Today, UPS delivered my replacement Motu A16. I got it plugged in and turned it on to something like this:
That was actually snapped while I tried to update the firmware in hopes that it would fix the problem. Nope. It looks like the front display is bad on this one. On the upside, all the inputs and outputs at least appear to work. Still, receiving a replacement unit with a defect that any casual QC would have revealed does not inspire confidence. What really burns is that I can use this thing with the display broken, but it's a major nice-to-have because it has level meters for all 16 inputs and outputs. And of course, there's the principle of holding the company responsible for delivering a fully working product to me. I just hope they'll *at least* cover my side of the shipping this time around.
On another note, I forgot to mention a few other things about the surround design.
First, I modelled a ported version of the two TD6Hs, but I didn't like what I saw. These woofers seem to want a big box with a low tuning frequency, despite their small size. Otherwise the result is way too resonant and/or the ports can't be made to fit without unacceptable port velocities. Even in the large/low alignments, there's still some roll-off in the 100-300 Hz range due to the extreme over-damped nature of the driver. Where these woofers seem to excel is in providing a good balance of sensitivity and bass response in a very tiny box that's intended to be used in a car or other environment in which room gain makes up the difference.
The other thing I worked out is that the acoustic interaction of the surround speaker with the ceiling is actually fairly simple to model by treating the ceiling as a mirror plane. Instead of thinking about reflections, I can instead consider the ceiling to be transparent and that a mirror image of the speaker exists above the plane of the ceiling. In other words, our modelled speaker is actually two horns high and four woofers tall. The mirror image is inverted, as would be expected for a mirror. In other words, the bottom of the real speaker is actually the top of the mirrored speaker. Using this analogy, I can understand how the ceiling reflections are heard by the listener by simply looking at how all the different sources (real and mirror) interfere with one another.
Right away, I can say that I don't want two horns at different locations playing together. That creates a lot of nasty comb filtering. Hence, I'll want to "block out" the sound from the horn above the plane of the ceiling. I can do this by acoustically treating the part of the ceiling through which the sound from the mirrored horns would travel to the listeners. I want either good high frequency absorption or diffusion. The up-side to using diffusion to to preserve high frequency room energy and improve spaciousness of the sound. The down-side to using diffusion is that some sound still gets reflected to the listener, which blurs the otherwise sharp images produced by the images. For surrounds, the diffusion should work fine. I'm thinking 2D grid-style diffusers would look super cool and would be totally called for as a lot of HF energy hits that area of the ceiling.
It gets even more interesting when I consider the four vertically-stacked woofers (two real and two mirror images). The presence of four woofers means we get double the bass output for free, which is of course what we expect with wall-ceiling corner loading. However, those four vertically-oriented woofers also have a pattern that extends to a much lower frequency, and indeed, the pattern at higher frequencies is both too narrow and full of lobes in the listening area. So we also need acoustic treatment to selectively absorb or scatter the mid-range, roughly down to a frequency at which the pattern is not so yucky. I haven't done the calculations, but my rough estimate suggests the center lobe will be -6 dB @ 90 degrees at a frequency at least as low as 500 Hz. Unfortunately, low frequency directivity like that isn't really desirable if the pattern widened somewhere between there and the crossover. I may have to want to absorb or break-up frequencies even lower than 500 Hz. That's kind of a bummer, because I'm not sure I can adequately scatter sound much lower than 1000 Hz or so. Instead, I may need to use absorption to get the best 250-1000 Hz response at the seats. Some 4" OC703 right on the ceiling would probably work great and would not absorb too much bass.
One more thought is that if I could somehow take an SEOS horn and cut it perfectly down the middle, then I could mount the cut edge perfectly flush with the ceiling. The inverted mirror image would complete the half horn into a full horn again. If I could do this and opted for a different woofer layout (horizontal MTM?), I wouldn't have to treat the ceiling at all. I'd also benefit from a doubling of output across the entire spectrum. Not bad ehh? Of course, it's just a bit impractical due to what you'd have to do with the compression driver. You can't exactly cut it in half. I won't say it's impossible, but I'll leave that for someone else to experiment with.