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  • Re: Flex Your PCD Mettle:

    Hey Z, do you have an automated system for taking those 36 measurements for the polar maps? If not, it's got to get pretty boring tweaking that turntable in 5 deg. increments over and over again. :D

    BTW, thanks for the wavelet links!
    Live in Southern N.E.? check out the CT Audio Society web site.

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    • Re: Flex Your PCD Mettle:

      Originally posted by Mayhem13 View Post
      Build a sub!:D
      or three!

      Comment


      • Re: Flex Your PCD Mettle:

        Originally posted by carlspeak View Post
        Hey Z, do you have an automated system for taking those 36 measurements for the polar maps? If not, it's got to get pretty boring tweaking that turntable in 5 deg. increments over and over again. :D
        Oh, the EXCITEMENT! :p

        It takes about an hour to do one, but we sure have learned a bunch from them.

        [It's 19, actually; I just click the "mirror" button with these symmetrical designs.... ]

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        • Re: Flex Your PCD Mettle:

          Originally posted by Zilch View Post
          Oh, the EXCITEMENT! :p

          It takes about an hour to do one, but we sure have learned a bunch from them.

          [It's 19, actually; I just click the "mirror" button with these symmetrical designs.... ]
          I thought it was 90 deg each side of zero deg. to map the entire shape.
          90/5=18X2=36.
          Is your turntable automated? or do you move it manually ea. 5 deg?
          Live in Southern N.E.? check out the CT Audio Society web site.

          Comment


          • Re: Flex Your PCD Mettle:

            Originally posted by carlspeak View Post
            I thought it was 90 deg each side of zero deg. to map the entire shape.
            90/5=18X2=36.
            Is your turntable automated? or do you move it manually ea. 5 deg?
            Last edited by Zilch; 09-09-2010, 03:15 AM.

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            • Re: Flex Your PCD Mettle:

              We all appreciate your hard work, Zilch. One small quibble with the polar measurements: your axis of rotation appears to overstate the directivity a bit, i.e. the AC is moving farther from the mic as it rotates. You're showing 'constant directivity' on the polar maps down to 300 or so when we all know the woofer is nearly omnidirectional down there. Like I said, a small quibble.
              Dennis

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              • Re: Flex Your PCD Mettle:

                Originally posted by Dennis H View Post
                We all appreciate your hard work, Zilch. One small quibble with the polar measurements: your axis of rotation appears to overstate the directivity a bit, i.e. the AC is moving farther from the mic as it rotates. You're showing 'constant directivity' on the polar maps down to 300 or so when we all know the woofer is nearly omnidirectional down there. Like I said, a small quibble.
                Attached Files
                Last edited by Zilch; 09-09-2010, 04:31 AM.

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                • Re: Flex Your PCD Mettle:

                  There's always concern, as mentioned above, that variability among drivers will render the crossover design an academic exercise. In this case, the woofers are very old (date code 391742?) and of indeterminate provenance. The moment of truth comes with swapping in a different driver set (the 4555 also) and clicking the "Start Measure" button:




                  L-pad's at 1:00, and as in other recent designs, I have further provided means to adjust the HF "tilt," i.e., alter the power response. It's running the red curve right now:



                  In this instance the new baffle has a 3/4" rounded over woofer cutout, as well. We'll see if that has significantly altered the directivity, next....




                  Toggle:

                  http://techtalk.parts-express.com/at...7&d=1284011969

                  http://techtalk.parts-express.com/at...7&d=1284178267




                  Toggle:

                  http://techtalk.parts-express.com/at...9&d=1283925332

                  http://techtalk.parts-express.com/at...1&d=1284179200


                  Attached Files
                  Last edited by Zilch; 09-11-2010, 06:08 PM.

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                  • Re: Flex Your PCD Mettle:

                    Those woofers are tight!
                    Are both red and green from the top graph mounted in the round-over baffle(s)?
                    http://www.nytimes.com/2010/10/14/bu...html?src=busln

                    http://mixonline.com/mag/audio_new_york_metro_46/

                    Comment


                    • Re: Flex Your PCD Mettle:

                      Originally posted by Skywave-Rider View Post
                      Those woofers are tight!
                      Are both red and green from the top graph mounted in the round-over baffle(s)?
                      No roundover in the red one; tryin' to see the difference.

                      Click the toggles, two sets, now....
                      Last edited by Zilch; 09-11-2010, 02:41 AM.

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                      • Re: Flex Your PCD Mettle:

                        On the horizontal polars, toggling between round-over and not, I believe the round-over distributes the energy better. If you can post an image of the rounding, that would be great.

                        Looking at the second set you just posted makes it easier to see. Not sure what you did with the gain.
                        http://www.nytimes.com/2010/10/14/bu...html?src=busln

                        http://mixonline.com/mag/audio_new_york_metro_46/

                        Comment


                        • Re: Flex Your PCD Mettle:

                          Zilch, if you choose to go with a round-over does that mean you would take new base measurements for both drivers on the baffle and bring those into PCD? I am asking because it seems to affect the on-axis response.
                          http://www.nytimes.com/2010/10/14/bu...html?src=busln

                          http://mixonline.com/mag/audio_new_york_metro_46/

                          Comment


                          • Re: Flex Your PCD Mettle:

                            Zilch, could we do less smoothing on those? That might make the difference more easily visible.

                            Dan
                            "guitar polygamy is a satisfying and socially acceptable alternative lifestyle."~Tony Woolley
                            http://dtmblabber.blogspot.com/
                            http://soundcloud.com/dantheman-10

                            Comment


                            • Re: Flex Your PCD Mettle:

                              Did you change the core filter in the second set?

                              OK, I'll shut up now....
                              http://www.nytimes.com/2010/10/14/bu...html?src=busln

                              http://mixonline.com/mag/audio_new_york_metro_46/

                              Comment


                              • Re: Flex Your PCD Mettle:

                                The earlier directivity maps were made with the red driver set and baffle without roundover, V1.1 XO; the new ones with V1.2, which is +/- 0.25 dB flatter. The Red/Grn comparison is both with XO V1.2. I suppose it would be more definitive if I were now to move these drivers onto the non-roundover baffle and remeasure the directivity, but I believe the trend is clear -- the roundover is better in the region of interest, but not hugely so. There's more baffle work to be done; the improvements are incremental at this point.

                                Yes, I can reprocess with less smoothing, but that may obscure what we're looking for. Here's the normalized views at 1/6 octave, which should ignore the small response differences:



                                Attached Files
                                Last edited by Zilch; 09-11-2010, 04:53 AM.

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