This hasn’t got anything to do with guitar or bass setups. But I see so much confusion out there on the inter webs that I thought I would share what I know* on the subject.
“I read somewhere that you should not use a bass amp head with fewer watts than your speaker cab, or you could damage your amp.”
Wrong. Your amp is in no danger whatsoever if you run it into cab(s) of greater watt ratings than the amp puts out.
“I read somewhere that you should not use an amp head with more watts than your cab(s) are rated for, lest you damage the speakers.”
This is pretty much wrong, too. It’s true that you should use your ears and, if your speakers sound distressed, turn down the amp. But this is true even if your amp is putting out fewer watts than the cab is rated for. That’s right! You can damage your speakers with a 400 watt amp going into a 500 watt cab.
“Cab watts” and amp watts are not put on the sides of their respective boxes so that you can match them up like Garanimals kids clothes. (Yeah, I’m old.) Speaker cab watts are the manufacturers estimation of how many watts the speaker(s) will take before the voice coil inside melts down in a puff of smoke. That is, it’s the cab’s thermal limit. But the truth is, bass players do not need to worry about this. Why? Because the mechanical limit will be reached long before that and cause you to damage the speaker cone. This is called “blowing a speaker.”
I hear you ask: Why do speaker cab makers report these unhelpful thermal limit numbers? My answer is: Hey, man, I just work here. 🤷♂️
There is really only one downside to mismatching your amp watts and your speaker cab watts: inefficiency. Let’s say you buy yourself a Porsche 911 sports car. Sure, you could prowl around the neighborhood in second gear, but should you? Why pay for all that performance if you’re not going to use it? Supposing you buy a 1,000 watt amp head. Sure, you could plug it into a 350 watt cab, but should you? Why pay for all those watts when you’re not going to use them? This works both ways, too. You buy an 800 watt cab but should you power it with a 200 watt amp head? Why pay for (and carry!) all that cab if you’re never going to get your money’s worth out of it?
Should you worry about efficiency if you’re running a 500 watt amp head into a 400 watt cab? No. Should you worry about efficiency if you’re running a 500 watt amp into a 600 watt cab? No. It’s only when you’re wildly mismatching them that you should start questioning your purchasing decisions.
Before you start saying whew! What a relief! I don’t have to worry about amps and cabs if I just–hang on there partner. Because there is one thing you do have to get right and you have to get it exactly right. That thing is ohms. But I’ll leave that for another post.
* Hey, so “what I know” basically means, this is my understanding. I’m not an expert in electronics or sound engineering. Read and abide by your manufacturers manuals. Take my advice at your own risk.