How to revise the Monolith III passive crossover to be a 300 hz hi pass filter

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ted betley

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I have the schematic for this crossover but cant figure out if its a 2nd or 1st order x-over. Anybody have an idea? Thinking it was a 2nd order and looking up the transfer functions of 2nd order hi pass filters I figured I needed to add 200 uf to the 39 uf in there. Is this right?

I should add that I use a dBx Driverack Pa as an active x-over with bass to panel crossover @ 300hz. But I believe the purist highs I have ever gotten is via the ML III passive x-over which is set to cross over @ 120 hz. I tried passives for highs and dBx for lows but there is too much overlap @ 120, So I'm looking for an easy way (add a cap here or there) to revise the Logan x-over to give me 300 hz for hi-pass.
 
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I have the schematic for this crossover but cant figure out if its a 2nd or 1st order x-over. Anybody have an idea? Thinking it was a 2nd order and looking up the transfer functions of 2nd order hi pass filters I figured I needed to add 200 uf to the 39 uf in there. Is this right?

Can you post the schematic?
 

Ted:

I believe that as far as the woofer is concerned, it see's a 2nd filter at its input (L1+L2 plus C1). The i/p to the transfomer is a more complex 4th order filter HP filter. It becomes a 5th order filter with the switch S2 engaged.

If you add a 200uF in parallel with C3, for an effective capacitance of 239uF, that would lower the xover point from whatever value it was before as more lower frequecies will be allowed to pass on to the ESL panel. Filter simulation runs will be able to pin-point the actual values of the frequency cutoffs and bandwidths.
 
Actually I was trying to raise the hi pass x-over from 124 to 300 hz. Are you saying if I parallel the 39 uf cap with a 200 uf cap I will lower it? If yes I'm glad I asked.
 
After I compared and measured the passive x-over performance vs actives, I never looked back, so not much help on this endeavor.

I'll be interested to see how the split crossover thing works for you. The passive on the highs will seriously impact the efficiency relative to the woofer, but you can control gain balance on the woofer, so no problem.

I'd be more worried about the asymmetric phase angles in the crossover region between that complex passive x-over and the LR low-pass on the DriveRack.


Use your measurement rig to first check for impulse response polarity alignment, then for crossover region phase issues. IIRC even the DriveRack PA lets you adjust output phase in 1 degree increments right?
 
Hi Jonathan ... the driverack does time delay from 0 -> 11 feet but I am not aware of phase angle adjustments. I dont know if my proposed scheme will work or not I just believe it might be better. One other thing I have in my 'mind's eye' is revising the driverack's digital ps to LiFePo4 batteries but there is not a lot of space to work in there on the pc board. I am happy with where I am ...just looking for the next upgrade. I would only do the passive x-over thing if I can get the knowledge to revise and it is not costly. So I will continue to search for a solution.
 
Actually I was trying to raise the hi pass x-over from 124 to 300 hz. Are you saying if I parallel the 39 uf cap with a 200 uf cap I will lower it? If yes I'm glad I asked.

ted ..sorry for the responsing late as they moved this post to another forum. To fully flsh out the frequency response(FR) of your proposed xover, you can download some freeware/shareware filter design programs on the net to look at the FR of the filter you are trying to build.
 

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