Building a 2x12 cab

The impedance of the speaker does not change regardless of whether you connect them in series or parallel. What changes is the effective impedance seen looking into cabinet. If they are in series, it is the sum. If they are in parallel, it is half. So, in one case you will get 16 and the other case 4. Depending on what your amp supports, you may prefer one or the other.

Also, if you really want to have one of them turned off, it is probably easier to do that in the parallel case. In any case, turning off one will result in changing the impedance (either way, you will now end up with 8 ohms).

Ohms is a measure of resistance. The higher the ohms, the more resistance to current flow.

You want to match your total ohms to your particular guitar amp. If you have an amp that operates at 8 ohms, that is what you want to use. If you ran a cab rated a total (or sum) of 4 ohms off this amp, then there will be too much current flow through the amp. The amp can overheat and burn up, especially a solid state amp. Tube amps can handle lower impedence.

If you ran a cab rated 16 ohms off this amp, that is sort of like driving with your foot on the brake pedal, your amp will not be able to produce full power. It will probably not be nearly as loud, and probably not sound as good as well.

Here is a web site with diagrams for wiring in parallel and series for 2 X 12s and 4 X 12s.

http://www.dallasguitarrepair.com/news.html

Sweet. This is exactly what I needed. Although my supervisor and my supervisor's supervisor (the military guy) knew wha they were talking about, they don't really have experience with guitar cabs; they were strictly thinking in electrician's terms.

Another question I have, I just forgot it, dammit.

Right.

I have heard that if you try to use an amp without speakers, you can blow the amp. However, this guy said it isn't really true - he said, from an electrician's background, that it probably wouldn't happen. True or not? I'm asking because I wanted to be able to turn off one of the speakers at any given time, but i didn't want a switch for each speaker - because if they both are off (by accident or something like that), then the amp will overload.

More questions.

Will half-inch ply suffice for the enclosure? It's going to be reinforced with some 2x4s, but I'm wondering if the half-inch plys can handle the vibrations, as that's the extra I've got in my shed.

Half inch plywood could work, some extention cabs are built that way. Go easy on the 2X4 framing, if you make it too massive the cab will have a dead sound to it. I just finished a 2X10 cab built out of 1X12 pine with a half inch birch plywood baffle. I used 2X4's that I ripped down to 1-1/2"X1-1/2" for bracing and that was over-kill. I bought 2 - 10" private label eminence speakers off e-bay for $10 each and wired them up parallel to my EVJ head, it doesn't sound too bad for less than fifty bucks.

Good luck.

If you still plan to disable one speaker, be sure that you short the leads together. Otherwise, the unused speaker will flop around freely and confuse your sound in the low end.

Also, most people put some padding on the inside of the plywood, to keep the stray reflections down. House insulation is effective (but itchy!). Low density foam is also OK.

lunchmeat

Tube amps are different from Solid State or Hybrid (tube in preamp-solid state power section) amps.

NEVER operate a tube amp without a speaker load. It can damage the amp quickly.

Modern Solid State amps can usually be operated without a speaker load with no damage to the amp. This would include Hybrid amps as well.

Thanks. I knew tube amps could be dangerous, but I wasn't sure about solid-state.

I'm switching speakers...the beta 12A, even though it's really powerful and inexpensive, is really meant for monitor speakers in a PA system; although there's really no reason not to use them my friend convinced me otherwise. I will probably pick one of the guitar speakers from the eminence line.

I've also changed my wiring diagram - I'm going to have a separate input for each speaker, with a switch to switch from double-input, dual-speaker stereo to single-input, dual-speaker mono in the left speaker; it's wired in parallel, so stereo and mono should be the same impedance, unless I plug into just the right speaker (set to stereo); then I'll only be using one speaker, and my impedance should be doubled.

I think it's gonna work out.

How do I short the leads? I don't quite understand (sorry, I'm new at this and VERY ignorant, as I have recently learned. It's a humbling experience! :D )

I've also changed my wiring diagram - I'm going to have a separate input for each speaker, with a switch to switch from double-input, dual-speaker stereo to single-input, dual-speaker mono in the left speaker; it's wired in parallel, so stereo and mono should be the same impedance, unless I plug into just the right speaker (set to stereo); then I'll only be using one speaker, and my impedance should be doubled.

