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  • Help with asymmetric crossover...

    I have constructed a 2 way 3rd order butterworth crossover at 860hz. My tweeter is a horn and my woofer is a sealed cone driver. I understand that you can electronically adjust the phase of a driver by changing its order. Therefore I could increase the order of the woofer network to 4th order (or higher) to account for the phase offset. Measurements show that it is out of phase in the listening position. Basically I'm wondering if there is any change I can make to the woofer network to adjust its order so I don't have to buy all new parts for it. I'm also wondering how to calculate which order to use to put the drivers in phase.

  • #2
    Not to be "snobby" (exactly) but "textbook" filters basically NEVER work the way you'd like them to. People here on PETT use XO "sim" software which necessitates the use of .frd (frequency) and .zma (impedance) data files which are unique to every driver.

    Not being familiar w/REW, how can you (or I) tell by looking at that phase graph that the drivers are NOT in phase at the Fc? Have you tried flipping the polarity of the tweeter?
    What drivers are these?

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    • #3
      What software do they use?

      Comment


      • #4
        You didn't answer my ?s.

        The 1st WIDEly used package was by Jeff Bagby, called "PCD" (Passive Crossover Design).
        If you look at the "stickies" at the top of the TT section, you should find links to the softwares.
        Paul Carmody (ka "undefinition") has a step-by-step procedure for getting good results from published graphs.
        It IS a fairly long (and tedious - for beginners) process to get to the end point, but MANY guys (on here) can end up with a system that actually measures within a couple dB of the initial sim.

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        • #5
          You need to do some more reading on phase. I don't think you understand the concept yet.
          craigk

          " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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          • #6
            On line crossover calculators assume the same impedance either side of the crossover frequency and they also assume you enter the actual driver impedance at the crossover frequency. Take a look at any website selling drivers and look at the impedance curve. You'll notice the impedance varies over the frequency range. Therefore to accurately model and target a crossover slope - you need to allow for this varying impedance.

            Also - when you say choose a BW3 crossover - you are aiming at a "target" acoustic slope. You may need less or more electrical filter - depending on how far away you are from the driver's natural roll off.

            Lots to learn. Master some simulation software and make sure your input FRD and ZMA files are not garbage (or garbage in / out) applies. The rest is just persistence and patience.

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            • #7
              Another angle, perhaps…..

              How do your system sound today??

              regards//lasse
              Perry Mason talking to his dentist:

              "Do you swear to take the tooth, the whole tooth and nothing but the tooth, so help you God?"

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              • #8
                One advantage you might have here is that typically you need to pad the horn down so much (15 - 20dB) that its load will look fairly resistive to the crossover. That's if you do all the padding right at the horn. The woofer impedance will still vary over frequency, and not necessarily be purely resistive. So one way or another, you'll need to account for the reactive load. Learning to use one of the sim packages is the easiest way.

                Also, unless your drivers are flat over frequency (and few are) they'll contribute their own phase shifts to the final acoustic response, just as if their response was caused by an electronic filter.
                Francis

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                • #9
                  It looks like you're using REW so you can make both .frd and .zma files for use in crossover simulation software.
                  http://techtalk.parts-express.com/fo...khanspires-but
                  http://techtalk.parts-express.com/fo...pico-neo-build
                  http://techtalk.parts-express.com/fo...ensation-build

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                  • #10
                    Originally posted by lasse View Post
                    Another angle, perhaps…..

                    How do your system sound today??

                    regards//lasse
                    It sounds OK. Doesn't quite hold up on rock tracks with lots of distortion. Something just sounds a little off, not sure what, just lacks that magic touch. But generally it's fairly correct sounding. I'm thinking I am getting time delays from the woofer tweeter placement with it being a horn and a cone driver, and that is slightly throwing off more complex sounding music. So if I could just correct that easily by adding something into the crossover that would be great.

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                    • #11
                      Originally posted by Chris Roemer View Post
                      You didn't answer my ?s.

                      The 1st WIDEly used package was by Jeff Bagby, called "PCD" (Passive Crossover Design).
                      If you look at the "stickies" at the top of the TT section, you should find links to the softwares.
                      Paul Carmody (ka "undefinition") has a step-by-step procedure for getting good results from published graphs.
                      It IS a fairly long (and tedious - for beginners) process to get to the end point, but MANY guys (on here) can end up with a system that actually measures within a couple dB of the initial sim.
                      I have not tried flipping the polarity, but I will try it.

                      The drivers are Radian 475pb tweeter and seas excel 8" woofer.

                      Comment


                      • #12
                        odd combo (imo)

                        Comment


                        • #13
                          Radians are very clear and open, but your sensitivity difference will be huge. Your offset of acoustic centers might account for the issues you hear.
                          Wolf
                          "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                          "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                          "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                          "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

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                          • #14
                            Did no one notice the FR is 20dB/div? There's nothing inherently wrong with using a high sensitivity compression driver with a low sensitivity midbass, but the CD will have to be padded down a good 20dB. These high cost drivers deserve better, this speaker as-is is a disaster. My recommendation to the OP is to invest in self education rather that parts, or throw your money at a properly designed speaker that performs well for your dollar.
                            "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
                            exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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                            • #15
                              Originally posted by imagery View Post
                              I could increase the order of the woofer network to 4th order (or higher) to account for the phase offset.
                              There's no need. With 3rd order/3rd order you don't have a combined phase shift of 180 degrees in the crossover region, the only thing you need to avoid. That only happens with 2nd order/2nd order. That's not a real problem, reverse wiring the tweeter fixes it, but the more usual scheme is to use 2nd order highpass with 3rd order lowpass. That minimizes the parts count on the woofer, where 2nd order is augmented by the acoustical roll off of the driver anyway, and increases protection and lowers distortion of the tweeter compared to 2nd order highpass.

                              www.billfitzmaurice.com
                              www.billfitzmaurice.info/forum

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