Can Someone Explain the Apparent Logical Inconsistencies of the JBL Tapped Inductor?
I have a pair of 3115 crossovers that use a tapped inductor. The schematic shows the inductor to be 3.85 mH across the blue and black, with three taps, red, white and green, along the way.
I opened the crossover and cut the blue and black leads away from the circuit so I could measure the inductances. The R/W/G go directly to the HF +, so nowhere with no speaker and are disconnected.
With one probe on the blue wire, I read 0.90mH to the red, 1.29 mH to the white, 1.78 mH to the green and 3.63 mH to the black. The black should be the 3.85 mH and 6% is within tolerances. No problem.
OK, now the fun starts!
I would think that if I put a probe on black and a probe on green the value should be 1.85 mH (i.e., 3.63 - 1.78), but is 0.35 mH :confused:
Black to white should be 2.34 (i.e., 3.63 - 1.29), but is 0.63 mH. :blink:
Black to red should be 2.73 mH (i.e., 3.63 - 0.90), but is 0.98 mH.:banghead:
And...,
Red to white should be 0.39 mH (i.e., 1.29 - 0.90), but is 0.06 mH :blink:
Red to green should be 0.88 mH (i.e., 1.78 - 0.90), but is 0.17 mH :frantic:
White to green should be 0.49 mH (i.e., 1.78 - 1.29), but is 0.03 mH :barf:
http://www.jblproservice.com/pdf/Net...%20Network.pdf
http://www.jblproservice.com/pdf/Net...%20Network.pdf
How did you measure the inductances?
What kind of measurement gear did you use?
Ruediger
2 + 2 +2 = 6..., or is it 8???
Here is an interesting observation.
I ordered six, 16 gauge, 2.0 mH inductors for the woofer. A single order 6.0 mH inductor would cross the 2241s over at 210 Hz.
When the three coils are connected, they produce 6.0 mH. But stack the three together, and you've got to get them near perfectly aligned, and they total 8.0 mH bringing the crossover point down to 160 Hz.