Re: Speaker/OHM question for two 2x12" ext cabs

ScoFF wrote:

I searched the group for similar topics but I got tired after 30
minutes looking for my answer, please help if you know.

I have a mono Marshall JCM 800 2204 Head.

I have two 2x12" extension cabinets.

One is a Marshall 1936 cab, the other is a Randall 212CS

They both are 8 ohm.  I've been switching back and forth trying to
decide which one I liked better by just using the 8OHM tap on the amp
to the 8OHM Mono input on one cabinet at a time.
I've decided to try running both at the same time using both taps on
the head.

***
If I used both taps for both separate cabs, what would the selector be
set at?  4?

Yup! 1/R(t) = 1/R(1)+1/R(2)+1/R(3)... 
***



From my understanding, parallel divides the impedance by the number of 
speakers:  2x16 ohm in parallel gives 8, 4x16 gives you 4.   1x16 gives
16.

Yes, if all impedances are the same. If you have different values, use the equation above (which also works for same impedance value, BTW).


What is series? Adding the impedance together? 

Yes.

2x8ohm speakers gives
16 in series?  If you had 2x16 in series it'd be 32. I never heard of a
cab offering 32.

What's the difference in parellel and series.  If a speaker blows in
one or the other, does one offer any protection?

If a series wired cab blows a speaker, you get instant open and big problemo for the output transformer. If one speaker in a series/parallel configuration blows, you're safe.


I'm assuming my factory configured cabs are in the safest scenerio.

Not always. Why? Because 16 ohms is often the preferred impedance, so a two speaker cab is often two 8's in series.


Also, is there anything wrong with running your amp selector at 4 or 16
assuming your cabs are wanting that?

Always best to match. Many prefer using highest practical value, because you use more of the secondary winding (although a properly designed OPT obviously should be safe at 4 ohms at full power). 

I think 4x16 cabs are in series/parallel configuration at 16 ohms.
That's that about?

Yup, but it'd be far easier to put 4 x 16 ohm cabs in parallel and use the four ohm tap. 


Thanks.

.

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