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building an audio crossover

Discussion in 'Audio' started by flippityflop, Feb 6, 2014.

  1. flippityflop

    flippityflop

    13
    0
    Feb 2, 2014
    i want to build an audio crossover and by the small amount of reading that i've done online, the most desirable crossover topology is the 4th order Linkwitz-Riley. linear gain in wide ranges, better Q, responsiveness, so forth...

    so i found this 4th order LR crossover online http://sound.westhost.com/project09.htm. i'm building the one that separates the signal to 3 passes (hi/mid/low). [​IMG]
    (i'm thinking of further filtering the mid in the future, but that'll have to wait until the whole speaker system is finished.)

    anyways, there are a few things that are not clear to me. the author, mentions that the passes may be a bit of out-of-phase, BUT it's very small, etc... but then i saw that he also provided a small buffer circuit for each signal. so i was wondering:
    [​IMG]

    1.) can the same buffer circuit can be used to insert a delay in each signal line, so they can be adjusted to be completely in phase with each other (or maybe i'm just getting the concepts from digital circuits mixed-up). i'm no electronics engineer. if not, is there any cheap buffer design out there that might do??
    i know that i would be needing an oscilloscope for this (which i don't have, but i'll be putting one together in the coming months). but for the mean time, i might have to do it by ear... or maybe the close tolerances of the parts that i would purchasing online would be good enough that won't be able to hear it in any case.

    2.) what are the best cut-off frequencies for high-pass, band-pass, low-pass to drive speakers. i think it might also be a matter of the quality and make of the speakers. so just give me the general values (20-500Hz/500-5000Hz/5000-20000Hz)??
     
  2. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    I would add another upper voice speaker as I think you have already mentioned. The cut-offs below are a good starting point which you can adjust for your preference.

    Bass 90-120Hz
    Lower Voice 120Hz-500Hz
    Upper voice 600Hz-4Khz
    Tweeter 4Khz-8Khz

    As always the author doesn't show the power supply connection. Looking at the connections I think he is using +/- supply. If you are planning on using a single supply you might want to modify your circuit. See diagram attached.

    Adam
     

    Attached Files:

  3. flippityflop

    flippityflop

    13
    0
    Feb 2, 2014

    sorry, the attached diagram is a sallen-key high pass filter, right?? so should i just substitute that for the high pass filters of the linkwitz-riley?? or is that the phase shifting buffer that i'm asking for??

    about the power supply, the author mentioned he was using a +/-15V (does the -15V refer to it being lower than "ground"??). he also provided the schematics for a power supply: http://sound.westhost.com/project05b.htm . but i think i'm just gonna purchase it online from ebay. i'm sure it'll easy to a good and cheap one there. this crossover, though, i'm building myself...
     
  4. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Your diagram is sallen key. You don't need to do anything just if your using single supply just follow my design.
     
  5. flippityflop

    flippityflop

    13
    0
    Feb 2, 2014
    oh... i misunderstood the purpose of the diagram you provided. yes, i know how to connect a generic opamp to the power.

    [​IMG]
    pin 4: -V
    pin 7: +V
    i've experimented with a few before. needless to say i busted a couple too (overloaded current from feedback).

    it's a sallen key?? i was under the impression it was LR... or is it a combination?
     
  6. flippityflop

    flippityflop

    13
    0
    Feb 2, 2014
    anyways, i did a few modifications. i'm purely an amateur in designing circuits... the most i could do is follow directions written in the datasheet. here it is:

    [​IMG]


    i've tweeked some of the values to my intended ranges:
    high pass: 3000-5000 (4000-higher) Hz
    low mid pass: 3000-5000 (4000) Hz
    high mid pass: 90-150 (120) Hz
    low pass: 90-150 (120) Hz
    i've also made them overlap on their boundaries lower and higher by about 25%. i've chosen overall slightly higher capacitances to prevent too much sensitivity from stray capacitance. i've also made the resistance for the higher frequencies lower, so that it wouldn't be attenuated.


    there most likely are not ganged potentiometers of:
    2 - 2.5k ohms/2 - 5k ohms
    4 - 2.5k ohms
    2 - 5k ohms/2 - 10k ohms
    4 - 100k ohms.

    but piher manufactures potentiometers with detachable shafts:
    [​IMG]
    i figure i could just insert a long shaft or something, going through several of these potentiometers. voila! now i've got meeself a custom ganged potentiometer. unfortunately, piher aren't not that big yet, so not many north american suppliers carry them.

    another option is to buys these potentiometers (categorized as trimmers in digikey, though i think they're quite big to called "trimmers"), which are similar. i bet i could do the same here:
    [​IMG]
     
    Last edited: Feb 12, 2014
  7. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    LR, what inductor and resistor? It has all the looks of a high pass Sallen and key filter, probably Butterworth response.

    Adam
     
  8. flippityflop

    flippityflop

    13
    0
    Feb 2, 2014

    what?? active filters don't have inductors --- in any case... so LR, being an active, never have inductors. so you can't say that just because it doesn't have inductors, it's not LR.

    btw by LR it means "Linkwitz-Riley filter"

    i didn`t keep on writing "Linkwitz-Riley", because i know people will default in the type of thinking, "oh, Linkwitz is german!! so that's why he favors the design! makes sense!".

    these days i keep finding myself more and more needing clarify what i mean
     
    Last edited: Feb 12, 2014
  9. flippityflop

    flippityflop

    13
    0
    Feb 2, 2014
    are there any other improvements that you guys might suggest??
     
  10. davenn

    davenn Moderator

    13,242
    1,741
    Sep 5, 2009
    they are called trimmers because they are defined as trimpots, where they are set and forget, ie. they are not constantly adjusted
    Trimpots vary in size from a few mm for surface mount ones up to ~ 1cm (10mm) as in those 2 that you showed above

    Dave
     
  11. flippityflop

    flippityflop

    13
    0
    Feb 2, 2014

    shouldn't have said that friendly side comment... starting to say too much again....
     
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