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  • A good crossover design?

    I have designed a crossover for a 1" vifa tweeter and a 6.5" vifa woofer. The values on my schematic are "mathmatical" values.

    Do you think this will work well for the speakers i am crossing over? I am fairly new to all this...

    Thanks
    Attached Files

  • #2
    Re: A good crossover design?

    Here is the short answer. The xo point looks right but the actual xo will not likely work. The result will most likely look like heck and will not be flat.

    Mathematical xos almost never work.

    1. the formula assumes a constant impedance across frequency.
    2. The formula doesn't account for phase interactions between drivers and acoustic offsets
    3. Formulas forget that the driver already has a rolloff

    Goals
    --Roll speaker off against a target slope
    --Make sure drivers interact appropriately

    Methods
    --Use measured responses to simulate crossover

    Comment


    • #3
      Re: A good crossover design?

      Originally posted by brianpowers27 View Post
      Here is the short answer. The xo point looks right but the actual xo will not likely work. The result will most likely look like heck and will not be flat.

      Mathematical xos almost never work.

      1. the formula assumes a constant impedance across frequency.
      2. The formula doesn't account for phase interactions between drivers and acoustic offsets
      3. Formulas forget that the driver already has a rolloff

      Goals
      --Roll speaker off against a target slope
      --Make sure drivers interact appropriately

      Methods
      --Use measured responses to simulate crossover
      You can use the plots from the manufacturer. Vifa is usually pretty close to actual.

      What is needed is a way to take those plots, convert them to data, and then use a crossover modeling program to factor in all the topics you mentioned above.

      SPLTrace will convert the plots to data.

      Baffle Diffraction Simulator (BDS) will allow you to create data files that allow you to add in diffraction effects to the plots.

      Frequency Response Combiner (FRC) will then allow you to combine the baffle diffraction with the plots and extract minimum phase information so that you can account for acoustic offsets.

      Jeff Bagby's Passive Crossover designer will let you put the modified files into a program that will allow you to find the correct crossover values to get a smooth response.

      Jeff B's Response Modeler can take the place of FRC, and for smaller baffles, BDS as well. Baffles with a larger ratio of height to width will benefit from modeling in BDS.
      R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
      Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

      95% of Climate Models Agree: The Observations Must be Wrong
      "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

      Comment


      • #4
        Re: A good crossover design?

        So what exactly does this involve? Do i have to sit with the speaker in an enclosure, measuring the frequency responses with a microphone?

        I'm really new to all this stuff so it seems confusing :s

        Comment


        • #5
          Re: A good crossover design?

          Try reading over some of these answers at Paul's site.

          http://undefinition.googlepages.com/diy-faqs

          Comment


          • #6
            Re: A good crossover design?

            Originally posted by 14cells View Post
            So what exactly does this involve? Do i have to sit with the speaker in an enclosure, measuring the frequency responses with a microphone?

            I'm really new to all this stuff so it seems confusing :s

            Designing a XO without experience is confusing...so many variables to consider. You could generate your own measurements, which is the preferred way, or use the *.frd and *.zma driver files with Jeff Bagby's PCD program. It too, requires a learning curve, but the end results will be light years ahead of any algebraic/textbook formula calculations. The "math" values are never adequate, since a driver's specs vary with frequency. You cannot use a fixed value, like 4 or 8 ohms for your XO point calculation. The impedance varies over the driver's useable frequency range. And the frequency range that's listed in the specs is never real-world performance, either. That's why Jeff's program is so useful as it takes into account the variables you need to work with. I built many speakers before I found this forum and the great advice, using textbook/math calculations. Never did I get an acceptable result AFA SQ goes. I kept wondering "why isn't the math working?" It doesn't work because fixed-value formulas can't work when there's all those varying parameters to deal with.

            John A.
            "Children play with b-a-l-l-s and sticks, men race, and real men race motorcycles"-John Surtees
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            Vintage system: Yamaha CR-420, Technics SL-PG100, Pioneer CT-F8282, Akai X-1800, Morel(T)/Vifa(W) DIY 2-way in .5 ft3
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            Comment


            • #7
              Re: A good crossover design?

              Originally posted by 14cells View Post
              I have designed a crossover for a 1" vifa tweeter and a 6.5" vifa woofer. The values on my schematic are "mathmatical" values.

              Do you think this will work well for the speakers i am crossing over? I am fairly new to all this...

              Thanks
              14cells

              Have you already purchased those drivers?

              The acoustic response of the woofer looks fairly challenging and with the schematic that you've provided you won't get an acceptable response near your target x-over frequency and probably over the entire 1 to 6kHz range.

              Is starting with a proven design an option for you?

