'Paralleled out' on cabs

[Pinweaver]

Hey all, I've been wondering about this for quite a while, but I can't really find a decent answer to it.
I have 2 thiele's (8ohm) which I use at the same time plugged into the 4ohm outputs of my mark IV. Now on the back of the thiele's (and I suppose on other cabs as well) there's a covered plug labelled paralleled out.
How is this used and to what purpose?

The only thing I can think of is to connect one cab to another to form a so-called daisychain, but what does this do to the ohm value? If it changes the 8ohm to 4ohm, is it possible to connect 4 8ohm cabs using the 2 4ohm outputs? Sounds too good to be true, and I've never seen it used this way, so I guess not.

Any clarification appreciated.

 

[Schmoog]

alright so basically its like this. when you want to connect two speakers to 1 jack, you've got 2 wiring options, you can wire them in SERIES, or in PARALLEL. parallel is exactly like it sounds. the + from the amp goes to the + on the first speaker, and from the + on the first speaker you have a wire going to the + of the next speaker. the - from the amp goes to the - on the first speaker which goes to the - on the second speaker. what this does is it reduces the impedance according to this equation:

Zt = (Za x Zb) / (Za + Zb)

so if your speakers are 8 ohms each it looks like this:

Zt = ( 8 x 8 ) / ( 8 + 8 ) = 64 / 16 = 4

most people will say, oh it cuts the impedance in half. this isn't actually correct, it cuts the impedance in half if your speakers both have the same impedance. if they are different, say 16 and 8, it looks more like this:

Zt = ( 16 x 8 ) / ( 16 + 8 ) = 128 / 24 = 5.33

series is a little simpler. Series is when the + from the amp goes to the + of speaker 1. the - from the amp goes to the - of speaker 2. you then connect the - from speaker 1 to the + of speaker 2. what this does is simply adds the impedances together. so:

Zt = Za + Zb

so again, if you have 2 8 ohm speakers:

Zt = 8 + 8 = 16

or if you have 1 8 ohm and 1 16 ohm:

Zt = 16 + 8 = 24

when you look on the back of your mesa, where you see the 2 4 ohm jacks and it says something like "use for 2 8 ohm cabinets". those are basically parallel output jacks, and the parallel wiring is done inside the amplifier. you can also connect the 8 ohm jack to the input of your first thiele, then the parallel out of the first thiele to the input of the second. just make sure to connect it to the right jack on the amplifier. so to answer your question is it possible to connect 4 8 ohm cabinets using the 2 4 ohm outputs? yes and no. you can't just connect them in parallel the whole way. what you would want to do is connect the first 2 8 ohm cabinets using a series box, and the second 2 8 ohm cabinets using a series box, then plug each series box into one of the 4 ohm outputs. so basically each cab is 8 ohms, the series box adds this so you go from 4 8 ohm loads to 2 16 ohm loads. from there you go into the 4 ohm inputs which parallel them, giving you 1 8 ohm load, which is the proper impedance.

sorry, simple question, complicated explanation.

 

[Pinweaver]

Thanks for the detailed explanation. I had to read it a couple of times to make sure, but I do understand now. :wink: Cheers.

 

[t0aj15]

so to answer your question is it possible to connect 4 8 ohm cabinets using the 2 4 ohm outputs? yes and no. you can't just connect them in parallel the whole way. what you would want to do is connect the first 2 8 ohm cabinets using a series box, and the second 2 8 ohm cabinets using a series box, then plug each series box into one of the 4 ohm outputs. so basically each cab is 8 ohms, the series box adds this so you go from 4 8 ohm loads to 2 16 ohm loads. from there you go into the 4 ohm inputs which parallel them, giving you 1 8 ohm load, which is the proper impedance. sorry, simple question, complicated explanation.

This is not quite correct. When using four 8 ohm speakers they must be connected in series/parallel and then plugged into the 8 ohm output jack, NOT the two 4 ohm jacks.

 

[Schmoog]

so to answer your question is it possible to connect 4 8 ohm cabinets using the 2 4 ohm outputs? yes and no. you can't just connect them in parallel the whole way. what you would want to do is connect the first 2 8 ohm cabinets using a series box, and the second 2 8 ohm cabinets using a series box, then plug each series box into one of the 4 ohm outputs. so basically each cab is 8 ohms, the series box adds this so you go from 4 8 ohm loads to 2 16 ohm loads. from there you go into the 4 ohm inputs which parallel them, giving you 1 8 ohm load, which is the proper impedance. sorry, simple question, complicated explanation.

This is not quite correct. When using four 8 ohm speakers they must be connected in series/parallel and then plugged into the 8 ohm output jack, NOT the two 4 ohm jacks.

that can be done, but to do it you either need a cable wired in parallel, or you'd need to make a series box, or you can just plug into the parallel outs (4 ohm outputs). an 8 ohm load into a 4 ohm out is a safe mismatch so its ok. actually, for me this is desireable as this particular mismatch will lower the percieved volume of the amplifier, and it will make it seem like the tubes will break up earlier due to this.

