Need to wire a 4 x 12 cab for 4 & 8 Ohms

I understand impedence, but I am not really an electronics guy. The only way I can see it is:

Two 4 ohms speakers series (8 ohms)

Two 16 ohms speakers parallel (8 ohms)

Two 4 ohms speakers series (8 ohms) --- parallel --- Two 16 ohms speakers parallel (8 ohms) = 4 ohms.

If you do not always need all 4 speakers this could work. You could use either the two 4 ohms speakers series, or two 16 ohms speakers parallel to get your 8 ohm load, but you will be using only 2 speakers. But you will be using all four speakers for your 4 ohm load.

It would probably be best to wire like that diagram though. You could run all 4 speakers off a 4 ohm amp. Then you could put the 16 ohm load on a 8 ohms amp. It is not a problem to put a 16 ohm load on a 8 ohms amp, although the amp will only operate at about 70% power (a 50 watt amp would put out about 35 watts). It will not be quite as loud, and some claim not as dynamic, but it won't hurt the amp. Where you get into trouble is when you go below the amps designed impedence (like a 2 ohm load into an amp designed to operate at 4 ohms minimum). This allows too much current to flow through the amp, causing it to overheat and possibly damaging it very quickly.

I guess we're on the same wavelength, Wes, because that is exactly what I came up with - all the same scenarios that you did. I have been reading several sites, & a couple I came across were kinda against wiring speakers in series, I guess because of mis-match/slight differences in speaker resistance, & one would pull more wattage & be louder than the other.

I don't have enough experience in wiring multi-speaker set-ups to know if it would be a major difference or hardly noticeable. Either way, I will do some more study & see what I come up with.

There was a member on here that was building a cab, I think it was 4 x 12 several months ago. I tried looking back through the older threads & couldn't find it. The member posted pics of his progress. Does anyone maybe have a link?

Don't feel bad, I have gone through ads for many various cabs and haven't seen anything 4 & 8 ohms. Although the newer Marshall 4 X 12 1960 cabs operate at 8 ohms stereo, and either 4 or 16 ohms mono.

Marshall 1960 Extention Cabinet

Don't feel bad, I have gone through ads for many various cabs and haven't seen anything 4 & 8 ohms. Although the newer Marshall 4 X 12 1960 cabs operate at 8 ohms stereo, and either 4 or 16 ohms mono. Yeah, the other day I went thru all the 4 speaker cabs on Musicians friend, & none are 4/8 ohm switchable, except for the stereo switch where only 2 speakers function in the 8 ohm position.

I believe I will go with the 16/4 ohm scenario, I guess that will be the most versatile, since I want to use 4 speakers at all times.

Just out of curiosity - why do you want to have 8/4?

I have a Behringer that has 8 ohm out, & a friend has a 4 ohm head; This way, we could both use either amp if we desired & have an exact impedance match.

4x16ohm speakers. You need to wire them series/parallel with a dummy load of 16 ohms for 8 ohm and parallel/parallel for 4 ohm.

So, two series pairs of 16 ohm speakers wired in parallel along with a dummy load of 16ohm 100-200 watt resistor also in parallel. "Should" give you 8 ohms.

All four speakers wired in parallel, bypassing the dummy load "should" give you 4 ohms.

I wouldn't try this without a proper ohm meter. I think it would probably be best to have someone with experience do it. Otherwise you might fry your amp.

Anyway it's about a $600 mod. Cheaper to buy another cab.

Edit: incidentally, I'm not sure that the wattage rating is so important with the dummy load. Another reason to ask or deal with someone who knows this subject well.

So, two series pairs of 16 ohm speakers wired in parallel along with a dummy load of 16ohm 100-200 watt resistor also in parallel. "Should" give you 8 ohms.I had thought along those same lines, about putting a dummy load in the mix, but many of the speaker building websites say not to do that; wasting amp power, the danger of the resistor burning out, etc.

So, I decided on the 16/4 setup. I probably won't notice an appreciable difference in the 16 ohm mode, running it with an 8 ohm head. Has anyone here actually done that? Was it real noticeable to you, as far as volume/power loss?

When you go from 4 ohms to 8 ohms, you lose approximately 30% power. So, if you had a amp that puts out 100 watts at 4 ohms, and hooked it up to an 8 ohms cab, the amp will only produce about 70 watts.

And it's the same proportion going from 8 to 16 ohms. So, an amp that produces 100 watts at 8 ohms will produce about 70 watts at 16 ohms.

Going back to that first amp that produced 100 watts at 4 ohms, it would produce about 50 watts at 16 ohms.

But that is not much of a problem. Everytime you double the watts to a speaker(s) you get about a 3 decibel increase in volume. So the 4 ohm cab connected to the 100 watt head would only be about 3 decibels louder than the 16 ohm cab. 3 decibels is just a barely detectable increase or decrease in volume. You will hardly notice it.

I have read that many claim the sound is not so dynamic when you load too much impedence like running the 16 ohm cab on an amp designed to run at 4 or 8 ohms. I don't know if it is really so, I have experimented by running different cabs off my Epi Valve Jr which has 4, 8, and 16 ohm outputs, I couldn't hear much difference myself.

^^ I'd agree to 70% for tube amps, but it'll be closer to 50% for solid-state. SS amps don't usually have that much sag at 8 ohms, so they don't have as much recovery at 16. The sag gets worse at 4 ohms and 2 ohms. YMMV.