              Louis

              Comment


              • #8
                Re: A good crossover design?

                Off topic to the OP, but do you run RC vehicles by any chance? An E-Maxx in particular?

                Mark
                You go your way, I'll go mine. I don't care if we get there on time.

                ~Pink Floyd

                Comment


                • #9
                  Re: A good crossover design?

                  Originally posted by Mark65 View Post
                  Off topic to the OP, but do you run RC vehicles by any chance? An E-Maxx in particular?

                  Mark
                  Heh. I do.
                  Line Array: IDS-25 Clone, FE-83.
                  2-2.5 Way:
                  Zaph Audio's winning entry: ZA5+SB29. - Microliths: RS125+RS28. - Small Bangs: TB W4-1658SB+SEAS 27TBFC/G. - Monoliths: Peerless 830884+SEAS 27TBFC/G.
                  3-3.5 Way:Miniliths: SEAS P21/CA21REX+Neo8 PDR+Neo3 PDR. - Megaliths: 2xDayton RS270+2xT-B W4-1337SB+SB29. - ZDT3.5 +: 2xDayton RS180+Dayton RS52+Vifa DQ25. Reflexos: OB 4xDayton RS150 + Neo3 PDR.

                  Comment


                  • #10
                    Re: A good crossover design?

                    Yeah i already have these drivers. :s

                    So in that case, does anyone have a proven design i can try? As i do not have any of that software (or the knowlage to use it), can anyone suggest a place to start? I don't really want to waste money on a crap crossover if i can help it.

                    But at the moment i feel I am in over my head :(

                    On the plus side though, the cabinates are coming together, and are looking sweet!

                    Comment


                    • #11
                      Re: A good crossover design?

                      Originally posted by 14cells View Post
                      Yeah i already have these drivers. :s

                      So in that case, does anyone have a proven design i can try? As i do not have any of that software (or the knowlage to use it), can anyone suggest a place to start? I don't really want to waste money on a crap crossover if i can help it.

                      But at the moment i feel I am in over my head :(

                      On the plus side though, the cabinates are coming together, and are looking sweet!
                      From what I see in your crossover, you have the right topology, just not the right values.

                      For starters, you will need more padding on the tweeter. Baffle step will need to be accounted for which will decrease the woofer's upper range by between 3dB and 6dB. I'd increase the woofer inductor to between 2 and 3mH. My guess is that the shunt cap is maybe a little small, but close. And the zobel values can be modified to shape the crossover knee for the woofer.

                      I'm not quite as certain about the tweeter values, not having PCD to play with, but again, you've got a good start. And as ragged as the woofer response is above 1KHz, it should be able to be shaped into a workable response.
                      R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                      Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                      95% of Climate Models Agree: The Observations Must be Wrong
                      "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

                      Comment


                      • #12
                        Re: A good crossover design?

                        Ok great.

                        So im looking to attenuate the tweeter another 3-6 dB on top of what i have already calculated. Thats easy enough.

                        As for the shunt cap, maybe up to 6.8uF, or do you think it could be bigger than this still...

                        And how exactly can i tweak the zobel to change the knee and shape the woofers response?

                        Sorry to be a pain, but i really appreciate the advice!

                        Comment


                        • #13
                          Re: A good crossover design?

                          Originally posted by 14cells View Post
                          Ok great.

                          So im looking to attenuate the tweeter another 3-6 dB on top of what i have already calculated. Thats easy enough.

                          As for the shunt cap, maybe up to 6.8uF, or do you think it could be bigger than this still...

                          And how exactly can i tweak the zobel to change the knee and shape the woofers response?

                          Sorry to be a pain, but i really appreciate the advice!
                          Like I said, unless I were to put those curves into PCD, it's tough to tell what the actual values need to be.

                          As for how tweaking zobel values works, here's one way to look at it. If you increase the cap on the zobel and lower the resistance, you effectively lower the impedance at the output of the filter in the XO region, making the cutoff shallower. Increasing the resistance will tend to increase filter Q, extending the cutoff or giving it a bit of peaking. Again, without putting it into PCD, it's tough to make the exact call.
                          R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                          Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                          95% of Climate Models Agree: The Observations Must be Wrong
                          "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

                          Comment


                          • #14
                            Re: A good crossover design?

                            Ok, so where can i find these .zma and .frd files for these drivers. I downloaded the PCD software, just can't find the files for these drivers...

                            Comment


                            • #15
                              Re: A good crossover design?

                              Originally posted by 14cells View Post
                              Ok, so where can i find these .zma and .frd files for these drivers. I downloaded the PCD software, just can't find the files for these drivers...
                              Model numbers?

                              Comment

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