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Mackie thump15 intermittent sound, woofer resistance measured 1.7Ohms!
Mackie thump15 intermittent sound, woofer resistance measured 1.7Ohms!
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Old 26th July 2021, 09:08 PM   #11
conanski is offline conanski  Canada
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Quote:
Originally Posted by Yambo View Post
Thanks @conanski. Did you get a chance to measure the coil resistance of the new drivers that you replaced?
They were replaced under warranty(boxes weren't 1yr old) so I never saw them, but afaik they are a single coil 8ohm driver.
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Old 26th July 2021, 09:17 PM   #12
nigelwright7557 is offline nigelwright7557  United Kingdom
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DC resistance is usually slightly less than speaker impedance.
So your speaker is partly shorted.
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Old 26th July 2021, 09:44 PM   #13
kevinaston1 is offline kevinaston1  United Kingdom
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I have had that fault on Mackie and a couple of similar cabinets. Loud crump at high volume. Measuring the coil resistance as I moved the coil gave a short at various positions; new driver cured each one.
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Old 26th July 2021, 10:44 PM   #14
Yambo is offline Yambo  Maldives
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Quote:
Originally Posted by johnmath View Post
I think there might be a slight error. On the manual it shows that its +/-28V power rail.
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Old 27th July 2021, 02:20 AM   #15
conanski is offline conanski  Canada
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Originally Posted by johnmath View Post
There's quite a large disparity between the owner's manual which claims 400Wrms and the service manual which claims 280W and the chip data.
The compression driver has it's own amp doesn't it? At this end of the powered speaker spectrum manufacturers like to add together the amp power for both drivers and then double or even quadruple that for the advertising fairlytail.

Having owed these boxes as well as a bunch of other similar powered and passive PA speakers I can confirm that they produce the amount of sound that would be expected from a 250w speaker.
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Old 27th July 2021, 02:17 PM   #16
Mark Tillotson is online now Mark Tillotson
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Quote:
Originally Posted by johnmath View Post
There's quite a large disparity between the owner's manual which claims 400Wrms and the service manual which claims 280W

Sounds like max square wave power (marketing BS basically) v. rms sinewave power.


If the voice coil is 1.7 ohms maybe its burnt off its insulation, warped a bit and started welding itself together? Gross damage like this should be visible if you push the cone out and peer behind the spider at the voicecoil emerging from the gap.
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Old 27th July 2021, 02:28 PM   #17
nigelwright7557 is offline nigelwright7557  United Kingdom
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Its classic burnt coil.
I had 2 speakers and after a heavy session one was less loud than the other.
So I measured DC resistance and one was about 6 ohms and the other 2 ohms.
So tore bad speaker apart and the voice coil just fell apart with burnt windings.
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Old 27th July 2021, 04:47 PM   #18
Yambo is offline Yambo  Maldives
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Thanks guys for the confirmation and the inputs. Time to look for replacement woofers... Any idea if it would be possible to get a reconing kit for this particular model?
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