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  • The Joudas project

    For the past five years I have been slowly planning my first ground up passive crossover design (I move slowly). Along with some waxing and waning motivation the learning curve has been steep for this project.This is my first ground up speaker design to include passive crossovers.I am getting close to completion and am excited to share some ideas about the final crossover design. I very much welcome feedback here given this is all new territory for me.

    Goals: I wanted to design a floor standing, large format home theater front stage that is capable of reference level midbass. I wanted this to be a "cost is no object" design as it pertains to the drivers. I want this to be a two way system partly for ease of my first crossover design and partly because I do not have the height under my home theater TV to accommodate a three way design. Further, I would like the speakers to have a relatively narrow dispersion pattern throughout the frequency range so a large format midbass along with a horn loaded tweeter fit the bill nicely. The speaker needs to be flat down to about 60hz with the intention of crossing it to my Pyktis subs which I have already posted the completion of.

    The speakers will have passive crossovers for the simplicity of amplification. My home theater system will consist of a 9.4.6 atmos setup so having double the amplification channels and extra boxes required for an active design is just not feasible. The speakers will be powered by an Emotiva XPA-3 Gen 2 which is good for 200 watts at 8 ohm and 300 watts at 4 ohms.

    Driver selection: I have always been a fan of Acoustic Elegance and many have built designs with similar goals using these drivers. I chose the TD12M-8A model. These have the apollo upgrade. I also chose the Beyma TPL-150H horn loaded pleated diaphragm tweeter given their high efficiency and dispersion pattern that will match the 12" midbass at the intended crossover frequency. My original thought was to mimic the layout of the Vapor Audio Arcus using a TD10M but, after speaking with John he recommended the TD12M instead.

    Name: My wife is Lithuanian and helped me name the design. They are called Joudas as this is the name of the color black in Lithuanian. They will be painted in flat black automotive paint exactly as the Pyktis sub was painted.

    Enclosure: After measuring impedance and T/S parameters using DATS I designed a ported enclosure for the woofer using Woofer Box and Circuit Designer

    Click image for larger version  Name:	Joudas_DATS.jpg Views:	14 Size:	196.7 KB ID:	1449380

    The box is 94L And uses dual 3" ports flaired on both ends tuned to about 41hz. With an anticipated 80Hz HPF crosses to my subs vent velocity and excursion look good. In fact, I am good down to 50Hz full tilt at 300 watts if I so desire.

    I went through several design iterations in Fusion 360 to get what I was looking for. The box is modeled at 20" x 30" x 15" external dimensions. It is heavily braced and has a double thick front baffle. The entire outside of the box is MDF. The second layer of the baffle is baltic birch. Initially I did not build a separate enclosure for the TPL-150H but after getting some feedback it was recommended to remove the rear cover and put its own sealed enclosure. The edge of the baffle is chamfered to improve edge diffraction and for aesthetics. Dual round 3" ports flared on both ends was used. The ports will be molded seamlessly into the front baffle.

    Click image for larger version  Name:	Joudas LCR V3.0 Simplified v15.png Views:	14 Size:	268.4 KB ID:	1449382

    In the next post I will post pictures of the enclosure build process to date
    Attached Files
    Last edited by trevordj; 08-28-2020, 09:05 AM.

  • #2
    The braces and Baltic birch rear baffle:



    All the raw parts cut



    Assembly

    Comment


    • #3
      Prior to the glue up I stuffed the box with denim insulation



      Then I glued in the enclosure for the tweeter



      A template for the tweeter cutout was made and a flush trim bit used to make the cut outs.



      Side project: I wanted to glue the double baffle onto the speaker using a vacuum. I wanted a vacuum setup anyway so that I can get more into veneering in the future.

      I used the plans for project EVS. I wanted a nicer enclosure though so I designed this is fusion 360



      Then I cut out the parts on the CNC



      Vacuum done



      Then I glued and vacuum bagged the double baffle in place.



      -Trevor

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      • #4
        A recess was cut for the tweeter



        Everything fits



        I’ve been planning this project for too long...



        Driver cutout made and everything fits.



        Starting the body work.

        -Trevor

        Comment


        • #5
          The bottom of the box was primed after threaded inserts for speaker spikes were installed.





          Getting the inner flair into the box was tricky. I had to trim it a bit.



          Then the port was cemented together permanently in the box and epoxied in place

          -Trevor

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          • #6
            After some sanding, I created a template to spread body filler. Before applying body filler I sprayed the plastic with adhesion promoter.

            Some sanding and a couple applications and everything looked good.

            -Trevor

            Comment


            • #7
              Some more sanding and bottoms were finished. I am using House of Kolor Black Pearl. The bottoms are a gloss finish, the rest of the speaker will be a flat clear.



              The rest of the speaker was prepped and sprayed with polyester primer.



              This is how they sit today. I have one of them blocked out to 400 grit and I have to finish the other two. Then they will get an epoxy surfacer followed by base and clear. -Trevor
              Last edited by trevordj; 08-26-2020, 01:15 PM.

