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Old 08-04-2015, 06:53 AM   #1
projampro
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Ohms details

Hey guys, Iím having some mild trouble with my Ampeg 810E cab, which I think is about 10-15 years old. I should start by saying that it actually sounds fine. However, as I like to ensure my equipment is working exactly as it should be, I checked the ohms a while ago and was slightly surprised to see it reading about 4.5 ohms through all eight speakers, which seemed a little high, considering it should be less than 4 ohms.

Iíve done various tests on it. The eight individual speakers are all okay at about 28 +/-.3 ohms (rated at 32 ohms). In groups of four in parallel, theyíre about 7.6 ohms--fine, as it should be less than 8ohms at this point. But when I put a wire (in parallel) between the two groups of four speakers, it reads 4.2 ohms when directly measuring on the speakers with a multimeter, and 4.5 ohms when measuring on a speaker cable plugged into the rear jack plate.

I was considering hard-wiring to a single jack to bypass the (possibly-faulty) switching rear jack plate, but even doing this, 4.2 ohms seems a little high, does it not? Am I missing something? Does it really matter? My multimeter is just a cheap one. Ultimately, I just want to make sure Iím not going to blow my Orange AD200B head (although at least the ohms are a little high rather than low).

Thanks,
Matt
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Old 08-04-2015, 07:06 AM   #2
Deliriumbassist
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As far as I'm aware, you'll be fine. Cabs are rarely on the nose at 2, 4, 8 or 16 ohm nominal impedance anyway. Even when you play, the impedence changes depending on the frequency. My hifi speakers, for example, have a 8 ohm nominal impedance, but can drop down to 5.1 ohms. Your 4 ohm nominal impedance is merely an average impedance value across it's useful frequency band.
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Old 08-04-2015, 09:55 AM   #3
sashki
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Do the cables connecting the speakers have a significant resistance?
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Old 08-04-2015, 11:31 AM   #4
Blademaster2
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If you are getting on the order of the correct resistance then you need not worry. A blown or shorted driver will throw it off by much more than that, and they rarely (never) would 'partly' fail. The cable feeding the cabinet should be much, much lower (10's of milliohms) and should not impact the resistance reading at all.
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Old 08-05-2015, 05:10 AM   #5
projampro
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Thanks for the feedback. I find it odd that the speakers individually are reading fine but that altogether it's a bit high. But it sounds like the consensus is that it's fine, which is basically what I was thinking too.
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Old 08-05-2015, 11:39 PM   #6
dspellman
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Quote:
Originally Posted by sashki
Do the cables connecting the speakers have a significant resistance?


Highly unlikely.
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