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  • Re: Flex Your PCD Mettle:

    I cannot imagine damaging that driver with a 2.83V signal, regardless of frequency.
    Operator error (routine at ZilchLab), amp anomalies/failures, and turn on/off transients are perils best subverted with this precaution. We're talking sub-mm excursion limitations between diaphragm and phase plug here.... :(

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    • Re: Flex Your PCD Mettle:

      Originally posted by Zilch View Post
      I have no clue where the acoustic center of a differential-drive woofer might actually be, but it looks like we're in the realm. Flush mounted, the woofer would be about 1/4" farther back relative to the compression driver:

      In looking back at your post methinks the AC is near the rear flange of the WG
      Regards,
      Dan

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      • Re: Flex Your PCD Mettle:

        Originally posted by Zilch View Post
        Operator error (routine at Zilchlab), amp anomalies/failures, and turn on/off transients are perils best subverted with this precaution. We're talking sub-mm excursion limitations between diaphragm and phase plug here.... :(
        I can see that.

        I turn everything on before I connect the D.U.T. to eliminate such transients.

        That WG seems to like to cross at 2KHz. Perhaps that particular WG should be considered for a smaller woofer, say 10".
        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:

          Do these look better? Graphics are straight from HOLMImpulse
          Attached Files

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          • Re: Flex Your PCD Mettle:

            You may have to elevate the speaker to delay floor bounce. Best location for the mic and midpoint between drivers is about 1/2 ceiling height, where both floor and ceiling bounce are equally and most delayed. That'll get the best resolution at lower frequencies in gated measurements.

            I forget what specific settings I used in HOLM earlier in this thread, but I let it do the gating so that it put out an approximation of minimum phase with the response. I post-processed it to raise the SPL, but did not alter the phase....

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            • Re: Flex Your PCD Mettle:

              Elevate the speaker? Bummer. It is shoved into the bottom half of a 6' tall cabinet....from the rear. Would laying down in the middle of the floor be OK? That probably gives me 8' clear in all directions.

              HOLMImpulse had the automatic gate at something like 1200-1500 Hz. I moved it back down to ~250 Hz based on your notes back at post # 136. I'm guessing that 250Hz is too low for my measuring setup with the mic 24" above the carpeted floor.

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              • Re: Flex Your PCD Mettle:

                That WG seems to like to cross at 2KHz. Perhaps that particular WG should be considered for a smaller woofer, say 10".
                I'm not ready to throw in the towel quite yet. ;)

                I've completed the rest of the minimalist presentation of directivity with the 2452H-SL driver in lieu of 2432H above:

                http://techtalk.parts-express.com/sh...46#post1662446


                The directivity is "regular" except at 1.2 and 2 kHz. Owing to its spike at 20 kHz, the hill/valley anomaly is best seen in normalized plots with this driver:






                I'm also seeing that steeper filters do not allow as much "blending" of woofer and waveguide directivities in the crossover region.... :o
                Attached Files
                Last edited by Zilch; 08-16-2010, 07:51 PM.

                Comment


                • Re: Flex Your PCD Mettle:

                  Originally posted by donprice View Post
                  Elevate the speaker? Bummer. It is shoved into the bottom half of a 6' tall cabinet....from the rear. Would laying down in the middle of the floor be OK? That probably gives me 8' clear in all directions.
                  That works, but you may want to elevate it on some short stands there, as well; lower frequencies wrap around the cabinet. Unless someone with experience doing that knows otherwise, I'd say that may be your best option in this instance....

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                  • Re: Flex Your PCD Mettle:

                    Measured at 44" on axis, midway between drivers, 54" above floor, 61" below ceiling. Gate values picked by HOLMImpulse.

                    First graph is the drivers measured independently. Second graph is both drivers at same time (w/36 uF cap on HF) measured with normal and reversed phase.

                    I doubt the FR curve for the DE250 means much below 500 Hz or so. Playing with the gate value makes it drop off the chart at 500Hz (which was where the sweep started).
                    Attached Files
                    Last edited by donprice; 08-10-2010, 07:50 PM. Reason: HF horn isn't as boomy as curve says.

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                    • Re: Flex Your PCD Mettle:

                      Originally posted by NEO Dan View Post
                      In looking back at your post methinks the AC is near the rear flange of the WG.
                      Attached Files

                      Comment


                      • Re: Flex Your PCD Mettle:

                        The on axis looks pretty good. However, there seems to be a bit of extra energy below 1KHz that may present a more "forward" sound. Is there any way to raise the tweeter level uniformly? Looks like it could use at least 1dB extra across the band.
                        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:

                          Originally posted by donprice View Post
                          Measured at 44" on axis, midway between drivers, 54" above floor, 61" below ceiling. Gate values picked by HOLMImpulse.
                          I'm liking that much better, but look where my gates were:

                          http://techtalk.parts-express.com/sh...16#post1633716

                          I vaguely remember sliding those manually to superimpose at 250 Hz for the display. You can see where they are falling on the impulse, just before the first reflection. HOLM sets where time zero begins and calcs minimum phase from there, was my assumption....

                          Comment


                          • Re: Flex Your PCD Mettle:

                            The on axis looks pretty good. However, there seems to be a bit of extra energy below 1KHz that may present a more "forward" sound. Is there any way to raise the tweeter level uniformly? Looks like it could use at least 1dB extra across the band.
                            SURE, our trusty L-pad! :D

                            Attached Files

                            Comment


                            • Re: Flex Your PCD Mettle:

                              Originally posted by Zilch View Post
                              SURE, our trusty L-pad! :D

                              Nice, easy, very cool.

                              Looks like you overshot just a tad. :p
                              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:

                                O.K., I'll notch out the spike and fix the directivity, then provide new measurements so Pete can make it play flat as Nebraska.... ;)

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