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best MTM /best drivers for MTM ?

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  • #16
    Originally posted by donc View Post
    if you were to build a high end MTM would you use Satori ,Revelators or Illuminators ? for tweeter ribbon , beryllium or other ?
    If "high end" translates to larger budget... I would change up the MTM to another different pair-wise symmetric multi-way floor standing loudspeaker centered on a coaxial instead of a simple tweeter.

    The KEF LS50 Meta small monitor exhibits good performance. I would look at stripping a lightly used pair of those to repurpose the coaxial and passive crossover, would keep the same baffle width (7.9 inch), and would use DSP crossover to shape the response of each active section. The good performance of the LS50 Meta can be retained and utilized using a hybrid passive and active crossover.

    To the aforementioned coaxial, in each floorstanding loudspeaker, include a quad of RS180-8 midwoofers in sealed alignment (two above and two below the coaxial) and a single side firing RSS390HF-4 at the bottom keeping the same 7.9 inch front width all of the way down. Maybe use two boxes, a shallow box up top and deeper box at the bottom with the lower box extending back to near the wall behind.

    In the upper box, locate the inner pair of midwoofers with minimized CTC distance mirrored about the coaxial and wire the inner pair in parallel. Likewise wire the outer pair in parallel, and wire the two pairs in series while bypassing the outer pair with a capacitor. That forces the inner pair to dominate the quad at higher frequencies in the region of the crossover to the center coaxial. The outer pair is included at lower frequencies and serves to nearly halve excursion of each midwoofer in the quad while having little effect in the radiated SPL in the passband, rather just serves to spead the swept volume across the four drivers providing some reduction in nonlinear distortion on high level crests in the signal. Recall that below the baffle step in sealed alignment, halved frequency requires quadrupled excursion for constant SPL, flat response. So the outer woofers are worthwhile in the bottom octave of the bandpass of the midwoofer quad.

    While I did not model those RS180-8, PE's webpage claims F3 acoustic high pass corner at 105_Hz from the sealed alignment (0.16ft³ for each, 0.64ft³ for a quad). Giving PE the benefit of the doubt in their models, and cascading another 2nd order with the DSP, that would be a good crossover point LR4 to the side firing RSS390HF-4 (utlized as woofer, not subwoofer) using the DSP crossover. You can find ways of spending a lot more, but these drivers should perform well in the target passband. I am not suggesting pair-wise symmetric RSS390HF-4, rather just one side firing in the bottom section of each floorstanding loudspeaker, and augment those with separate subwoofers.

    Do the DSP in software.

    An Okto Reasearch DAC8 Pro could provide a good audio front end. Among other features it includes eight channels of very high quality DA conversion with balanced outputs and bespoke custom output voltage along with integrated volume control and a remote control. That could provide output for two 3-way DSP active crossovers plus two separately filtered subwoofers.

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  • #17
    The only thing I can see about an MTM that would make a difference is vertical dispersion pattern. Because of that, I would expect a tall, skinny tweeter to work better than a round one. HiVi RT2C, for instance. Or B&G Neo8, if you are willing to listen off axis. GRS PT6816, on a budget.

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    • #18
      I used Scan-Speak midranges 15M/8631G00 as midbass drivers with Mundorf 21CM2.1-С tweeter.
      8 Ohm Revelator midranges have higher BL/Mms, than 4 Ohm 15M/4531.
      MTM has 6dB higher SPL and lower THD as the power applied to each driver is much lower at the same SPL level. Click image for larger version

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      Crossovers are outside: the design was not finished at the time the photo was taken.

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      • djg
        djg commented
        Editing a comment
        The look of a true enthusiast.

    • #19
      MTMs don't have to be odd order slopes. I've heard some nice Audio Concepts kits with 12/12 slopes. I'm just a D'appolito nut. They do give a
      point source presentation when properly implemented unlike the 12/12s. Not only imaging but the frontal lobe only has an on axis listening area of about
      +/- two feet in the vertical axis. Everything else is off axis and mid and upper frequencies are rolled off to minimize ceiling and floor reflections.
      Yet horizontal dispersion is excellent. Stereo imaging is good from anywhere in the room. I built mine over 20 years ago so drivers are NLA but
      Ebay has many still available of these very high end drivers from Dynaudio and Focal. I'm not much impressed with the newer stuff mainly due
      to the lower efficiency of many modern drivers and the use metal cone drivers. They just don't sound right to me.

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