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Two 4 ohm cabs in series = rise in impedance???

PikeoftheLake

PikeoftheLake

Oct 11, 2005
1,181
409
Whitby, Ontario
#1
Hi,

I'm hoping that some of the speaker gurus can help me on this one. I'm about to combine two cabs which are exactly the same, just one has a tweeter. They will be combined using a series cable so that the two 4 ohm cabs will make an 8ohm impedance for my tube head.

I'm told that this combo will cancel out the tweeter because there will be a rise in impedance in the cabinet without the tweeter. Could someone spell out the science behind this? Is it that the cab with the tweeter doesn't actually see the high frequencies or is it that the high frequencies somehow get cancelled out during the output of the speaker?

Many thanks!
 
#4
Even run in series, from one cab to another, it equals a 2 ohm load. Seriously. Go to your search function and look for the info you request. There are lots of players here that will tell you the same. Just wait for other responses before you try what your asking about.
 
#5
No, the OP is right. Two 4-ohm cabs in series will present a 4-ohm load to the amplifier.

If they were in parallel, it would be two ohms.

My only warning about a series setup is that if you ever forget to use the special series cable, you're going to fry the amp before you know it. (Though most amps will start out working OK, then shut down after a while. This could be a real annoyance at a gig.)

EDIT: The first sentence should read "...present an 8-ohm load..." Can't believe I mistyped that.
 
#6
I'd be wary of the crossover, because I have heard before that series connections and crossovers don't mix.

But yeah, series connection of two 4 ohm speakers will certainly yield 8 ohms. Hence the purpose of a series cable. If one was to not use a series cable, sure, it'd be 2 ohms, but he's using a series cable.

EIGHT OHMS.
 
#8
Johnnywad said:
Even run in series, from one cab to another, it equals a 2 ohm load. Seriously. Go to your search function and look for the info you request. There are lots of players here that will tell you the same. Just wait for other responses before you try what your asking about.
Click to expand...

two 4ohm in parallel is indeed 2ohms, but the OP is combining the cabs in series, not parallel, hence the impedance will be 8 ohms. The OP is right.
 
#9
I believe the cab with the tweeter will have a shift in crossover frequency due to the 4 ohm load in series with it. Impedance changes affect the crossover frequency.

Yes you ARE correct that using a special SERIES cable to connect two 4 ohm cabs will make an 8 ohm load to your amp.
 
#17
Muckaluck said:
B-string said:
I believe the cab with the tweeter will have a shift in crossover frequency due to the 4 ohm load in series with it. Impedance changes affect the crossover frequency.
Yeah, this is what I was suspecting. So will a signal still be sent to the tweeter? Do you have a sense of how the frequency will be affected?
Click to expand...

Roughly if the crossover frequency is 5KHz it would change to around 10 KHz.
Click to expand...
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#18
nashvillebill said:
I don't claim to be a crossover expert, but my understanding is: if a speaker in series was a pure resistor, the crossover would not be affected. However, speakers are inductors in the real world. So adding an inductor in series will block high frequencies a tad.... but I'm not much of an expert on LC networks
Click to expand...

B-string said:
Muckaluck said:
B-string said:
I believe the cab with the tweeter will have a shift in crossover frequency due to the 4 ohm load in series with it. Impedance changes affect the crossover frequency.

Roughly if the crossover frequency is 5KHz it would change to around 10 KHz.
Click to expand...

Ok, I think I'm seeing. So as the crossover frequency is pushed up (as high frequencies are blocked), very little sound will come to the tweeter from the bass guitar because the bass does not make much sound in the 10 khz frequencies?
Click to expand...
Click to expand...
 

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