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Weird measurements with Fancy LCR Meter
Weird measurements with Fancy LCR Meter
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Old 11th June 2019, 09:56 PM   #1
ericimage2 is offline ericimage2  United States
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Default Weird measurements with Fancy LCR Meter

Hi, I have a technical question if anyone can answer, I was measuring the DCR of my ribbon tweeters of my GT3R GT Audio works speakers and I am confused, If I use my $30 SouthWire multi-meter i get a resistance of 3.7 ohms but if I use my fancy $400 BK LCR meter using DCR setting I get 19.2 ohms but if I measure the resistance (R) or Impedance (Z) at 1 Khz I get 3.675 ohms and 3.854 ohms respectively.

Also w hen I measure the DCR with the BK LCR Meter the ribbon tweeter moves a lot but with no sound, and when measuring R or Z I can hear the expected 1 Khz tone. In the other hand with the SouthWire MM It does not move or make any noise when I measure the Ohms.

Why does it moves so much with the BK measuring DCR and why is the DCR value so high on the BK?

BTW I tested the BK and is calibrated!

Thanks a lot for the answers!
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Old 12th June 2019, 04:52 AM   #2
w_oswald is offline w_oswald  Canada
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When you measure DCR with the BK LCR Meter, you say the ribbon tweeter moves a lot but with no sound. Is the ribbon's movement static, as in a one-direction offset, or is it oscillating? If the latter, I can only guess that the Meter is not actually producing a DC signal to make the measurement; rather perhaps an AC signal at a frequency low enough that the sound is inaudible. Is there any hint in the Meter's documentation? Can you hook up an oscilloscope to see exactly what's going on?

I'm not too familiar with ribbon tweeters, but can surmise that the resonant frequency could be much lower than that in conventional dynamic tweeters. If the Meter is indeed producing an AC test signal at or near a resonant frequency, that could lead to a much higher resistance (Rs) reading.

Coincidentally, I've just been taking some measurements on Fostex D262 compression drivers with my DER EE DE-5000 LCR Meter (sorry - I didn't make up that cumbersome name ; it really is an excellent device!), and, for example, on one driver: Rdc is 6.18 ohms, while Rs @ 1kHz. is 22.29 ohms. Hooking the test unit up to my speaker test jig, I find that the (fundamental) resonance is @ 1.038 kHz., with a complex impedance of 22.7 ohms.

Sorry if the above is vague and of little help to your question; just trying to get the ball rolling towards an answer for you!

Wilf
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Old 12th June 2019, 05:29 AM   #3
ICG is offline ICG  Germany
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Location: I had a Déjà Moo - I've seen that BS before!
Quote:
Originally Posted by ericimage2 View Post
Also w hen I measure the DCR with the BK LCR Meter the ribbon tweeter moves a lot but with no sound [...]
If you can see it moving then the frequency is too low to be audible but that also means you are about to kill your ribbon tweeters. Ribbons may not do excursion, that bends and stretches them, they are then worn out and perform a lot worse. If you can see the excursion, it's already way too high. I hope you didn't kill them but that's likely already happened.
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