How hard to change a cab from 4 to 8 ohms?

[Gordon of Eden]

I have one of the old Ampeg PB112 cabs which is great for rehearsals and really small gigs. It sounds very nice with my shuttle but I am a little timid about turning it up as the cab is 4 ohms. I would also like to use the PB cab in conjunction with my Eden 112 (8 ohm) with the shuttle for a loud easy to transport rig.
Is this an operation I can do myself? (I'm not very trustworthy with a soldering Iron). Do I even need to worry about it? Thank you all in advance for any advise and or tips you can give.

 

[synterx]

can't do it. A speaker is what it is. If you had two 8 ohm speakers, and wanted to make either a 4 or 16 ohm cabinet, that could be done. But you simply can not do what you want. You'd have to buy a replacement 8 ohm speaker.

 

[KJung]

Can't do it without changing speakers. Four ohms is typically achieved by putting two 8ohm speakers in parallel. Eight ohms is achieve by putting two 16ohm speakers in parallel, or two 4ohm speakers in series (I think).

There is no combination of two 8ohm speakers that will result in a total nominal impedance of 8 ohms.

 

[IvanMike]

how hard is impossible?

lol. the speakers/transducers are set to a specific impedance. in the case of a single driver cab the speaker itself would have to be swapped out for another of the proper impedance, but you also have to make sure that it is similar enough to sound reasonable good in the cab. however, if you have an amp that has stereo power amps or if your amp is stable down to two ohms in mono you can try using the 4 and 8 together. it might sound ok to you.

and heck, turn the 4 ohm cab up...........just listen to it, it will tell you if it is being overdriven and you can back off.

 

[Gordon of Eden]

There is no combination of two 8ohm speakers that will result in a total nominal impedance of 8 ohms.

Thanks for the response guys.
The cab only has 1 speaker and a HF tweeter. I wanted to make it 8 ohms so I could achieve 4 ohms when used with the other cab.
I kind of figured I would need to replace the speaker but was hoping there would be an easier solution.

 

[KJung]

Thanks for the response guys.
The cab only has 1 speaker and a HF tweeter. I wanted to make it 8 ohms so I could achieve 4 ohms when used with the other cab.
I kind of figured I would need to replace the speaker but was hoping there would be an easier solution.

Ah, single speaker cab.. I misunderstood... same deal though, you would need a new 8ohm driver.

K

 

[Ramanujan]

I don't know how it works, but there is this thing:

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[Gordon of Eden]

I don't know how it works, but there is this thing:

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Man that thing looks kind of scary
And most likely more expensive than the actual speaker

 

[amper]

It's just a transformer, the same thing you'll find in the output section of just about any tube amp. I wonder how much they charge for those, though, because big iron isn't cheap.

 

[sKu]

in germany this transformer is sold for 145 euros (about 220$).
or 200 euros (290$) including case and speakon connectors...

 

[amper]

Thanks for that info. That price doesn't seem as high as I thought it would be.

What's really cool about it is that although Glockenklang bills it as an 8 Ohms <-> 4 Ohms transformer, it's really just a 2:1 transformer, so it could be used with any load impedance. That is, you could use it to plug four 8 Ohm cabs into a 4 Ohm capable amplifier, or four 4 Ohm cabs into a 2 Ohm capable head, or any similar combination, like plugging three 8 Ohm cabs (2.67 Ohms) into a head that can't go less than 4 Ohms (would be transformed to 5.33 Ohms).

 

[Rick Auricchio]

There will be losses in that 2:1 transformer. Possibly as much as 30%; transformers aren't that efficient.

At some power level, the transformer will be driven into saturation. When it saturates, the tone will get rather wooly. Maybe good, maybe bad, depending on your taste.

 

[GreyBeard]

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I've never seen or used one but, it might solve your problem.