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So I have an eden 4x10 that is 8 ohms and I'm about to get an additional Emperor 1x18 that is 4 ohms (SO EXCITE). I use an old custom pa head that I'm pretty sure runs at 8 ohms.

Would it be possible for me to run everything at once without blowing something up?

Your amp would need to handle 2 ohms (2.66) to run those in parallel and then the power to each would still be unbalanced (66%/33% power split). So you could blow a transformer, need more amp details.

With a Tube amplifier this would be a terrible idea unless your amp is designed to handle it.

With a solid state power amp that doesn't have a power transformer, it'll just be really inefficient.

The formula for parallel wiring with 2 speakers btw is (S1*S2)/(S1+S2). So like grygygx said, 2.6667 Ohms.

so both cabs should be running at the same ohms to make this work?

Not clearly. Two 8 ohm cabs = 4 ohm load. If the amp doesn't support a 4 ohm load, it because questionable. Tube amps often have transformers that can handle 100% mismatch (but not always), so if you amp supports 8 ohms it MIGHT be able to run a 4 ohm load without doing damage (depending on the amp). A solid state without a transformer would probably just work, but I don't know much about that.

grygrx wrote:A solid state without a transformer would probably just work, but I don't know much about that.

With no transformer you're not gonna break anything but it might not be getting full volume or sound bad.

Ohm Matching is good form just for simplicity and efficiency but yeah, you need to read the amp's manual somewhere to know for sure.

So what are my options here?

Replace the emperor speaker with an 8 ohm speaker? Buy an amp that runs at two ohms?

The kustom apparently runs at 4 so that's a no go.