              Comment


              • #8
                While I have been working on these enclosures I have been diving head first into passive crossover design. Once the boxes are complete I will take measurements of the drivers in the boxes in the room. I have a Steinberg UR22C digital interface and an Audix TM1 microphone that has been calibrated at CSS. I will use that along with REW to get accurate measurements in the horizontal plane. I am completely new to that so I may have to do some trial and error to get the measurements right. I will use DATS to get in box impedance measurements.


                Until that happens I have been practicing with Vituixcad and Xsim. I did an frd trace for both the woofer and the tweeter. I was able to pull simulated zma from Woofer Box and Circuit Designer. In Vituixcad I simulated the baffle diffraction and combined that with the frd trace and the box data to get a simulated in box frd with baffle diffraction. I know its not perfect, but I think it was a good exercise to go through and it kept me occupied until I can get actual measurements.

                Even though this will not be my final crossover I would love some feedback about whether I am on the right track with my circuit. All of the values I have come up with actually exist and can be purchased.

                Here is what I came up with:

                Click image for larger version

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                Here is the simulated FR

                Click image for larger version  Name:	image_86772.jpg Views:	41 Size:	146.1 KB ID:	1449411

                And transfer function

                Click image for larger version  Name:	crossover_transferfunction.jpg Views:	0 Size:	151.1 KB ID:	1449410

                Phase

                Click image for larger version  Name:	crossover_phase.jpg Views:	0 Size:	124.9 KB ID:	1449409
                Attached Files
                Last edited by trevordj; 08-26-2020, 12:08 PM.

                Comment


                • #9
                  Impedance

                  Click image for larger version  Name:	crossover_impedance.jpg Views:	0 Size:	99.0 KB ID:	1449416

                  And power dissipation (of the resistors). I wasn't sure if M-Noise was the most accurate to use. I looked into it and M-Noise seems to be the most representative of musical content. If I do pink noise then those resistors are absorbing quite a bit more power, like 150 watts. It is even worse if the spectrum is flat, then they are absorbing over 200 watts. I would love feedback on this. My circuit works with 20 watt resistors if M-noise is appropriate. Otherwise I will have to get like 10 resistors to absorb 200 watts and that didn't seem right. I was able to find some 250 watt resistors on digikey though...
                  Click image for larger version

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                  • #10
                    Looks great so far, keep us posted

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                    • #11
                      trevordj - thank you for the details and all the pics. Threads like this are a great to follow.

                      I have already gone to Amazon to read reviews of Bulldog Adhesion Promoter, thanks for the tips along the way!

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                      • #12
                        You really should not place resistors or that low in value across the woofer as they will run very hot. What is it you are trying to do with it? Cut level? Just use a larger DCR coil if that is the case.
                        What is the purpose of the notch on the woofer as well? 7mH and 2.2uF?? Does it do anything at all to the response? Look at it this way- that notch passes frequencies to ground you want less of, or at least it's supposed to. You have a lowpass at a very low frequency, and a highpass at a very high frequency strung in series to an 8 ohm resistor. I'm not sure it will do much at all, and certainly not worth the cost of a 7mH coil.

                        Later,
                        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

                        *InDIYana event website*

                        Photobucket pages:
                        http://photobucket.com/Wolf-Speakers_and_more

                        My blog/writeups/thoughts here at PE:
                        http://techtalk.parts-express.com/blog.php?u=4102

                        Comment


                        • #13
                          Originally posted by Wolf View Post
                          You really should not place resistors or that low in value across the woofer as they will run very hot. What is it you are trying to do with it? Cut level? Just use a larger DCR coil if that is the case.
                          What is the purpose of the notch on the woofer as well? 7mH and 2.2uF?? Does it do anything at all to the response? Look at it this way- that notch passes frequencies to ground you want less of, or at least it's supposed to. You have a lowpass at a very low frequency, and a highpass at a very high frequency strung in series to an 8 ohm resistor. I'm not sure it will do much at all, and certainly not worth the cost of a 7mH coil.

                          Later,
                          Wolf
                          I will say that much of the work I did was simply putting different circuit blocks in and playing with it until it looked good. I used the speaker building bible, a bunch of youtube videos, and the vituixcad manual as references but I have zero practical experience with this so I appreciate your input and experience. I added the resistor to bring the level down as the woofer appeared to be running hotter than the tweeter. Now that you point it out I feel very foolish as clearly something isn't right with the data I used. The woofer is listed as 96.5dB sensitivity 1W/1M while the tweeter is listed at 102db. I believe I did the FRD trace from a pdf I found on AE's website, although I can't find it now. Someone on AVS pointed me some frequency response curves on driver vault that look more appropriate.

                          That's why I am doing this now with theoretical measurements. It will add a layer or complexity when I actually start trying to figure out how to properly make the measurements.

                          Comment


                          • #14
                            I would suggest that when you get measured results of frd and zma files to post them here to get feedback. I have designed just one speaker and I posted my measurements and there were some issues that were obvious to those more experienced users on the forum but I would have never realized. Once I got that fixed, someone offered a sample xo that was quite good and I just tweaked it from there.

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                            • #15
                              It helps me to see the raw woofer response before any xo filters have been added. That way, you see potential issues that the x-over may need to deal with.

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