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MTM driver spacing using XDIR

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  • #31
    80 degrees is too narrow, assuming you have an audience of more than one or two. Keep in mind that 80 degrees is a nominal average, and that it will be narrower than that as you go higher in frequency.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • #32
      This may be of interest in the discussion of MTM, particularly in comparison to an equivalent MT. This is from John k's archived site, page 5:

      Consideration of Power Response in Speaker Design

      In short, these results show the general trend that even order LR type crossover can be expected to perform worse in an MTM format than their MT counterparts both in power and polar response. Butterworth crossovers, by contrast, show the well known improvement in polar response is at the expense of some degradation in the power response. Still, if an MTM design is favored it would appear that odd order crossovers are superior to even order ones.
      dlr
      WinPCD - Windows .NET Passive Crossover Designer

      Dave's Speaker Pages

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      • #33
        Originally posted by billfitzmaurice View Post
        80 degrees is too narrow, assuming you have an audience of more than one or two. Keep in mind that 80 degrees is a nominal average, and that it will be narrower than that as you go higher in frequency.
        Got it. Thanks for the added context.
        Indeed, in the TPL-150H, per Beyma graphs, horizontal directivity stays at 80 degrees up to 10kHz, then narrows to 60 degrees by 20kHz - and I believe I can't hear much past 15kHz
        In this setup, the audience is one or two, generally one dead center at the vertex of an equilateral triangle with the speakers, and speakers can be toed-in so the listening position could be on-axis with the tweeter. And if I had a 2-people audience and moved the seats to accommodate both as close to the center line as possible, both seats would be within 30 degrees from the tweeter axis (60 degree dispersion).

        In that context, does using the TPL-150H and seating 6-7 feet away look like a bad idea?

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        • #34
          The midbass driver spacing on the original D'Appolito 4/84 design was 9.25 inches center to center with the crossover at 2 khz.

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          • #35
            Originally posted by dlr View Post
            This may be of interest in the discussion of MTM, particularly in comparison to an equivalent MT. This is from John k's archived site, page 5:

            Consideration of Power Response in Speaker Design



            dlr
            Oddly enough, no one told the MTMs that they can't work with LR4, and even sound pretty darn good.
            Francis

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            • #36
              The problem with looking at polars with different crossover slopes is the result depends on the distance they're measured at. With sufficient distance the three wave fronts will all integrate into one coherent wave front, no matter what the crossover slope may be.
              www.billfitzmaurice.com
              www.billfitzmaurice.info/forum

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              • #37
                Originally posted by fpitas View Post
                Oddly enough, no one told the MTMs that they can't work with LR4, and even sound pretty darn good.
                It was a theoretical analysis, just as D'Appolito did in describing the MTM configuration and Linkwitz did in describing the L-R crossover and it's off-axis response vs. other standard crossovers of the day. John's point was that power response of LR4 is slightly degraded vs. power response of Butterworth. Where did you see John say that LR4 can't work?

                dlr

                p.s. Added a bit more below.
                WinPCD - Windows .NET Passive Crossover Designer

                Dave's Speaker Pages

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                • #38
                  Originally posted by billfitzmaurice View Post
                  The problem with looking at polars with different crossover slopes is the result depends on the distance they're measured at. With sufficient distance the three wave fronts will all integrate into one coherent wave front, no matter what the crossover slope may be.
                  You missed the point of John's comment on the analysis. It had to do with the polar and power responses, not the integration of the on-axis response. All non-coincident systems will have irregular vertical off-axis response lobes. No reasonable amount of distance can eliminate these lobes. The analysis demonstrates that for an MTM, the vertical off-axis lobes and the power response will be degraded for an LR4 vs B3. No amount of distance alters this fact. That is the only reason I posted it, as information on the theory of it. It has nothing to do with integration at a distance nor is the analysis affected by consideration of any normal distance.

