4x12 resitance was 11.5 ohms?

the boogie man · Post by **the boogie man** » Sat Oct 01, 2011 7:00 pm

I am a electronics noob so bare with me. I measured the resistance from the jack of my 8 ohm cab which resulted in a measure of about 7 ohms (seems normal, right?) Then, I measured the resistance from the jack on my 16 ohm cab and I got about 11.5 ohms?; is that a normal reading?

Jason

toner · Post by **toner** » Sat Oct 01, 2011 9:13 pm

It's normal for readings to be lower than the stated speaker impedance. 11.5 seems too low however. I doubt it's a problem but I'm not a speaker expert. My 16 ohm cabs read around 14.

908ssp · Post by **908ssp** » Mon Oct 03, 2011 9:27 am

Just to be safe measure the resistance of each speaker. If one is an 8 it will get more power and could blow prematurely.

the boogie man · Post by **the boogie man** » Mon Oct 03, 2011 6:15 pm

908ssp wrote:Just to be safe measure the resistance of each speaker. If one is an 8 it will get more power and could blow prematurely.

That's a good idea. Thanks. The volume seems uniform but I will measure it tonight. I measured another 60's cab with pre-rolas and it too had a low resistance.

Cabbagebreeze · Post by **Cabbagebreeze** » Tue Oct 04, 2011 11:37 am

Please keep in mind you are measuring DC resistance which is related to impedance but is not the same. You have to add in resonance and voice coil inductance to your DC resistance measurement.
11.5 seems a little low, but I wouldn't worry about it.
perhaps measuring the DC resistance of each driver might help.

joey · Post by **joey** » Tue Oct 04, 2011 2:09 pm

Cabbagebreeze wrote:Please keep in mind you are measuring DC resistance which is related to impedance but is not the same. You have to add in resonance and voice coil inductance to your DC resistance measurement.
11.5 seems a little low, but I wouldn't worry about it.
perhaps measuring the DC resistance of each driver might help.

+1, you can't simply measure the DC resistance of a reactive device, and expect it to match the published nominal impedance. a speaker has anything but flat a constant impedance, unlike a purely resistive load. Thats why you see the term Nominal used on datasheets.

the boogie man · Post by **the boogie man** » Tue Oct 04, 2011 6:30 pm

Cabbagebreeze wrote:Please keep in mind you are measuring DC resistance which is related to impedance but is not the same. You have to add in resonance and voice coil inductance to your DC resistance measurement.
11.5 seems a little low, but I wouldn't worry about it.
perhaps measuring the DC resistance of each driver might help.

Absolutely. I wasn't try to equate resistance and impedance. I understand that impedance is a function of frequency and reactance.

As a side note, I have a late 60's cab with pre-rolas (15ohm) that measured a similar resistance. I wonder what meaning "nominal impedance" has anyway?

DaveMcLain · Post by **DaveMcLain** » Fri Oct 28, 2011 1:28 pm

I think that "nominal impedance" meant the approximate average impedance over the useful frequency range of the driver.

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4x12 resitance was 11.5 ohms?

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