 

[Vigo1999]

so, lets say i have 3 1x12 cabs, all 8ohms, being one with a parallell out.

to hook up all the 3 cabs, how i connect them?? 2 cabs (being one with the parallell out) connect to the amp outs (4 ohms) and the one left i can connect to the paralell out of the thiele?? this is it ?? :?:

 

[Schmoog]

so, lets say i have 3 1x12 cabs, all 8ohms, being one with a parallell out.

to hook up all the 3 cabs, how i connect them?? 2 cabs (being one with the parallell out) connect to the amp outs (4 ohms) and the one left i can connect to the paralell out of the thiele?? this is it ?? :?:

ok, the first 8 ohm cab would connect to one of the 4 ohm outputs, the other two would have to go into a series box, and then into the 8 ohm output. this would produce a safe mismatch at both inputs and equally balance the output of the amp. if you were to run two of them in parallel the output would be unbalanced, and some speakers would get more power than others, and that would be undesirable

 

[t0aj15]

Again this is not correct. Either the 8 ohm jack should be used OR one or both of the 4 ohm jacks should be used, but not all three at the same time. As for three 8 ohms speakers at once I advise against it.

 

[Schmoog]

The three 8 ohm configuration is what I run normally, with two on a series box into the 8 ohm jack and 1 straight into the 4 ohm jack. I pulled this directly from the mesa/boogie manual when I did it. and I never suggested that all three be used at once

 

[mr_fender]

Schmoog is correct. This configuration is in the Boogie manual and will product a "Safe Mismatch". That means that it will not hurt your amp to use it. However, it may not be the best choice depending on the tone you are looking for. Plugging an amp into a cab that has a higher impedance that the amps output, i.e. plugging a 8 ohm cab into a 4 ohm input, will produce less volume and a darker, more compressed tone. Some like this effect, some don't. Bottom line, a higher impedance than indicated on the output is safe, a lower one is not. For example, you can safely use a 4, 8, or 16 ohm load into a 4 ohm output, but anything lower than 4 can damage the amp. With an 8 ohm output, 8 and 16 ohm loads are ok, but 4 is not. With a 16 ohm output, only a 16 ohm load or higher will be safe. Your milage may vary.

 

[Pinweaver]

So from what I've read so far, when using 2 8ohm cabs the parallel out on the cabs has no real use when you have 2 4ohm amp outputs. Either you connect one cab to each 4ohm output or you connect one cab to one 4ohm output and the other cab to the output of the first cab. It's the same thing, since in both scenario's the speakers are connected in parallel.

So if the output on the cabs were to be serial, I would be able to connect 4 8ohm cabs right? 2 in daisy-chain connected to each 4ohm output in which case I'd have a safe mismatch.

 

[Schmoog]

Absolutely correct. Or you can buy 2 series boxes rather than having a series out on the cabinet

 

[Vigo1999]

so, lets say i have 3 1x12 cabs, all 8ohms, being one with a parallell out.

to hook up all the 3 cabs, how i connect them?? 2 cabs (being one with the parallell out) connect to the amp outs (4 ohms) and the one left i can connect to the paralell out of the thiele?? this is it ?? :?:

ok, the first 8 ohm cab would connect to one of the 4 ohm outputs, the other two would have to go into a series box, and then into the 8 ohm output. this would produce a safe mismatch at both inputs and equally balance the output of the amp. if you were to run two of them in parallel the output would be unbalanced, and some speakers would get more power than others, and that would be undesirable

I was wondering about a way to hook up all the 3 cabs without a series box . . . for what i am seeing, this is not quite possible . . . ****, so the parallell out on my Recto cab is practically useless . . . :?

 

[Russ]

Again this is not correct. Either the 8 ohm jack should be used OR one or both of the 4 ohm jacks should be used, but not all three at the same time. As for three 8 ohms speakers at once I advise against it.

This is strange because Mesa told me that I could run a 16 ohm cab into 8ohm and run 8ohm cab into 4 ohm and it would be fine. Thus, you can use the 8 ohm and 4 ohm jacks at the same time.

 

[MesaDCLP]

run a 16 ohm cab into 8ohm and run 8ohm cab into 4 ohm

I ran my combo (c90@8ohms) and a 4x12 (v30's@16ohms) for over a year like this without a problem, and all of the speakers seemed to have the same volume.

I think if the cabs drop the load below 4ohms total, that would be pushing the transformer too much.

 

[eltrain858]

i called mesa about a really similar question to Vigo's a few weeks ago after posting a thread on this board, except i wanted to use the speaker in my combo, a 1x12 ext cab, and a 2x12 ext cab. i talked to michael taylor to see if there was any better way to do it than running the series box and he basically echoed what schmoog said, it was either the series box and a safe mismatch or a horribly complicated and unwieldy mess of wiring all four speakers together in series parallel to get proper impedance (not too portable for gigging), and that it would give that darker, vintage "brown" sound.

 

[Russ]

Mike T is cool. He has spent some time talking to me about a few things I wanted some help with (the speaker load issue, tube substitutions, and cabinet design and build concerns).