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Diffraction effects

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  • Diffraction effects

    In terms of diffraction. how does a faceted baffle compare to one using simple roundovers on the edges? Certainly like the appearance of the facets, but it is a lot more work from what I see.

    Steve
    Last edited by skatz; 03-17-2019, 10:44 AM.

  • #2
    I believe facets are not as effective, there is still a sharp transition even though the angle is reduced. Following Bill 4thtry side tower build, he seems to confirm that which is moving him toward the variable radius round-overs instead of his original facet plans.

    Facets look sweet though, I'm really enjoying the current build logs cutting them up. Lots of work and engineering going on.
    Electronics engineer, woofer enthusiast, and musician.
    Wogg Music
    Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat

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    • #3
      Originally posted by skatz View Post
      In terms of diffraction. how does a faceted baffle compare to one using simple roundovers on the edges? Certainly like the appearance of the facets, but it is a lot more work from what I see.
      Distance from the edges is as important as anything.

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      • #4
        I can't remember where, but I've seen some comparisons. Just generalizing (I'm sure the details matter): A round over is best, usually the larger the radius the better; A facet was not as good as a roundover, but was a lot closer to a roundover than a flat edge.

        If you are going to design a crossover using real measurements, you'll get the diffractions on the baffle (no roundover, roundover, or facet) and then try to work out the wiggles the best you can.

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        • #5
          You can simulate with edge and get pretty close. I like the idea of unequal facets to change the diffraction pattern. Like anything else you should look off axis. Here's a Peerless tweeter off axis in 10 degree increments with a faceted baffle.
          John H

          Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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          • #6
            Here's the stuff that Olson did from back in the 50s. The bigger the radius the better. I couldn't find in the mess on my computer, but you might want to look for a white paper from Grimm Audio where they describe the design process of the LS1. If I remember correctly they describe how they decided on the rounded edges of the enclosure.
            Attached Files

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            • #7
              I remember Olson's stuff about the enclosure shape, thanks for the reminder. I guess what I'd like to see is a comparison of the same tweeter in a faceted baffle and in a roundover baffle, but it might be a challenge to decide what are the equivalent positions on the baffles.

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              • #8
                Olson and some other material encountered years go was also used during my research into this aspect. Having the audio smoothly track along/around the round-over versus having the audio follow a linear beam directed from facets made sense for my placement and purpose.

                For me using rounds are more generalized allowing better reproduction in larger variety of spaces where hard angles could cause several un wanted side-effects.

                Didn't read it again but IIRC some benefits or differences:
                • Round is more subtle transition / blending. Larger round-over = more subtle transition (better sound) versus tiny round-over as not enough time exists to transition in a subtle way.
                  • A limitation would include material thickness preventing the max size round-over bit usable at the location. at-least this is probably one of the largest, most encountered issues especially with smaller projects.
                  • I have a fairly decent bit kit up to 3" round available so designs can be pretty flexible.
                • Facet is/can be abrupt transition. Have seen some fairly complex designs for these things, including where it seemed offsetting voice coil distances plaid major roles.
                  • Someone with a very specific room architecture, placement of angles could probably have a hell of a good time bouncing beams around until an audio waterfall absolutely drowns a subject inside a bubble of bliss.

                I'd also imagine situations facets are used with incredible precision to ensure waves are sent like sniper shots precisely toward an area for a boost, cull or other real reason. Someone designing an incredible theater room with OCD-level care paid toward angles would likely have something truly special. With everything lined up just right... mm.

                With the added complexity of atmos done correctly, facets likely gain more utility. I'm talking real atmos with drivers in ceiling, not cheap attempts by bouncing audio at the ceiling trying to fake it.

                Most of this is accurate enough from memory for hand grenades. Folks will debunk as needed.
                Feel free to rip my assumptions apart when wrong, or fix if close.

                Passive Radiators:
                All PR(s) Vd must at-least double all woofer(s) Vd. Calc = Sd x Xmax to get Vd for all PR(s) and all woofer(s). If all PR(s) Vd at-least double all woofer(s) Vd they'll work.
                For woofer(s) with large Xmax vs Sd, all PR(s) with Xmax at-least double all woofer(s) Xmax will work.
                A PR max weight is said to be its Mms x3

                PR Systems - tight focus with key parameters.
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                • #9
                  Originally posted by wogg View Post
                  I believe facets are not as effective, there is still a sharp transition even though the angle is reduced. Following Bill 4thtry side tower build, he seems to confirm that which is moving him toward the variable radius round-overs instead of his original facet plans.

