Speaker ohm question

Beav

Maybe someone can help. I have a Marshall JCM 2000 head and a Peavey 4X12 cab with celestion g12k-85's and two 1/4" inputs. My head has one out for 16ohms and dual outputs for either 4 or 8ohms. Should I use the dual 8ohms since my cab has two inputs? Or should I use just the one 16ohm output?
Maybe the other 1/4" input on the cab is meant to be an out for a second cab? I dunno.. Hope someone can help me before Saturday because I have a show.. Thanks!

ianvomsaal

It depends on how is the speaker cabinet is wired ???
Series, parallel, series/parallel, in phase, out of phase, ect, etc???

Okay, don't get scared - Typically a 4x12 cab is 16ohm.

Most single speakers are 8ohms,
Generally two 12" speakers together knock it down to 4ohms a piece,
Therefore four 12" speakers are usually 16ohms (4 + 4 + 4 + 4 = 16).
Cheers . . .

- Ian C.T. vom Saal

PS - here's a link
http://colomar.com/Shavano/spkr_wiring.html

ianvomsaal

Hope that answered your question?

- Ian

dirtyfrankdahmer

to make things simple.... since the cab has two jacks, one for 8 ohm load and one for 4 ohm load, that means the cab runs at 8 ohms in mono (1 cab ) and 4 ohms in stereo ( 2 cabs ). in your case, since you are running the amp in mono operation, plug the chord from the 8ohm jack in the head to the 8 ohm jack in the speaker. make sure you use a speaker cable and not a regular guitar chord.

dirtyfrankdahmer

ianvomsaal wrote:

It depends on how is the speaker cabinet is wired ???
Series, parallel, series/parallel, in phase, out of phase, ect, etc???

Okay, don't get scared - Typically a 4x12 cab is 16ohm.

Most single speakers are 8ohms,
Generally two 12" speakers together knock it down to 4ohms a piece,
Therefore four 12" speakers are usually 16ohms (4 + 4 + 4 + 4 = 16).
Cheers . . .

- Ian C.T. vom Saal

PS - here's a link
http://colomar.com/Shavano/spkr_wiring.html

your going to confuse him.

Beav

Upon further examination, I noticed the one 1/4" input went to the left two speakers, top and bottom, and the other input to the right side speakers. Each speaker is stamped 16ohm but I've been plugging in both sides with the 8ohm setting on my head. This has worked for a while now so I figured it was ok. The problem I have now is one of the speakers isn't producing sound. I don't know if it's blown or what but I don't see any physical damage or loose wires. Do you think it'll cause any damage running it like this for a show?

ianvomsaal

Well - OHM load can be a tricky thing, I'd suggest getting it checked out.
Generally you only plug into one side of a cab, and the speakers are all connected in series internally.
However, if they really are separated (hmm, two sides??), well then I'd say to just run half the cab.
You shouldn't have any problems for a gig running it that way.
Then, just make sure you take the cab in and have it looked at.
Once you get the speaker problem resolved you can ask the tech that did the work about the best way to run them, ohm load, ect.
Cheers . . .

- Ian C.T. vom Saal

dirtyfrankdahmer

sorry man, the advice i gave you above applies to a cabinet wired in series/parallel ( most guitar cabs are). from what you said above, i'm pretty sure your cab is wired parallel. in a parallel wired cabinet with 4 16 ohm speakers, the head would run at 4 ohms. since you said only two speakers are working, you would run the head at 8 ohms. if you absolutely have to use the amp, run it that way, but have a tech look at it asap. here is a link to a less confusing explanation of speaker ohms....

http://usspeaker.com/homepage.htm

scroll all the way down and click on the link that says speaker wiring if that link does not bring you directly to the page.

dirtyfrankdahmer

edit to delete post. i posted twice by accident. dont know how this happened.

Beav

Thanks for the help guys. Oh and I have three speakers working not just two. But yeah, like I said one 1/4" input is wired to the left side and the other to the right. I'm going to keep both sides plugged in at 8ohms then get it looked at to see why the one speaker shit the bed. thanks!

ianvomsaal

Remember - the majority of the time people blow their speakers because they UNDER-power them.
(that's the best way to blow a speaker).
Make sure you match up the OHM loads correctly or you could be doing just that.
Get your cab looked at - I don't know if you can safely run 3 speakers if ithe cabs wired like that - I'd suggest just running two.

- Ian C.T. vom Saal

who's_pearljam?

If you're playing tonight,,, then just plug into one side.

You don't know why that other speaker isn't working, and it may be only a loose wire, but you don't know if that side is running at 16 or 8 ohms right now.
Also, that iffy speaker is SURE to start working again intermittently right during your best solo!