I think it's gonna work out.

How do I short the leads?

If you can draw a picture of your circuit diagram and post, then we could help .. what you said above didn't make sense. Let us say you have 8 ohm speakers. When they are separate (two channel stereo), you will have 8 ohms impedance on each input. If you switch them to be single channel mono, then the speakers are in parallel, and they will have 4 ohms impedance.

Unless, you mean that you are going to leave them wired in parallel and plug in two amps, one into each input. I don't quite know what will happen with that, but I don't think it is something I would want to find out with my equipment :-)

(Just to clarify: The impedance of the speaker does not change, regardless of how you connect it. The effective impedance seen by the amp, looking into the speaker input jack, changes. Two of them in parallel present half the impedance to the speaker. So, if you want to use both speakers together in one channel, they cannot present the same impedance as each of them individually. They have to be either in series or in parallel, and in one case you will get half, in the other case you will get twice).

It'd be the same, depending on the amplifier.

If I'm going for mono, the resistance would be 4 ohms (whoops, yeah, I wrote 8.) overall. However, if I went for stereo, the individual load of each speaker would be 8 ohms - but the parallel split occurs at the amp, if I'm not mistaken, so the amp would see a 4 ohm load. So it should equal out.

I'll try to get a diagram up in a sec.

Also, hooking two different amps up in stereo mode shouldn't cause a problem as long as the grounds aren't connected; it'd be the same as each amp having a separate cab. Nothing bad would happen. (Well, I can't think of anything, anyway.)

On the subject of grounding, does anyone know if I can simply use a guitar plate (say, these) on the back of a speaker box to save space and money, or do i need to go for the full jack plate? I don't want the grounds conducting through the metal in stereo mode; that would cause problems. However, I don't want to buy two single-jack plates, as they're about the same size and price as one with two input slots. Opinions?

Edit: Actually, hey, I don't have to draw it myself - someone has already done the same thing. ( http://colomar.com/Shavano/2x12wiring.html ) I'm doing Mono/Stereo in the same cabinet; it's about halfway down the page.

Ok, this is cool. Actually, there is no reason to connect in stereo from the same amp. It is exactly the same as connecting in mono with both the speakers parallel. Stereo only makes sense if you have two amps. If you have one amp, either use the parallel mode with the amp set to drive at 4 ohms, or use a single speaker with the amp set to drive at 8 ohms. In stereo mode, set both amps to drive at 8 ohms.

Don't stereo amps run effects through one channel and leave the other dry? Like reverb, and stero delay and whatnot...and then, panning as well? Thought stereo amps did quite a bit. I dunno.

I'm really indecisive about this entire thing because I don't want to waste my money, and this thread has been running way too long - I just need to get it over with. But one final question: choosing between "guitar" speakers and actual PA speakers, is there any reason to get one over the other, if they're the same price? Any disadvantages to having true PA speakers in a speaker cab, versus speakers meant for guitar cabs? Any disadvantages of guitar speakers over PA speakers? The only thing I can think of is that perhaps guitar speakers color the sound a bit. Perhaps, with the PA speakers, I can also run other instruments through the cab, like a piano, a bass, or drums, or something else (due to the better frequency range and the sound clarity). Any final suggestions before I put my money down on some speakers.

Sorry about being so indecisive about this - it's just that I'm putting quite a bit of money down on this, so I want to make a good choice.

Don't stereo amps run effects through one channel and leave the other dry? Like reverb, and stero delay and whatnot...and then, panning as well? Thought stereo amps did quite a bit. I dunno.

Oh, if you get a stereo amp, indeed connect the two channels to the two speakers in stereo mode. I meant that if you have a mono amp, there is no reason to split the output and connect it to two speakers separately, it is the same as connecting the speakers in parallel.

Don't know about the PA speakers much .. can't help you with that one. But most people seem to use guitar speakers, there must be a good reason :-)

2x12 Cab

:lol: :lol:

Whoops.

The speakers are actually meant for monitors...they're part of the PA system, but yeah, monitors are a different story. Better than guitar speakers or no, for the same price?

Greybeard, I really like that - you might be on to something there! You might try making some yellow cabs with checkered striped, under the name "Taxicabs" - I think it might sell!