Fixed L-Pads

[Earl K]

Hi Mark

This is a bit discouraging.

( Zilch )Are you using an 8 ohm LE85?

- Mark, the stock ( original ) diaphragm in the le85 was only available in one impedance ( no matter what the foilcals say on the back of the le85 drivers ). It's closer to 11 or 12 ohms .
- We "regulars" know this because the topic comes up pretty regularly / / I guess it's not that surprising that you're unaware of this .
- JBL ( at some point ) changed ( how they "interpreted" the drivers' "impedance curve" ) and then they changed the "listed" impedance .

In addition to the 8 ohm R4, I notice you have L3=0.08 mH vs my 0.15. C6 is the same @ 1 uF. I also do not have R5 (20 ohm).

- I'd recommend just building your hipass section according to the schematics that Zilch has published.
- The response curves he has published look a lot better than what you've achieved on your own.
- He has done extensive testing of his circuit and has "shown" the type of response one can expect to get ( if you follow directions ).
- What more motivation do you need to accept the results of his hard work ?

Or do R4/R5 form another L-pad that is further attenuating the LE85? And how does the HF bypass feeding into the 'knee' of the L-pad effect that? Hmmm, with R5 parellel LE85, the HF bypass would be 'seeing' about 8 ohms anyway, wouldn't it?

- There's nothing wrong with wanting to understand what you're building .

- One can argue that R4/R5 form another "Lpad".
- Alternatively, one can argue that R4 coupled with the preceeding variable Lpad, now form a "T" pad followed by a single "load resistor".

- Either perspective is correct. The important point to remember is that all these resistive elements represent attenuation and offer some circuit isolation .

I'm sure I have 20 & 8 ohm reisitors. I'll see if I have a 0.15 mH or another 0.08 mH coil to try out your circuit.

- Good ! Use the 0.08 mH coil. That'll at least make me feel that I wasn't wasting my time when I posted the formulas for "resonant LCRs" ( much earlier within this thread ).

( I was following the 16 ohm version posted elsewhere - not sure I still have the thread reference) I also want to try the other LE85 as all my testing to date has been done with the same unit.

- I believe that you've needlessly confused yourself into thinking that there should be 16 & 8 ohm versions for this crossover.
- So far ( from my perspective ) there's just a single usable version for the le85. That happens to be Zilches' version ( though I feel the lowpass may still need some tweaking / we'll have to see ) .