                  Facets look sweet though, I'm really enjoying the current build logs cutting them up. Lots of work and engineering going on.
                  I agree. The sharp edges, even though they were only 45 degrees, were still located roughly 2.5 inches from the center of the tweeter dome, and were going about 60% of the way around the tweeter flange. Also, the fact that this particular tweeter, the Peerless DA25TX00-08, has a very thin faceplate (1/16") with no horn loading, also contributed to the problem. Tweeters with more horn loading tend to send less acoustical energy to the edges and therefore have less diffraction problems.
                  SideTowers: http://techtalk.parts-express.com/fo...corundum-build
                  Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
                  Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
                  Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

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                  • #10
                    Originally posted by skatz View Post
                    I remember Olson's stuff about the enclosure shape, thanks for the reminder. I guess what I'd like to see is a comparison of the same tweeter in a faceted baffle and in a roundover baffle, but it might be a challenge to decide what are the equivalent positions on the baffles.
                    My very next project will be using the same tweeter mounted on a baffle with 1.25" round-overs instead of facets. I will report my findings in a new thread when I get that far. This new baffle will not be exactly the same size, but I have a leftover baffle from the SideTower project that could be used for comparison. I have the FRD's of this tweeter with my original facets and I could round-over the edges of my leftover baffle, take some measurements, and post. Will take me a couple weeks or so to do this if you are interested,

                    What size round-overs do you think I should use on the test baffle?
                    SideTowers: http://techtalk.parts-express.com/fo...corundum-build
                    Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
                    Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
                    Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

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                    • #11
                      I would be very interested to see this comparison.
                      As far as round-over size, I suppose the larger the better vis-a-vis diffraction, but most people are unlikely to go more than a 3/4 " size I would think, so that is probably the choice. It is likely the most practical size.

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                      • #12
                        To me a bad no no I see often is to have the tweeter roughly the same distance from the top and sides of
                        of the box, this might not be the type of "diffraction" you are referring to but these designs are creating
                        huge ripples in the FR and the dimensions are usually close to the wave length of the XO Fc.
                        So its a double mistake when trying to achieve a cohesive transition from mid to tweet.

                        On many high end designs you will see truncated baffles often with additional felt/foam or waveguides.
                        As you can see from the above post it can be quite effective (and baffle width at tweeter is small
                        enough to keep the wavelength out of the XO region.)
                        Guess xmax's age.

                        My guess: 15. His grammar is passable. His trolling is good.

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                        • #13
                          Wolf's "Attitudes" had maybe a 2"? rad. roundover (8 yrs. ago). One of his best. Click image for larger version

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                          • #14
                            Originally posted by xmax View Post
                            To me a bad no no I see often is to have the tweeter roughly the same distance from the top and sides of
                            of the box, this might not be the type of "diffraction" you are referring to but these designs are creating
                            huge ripples in the FR and the dimensions are usually close to the wave length of the XO Fc.
                            So its a double mistake when trying to achieve a cohesive transition from mid to tweet.

                            On many high end designs you will see truncated baffles often with additional felt/foam or waveguides.
                            As you can see from the above post it can be quite effective (and baffle width at tweeter is small
                            enough to keep the wavelength out of the XO region.)
                            This is exactly what I did. A major boo-boo. But I was able to "patch" my mistake with mortite caulking cord and foam rubber.
                            SideTowers: http://techtalk.parts-express.com/fo...corundum-build
                            Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
                            Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
                            Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

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                            • #15
                              Originally posted by skatz View Post
                              I would be very interested to see this comparison.
                              As far as round-over size, I suppose the larger the better vis-a-vis diffraction, but most people are unlikely to go more than a 3/4 " size I would think, so that is probably the choice. It is likely the most practical size.
                              Ok, 3/4" sounds good. I think I will also pick up one of the 1.5" radius roundover bits that Javad is using and see how that compares as well. Larger radii would probably require some type of translam process (too much work).
                              SideTowers: http://techtalk.parts-express.com/fo...corundum-build
                              Totally Flat: http://techtalk.parts-express.com/fo...5-totally-flat
                              Plumber's Delight: http://techtalk.parts-express.com/fo...notech-winners
                              Linehopper: http://techtalk.parts-express.com/sh...Esoteric-build

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