Guitar Amp/Speaker Impedance Wattage Question... HELP!

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388
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Guitar Amp/Speaker Impedance Wattage Question... HELP!

Post by 388 » Thu Dec 13, 2007 2:12 pm

I have a '65 fender bassman head and a '74 marshall 50 watt JMP head. I want to get a new 1x12 cabinet to use with both but how do I know what the proper impedance should be for the speaker? Is there a way to measure it out of the speaker output?

Also both amps are rated at 50 watts, does it matter how many watts the speaker is? I was looking into a cabinet loaded with a celestion g12h speaker that is rated at only 30 watts. That leads me to believe that just because you have a 50 watt amp doesn't mean you need a speaker that is rated at 50 (or more) watts. Am I wrong about that?

Thanks.

RefD
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Post by RefD » Thu Dec 13, 2007 2:20 pm

the speaker outputs on the backs of the amps aren't labelled with the impedance load they're expecting?

you should get a speaker rated for greater than the output of the amp, cos the peak output of a 50 watt amp will actually be well above 50 watts.

i mean, you can use a 30 watter with a 50 watt amp so long as you never crank it up...but you'll run into speaker breakup alot sooner than you might want and if you DO goose the output you could damage the speaker.
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388
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Post by 388 » Thu Dec 13, 2007 2:33 pm

RefD wrote:the speaker outputs on the backs of the amps aren't labelled with the impedance load they're expecting?
not as far as i can see.

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A-Barr
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Re: Guitar Amp/Speaker Impedance Wattage Question... HELP!

Post by A-Barr » Thu Dec 13, 2007 3:36 pm

388 wrote:I have a '65 fender bassman head and a '74 marshall 50 watt JMP head. I want to get a new 1x12 cabinet to use with both but how do I know what the proper impedance should be for the speaker? Is there a way to measure it out of the speaker output?

Also both amps are rated at 50 watts, does it matter how many watts the speaker is? I was looking into a cabinet loaded with a celestion g12h speaker that is rated at only 30 watts. That leads me to believe that just because you have a 50 watt amp doesn't mean you need a speaker that is rated at 50 (or more) watts. Am I wrong about that?

Thanks.
No real way to measure, but the Bassman is 4 ohms. Aren't Marshalls usually selectable? Is there a switch on the back that lets you choose? Otherwise, I'd look on some Marshall forums and post your question, I'm sure there are plenty of amp geeks out there that can tell you.

As to power rating, I'd get a 100 watt speaker for a 50 watt amp, at least if it's a ceramic speaker magnet, alnico, you might get some sonic benefits from pushing it a bit, but the opposite is usually true with ceramic.

Hope that helps!

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A-Barr
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Post by A-Barr » Thu Dec 13, 2007 3:40 pm


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Post by farview » Thu Dec 13, 2007 7:37 pm

The marshall will have an impedance selector switch on the back.

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