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compression driver technical expert please?


aertex

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Easy question for a technical expert or the like>

 

  1. What does it mean if, with a pair of 16 Ohm compression drivers, 1 measures 30 Ohm and the other 13 Ohm resistance across the terminals  with Fluke Ohm meter?
  2. what are the implications? I cant really play them to test in a meaningful manner so thats not an option
  3. is it really an issue to test compression drivers with an Ohm meter in this manner?

 

Thanks

Alan

 

 

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The most likely explanation for the high DC resistance reading for one of your compression drivers, is that  a solder joint of a lead out wire to one end of the voice coil winding has failed. Quality compression drivers  use aluminium ribbon wire ,ultrasonic tinning and/or  special soldering alloys which need to be sealed to prevent corrosion  . Other causes of a high resistance can be a burnt coil or a break in the wire.  Removal of  the diaphragm assembly for a visually inspection would be the next step.  It is a basic procedure to test the DC resistance of a speaker with a multimeter and this is not an issue.

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Thanks guys. This issue is a bit of a problem for me now and I am hoping it can be worked out quickly and cheaply.....cheaply being the highly variable word, which could translate into very expensive

 

I also have more questions based on various posts I have read from others in other arenas. 1 is the actual relevance of the high DC resistance reading. I have read for example (if I understand it correctly) that the "nominal" resistance is irrelevant and will vary significantly. If thats the case however, there must be an upper and lower limit of "satisfactory"? Is 30 Ohm really too high indicating an problem for sure?

 

I have more but it must wait till tonight after I finish work. Thanks and cheers, Alan

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2 hours ago, aertex said:

I also have more questions based on various posts I have read from others in other arenas. 1 is the actual relevance of the high DC resistance reading. I have read for example (if I understand it correctly) that the "nominal" resistance is irrelevant and will vary significantly. indicating an problem for sure?

 

No.  That's not the case.   The DC resistance (what you've measured with your MM) should be what is on the datasheet.  

 

Measuring the AC resistance (ie. impedance...  which varies with frequency so it will be a graph) - will shed more light on whether the driver is broken, or if it is a 32 ohm driver that is behaving normally.

 

Quote

If thats the case however, there must be an upper and lower limit of "satisfactory"? Is 30 Ohm really too high

 

Yes - Significantly higher or lower DC resistance than expected  (13 ohm is a typical DCR for a 16ohm driver), indicates a problem for sure.

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@aertex, do you know anyone with a DATS?  I have one here but alas am too far away to be useful.  You can use it to measure an impedance graph of the drivers...it's very simple to do.

 

Otherwise, I would work backwards with the multimeter from the binding posts to the diaphragm trying to find a spot where the DC resistance measures as you would expect it too.  That may be all the way back to where the voice coil connects to the diaphragm and if you still measure high there then there is likely an issue with the voice coil.  The problem could be as simple as dirty binding posts or a damaged wire  or connection leading to them...or it may be more expensive. 

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Thanks Dave and Anthony. That DATS looks incredible-very handy bit of gear. Alas, I dont know anybody here in WA who owns one

 

I will have to carefully work backwards as you suggest Anthony, on the weekend. Lets hope I can find something simple to fix?

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 On all the compression drivers that I have seen, the diaphragm has to be removed  for the internal connections to be tested with a multimeter.  Caution is needed if you do this, as the diaphragms are made of delicate  metal around 0.06 to 0.07 mm thick  and one slip with a probe can do much damage. Are we dealing with the GOTO  units that show up in the list of equipment ? If you really feel the need to run an impedance graph, you could contact Pat at WAR Audio to see if he can do some measurements for you; he was an agent for the CLIO Audiomatica  systems. Some old readings that I have on  a JBL 2241 compression driver  have an 8.17 ohm DC resistance for a  nominal  16 ohm rated impedance diaphragm assembly. The graph shows the impedance varying  from 12 ohm at 800 Hz up to 18.5 ohm at 8kHz fitted to a H 5038 horn.

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