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HOWTO: Design crossovers using free software

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  • HOWTO: Design crossovers using free software

    This is my method of doing things:

    I use speaker workshop, spltrace, and jeff B's response modeler all of which are free to do crossover simulation. Jeff B also has a free crossover simulator called PCD but I'm more experienced with speaker workshop so that's what I use. Maybe someone who uses PCD can post a quick PCD guide if they feel up to it.

    Speaker workshop: http://www.speakerworkshop.com/SW/Download.htm
    SPL trace: http://www.pvconsultants.com/audio/utility/spl.htm
    Response modeler: http://audio.claub.net/software/jbagby.html#FRM (requires excel)
    PCD: http://www.pvconsultants.com/audio/crossover/pcd.htm (requires excel)

    My process is as such:
    Find decent response plots of drivers (if you can get them all from the same site for example zaph's site, your results will be better as testing conditions will not be way off between drivers).
    Save the plots to your disk, open them in paint, select all, copy.
    Open SPL trace, file>import from clipboard.
    Set low amplitude (I do 60dB)
    Set High amplitude (I do 90dB)
    Move your mouse around and look in the lower right corner to be sure the values it's reading are correct. If not then reset the lines.
    Then set the low and high frequencies (i always try to do 20-20000)
    Under trace>options, I set the trace limits to 20-20000, 200 samples.
    Then trace>start spl trace. Line up the white line on the left with the point in the graph where the response is, then click. Repeat 200 times :P
    When you reach the end it will say "trace limit reached."
    Then go to trace-stop trace. It will ask if you want to save it. Say yes. I label it the name of the driver plus trace. For example RS180-4trace.frd
    I do not trace impedance as I model this in response modeler.
    Repeat the SPL trace for any drivers you might be using.

    Now onto response modeler.
    Fire it up and make sure you enable the macros. You should see a blue trace in the graph like in the screenshot.
    Click the blue button "import frd file to modify" and find one of the files you traced earlier. It will load it an it will show up in the graph.
    Next I model the impedance. Scroll down to the impedance/box model section and input the T/S parameters of the driver you want to model. Look at the impedance from the measured driver plot and adjust the Le coeff. and Le exp. (red text) until the rising impedance curve in response modeler matches what the actual measured impedance looks like. I model it instead of tracing because there's never enough detail when tracing to get a smooth plot. Once it looks good click "save modified result to zma file" (in red) and save it. I name it driver+impedance to keep it simple. So going by the previous example, RS180-4impedance.zma

    I do the same thing for tweeters. Sometimes they don't have T/s parameters listed so you just have to fiddle. Put in the FS at least, then I set both qes and qms to 1.2. vas 1liter. Box type sealed, volume 1 liter. Fiddle with the box size and qes/qms until the "bump" at the resonant frequency is of the correct amplitude. For Le i start with .1mh, then adjust the Le coeff and exponent to match the measured impedance plot. The closer you can get things the better.

    Now we get to model the baffle effects. Scroll down the bottom area of response modeler for baffle diffraction response modeling. Input the baffle width and height, where the speaker is located on the baffle, what size roundover if any, and the approximate size of the woofer. Then click "save baffle diffraction curve to BDS register above" (in blue). If you scroll back up to the top you'll see it has been applied to your imported response.
    Now you could be done here but usually we don't need a full 6dB of baffle step simulation, so I then do the following:
    Near the top where it says "baffle step: simple step or from below," click where it says "off" a few times until it says "inverted." Then set the baffle width. I usually set it to about 45% inverted, which is like accounting for half baffle step which is a good comprimise for placement flexibility. You'll see that the curve is not as pronounced as it was with the full step.
    Now on the right, click "save modified result to frd file" (in red). I save it as driver name+baffle dimensions, for example RS180-4_10x15.frd
    Now one more step, we need to extract minimum phase. Scroll down a bit more and to the right slightly, you'll see a button labeled "auto-extract phase using hilbert bode transform." Click this and find the file you just saved. If it saved something about fft.dll just click ok and ignore it. Wait a few seconds while it thinks. Then it will prompt you to save the new file. I save it the same name as before but I add "phase" to the end so I know it's the one with phase data in it. So RS180-4_10x15phase.frd

    Repeat that whole proccess for the rest of your drivers (actually doesn't take all that long).

