I just picked up a 4x10 cab made by Dennis Cornell fitted with Jensen alnicos (P series?). Sounds sweet with the Carmen Ghia and the Z-28 but has disappointing bottom end, which is a shame as I wanted a beefier cab to move air at larger venues..
I was told it was 8 ohms, and it looks like it is wired series-parallel so each driver would have been 8 ohms each as well. When I checked the DC resistance with my multimeter the cab gives about 15 ohms.... Question for the experts - does measuring DC resistance indicate impedence, or anything near it?
Assuming it was indicating the cab was 16 ohms, the plot thickens when I unhooked one of the jensens and measured its DC resistance - 8 ohms (...well 7.5). How can this be if it is series-parallel? Well, I looked again at the wiring and there is more to it - the jack input splits and goes to two drivers, then these are linked to the next two in strange formation... here is a terrible sketch....
Is this series-parallel or am I missing something? Is this normal? It seems series-parallel to me but why is it giving 16 ohms from 8 ohm drivers? Or is measuring dc resistance the wrong way to check this? As neither the CG or Z-28 have 16 ohm taps then I need to be sure whats going on. Aaargh. Help!
DC resistance will always be lower than impedance, because impedance is the sum of DC resistance and REACTANCE (which varies with frequency).
Make sure you're checking the resistance properly, and know exactly what you are measuring. If you're getting 7.5 ohm on only one driver, than you can bet they are 8Ohms nominal drivers, and that you have an 8 Ohm cab.....
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Post by billyguitar on Jul 30, 2006 15:36:52 GMT -7
When you put a meter on a speaker it should measure about two thirds of the actual impedance. I don't know why, I just know that's what it does. Like an 8 ohm speaker should measure about 6 ohms on the meter. Jensen's don't do bass well. Listen to any 4 x 10 Bassman, new or old.