What would happen if...?
 

I use a 4 ohm cabinet with an amp expecting a 8 ohm load? Is there any way to rewire a 4 ohm cabinet to 8 ohms? It's two 15" drivers.

No way to "rewire" to 8 ohms, can't be done.
If It is a tube amp it will run hotter, might stress the OT and output tubes a little. If it is a SS amp and it says 8 ohm minimum load the amp most likely will be damaged.

You will overload the amp if it cannot handle a 4 ohm load. You would need to check the
amp specs.

Your only choice with that cabinet is 4 ohms (2 drivers in parallel) or 16 ohms (2 drivers in series).

ya. sorry. it is what it is. you could either get a different cab that is eight ohm, get a different amp that will operate at 4 ohms, or get another cab that is 4 ohm AND BUY OR MAKE A SERIES CABLE. but if you don't know what i'm talking about with that last one, just don't...:cool:

What amp are we talking about here that only does 8 ohms? It's kind of rare for a bass amp to only do 8 ohms unless you pulled it out of a combo or something

i thought the same thing, but i had a backline250 that was 8 ohm min. or maybe it's a guitar amp.

I'm asking about an extension cabinet for an old swr wm12. I have a 4 ohm cabinet and have never used it because of the mismatch, but was wondering what, if anything, could be done so it could be used.

Chances are your extension cab has a pair of 8-ohm speakers wired in parallel to achieve a 4-ohm load.
If thats how your cab is now, you could simply re-wire those 2 speakers in series to achieve a 16ohm load.

You don't want to mismatch in that direction(8ohm head - 4 ohm cab) but as stated above, you could rewire it to 16 ohms and run that safely. You might lose a little power, but it's safe.

Hi.

The WM12 users can either confirm or shoot this down, but IIRC the WM12 has a 4Ohm capable amp.
Since the internal speaker is 8Ohm, the extension can't have less impedance than 8Ohms.
WM10 has the total polar opposite when it comes down to power amp topology, but it is designed like that.

Rather than rewire the cab and still have the combo's speaker determining the max SPL, I'd rewire the etension jack to defeat the internal speaker.

That way You can get the full potential of the 215 cab.

Regards
Sam

I am down with T-Bird's idea.
Chances are very good the combo internal speaker load is 8 ohms allowing an 8 ohm extension. Disconnect the internal speaker and you can then run the 4 ohm 215 cab.

It's definitely a good option to have the extension speaker jack bypass the internal speaker, but at that point, you'd be lugging around a head with a speaker attached to it. If you rewire the 215 to 16 ohms, and use it together, that might give you the most volume, and power distribution between the 3 speakers would be even, but you might run into issues with mixed speakers.