    Now they are ready for simulation! Fire up speaker workshop and create a new project, give it a name.
    Right click in the sidebar to the left and click "import."
    Set file type to .frd and find one of the "phase" files you made in response modeler. Import it. Repeat for the rest of the drivers you're using.
    Then right click>import, change file type to impedance .zma files, import those.
    The right click>new>driver. Name it the driver (RS180-4) .Right click the window that pops up and select "properties" down at the bottom of the list. Click over to the "data" tab.
    Click the question mark next to the "impedance" box and load the impedance date for that driver. Repeat for frequency response. Click OK, and you can close the driver window. Repeat for your other drivers.
    Now rightclick on sidebar, new>network. Call it crossover or something like that. Double click the icon for the network and it will pop up a mostly white window with a signal generator icon. Right click on the white space in that window and select "properties." Make sure "individual response" and "calculate network impedance" and both checked. Click "OK" to get out of properties.
    Rightclick on whitespace again, insert>driver. Click the question mark, select a driver. Make sure "individual response" is checked. Offset should be zero for mids/woofers, 1inch for tweeters. Click ok and poof! Your driver is there. Repeat for the other drivers. Now you can insert capacitors, resistors, inductors, etc to build your crossover. To connect multiple parts to the same point, you need to hold down the shift key while dragging them together. You'll get the hang of it. I usually use an online calculator to get rough values such as lalena.com
    Right click on the white space and select "calculate response" to simulate the crossover. It will show up on the lefthand sidebar as crossover.total response. Double click this to open a window where you can see it. Right click on this graph and select "chart properties." Under the data sets tab, i usually add the individual response plots of the drivers and make them different colors, so I can see what each driver is doing. X-axis is usually fine as-is. Y axis I turn off "auto minimax" under the scale section, and set the minimum at 50dB and the maximum at 95dB. Then under grid lines below that, major lines every 5dB. Y2 axis is the phase. I turn of minmax and set the min/max to -180/180, and then turn off grid lines to keep things uncluttered. Press OK and you're in business!

    Now just keep tweaking values and right clicking to regenerate the response.
    Keep in mind that sine we didn't measure the data ourselves, the final design will likely need tweaking by ear or with the aid of measurement to truly be perfect. Good luck!

  • #2
    Re: HOWTO: Design crossovers using free software

    Thanks for doing this Max. Looks like a nice treatment of the subject. I think this may be of real benefit to some people out there.

    bb

    Since we cannot know all that there is to be known about anything, we ought to know a little about everything.
    - Blaise Pascal (1623 - 1662)

    Comment


    • #3
      Re: HOWTO: Design crossovers using free software

      Originally posted by Max_Andrews View Post
      Offset should be zero for mids/woofers, 1inch for tweeters.
      Very nicely done Max! Great resource.

      Am I correct in assuming this offset is for the relative difference in acoustic centers? A potentially more accurate method for setting this would be to measure the relative differences between the driver flange and the front plate of the magnet assemblies, and enter those values.

      C
      Curt's Speaker Design Works

      "It is the mark of an educated mind to be able to entertain a thought without accepting it."
      - Aristotle

      Comment


      • #4
        Re: HOWTO: Design crossovers using free software

        Indeed Curt! For modeling purposes without drivers in hand, I usually just do 1-inch for tweeters since it's usually close to this, then tweak later. For a woofer/mid crossover, it doesn't matter since the offset is far smaller than the frequency of the crossover, yes?

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        • #5
          Re: HOWTO: Design crossovers using free software

          Originally posted by Max_Andrews View Post
          Indeed Curt! For modeling purposes without drivers in hand, I usually just do 1-inch for tweeters since it's usually close to this, then tweak later. For a woofer/mid crossover, it doesn't matter since the offset is far smaller than the frequency of the crossover, yes?
          Curt's Speaker Design Works

          "It is the mark of an educated mind to be able to entertain a thought without accepting it."
          - Aristotle

          Comment


          • #6
            Re: HOWTO: Design crossovers using free software

            For a more detailed tutorial on using Speaker Workshop for modeling crossovers you can go here...

            http://www.rjbaudio.com/Audiofiles/SWtutorial.html

            I really need to update my FRDTools tutorial for use with Jeff's newest software (I haven't touched that page in a long time).
            RJB Audio Projects
            http://www.rjbaudio.com

            Comment


            • #7
              Re: HOWTO: Design crossovers using free software

              Curt. A positive offset moves an AC further in front of the baffle in SW.

              Fractions of an inch difference in ACs have made a HUGE difference in how my crossovers have summed. I'm glad I have measurement capability now.

              Before I could measure, Roman's write up helped me a lot.

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              • #8
                Re: HOWTO: Design crossovers using free software

                There have been several in depth discussion regarding acoustic center estimation.

