Mismatched Impedance Question

mykljpao

Member
Messages
538
For various reasons I want to run an extention cab that is 16 ohms with a combo loaded with an 8 ohm speaker (thought it was a 16 until I put a meter on it). What will the practical result be? Less volume out of the ext cab? And, more importantly, what speaker output tap do I use. Interestingly enough, with a Y cord used to connect the 2 speakers, I am getting an ohm reading of 4.5. Another question...why can't I connect the 8 and the 16 ohm speakers to the respective output on the amp.
I know, I know, other than flipping switches and turning knobs, I haven't a clue as to what goes on inside, lol. Thanks in advance for your help.
 

rockon1

Platinum Supporting Member
Messages
13,698
More power will go the the 8 ohm speaker. The ohm rating of the combination will be 5,33 ohms-resistance measurd with a meter is lower. Either 4 or 8 ohm setting on the amp shouild be fine.
 

mykljpao

Member
Messages
538
Rockon1, thanks very much for the quick reply. The combo speaker is rated for the full power of the amp, just looking to move a little more air and elevate the combo by using the ext speaker. I wanted to make sure that I wouldn't be doing anything nasty to my Fuchs TDS.
 

Guitartim

Member
Messages
890
I also have an ohm dilemma. My Peavey Delta Blues amp is rated at 16 ohm and I have a Carvin 8 ohm Celestion extension cab. Should I not use the extension cab with this amp?
 

John Phillips

Member
Messages
13,038
You can certainly use the extension cab on its own, if you disconnect the combo speaker - pull one of the clips off and tape it. Using the extension speaker jack automatically switches the amp to 8 ohms.

You can probably use both together - there will be a downward mismatch (8 ohms to 5.33 ohms), which is safe for almost all tube amps, although the Peavey's output transformer is quite small and you may be pushing it a bit hard. I would still do it though - particularly if you're not intending to crank the amp right up. It should be safe.
 




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