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Bending the curve…

tajanestajanes
in DIY

Which component(s) of a 3rd order HP filter C1, L1, C2 most affect the steepness of the tilt (not the bend) of the filter?   I have the bend about right but would like to make the filter a little steeper.  The better half has (not) been enjoying my hours of measurement sweeps (???), so if I could get a head start on a component value change… 

I’ve been using calculators, and a lot of measurement to get the LP and HP about right, but don’t have the software to play with Sims- thx in advance

 

Comments

  • LOUTLOUT
    edited April 2020
    Can you share what C1, L1, C2 values (plus resistor ohms and positions if any) you're using right now along with the tweeter model?

    Roughly speaking you'll usually want C2 to be somewhere around the value of C1 or less to get the steepest slope..down to half the value can often work or even smaller if you're either after a sharper knee with a larger bump or if you've got a series resistor in there to tame the tweeter down (which often tames the knee as well). 
    I want to say making c2 smaller than half of c1 without a series resistor in there can often leave a deep valley in the impedance where it'll drop really low. Hard to say without knowing the tweeter or current crossover values though since I'm super inexperienced with using straight math and calculators..I'm usually playing between the free VituixCAD program, listen, tweak, repeat. :/
  • tajanestajanes
    edited April 2020


    got a chance to run a few quick scans

    blue trace relative to green lowered L1 value to .10mH (vs .15)
    yellow trace relative to green lowered C1 to 2.2uf (vs 2.7)
    didn't see much chg (rel to green) bringing C2 down (7.3uf vs 8.3)




  • WolfWolf
    The tilt is by the order, the knee is the Q and damping.

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  • tajanestajanes
    edited April 2020

    Sure.  But within an order be it LR or in this case BW, a minor component value may ? help tweak the overlay of the frequencies.  I had a bit of a hump just below the Xover point I wanted to see If I could attenuate.

  • WolfWolf
    Put a series resistor in the shunt path. With C for LP, with coil for HP.

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  • rjj45rjj45
    Wolf said:
    Put a series resistor in the shunt path. With C for LP, with coil for HP.
    Yep, that will work. Also (at the risk of swatting by crossover gurus) - For a 3rd order tweeter HP, the L controls the rolloff - larger L values (typ .30 - .45) give a slower or fatter rolloff,, and low values will drop the rolloff. In any event, try it and see. I often struggled to get the proper Fc on a HP with the capacitors, then realized that the L had a lot to do with that also.
    But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
  • tajanestajanes
    edited April 2020
    Lout (?), Ben and Hey you (Don) thanks.

    I did find out through trial and error (and I'm getting alot of experience at error to narrow things down...) that in a 3rd order BW HP that a smaller L did tilt steeper below the bend (blue vs. green line in my pic).  (Don, just duck- and thx)

    Ben, thanks. I hadn't tried a shunt resistor in series with L.
    rjj45
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