                Here is one.
                http://techtalk.parts-express.com/sh...coustic+center

                Comment


                • #9
                  Re: HOWTO: Design crossovers using free software

                  I wrote up something similar years ago, so I figured I'd post it here if anyone wants some extra reading: http://www.angelfire.com/electronic/...rworkshop.html

                  It's probably out dated now with newer tools available, but it might have some additional tips, particularly for anyone trying to learn how to use Speaker Workshop.

                  Comment


                  • #10
                    LINK to newer version of Jeff Bagby's PCD

                    The latest versions of Jeff's software, including Passive Crossover Designer can be found here:
                    http://www.audio.claub.net/software/jbagby.html
                    The link you provided does work but the page is no longer updated and it leads to an old version of the PCD. The latest is version 6.20.

                    -Charlie
                    Charlie's Audio Pages: http://audio.claub.net

                    Comment


                    • #11
                      Re: HOWTO: Design crossovers using free software

                      ttt

                      Comment


                      • #12
                        Re: HOWTO: Design crossovers using free software

                        Great thread.

                        I have a question in regards to BDS (Baffle Diffraction Simulator). Lets say you are designing a 2-way TM speaker. You are using the free software tools and assume all measurements (simulations) are 2.83V @ 1-m on-axis with the tweeter. Do you have to account for the acoustic center of the woofer? If so, how? Do you add baffle angle tilt for the woofer simulation? Just increase the Axis Dist. (from mic to the A.C. of the woofer)?
                        Thanks,
                        Zach Tripp

                        Comment


                        • #13
                          Re: HOWTO: Design crossovers using free software

                          Originally posted by zach_t View Post
                          Lets say you are designing a 2-way TM speaker. You are using the free software tools and assume all measurements (simulations) are 2.83V @ 1-m on-axis with the tweeter.

                          Do you have to account for the acoustic center of the woofer?
                          Yes

                          Originally posted by zach_t View Post
                          If so, how?
                          Many people estimate the distance. I would give you my method but I am not ready for the grilling that will ensue after I use incorrect vocabulary.

                          It is much easier to take the measurements with both drivers on baffle. Measure at the tweeter position for both measurements and do no extract minimum phase. These measurements will acount for the ac difference.

                          Originally posted by zach_t View Post
                          Do you add baffle angle tilt for the woofer simulation? Just increase the Axis Dist. (from mic to the A.C. of the woofer)?
                          If you enter in the driver diameters you can use the PCD to simulate off axis response. At the top right there is a section for vertical and horiztonal adjustments. Enter the appropriate listening angle, for testing.

                          Comment


                          • #14
                            Re: HOWTO: Design crossovers using free software

                            Originally posted by zach_t View Post
                            Great thread.

                            I have a question in regards to BDS (Baffle Diffraction Simulator). Lets say you are designing a 2-way TM speaker. You are using the free software tools and assume all measurements (simulations) are 2.83V @ 1-m on-axis with the tweeter. Do you have to account for the acoustic center of the woofer? If so, how? Do you add baffle angle tilt for the woofer simulation? Just increase the Axis Dist. (from mic to the A.C. of the woofer)?
                            I'll have to disagree with Brian here. The distance variable in BDS determines how the diffraction signature of the "baffle" looks at that distance and is primarily based on the distance to the baffle, not the driver's acoustic center. The acoustic center doesn't come into play until you simulate the crossover and need to estimate the extra phase shift due to the A.C. being further back than the plane of the baffle.

                            The same is true of the baffle angle tilt in that it reflects the diffraction profile of the baffle, independant of the driver acoustic center.

                            I also wouldn't link the initial measurement distance to the BDS distance (although I would typically use a 1m distance as well out of habit and you'll find that BDS profiles don't change that much between 1m and 2m, certainly not as much as the degree of error inherent to estimating driver responses through simulation and not measurements) because most drivers measured on an infinite baffle, in an anechoic environment, will measure the same at slightly longer distances, but the BDS program can evaluate the baffle diffraction properties at different distances and it can sometimes be nice to simulate the baffle to represent a typical listening distance for the speaker design. For simulating the crossover, sometimes you also have to adjust the relative acoustic center distance between drivers based on the listening distance as well because this "ratio" will change with different listening distances (I have a simple calculator in the "audiophiles" section of my site that describes this phenomenon well).
                            RJB Audio Projects
                            http://www.rjbaudio.com

                            Comment


                            • #15
                              Re: HOWTO: Design crossovers using free software

                              Roman is right. I think that I answered the wrong question on the assumptiont that the ACs would be adjusted in PCD not BDS.

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