able to see what you can get by going here

http://www.duncanamps.com/software.html

and downloading the Speaker Impedance Calculator.

You'll see that you'll have to settle for an in-between value such as 12-Ohms, which you could get by paralleling the two 8's (yielding 4) and and the two 16's (yielding 8), and then connecting those two pairs in series to make 12. You should be okay driving that from a 16-Ohm tap.

MPM

[Steve Conner]

There's no way of wiring this that will divide the power evenly between all four speakers.

In martin manning's example above, the 16 ohm drivers get about twice the power of the 8s.

By doing the opposite (series both 8s for a 16 ohm string, series both 16s for a 32 ohm string, parallel the strings) again you get 12 ohms, but the 8 ohm drivers get twice the power.

If your speakers have different power ratings, this could work to your advantage: arrange it so that the ones that can take more, get more.

[cbarrow7625]

You can do anything and not hurt your amp if you match the overall impedance properly. The problem is that in most reasonable configurations you are going to end up with different voltage drops across different speakers. Not a problem for the speakers or the amp (generally - depends what you do & how much power you throw at it) but if you put a 16 Ohm speaker in series with an 8 (or an 8 in series with a 4) the higher impedance speaker will be about 3dB quieter than the lower impedance driver (or set of drivers).

Paralleling your two 16 to 8 then paralleling your other 8's to that will give you an impedance of around 2.66 ohms. Not many amps have a tap for that impedance. You could probably run it off the 4 ohm tap but it probably wouldn't sound good.

Be patient, wait for the 16 Ohm versions. You'll be happier in the long run.

[defaced]

I'd trade and get the 8 ohm V30s, then trade/sell those to get 16 ohm V30s. And at the very worst, in the mean time, wire your cab for stereo operation and run either side independently.

[sebtones]

just an updated query,in the 4x12 ive swapped out the 16ohm speakers for 8ohm speakers, i'm assuming the 16ohm output is now 8ohms(and the two 8ohm outputs are now 4ohms)? also have a 2x12 8ohm cab(2 16's in series), is it ok to run this in the amp's second output with the amp set at 4 ohms? my apologies if these are obvious questions,, i just cant afford repairs for any stupid mistakes! thanks.

[martin manning]

Originally Posted by sebtones

just an updated query,in the 4x12 ive swapped out the 16ohm speakers for 8ohm speakers, i'm assuming the 16ohm output is now 8ohms(and the two 8ohm outputs are now 4ohms)?

That's correct if you replaced all four speakers with 8's, and replaced the wiring exactly as it was with the four 16's installed.

Originally Posted by sebtones

also have a 2x12 8ohm cab(2 16's in series), is it ok to run this in the amp's second output with the amp set at 4 ohms? my apologies if these are obvious questions,, i just cant afford repairs for any stupid mistakes! thanks.

The 2x12 will be 8-Ohms if the two 16's are wired in parallel (not series).

Usually the extension speaker jack connects the extension cab in parallel with the main, so yes that would present a 4-Ohm load to the amp if both cabs are 8-Ohm.

MPM