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  • Re: Flex Your PCD Mettle:

    Too bad the midrange dip is still there. John is saying it is a measurement artifact but it shows up in the impedance too...Maybe it is a back side chamfering issue? Wonder if those show up in impedance though?
    ~Brandon

    Soma Sonus
    DriverVault

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    • Re: Flex Your PCD Mettle:

      It's still not listed in the "store" so purchase would be difficult, unless you call them directly.

      The "dip" in response may not be that big a deal depending on where it's crossed to the woofer, baffle shape, and overall system sensitivity.
      R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
      Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

      95% of Climate Models Agree: The Observations Must be Wrong
      "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

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      • Re: Flex Your PCD Mettle:

        Also tried DE10 on PH715 with its asymmetric dispersion pattern, of which neither PE nor Pyle seems to be aware, or they're not telling anyone, at least, even though its obvious just by looking at it. I'll load them into something else to see if they'll do their image stabilization "trick."

        Toggle between inboard and outboard below to see the difference:
        Attached Files

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        • Re: Flex Your PCD Mettle:

          Originally posted by Zilch View Post
          Also tried DE10 on PH715 with its asymmetric dispersion pattern, of which neither PE nor Pyle seems to be aware, or they're not telling anyone, at least, even though its obvious just by looking at it. ...
          :p
          http://www.nytimes.com/2010/10/14/bu...html?src=busln

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

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          • Attached Files

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            • Re: Flex Your PCD Mettle:

              Zilch,
              Did you build out the waveguide forward to help clear the baffle recess? I see the woofer flange under the wg. And I think I see gasket material under there, but can't tell how far forward that is.
              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:

                Despite being recessed, the woofer flange sticks forward of the baffle ~1/8", so I had to make up the difference with thick foam gasket tape.

                Today, I'm using power tools (unsupervised ;) ), and barring incident(s), we'll have the answer here soon. Wavelets indicate I'm on track; if so, I'll post 'em.

                [If not, it is what it is.... :p ]

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                • Re: Flex Your PCD Mettle:

                  What it is is already not too bad, I bet.
                  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
                    What it is is already not too bad, I bet.
                    Yes to that -- I moved the baffle forward 3/4"; only a 1/4" recess remains:




                    Horizontal Polar Response:




                    Horizontal Polar Waterfall:




                    Horizontal Polar Map:




                    Conventional Polar Plot:




                    I've made them toggleable for direct comparison to those in Post #350.

                    It cleaned up considerably, and some of what remains is minimum phase (@ 2 & 3 kHz), now correctable via the crossover filters.

                    [The green tag is the price: $7 the pair, marked down from $12. :D ]
                    Attached Files
                    Last edited by Zilch; 06-08-2010, 05:31 AM.

                    Comment


                    • Re: Flex Your PCD Mettle:

                      Originally posted by Zilch View Post
                      It cleaned up considerably, and some of what remains is minimum phase (@ 2 & 3 kHz), now correctable via the crossover filters.

                      [The green tag is the price: $7 the pair, marked down from $12. :D ]
                      Once you do that will you post verticals?
                      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
                        Once you do that will you post verticals?
                        Yes, that's a routine part of the process, now. Even on this preliminary basis, the forward vertical lobe appears to be quite tall at this comparatively low crossover frequency and close (~9") center-to-center distance between woofer and waveguide. I want to take a closer look at the horizontal polars of both individually for some quantitative guidance as to where we might optimally set the crossover frequency for this combination.

                        For now, here's my theory regarding these findings: while the experts (Linkwitz, Elliott, Zaph, and others) tell us that, in theory, the controlled directivity of waveguides obviates conventional concerns regarding edge diffraction and overhang reflection effects, this is only true in the response region where they have full pattern control. If we use them at lower frequencies in the transition zone where they are losing control, the pattern widens, and they illuminate the cabinet edges, with concomitant consequences. Even where they DO have control, that is not perfect, i.e., the response is not fully attenuated off-axis, and in detail, measurable effects occur there, as well, as may be seen by toggling* between the response curves posted here.

                        Conversely, as the woofer's directivity narrows above a frequency related to its piston diameter, if that is occurring below the crossover frequency, or in the crossover region, its interaction with the cabinet edge is unstable, as well. Bottom line: we cannot mitigate design issues related to directivity but by dealing with them directly; the response anomalies they generate are not amenable to correction via the crossover filters alone, alas.... :(

                        *Toggle: open these two links and click back and forth between them:

                        Before: http://techtalk.parts-express.com/at...3&d=1275942236

                        After: http://techtalk.parts-express.com/at...4&d=1275976679

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                        • Re: Flex Your PCD Mettle:

                          Originally posted by Zilch View Post
                          Bottom line: we cannot mitigate design issues related to directivity but by dealing with them directly; they are not amenable to correction via the crossover filters alone.... :(
                          I see no reason for a frown. That is excellent information to know, and knowing it, can now be accounted for.

                          A clean baffle is a good baffle. Roundovers aren't just nice to look at, they remain functional and a useful tool when creating a completed custom product.

                          R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                          Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                          95% of Climate Models Agree: The Observations Must be Wrong
                          "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

                          Comment


                          • Re: Flex Your PCD Mettle:

                            Zilch, with your vintage cabinets, I'd think some absorbers (wool felt, open-cell foam, etc) on the baffle would help with diffraction effects. Your round pipe insulation didn't help much as I recall but that's closed cell so it acts more like a round reflector than an absorber. Dlr has some nice measurements of the beneficial effects of 1/2" felt on a dome tweeter. You'd probably want something at least as thick as the sidewall overhang.

                            http://www.speakerdesign.net/felt_am...ltssenter.html

                            Dennis

                            Comment


                            • Re: Flex Your PCD Mettle:

                              Originally posted by Zilch View Post
                              ....Bottom line: we cannot mitigate design issues related to directivity but by dealing with them directly; the response anomalies they generate are not amenable to correction via the crossover filters alone, alas.... :(....
                              http://www.nytimes.com/2010/10/14/bu...html?src=busln

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

                              Comment



                              • Edit:
                                Here is RobH's software generated polar plot for the 12" JBL 2206H:




                                And the 10" JBL 2123H:

                                Attached Files

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