Cabinet impedance question

[drburns73]

Hi,
I have 3 different 4x12 cabinets that all are marked at 16 ohms.
When I plug a speaker cable into them and measure them with my multimeter, one measures in the high 14's, and one is in the low 13's.
The last cab reads around 12.1. Can this be right? It is my most recent and least played cab so far. Does this reading seem like there may be an issue with the cab or can it just be that low? Any insight would be greatly appreciated.
Thanks,
Mike

 

[glpg80]

cabinets are rarely dead on 16 ohms.

your OT transformer secondary will give and take on the impedance differences and match the cabinet over the course of 10 minutes or so. proper gauge speaker wiring as well as speaker cables will help to reduce loading effects.

as long as the amplifier's OT setting is never larger than the actual cabinet impedance load you are fine.

 

[glpg80]

beat me to it

 

[JakeAC5253]

Interesting topic. With lower impedance at the cab being the worse of the two you would think that most speakers would err on the side of being OVER their stated rating and not under... no?

 

[glpg80]

Interesting topic. With lower impedance at the cab being the worse of the two you would think that most speakers would err on the side of being OVER their stated rating and not under... no?

too many variables that cannot be contained when making a speaker coil - eventually you will get some minute differences in each speaker. wired series parallel the summation of these differences can lead to a Q factor that differs a few ohms. the extreme variables that designers cannot control or would be wasted engineering in trying to contain are the minute' variables which is why it is less, not exact, or more.

the stated number is what designers shoot for in building it. the actual design will differ unless the extra math is crunched and the speakers are built to .00001% tolerances

 

[steve_k]

A few cab suggestions:

If you are real concerned, open the cab up and unsolder all the wiring. Measure the impedance of each individual speaker at their terminals. You will certainly be surprised.

You will have some degradation of speaker impedance over time.

Speaker wire will have big effect on impedance. The bigger the wire, the more reduction in effective impedance at the jack. 16 AWG is usually a good size.

Of course, dodgy soldering can have an effect, as does the slip on terminals. They can work loose or solder joints become dry, brittle or crack.

And, the big thing is all the fancy wiring options. First thing I do on a new cab is snatch all the extension wiring out on the Mills cabs and on my Mesa cabs I yank all the switched stereo wiring out. Replace the the wiring with straight input series-parallel, which is the minimum, and I keep a supply of jack cups that I replace the stock one's with. I use Neutrik locking connectors on my cabs. The jack cups are predrilled for the locking jacks. If the cab had unsoldered connections, I go back with them soldered.

I am usually inside a cab the day it arrives messing with speaker options anyway. So, the modding of the cab only takes a little more time.

If your speakers are made in China.....watch out.

Steve

 

[drburns73]

Thanks for all of the info, guys.
Much appreciated.
Take care,
Mike

 

[jet66]

The DC resistance isn't actually a measurement of the impedance. While both are measured in Ohms, they are not the same. More accurately, impedance is the opposition to the flow of AC. There are ways to read/plot the true impedance, but it's something I've never really considered doing. I only use a DC reading to make sure I have continuity, no shorts/grounds, and that my resistance is in the ballpark for the configuration I have wired. (around 3.x for 4 Ohm, 13.x for 16 Ohm, 6.x for 8 Ohm.)