# Wire two 8 ohm cabs for 16 and 8 ohm



## Bevo (Nov 24, 2006)

I have had two Theile cabs built and have single 8 ohm speakers in each, to run one at a time is no problem.
My amp likes 8 or 16 ohm only.

I have jumped the two cabs together to get 16 ohm but would like a way to use them using permanent jacks. Right now I have it wired through the ports.

In my perfect world I would have standard 8 ohm speaker jacks with a second jack to run between the two cabs making it 16 ohms...maybe..

Would I be able to use a Y connector and reverse one cable. 
So normaly wired jacks but one reversed polarity cable..Think it would work..

What do you think?


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## greco (Jul 15, 2007)

I don't think the Y connector will work. But I'm not 100 % sure.

Do each of your cabs have a plate on the back with 2 jacks? 

Cheers

Dave


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## Bevo (Nov 24, 2006)

No not right now, I still have to fit them but not sure what to get yet.

The more I think of it I think making a long cable may work, something like this.

Standard speaker cable, cut the wires, come out of one cab normal, solder in the second cable but at the joint change polarity, into the second cab making the negative on the first power the positive on the second, final negative goes back to the original guitar cable jack.

What do you think?


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## dwagar (Mar 6, 2006)

maybe it's cause I'm 1/2 asleep, I don't know what you mean by reversing one cable. You want to hook them up in series, the '-' from one joins the '+' from the other. You could make a Y cable to do that, or you could make a little box to do that. I think I'd make a box, gives you the option of using longer cords if need be.


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## greco (Jul 15, 2007)

Bevo said:


> What do you think?


I'm still not convinced it will work...but maybe I'm wrong.

I would think it would be easier to sort out the speaker wiring by using plates with 2 jacks on each cab. (gives you lots of options for possible speaker changes in the future) Again, maybe I'm wrong here also.

When you said that you weren't sure what plates to get...did you mean that you weren't sure where to order them from, or what?

QComponents www.loudspeakers.ca has this type of hardware and are in Waterloo.

Cheers

Dave


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## keto (May 23, 2006)

I'd be curious to know how you 'jumped' the cabs together. I've read up on series and parallel 1,000 times and still don't get it.....but I do know that 8 ohms + 8 ohms = 4 ohms. Or 8 if wired right.


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## keeperofthegood (Apr 30, 2008)

keto said:


> I'd be curious to know how you 'jumped' the cabs together. I've read up on series and parallel 1,000 times and still don't get it.....but I do know that 8 ohms + 8 ohms = 4 ohms. Or 8 if wired right.




It is maths, both complicated and simple, once you get the formula 

Resistors and Inductors in SERIES add, in parallel they do something funky:

Series 8 ohms, 16 ohms, would give you 8 + 16 = 24 ohms.

Parallel 8 ohms, 16 ohms gets a little complicated so show the formula first and then show it working out:

1/R = 1/R1 + 1/R2 - - - 1/Rn (n because this works for any number in parallel)

With the example, R1 = 8 and R2 = 16 it becomes


1/R = 1/8 + 1/16
1/R = 3/16 (or 0.125 + 0.0625 = 0.1875)
R = 16/3 (or 1/0.1875)
R = 5.3repeating Ohms.

This can stretch on far, so say you have 4 speakers in parallel, 32 ohms each, that would be

1/R = 1/32 + 1/32 + 1/32 + 1/32
1/R = 4/32 (this is handy when the denominators are easy to simplify)
R = 32/4 (that gets you hear fast and lets you do this step easier)
R = 8 Ohms

The verbal way of explaining this is: The Reciprocal of the Sum of the Reciprocals.

So, if you are starting with two 8 Ohm speakers, you have two possible ways of going. Series, and Parallel. In series, it simply adds up, 8 + 8 = 16, in parallel it is 1/(1/8 + 1/8) = 4. If you had 4 speakers, each 8 Ohms and you wanted to have 8 Ohms in the end, you would do 2 in Parallel and 2 in Parallel, these would then be wired in Series, you would have (1/(1/8 + 1/8)) + (1/(1/8 + 1/8)) = 4 + 4 = 8 

Speakers don't have a "polarity" to worry about either. BUT, they do have *motion* direction. If you look at your speaker, and there is a + or - or red dot or different shaped connectors or two different coloured wires to the cone etc anything that makes one different than the other, this is done to let you know how to wire them up in multiples. When using the SAME manufacture, then you are 'reasonably' sure that their markings speaker to speaker will mean the same thing. So say the red dot approach, three speakers, wired in parallel, red dot to red dot to red dot, then you can be reasonably sure that when a Positive voltage in the signal comes to them, all three cones will either move out at the same time, or in at the same time. Messing this up can muddy your sound, cause beat frequencies, and other unpleasing things


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## Bevo (Nov 24, 2006)

Yiks!!

I followed a diagram http://www.avatarspeakers.com/wiring diagrams.htm
If you look at the series speakers you can see what i did, very simple yet checked 20 times before I soldered.

The jumper wire is from the first speaker negative to the second speaker positive.

Greco, was wonder if I should go with two jack plugs or one jack plug.
That link is great thanks!


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## keeperofthegood (Apr 30, 2008)

kkjuw Checking twice is a way of life for me too, and I STILL manage to go dyslexic!!!


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## greco (Jul 15, 2007)

Bevo said:


> Greco, was wonder if I should go with two jack plugs or one jack plug.
> That link is great thanks!


I would go with the 2 jack plug plate/cup for TRS jacks

http://www.loudspeakers.ca/Qmedia/Qcat66.pdf

Page 54 Item TC31 

(plus 2 x 1/4" jacks for each terminal cup...they sell Switchcraft jacks also)

Amp into 1 jack on Cab #1...out from 2nd jack on Cab #1 into Cab #2 .

Wiring could be for 4 ohms *OR* 16 ohms. You want series wiring as you need 16 ohms total.

cheers

Dave


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