4ohm Head into 16ohm cab.

[Cygnus X1]

I run my one amp without a load all the time... then again, it's a THD Univalve that has its own built-in load and can be used that way.

For the most part, anyways. No load=bad for output transformer.

[CharvelRocker]

Yes, the resistance will be changed. If the extension cab is the same impedance as the speaker, the impedance seen by the amp will be halved, or 4 ohms in this case. If they are different you can use the formula:

R1*R2/(R1+R2)

where R1 and R2 are the impedances of the cabinet and the speaker.

Unfortunately, that won't work, as it would give me an impedance of roughly 2.6 according to your equation. So, is it possible to rewire a 4ohm cab with 4 16 ohm speakers to 16 or 8 ohms? 8 would be ideal as I could run it with the combo's speaker, but 16 would work as well as it has an 8/16 switch (just would have to disconnect the combo's speaker).

[MountainDog]

So, is it possible to rewire a 4ohm cab with 4 16 ohm speakers to 16 or 8 ohms?

Your 4 ohm cab using four 16ohm speakers is wired in Parallel (first example below). To get 16 ohm cab from four 16ohm speakers, you need to wire in Series/Parallel (2nd example below): (you can't get an 8ohm load from the four 16ohm speakers)

4 Speakers - Parallel Wiring; In Phase

• 16 ohm loads - total load = 4 ohms

The impedance decreases. The equation is
1/Total Load = 1/S1 + 1/S2 + 1/S3 + 1/S4
Where:
S1 = the impedance of Speaker load # 1
S2 = the impedance of Speaker load # 2
S3 = the impedance of Speaker load # 3
S4 = the impedance of Speaker load # 4


4 Speakers - Series/Parallel Wiring; In Phase

• 16 ohm loads - total load = 16 ohms

The impedance is the result of the
series load being wired in parallel.
Add up all the series loads:
SL1 = S1 + S2
SL2 = S3 + S4
Then Figure out the Parallel load
Total Load = (SL1 x SL2) / (SL1 + SL2)
Where:
S1 = the impedance of Speaker load # 1
S2 = the impedance of Speaker load # 2
S3 = the impedance of Speaker load # 3
S4 = the impedance of Speaker load # 4
SL1 = the impedance of Speaker load # 1 + 2
SL2 = the impedance of Speaker load # 3 + 4


Here's the website I found the above on:
http://colomar.com/Shavano/spkr_wiring.html

[marcus]

Also, its important to keep in mind that if you hook up an 8 ohm speaker in parallel with an 8 ohm 4x12, the 4x12 is going to get the same amount of juice as the one speaker in the combo. So each speaker in the cabinet is going to get 1/4 of the power that the combo speaker gets. It is best in the cabinet to use speakers with higher sensitivity, so that they can generate the same amount of sound as the combo speaker. Otherwise, you may be disappointed in the sound being generated by your 4x12. Just some food for though

Also, I'm not sure about the amp you are talking about here, but a lot of times the main speaker output and the extension cabinet output are wired in parallel, so plugging an extension cab into the extension output, and leaving the main output open should be fine. The load seen by the output transformer would be the same. Consult your manual.