Announcement

Collapse

Midwest Audio Fest

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
See more
See less

Help understanding Crossover schematic

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Help understanding Crossover schematic

    schematic_rta11t_rev (1).pdf

    With the schematic I have in PDF form,

    1. What are the reasons and possible response changes on the high pass, where they used a 12uf cap and a 2.0 ohm resistor in parallel?

    2. What is the purpose of the .4mh inductor and 2.7 ohm resistor? ( I mean as far as how would it model the high end response) being in series?

    I understand crossovers, and the components and what they do, but have not seen many circuits similar to these exactly
    Attached Files

  • #2
    Re: Help understanding Crossover schematic

    what exactly did you need help understanding?
    | | = capacitor
    /W\ = resistor
    curly q = inductor

    Comment


    • #3
      Re: Help understanding Crossover schematic

      Originally posted by VegaMan View Post
      what exactly did you need help understanding?
      | | = capacitor
      /W\ = resistor
      curly q = inductor


      How those 2 circuits would affect the high end response. I have seen somewhat similar circuits but done differently.


      You know, if one was to model them, how would it alter the output.

      Comment


      • #4
        Re: Help understanding Crossover schematic

        Originally posted by kevintomb View Post
        How those 2 circuits would affect the high end response. I have seen somewhat similar circuits but done differently.


        You know, if one was to model them, how would it alter the output.
        in my basic understanding of crossovers it would be completely driver dependent. do you have drivers in mind so perhaps someone a bit more knowledgeable than myself on the subject may be able to help?

        Comment


        • #5
          Re: Help understanding Crossover schematic

          Originally posted by kevintomb View Post
          How those 2 circuits would affect the high end response. I have seen somewhat similar circuits but done differently.


          You know, if one was to model them, how would it alter the output.
          The 2 ohm resistor in parallel with the 12uf cap would have a dropping impedance as the frequency rises. I've seen that circuit used to hold up the high end if you have extra tweeter efficiency to spare. The cap would have an impedance of 2 ohms at around 6.6K.

          Ron
          C-Note Iron Driver Build
          The Lydias
          The Cherry π's
          The Champs - Iron Driver 2015 Entry
          My Projects Page

          The good thing about science is that it's true whether or not you believe in it. - Neil deGrasse Tyson
          http://www.youtube.com/watch?v=cjuGCJJUGsg

          Comment


          • #6
            Re: Help understanding Crossover schematic

            We have to assume a few things for the sake of discussion. Let's say this is an 8 ohm tweeter, and that it has a flat Z profile (like most ribbons, but not domes).

            We can make this a simple 1st order filter by dropping the 2 ohm (2n) resistor down to 0.002 ohms, effectively bypassing the other cap, and by raising the 2.7n resistor to 2700n, taking the coil out of circuit. You'd end up with a transfer fn (function) that was essentially flat from 20k (and beyond) down to 5-6k or so, -3dB down near 1.7kHz, and -6 by 950Hz.

            If we made the 2n resistor 2000n, we'd basically then have a 1st order rolloff, but at twice the Fc ('cause we'd have the same thing as a single 6uF cap in series with the tweeter). If we just "opened" the (1st) 12uF cap, and used the 2n resistor, we'd have the initial curve's rolloff, but w/probably about -2dB attenuation across the board. Using the parallel res/cap (as in your schm) gives us a lower Q initial rolloff, but ultimately ends up about the same. This would NOT be flat down to 6k, but starts dropping right from 20k on down (very gradually), being -1dB near 10k, -2 near 5k, -3 near 3k, and -6 near 1.1k.

            With THAT in place, if we dropped the resistor on the coil from (our temporary) 2700n, down to something "normal" for a .40mH shunt (like 0.3n), we'd have a 2nd order filter, dropping fairly steeply below 3k. The added resistance (in the coil shunt leg) lowers the Q of this circuit, making the transitions "smoother".

            Final xfer fn of your circuit (given a flat Z tweeter) is almost flat from 20k down to about 8kHz, hitting a "shoulder" between 4k (-1dB) and 3k (-2dB), -3dB @ 2.5k, and -6 @ 1.9kHz. Quite frankly (in THIS particular example) I can get the same xfer (transfer) fn using just a 6uF series cap and a 1.1mH shunt coil (with the possibly added benefit of holding the impedance up higher). Of course, you'd expect a 1.1mH coil to cost a bit more than the 0.40mH, and who knows, maybe the mfr. had a pile of 12uF caps and 0.40mH coils?

            Comment


            • #7
              Re: Help understanding Crossover schematic

              Originally posted by Chris Roemer View Post
              We have to assume a few things for the sake of discussion. Let's say this is an 8 ohm tweeter, and that it has a flat Z profile (like most ribbons, but not domes).

              We can make this a simple 1st order filter by dropping the 2 ohm (2n) resistor down to 0.002 ohms, effectively bypassing the other cap, and by raising the 2.7n resistor to 2700n, taking the coil out of circuit. You'd end up with a transfer fn (function) that was essentially flat from 20k (and beyond) down to 5-6k or so, -3dB down near 1.7kHz, and -6 by 950Hz.

              If we made the 2n resistor 2000n, we'd basically then have a 1st order rolloff, but at twice the Fc ('cause we'd have the same thing as a single 6uF cap in series with the tweeter). If we just "opened" the (1st) 12uF cap, and used the 2n resistor, we'd have the initial curve's rolloff, but w/probably about -2dB attenuation across the board. Using the parallel res/cap (as in your schm) gives us a lower Q initial rolloff, but ultimately ends up about the same. This would NOT be flat down to 6k, but starts dropping right from 20k on down (very gradually), being -1dB near 10k, -2 near 5k, -3 near 3k, and -6 near 1.1k.

              My idea is to find new tweeters from Vifa and do a much simpler crossover ( cap and coil) and remove the peak and the other issues.

              With THAT in place, if we dropped the resistor on the coil from (our temporary) 2700n, down to something "normal" for a .40mH shunt (like 0.3n), we'd have a 2nd order filter, dropping fairly steeply below 3k. The added resistance (in the coil shunt leg) lowers the Q of this circuit, making the transitions "smoother".

              Final xfer fn of your circuit (given a flat Z tweeter) is almost flat from 20k down to about 8kHz, hitting a "shoulder" between 4k (-1dB) and 3k (-2dB), -3dB @ 2.5k, and -6 @ 1.9kHz. Quite frankly (in THIS particular example) I can get the same xfer (transfer) fn using just a 6uF series cap and a 1.1mH shunt coil (with the possibly added benefit of holding the impedance up higher). Of course, you'd expect a 1.1mH coil to cost a bit more than the 0.40mH, and who knows, maybe the mfr. had a pile of 12uF caps and 0.40mH coils?

              Thanks Chris, what I was looking for. So basically an odd rate of decrease as the frequency lowers. Somewhat of a shelving response, but close to a typical roll off but starting up higher? (kinda sorta I realize)


              I was wondering also the benefit of the 2-12uf caps in series. It seems a bit too complicated for its own good.

              This is a schematic from a vintage Polk audio RTA11t speaker. I am re-purposing the drivers into a smaller narrower box. The original box sufferered moderate water damage and mold sorta, but the drivers are like new and so is the crossover.

              It is a one inch dome tweeter, with a strong peak at around 13khz ( about 5 db) The stereophile measurement shows a roll off above the 3khz crossover kinda like what you mention. Honestly not sure why they voiced it that way. A weak lower treble, and a very strong 12-13 khz peak.

              I plan on finding better tweeters from maybe Vifa, and doing a 2nd order crossover.

              Comment

              Working...
              X