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The SideTowers - An F6 Corundum Build

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  • #31
    Originally posted by 4thtry View Post
    Here are a few measurements. Polars look good. Z curve looks like an easy load for amp. Well balanced sound as I move about the room, stand, or sit down. BSC seems about right so far, need to compare it to some other speakers before making adjustments.

    Note that the tweeter's on-axis FR has a dip at 4.6kHz that completely disappears when you move slightly off-axis in either direction. Very strange. It is not caused by the protective screen or xover, as I get the same dip with or without the screen or xover installed. 4.6kHz has a half wavelength of roughly 1.5". I have a guess as to what is happening here, but will need to run a few more tests to see if I am on the right track.
    That dip appears to coincide with a peak in the woofers response on your xover sim pic, I would have to agree with wolf.

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    • #32
      Originally posted by AdamM3 View Post
      That dip appears to coincide with a peak in the woofers response on your xover sim pic, I would have to agree with wolf.
      If you look at the sim, you can see the red line doesn’t drop below the black, which means it’s not a cancellation. It’s in the actual tweeter measurement, not just the system response. It looks like Bill has the woofer surface mounted so my guess would be reflection off the woofer frame causing diffraction. This would also be why it disappears off-axis.
      -Kerry

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      • #33
        Thank you for the suggestions. Yes, I agree, this is a very serious problem, as the ear is very sensitive in this frequency range.

        I tested the speaker with the crossover and the woofer completely disconnected, with only a 50uF protection cap in series with the tweeter. The dip remains the same.

        So it seems that this is being caused by some type of reflection from the baffle or woofer flange. Tomorrow, I will cut up a series of foam or felt strips and stick them along the edge of the woofer flange to see if that makes a difference.
        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

        Comment


        • #34
          Originally posted by Navy Guy View Post
          If you look at the sim, you can see the red line doesn’t drop below the black, which means it’s not a cancellation. It’s in the actual tweeter measurement, not just the system response. It looks like Bill has the woofer surface mounted so my guess would be reflection off the woofer frame causing diffraction. This would also be why it disappears off-axis.
          Good point, I stand corrected.

          Comment


          • #35
            That's what I had to do in my Cecropia build. The faceted ridges needed the felt badly, and it did fix the issues.

            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


            • #36
              Cool looking design and craftsmanship, I expect they will image very well...

              Can you hear that dip in the tweeter? If it is only on one axis, it may not be an issue at all.

              Comment


              • #37
                Originally posted by Billet View Post
                Cool looking design and craftsmanship, I expect they will image very well...

                Can you hear that dip in the tweeter? If it is only on one axis, it may not be an issue at all.
                Thanks, Bill. At a distance of about 6 feet, as I move my head from side to side (or up and down) by about 10 to 15 degrees, the overall tonal balance remains the same. The speaker does not, all of a sudden, sound dull in the 3-7kHz region when I listen directly on-axis. But I can detect a slight change in the imaging, kind of a "phasy" type quality, which seems to do something to the soundstage. Still working with pieces of felt around the edges to see if I can clear up the problem.
                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

                Comment


                • #38
                  Looking good Bill! You can always do a near field on the tweeter then back away to see where the dip occurs.
                  John H

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

                  Comment


                  • #39
                    Originally posted by jhollander View Post
                    Looking good Bill! You can always do a near field on the tweeter then back away to see where the dip occurs.
                    Thanks for the tip, John. Here is what I get by following your suggestion:


                    1) Mic 6" or less from the tweeter protective shield, on axis with dome: At this distance, the dip at 4.6khz does not exist. Response is very flat from 3-15kHz. And no dip can be seen as I move the mic up or down or side to side 0-30 degrees.

                    2) Mic approx 8" away. A very slight depression (approx 1dB) begins to appear at 4.6kHz on axis. But this slight dip goes away as I move the mic up or down or side to side 0-30 degrees.

                    3) Mic approx 12" away. The dip on axis is now approx 3dB centered at 4.6kHz. The depression begins at about 3kHz and ends at about 7kHz. As before, the dip goes away as I move the mic up or down or side to side 0-30 degrees.

                    4) Mic approx 20" away. The dip on axis is now approx 5dB centered at 4.6kHz. Again, the depression begins at about 3kHz and and ends at about 7kHz. As before, the dip goes away as I move the mic up or down or side to side 0-30 degrees.

                    5) Mic approx 30" away. No change, same as #4.


                    Seems promising. Will continue to experiment until I solve the problem.
                    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

                    Comment


                    • #40
                      From Edge
                      John H

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

                      Comment


                      • #41
                        off axis, note 1 db scale
                        John H

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

                        Comment


                        • #42
                          So the facets are doing more harm than good here...
                          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


                          • #43
                            Yeah looks like it. The starting edge of the facets lie almost equal distant from the dome around 2/3 to 3/4 of the tweeter's circumference. So there is a pronounce diffraction effect just like John's sim shows.
                            Craig

                            Comment


                            • #44
                              It looks like an asymmetric baffle would minimize the diffraction lumps in the higher frequencies. The SB Acoustic Rinjani and Ara kits are using a unique faceted baffle. http://www.sbacoustics.com/index.php...-kits/rinjani/
                              John H

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

                              Comment


                              • #45
                                After several days of testing, I am starting to reach some conclusions as to what is causing the 4.6kHz response dip. I taped a temporary cardboard template over the facets to flatten them out to see what happens. I also removed the woofer and taped a piece of fiberboard over the woofer hole to eliminate the woofer flange reflection from my measurements.

                                Switching back and forth with the OmniMic sine sweep running, the dip seems to be mainly caused by the proud, surface mounted woofer flange, especially the part of the woofer flange and surround located closest to the tweeter. The faceting also appears to be enhancing the 4.6kHz dip, but only by about 1dB or so. Most of the dip appears to be coming from the proud woofer flange. To confirm this, I ran a test with the woofer removed and replaced by a flat surface and the dip almost completely disappears (no change to the facets).

                                Also, if I cover the baffle, up to the edge of the woofer flange, with 1/16" foam rubber and then cut a small 1.625" hole to expose the tweeter dome, wrapping this foam tightly around the facets, the dip at 4.6kHz almost completely disappears, both on and off axis. I can also eliminate most of the dip by placing two 1/16" thick foam rings around the tweeter dome (no other changes).

                                Attached are a couple graphs showing my results so far. Looks very promising.
                                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

                                Comment

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