Impedance question

[Tonelover]

I have a 100w 2x12 combo with two 16 ohm speakers wired in parallel and have been running it with the 4/8/16 ohm selector switch on the back of the amp at 8. Now I want to simultaneously run a 16 ohm 4x12 cabinet using the second speaker out jack.

Any idea what the best impedance setting to use is? I've tried researching the answer but am not having any luck yet. Thanks.

[jet66]

If the output jacks are wired in parallel, set it at 4 ohm. The 16 ohm cab and 8 ohm combo load in parallel make a total load of 5.33 ohms. So that gives you a 'safe mismatch' that is pretty close to 'correct.'

Handy-dandy impedance calculator: http://www.colomar.com/Shavano/impedance_proc.php

[Spivonious]

For parallel connections, use the following equation:

1/r1 + 1/r2 + ... + 1/rN = 1/R, where R is the setting you should use.

So for your case, we have three parallel 16 Ohm circuits.

1/16 + 1/16 + 1/16 = 1/R

3/16 = 1/R

R = 16/3 = 5 1/3

For series circuits, you simply add them all together (r1+r2+...rN = R). So if your 2x12 was wired in series, you'd need a 32 Ohm setting on your amp.