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It’s that time audio enthusiasts! Registration for the 2019 Speaker Design Competition is now open! Visit midwestaudiofest.com for details and to list your speaker project. We are excited to see all returning participants, and look forward to meeting some new designers this year, as well! Be sure your plans include a visit to the Parts Express Tent Sale for the lowest prices of the year, and the Audio Swap Meet where you can buy and trade with other audio fans. We hope to see you this summer! Vivian and Jill
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Passive low pass filter?

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  • BOBinGA
    replied
    That would be a high pass filter.

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  • bard
    replied
    From what you've requested, I assume you're looking for a good, fairly sharp, low-pass filter for a sub-woofer.

    If that is so, I would suggest a 3rd order, series, low-pass Butterworth filter with an F3 of roughly 240 Hertz.

    That would mean 3 parts: The input parallel cap to ground should be 35volt, 150uF non-polar electrolytic capacitor, the mid point series inductor should be 6 milli-Henries, and the output parallel cap to ground should be a 35 volt, 50 uF non-polar electrolytic capacitor. This will provide a fairly steep rolloff at 18 dB per octave with an F3 of approx. 240 Hertz. (Great sub-woofer specs) {edited}

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  • DanP
    replied
    You mentioned the lowpass feeding an amp for a subwoofer (low level signal) but the picture you've shown would be used after an amp, just before the actual driver. Which one are you looking for?

    Dan

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  • Chris Roemer
    replied
    They do, don't they.

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  • jhollander
    replied
    Nice work Chris, that's what it looks like to me, i.e the last cap switched. 25V caps seems a bit low.

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  • Chris Roemer
    replied
    Pretty sure PE's XOs don't claim "Material is very full" (1st thing I look for in ANY XO design), also the "57 lbs of large inductance" is a very nice touch, as is the "instantaneous range of direct access to the target".

    (making some ASSumptions here) IF (big if) that coil is about 3.5mH, and (my take on that "switched" circuit) it's used w/an 8n(ohm) woofer w/the switch in the "0dB" position, the shunt capacitance (to gnd) looks to be about 16uF (2 caps in parallel) which puts a (true) 8n load down -2dB @ 400Hz (-3 near 450Hz).
    If used w/a 4n woofer (with the sw. in the "3dB" pos. - which means what - who knows?) it ends up being -7dB down @ 400Hz (-6 @ 330). I believe the 3rd cap gets added (in parallel) increasing the shunt capacitance to around 25uF.
    So... the circuit is just the coil in series w/a woofer, w/some cap. (either 16uF or 25uF I think) in parallel w/it (to ground).

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  • jhollander
    replied
    If you had an impedance graph this would be easy. Do you know the woofer and any specs?

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  • tomzarbo
    replied
    Parts Express sells a few...
    Search for crossovers, subwoofer...
    thought they had a few more. Don't seem to be there anymore.
    TomZ

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