                  dlr
                  WinPCD - Windows .NET Passive Crossover Designer

                  Dave's Speaker Pages

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                  • #39
                    My own experience with BW3 vs LR4 for my MTMs: BW3 gave a floor-to-ceiling image, LR4 gives a pinpoint image at horn height, the center of the array. The huge vertical image from BW3 was kind of novel, but not very realistic. The LR4 image is very realistic; one can easily envision an actual person or instrument there. Also, LR4 gives limited vertical directivity, which definitely aids clarity.
                    Francis

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                    • #40
                      Originally posted by fpitas View Post
                      My own experience with BW3 vs LR4 for my MTMs: BW3 gave a floor-to-ceiling image, LR4 gives a pinpoint image at horn height, the center of the array. The huge vertical image from BW3 was kind of novel, but not very realistic. The LR4 image is very realistic; one can easily envision an actual person or instrument there. Also, LR4 gives limited vertical directivity, which definitely aids clarity.
                      I have and continue to question this kind of assessment, but to each his own. Floor to ceiling image vs pinpoint when the difference is in a very narrow range? I can only say that I have never detected a vertical image change between BW3 and LR2 or LR4. What is most often overlooked is that the difference in the off-axis is strictly in the crossover region, a narrow region, more narrow the higher the order. Outside of that the off-axis of any kind of crossover network used is essentially identical and that is the majority of the bandwidth, so what you're saying is essentially that the region outside of the crossover has no influence over the vertical imaging, it's all in the crossover region. I've had 3-way Butterworth in a standard WMT auditioned at DIY NE. I and most attendees preferred the BW1 version vs. LR2 in this case, a broader bandwidth overlap. Power response is, IMO, the primary reason for perceived differences when the on-axis is identical, which it was in my case as I was using the Ultimate Equalizer for flat SPL and phase on-axis. Remember as well that inverting an odd-order Butterworth leaves the on-axis flat, but inverts the lobe positions, so if you're sensitive enough to tell the difference between LR4, then you should be able to compare BW3 for the two connections. Have you ever inverted for comparison? One will place the lobe above the on-axis with the null below, reducing any floor reflections vs. the inverse. But this is strictly in a limited area around the Fc, so the impact is limited to that small bandwidth.

                      dlr
                      WinPCD - Windows .NET Passive Crossover Designer

                      Dave's Speaker Pages

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                      • #41
                        Originally posted by dlr View Post
                        I have and continue to question this kind of assessment, but to each his own. Floor to ceiling image vs pinpoint when the difference is in a very narrow range? I can only say that I have never detected a vertical image change between BW3 and LR2 or LR4. What is most often overlooked is that the difference in the off-axis is strictly in the crossover region, a narrow region, more narrow the higher the order. Outside of that the off-axis of any kind of crossover network used is essentially identical and that is the majority of the bandwidth, so what you're saying is essentially that the region outside of the crossover has no influence over the vertical imaging, it's all in the crossover region. I've had 3-way Butterworth in a standard WMT auditioned at DIY NE. I and most attendees preferred the BW1 version vs. LR2 in this case, a broader bandwidth overlap. Power response is, IMO, the primary reason for perceived differences when the on-axis is identical, which it was in my case as I was using the Ultimate Equalizer for flat SPL and phase on-axis. Remember as well that inverting an odd-order Butterworth leaves the on-axis flat, but inverts the lobe positions, so if you're sensitive enough to tell the difference between LR4, then you should be able to compare BW3 for the two connections. Have you ever inverted for comparison? One will place the lobe above the on-axis with the null below, reducing any floor reflections vs. the inverse. But this is strictly in a limited area around the Fc, so the impact is limited to that small bandwidth.

                        dlr
                        It's MTM. Inverted BW3 or not, the lobe is only forward.
                        Francis

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                        • #42
                          Originally posted by fpitas View Post
                          It's MTM. Inverted BW3 or not, the lobe is only forward.
                          You're right, for MTM, I was thinking of MT.

                          But the rest stands. The difference is only within a range around Fc. BW3 has a much smoother vertical polar response in the crossover area and a smoother power response.

                          dlr
                          WinPCD - Windows .NET Passive Crossover Designer

                          Dave's Speaker Pages

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