Cabinet wiring question

Mark C

Member
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4,418
I am about to order speakers for a 6x10 bass cab. I can get the speakers in 4,8,16 or 32 ohm ratings and I need to wire the cab for a total load of 4 ohms. I have a couple ideas, but I was wondering if any experts out there can contribute some wiring ideas. Thanks
 

Jim Collins

Member
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1,939
Six, 8-ohm speakers, when wired in series-parallel, will yield about 5.4 ohms, which is about as close as you can get. Three, 8-ohm speakers in parallel will give you about 2.7 ohms. Put two of those in series, and you have about 5.4.
 

Mark C

Member
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4,418
Jim, do you think that 5.4 ohms will be safe with a 4 ohm load out of a 70's ampeg SVT tube head? I'm guessing it will be.
 

Jim Collins

Member
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1,939
You'd be better off getting some real technical advice, as far as that particular rig goes, but if the OT can't handle a mismatch of less than 2 ohms, I'd be surprised. With 6, 4-ohm speakers, wired series-parallel, you'd get a total of about 2.6 ohms. It is actually preferable to have a load that is less than the OT expects rather than greater than the OT expects, so the 4-ohm speakers are probably a safer choice, but we aren't really talking about a huge difference, here.
 

John Phillips

Member
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13,040
What Jim says. Given the degree of mismatching (only 33% in either direction) it probably doesn't matter whether the mismatch is high or low really.

Fender used the series-parallel arrangement with 8-ohm speakers in their Super Six amps of the 1970s to give a 5.33 ohm load with a 4-ohm transformer, FWIW.

Another possibility would be six 32-ohm speakers all in parallel, which arguably might sound better for bass (the normal SVT cab has eight parallel-wired 32s as you probably know), but that would be less flexible if you wanted to use the same speakers for some other purpose later.
 

Pedro58

Supporting Member
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5,782
Mark and I looked at this problem yesterday and found a cool site that calculates everything for you quickly. Arguably unnecessary for those of us who can do math! But fun anyway!
http://www.eatel.net/~amptech/elecdisc/spkrmlti.htm
I agree that the 32-Ohm per-speaker choice is the lesser option. That is a difficult thing to find in the case of a blown speaker! Thanks for the help guys!---Peter
 

Mark C

Member
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4,418
Ok, I looked at another possibility - running 4 8ohm speakers in parallel for 2 ohms and then a pair of 4ohm speakers in parallel for 2 ohms. Put them together in series and you get 4ohms. Do you guys think there would be any problems with this, such as having some speakers taking on a greater load than others?
 

John Phillips

Member
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13,040
Originally posted by Mark C
Do you guys think there would be any problems with this, such as having some speakers taking on a greater load than others?
Yes. Power divides according to the impedance, so each 2-ohm combination will take the same amount of power, half of the total from the amp.

Thus the two 4-ohm speakers will each be taking twice the power (and 1/4 of the total) of any of the 8-ohm speakers.

Generally it isn't a good idea to mix up impedances and power loadings like this - better to go with a slight impedance mismatch on the amp.
 




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