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Smaller OS MMTMM center? (Warning: Newb With A Bad Idea)

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  • Smaller OS MMTMM center? (Warning: Newb With A Bad Idea)

    So, lonnnng time lurker, first time poster. (Thought I had an account years ago, but couldn't find it. Please don't write me off as a spammer! ; ) ) Read and lurked and enjoyed and learned for years. Built a pair or two of speakers and a sub or three here and there, but never anything interesting enough to post, and always someone else's work / kit.

    (n.b.: I type way too quickly *and* err on the side of giving plenty of information... this got long... sorry!)

    In other words, I know enough to know I don't know anything, and this is almost certainly all a dumb idea -- I have read, many times, the good advice "don't design your own crossover!" -- and this tinkering only seems rational because I don't know enough to know I'm wrong. ; ) But, hey, I need a distraction right now, ok?

    So, anyway, hoping for some help here... maybe I missed a good existing design, or maybe y'all can help put one together?

    Here's the challenge:

    I have two new TVs that deserve better sound, with the now common "feet out at the outer edges"-style stands. They're sitting on a dedicated bookshelf / console, and that empty space under the screen is just crying out to be used, in a mixed-room/WAF-friendly way. No "critical listening," no "dedicated room," but hoping for something DIY and better (and lower cost) than a commercial soundbar, ya' know? I have looked and looked for a short center that would slot into that gap, but to no avail. There are two that were promising, the Cynosure and the Overnight Sensation MMTMM... but they're both too tall.

    There's 2.5" to work with, but width might as well be unlimited and depth is about ~10". And I can't help but think that a decent design could be useful to others, since nearly every big tv these days comes with that style stand.

    I started obsessing about that notion -- "Is there a way to make an even slimmer center?"

    I toyed with the notion of an L-shaped cabinet for the OS mmtmm, hanging the drivers off the front, and calling it done, and may still end up with that. But that's going to be tricky, and likely look weird, at _best_.

    Then I got all foolish and downloaded XSim and started poking around. (Like I said: Newb with a bad idea!) I initially wanted to try just swapping in the 2" version of the driver used in the OS MMTMM, but I couldn't find the frd and zma files, and trying to trace the plots I could find was not confidence inspiring. So I dove into PE's woofers, found the 2" DMA-58-4, and was off to the races. Hey, it was even a buck or so cheaper each, too! Win!

    I learned a bunch about the parts involved in the crossover and what they did (even if I don't quite have a handle on the terminology yet), just by playing with XSim (which is AWESOME, if perhaps too confidence inspiring, making me think this is worth even thinking about!), starting with the public XO for the OS mmtmm, and spending a lot of time googling and reading and trying to figure out what I was getting myself into. Played with several different tweeters, went down dead ends, etc. Then there was WinISD to figure out! Etc.

    If nothing else comes of it, I've enjoyed the learning and the distraction, and am grateful to everyone who contributes their knowledge so generously to let me learn this much.

    Rooms are mixed-use; the living room tv is in a corner and just uses bookshelves as mains (about to be replaced with a pair of C-Notes, in fact, thanks to a PE kit in progress!); the "theater" room has a pair of 8"+waveguide speakers designed from another site, with two 12" subs for the bottom (CL finds likely to get remodeled, but that's a different project), and will eventually get cheap in-walls for rears... maybe. I know I should put a matching center in there, but (a) don't have the space as-is and (b) the tweeter is NLA so whatever I would do wouldn't match... and the center will only be used occasionally when watching a movie... most of the use is just 2-channel stereo, I've come to realize. Listening levels for movies are almost never above -15 at most, anyway, so a simple, small center might be enough.

    I should probably just stick with a phantom center, but I need a project, and curiosity has me wanting to build something... if I stick a spare bookshelf speaker in front of the tv, it has promise, but I'm not sold yet.

    Long way of saying:

    1) Does anyone know of a center that is less than 2.5" high already designed and public?

    2) If not, is throwing together one based on the HiVi B2S a better idea, and/or easy for someone with the data / knowledge I lack?

    2) Is the below the _worst_ idea? If not, should I dive in, or could it be improved / fixed? Seems like BOM cost comes out at about $100, which would be _perfect_ for my cheapskate self, but, while I feel like the squiggly lines look as good as some other public projects, I really don't know what to watch out for. WinISD says a ~3L box tuned at ~120hz even gets it a helpful boost from 100-150, if I'm reading it right, and it'd be cut over around 100 hz to the subs...

    What am I missing?

    I do have a UMIK to test results (well, as much as a newb can) but not the gear required for more sophisticated driver testing...

    I nearly just pulled the trigger on parts to throw it together and see what came of it, but thought maybe someone might be able either to point me to an existing solution, improve this dumb idea, or tell me I'm not crazy -- or tell me I am!

    Thanks for any thoughts! For the record, happy to be told I'm missing something and/or way off base, of course: There are dumb questions, but sometimes someone needs to ask them, ya' know?

    Y'all are awesome. Even if I don't build many designs or have anything of value to contribute, I appreciate reading and learning and lurking and living vicariously.

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  • #2
    I don't get your tweeter dropping above 10k using EITHER ND20. Did you use #275-030 (FA)?
    Is your schemo. correct: 3uF, 0.05mH shunt, 13uF, parallel resistor - that's it? ?

    For me, the work and expen$e to build a custom bar that only goes to 125Hz wouldn't be worth it. Also, I get a box that's about (internally) 2"h x 2.5"d x 12"w. VERY small.

    Instead of limiting yourself to 2" woofers (because your "end feet" are only 2-1/2" high), EYE would make a box that was taller (like, maybe 4"?) that ran the full width of the set and just stepped down 2.5" (for a total height of 1.5" - about) on each end for the feet to sit on. You'd end up lifting the TV by that amount (2" - 2.5"?) but you'd gain some bottom end so the TV wouldn't sound bad, even w/out a sub on.

    Otherwise your sim SEEMs proper, 'cause I got the exact same Z-profile that you got !


    • #3
      You can't raise the TVs up with blocks under the feet to give you more space?