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  • Open and Wide

    Been working on (really wide) baffle design for a passive open-mid TMW, and have finally settled on driver placement, spacing and edge treatment:



    I went with a 22.5 degree angled edge to minimize the midrange dip above 1kHz and flatten out the response between 2-3kHz (and because I think it looks better than a really large radius roundover). Since Paul V's Baffle Diffraction Simulator does not do open baffles and Jeff B's Baffle Diffraction & Boundary tool does open baffles but not chamfered edges, here is how I modeled it:
    • Modeled the mid on open and closed baffles in Jeff's tool and saved both FRD results
    • Used the 'subtract' function in Frequency Response Combiner and got the delta between the two
    • Modeled the 3" chamfer in Baffle Diffraction Simulator
    • Used the 'add' function in FRC to combine the chamfered baffle response with the delta diffraction signature


    The XO does not look too bad, at least in simulation-land: 14 components, 2nd order electrical all around, except the midrange low-pass, which is 3rd order electrical. The tweeter and woofer both have resistors resistors for padding and there is a notch to deal with the midrange hump at 400Hz. I'm crossing at 280 and 2500Hz.

    Impedance drops quite low but impedance phase looks OK, staying within +/- 60 degrees:



    I plan to use baltic birch baffles with exposed edges. I just need to figure out how to do the joinery for the angled wings...rabbets maybe?

    Attached Files

  • #2
    Re: Open and Wide

    I like where you're going with this..minimal diffraction can have a profound effect on vocal songs and chamber music......:D

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    • #3
      Re: Open and Wide

      Angled wings: sounds like a job for a biscuit joiner.
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      • #4
        Re: Open and Wide

        I would be tempted to run a spline full length except the top inch or so. It would be easy to get aligned on a table saw. No table saw; then I would say biscuits for sure.
        Interesting build all around.

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        • #5
          Re: Open and Wide

          I wonder if you could just cut a groove in the back side of the ply and bend it?
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          • #6
            Re: Open and Wide

            Guys, thanks for the construction tips and ideas. I only have a router and circular saw at my disposal, so it will either be biscuits (with purchase of biscuit cutting bit) or a dado/groove.

            The 22.5 degree angle for the wing is because I have a chamfer bit of that angle. My idea was to cut the 3 1/2" wide wings and then use the chamfer bit to make a parallelogram. Then joining the parallelogram flush with the baffle center, the wings would be at the desired angle.

            I see much experimenting with cheap Home Depot MDF in my future...

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            • #7
              Re: Open and Wide

              May I recommend the KREG jig for your baffle wings. The master kit comes with a guide how to make cabinet strength joints with and cut angle possible. All hardware in your case will be on the rear side and out of view.

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              • #8
                Re: Open and Wide

                Originally posted by ROTECH View Post
                May I recommend the KREG jig for your baffle wings. The master kit comes with a guide how to make cabinet strength joints with and cut angle possible. All hardware in your case will be on the rear side and out of view.
                Thanks for chipping in this suggestion. I just finished viewing a few web videos on the jig. I maybe leaving the glue bottle on the shelf for the wings.

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                • #9
                  Re: Open and Wide

                  As far as the joints are concerned, build a "male" clamping template, cleat that fits into the back of the joint. If you can't clamp completely, use small screws or finishing nails to attach the baffle to the cleat. Put some wax paper between the cleat & baffle. Maybe a couple band clamps to snug up the joint.
                  Lou's Speaker Site [speakers.lonesaguaro.com]
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                  • #10
                    Re: Open and Wide

                    I ran with ROTECH's suggestion and picked up a KREG jig at Lowes. I went with the K4 version, not the more expensive K4MS option. Working with scrap MDF (not accurately cut or squared) for a proof of concept, I was able to put together these joins in about 15 minutes:



                    There are only 2 variables to play with: the location of the collar on the supplied drill bit, and the screw length. I took a few minutes monkeying around with scrap to get it right for 3/4" MDF. My plan is to use Baltic Birch which is a slightly different thickness, so I may need to monkey a bit more.



                    The KREG jigs are not cheap, but they are extremely easy to use.
                    Attached Files

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                    • #11
                      Re: Open and Wide

                      I have a pair of darn-near identical cabinets from when a friend of mine and I cloned a Proac Future .5 speaker.

                      Challenges you will not see in simulation land: The cupping of the OB mid and reflection off the top of the woofer box.

                      In fact, I am saving those cabs for a CERTAIN SOMEBODY...if he will EVER TAKE THEM they are taking up room in my garage!
                      .

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                      • #12
                        Re: Open and Wide

                        Originally posted by mzisserson View Post
                        I have a pair of darn-near identical cabinets from when a friend of mine and I cloned a Proac Future .5 speaker.

                        Challenges you will not see in simulation land: The cupping of the OB mid and reflection off the top of the woofer box.

                        In fact, I am saving those cabs for a CERTAIN SOMEBODY...if he will EVER TAKE THEM they are taking up room in my garage!
                        I'd be interested in seeing pics of your cab (before they disappear). I wasn't aware of other speakers similar to what I was planning. For OB hybrids I got inspiration from Paul C's Sunflowers, but he employs a U-frame. I also considered a very large radius roundover for edge treatment, but in the end went for angled wings for simplicity of construction and because I like the look. ;)

                        Thanks for the heads-up on the modeling challenges. I think I have accounted for the mid-range dip. It is possible to model in both ABC Dipole and Frequency Response Modeler. I did both and compared the results; they were very similar. You can see it in the response at 1k in the first post.

                        The reflection from the woofer box I hadn't thought of, but don't think I will worry too much about for now.

                        Since then I have decided to go with the Vifa XT19 in stead of Hiq OW1, mostly due to cost reasons. But the modeling results look better too:



                        The midrange dip appears smaller, but I'm a bit surprised by the large cap values in the woofer low-pass. Being where they are in the filter, I plan to use NPE's. I hope this is OK.

                        Attached Files

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                        • #13
                          Re: Open and Wide

                          So you havent done any "playing" yet with the angle of those wings? You should. Install you driver selection on a flat baffle then use some carboard "wings" that you can angle in and out while watching what it does on an RTA like ARTA.
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                          • #14
                            Re: Open and Wide

                            Originally posted by mzisserson View Post
                            In fact, I am saving those cabs for a CERTAIN SOMEBODY...if he will EVER TAKE THEM they are taking up room in my garage!
                            LOL I'll snag them next sunday when I take the breakfast stouts down.

                            http://www.stereophile.com/floorloud...oac/index.html here's a link to what mikes cabs were based on.

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                            • #15
                              Re: Open and Wide

                              Originally posted by jclin4 View Post
                              Okay- what is the notch doing on the woofer? Those values will place the notch in the woofer's passband the way I see it, and are likely a means of doing something that should take fewer components to accomplish.
                              What I think you're using it for is to remove the bump in the woofers' response that comes from using a xover so low in frequency. If you use a higher DCR coil it will minimize this effect, and likely allow you to remove the series 1.2 ohm resistor- which is never a good idea anyway on a woofer.

                              I would also recommend you try a 3rd order electrical on the woofer to tame this easier, and just leave the notch out of it. I'm certain there's an easier way to achieve what you want.

                              As to the NPE caps used, look at the new Audyn caps here at PE- the 100uF cap is only 22 clams.

                              Later,
                              Wolf
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