I used my B&K LCR meter to measure impedance of the three drivers in my speakers. I disconnected the spearker wires from the outboard XO and connected the meter leads to the wires. Meter showed 4.5ohm for tweeter, 8.2 for mid and 21.3 for woofer. 21.3 seemed vey odd so I calibrated the meter and then tested it on some resistors. Results were accurate and matched resistors markings. The speakers sound very good and the bass is well balanced with the other drivers. How could woofer have 21.3ohm impedance?
The all the drivers were disconnected from the crossover so no changing frequencies so I thougt it would measure as the tweeter and mid range did.
An LCR meter measures which an sine wave not DC so if it measures at 1kHz or 50Hz the impedance could be high like your measurement.
Rob
Rob
As Rob mentioned, the AC the LCR meter uses for testing has a frequency.
"Selectable test frequencies
Because impedance is a function of frequency and application uses can benefit from knowing the
impedance at the frequencies designed for use, it is useful to have an LCR meter that can make its
measurements at different frequencies.
The two most popular frequencies for measurement are double the line frequency (i.e., 100 or 120
Hz) and 1 kHz. Twice the line frequency is used for filter capacitors and chokes that typically see a
full-wave-rectified waveform to filter.
For many applications, being able to measure at twice the line frequency and 1 kHz provide enough
flexibility. More sophisticated LCR meters include more measurement frequencies, such as 10 kHz,
100 kHz, and higher. Higher-end LCR meters can sweep the frequency and plot impedance
magnitude and phase as a function of frequency."
B&K Precision LCR Meter Guide Page 25
I have an old BK Precision 875A LCR Meter, it is fixed at 1kHz.
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The BK 878 tests at 120Hz or 1kHz. I also found "https://soundcertified.com/how-to-tell-impedance-of-speaker", which shows "How To Tell The Impedance Of A Speaker And Understanding Speaker Ohms" using a multimeter. I tried it and the tweeter measured the same as the BK 878 LCR meter. The Mid range was close to the BK but the woofer was way off. So I took the back cover of the speaker and saw the woofer label is marked 8ohm. Three feet of teflon coated 16AWG silver plated stranded copper wire are soldered to the driver tabs so the meter leads are three feet away from the driver tabs. Could that cause the crazy reading?
That writeup is using a resistance measurement to guess the nominal impedance. Do you have your tester on an impedance setting instead?
Unless you do a sweep it's moot. Just measure dcr and if that's in spec you should be fine.
Rob 🙂
Rob 🙂
The site I listed made it look so easy using a multimeter. So now that I know the driver is marked 8ohms why I can't get a reading close to that
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The information on that site is rather simplified. You are not measuring resistance are you, but impedance? That would be a problem.
It wouldn't be the easiest thing to spot a shorted turn in a resistance measurement.
To verify what Ohm is on a speaker's label, measure its DC resistance then add 30%. To see full impedance curve like in its datasheet buy a DATS V3 analyzer.
Because your LCR meter measures the 1kHz point at the woofer's impedance vs frequency curve where the heavy voice coil's inductance already reacts strong enough.
Nominal is generally characterized on the flatter area of a driver's impedance curve, away from the main resonance bell and before curving up much.
I'm surprised that this is so complicated based on the numerous sites showing how easy it is. So just to clarify, if I buy a driver with a label marked 8ohm, take it out of the box, set the mutlimeter to ohm and connect the meter leads to the driver input tabs what should the results be?