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"Golden Unicorns" - Low Profile, On-Wall, 2.1 System

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  • "Golden Unicorns" - Low Profile, On-Wall, 2.1 System

    Hello all! This is my very first post so it's going to be long and convoluted. I'll certainly write a bunch of gibberish (like this intro) and ask a lot of stupid questions, but here we go!

    I'm new to the DIY speaker world, though I've been trolling these sites for years. A quick look into the lack of experience I have (I'll try anything once) goes like this:

    A million years ago, I replaced blown out drivers on an ancient pair of Sony towers and thought that the Dayton DA135-8 woofers were nice looking and well priced. The resulting sound from the towers was much richer and handled the increased power output of my new receiver quite happily. A few years went by with us (wife and I) loving the speakers. We moved out of our condo and into a house and my wife decided that she hated the look of the towers and they would never make it into our new living room. So, they moved into the attic. I then set out to design something more 'modern' looking and tried to re-purpose the woofer in a funky open-baffle design with some Alucobond (aluminum-acrylic sandwich).

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    Basic design principals of open-baffle speakers thrown right out the door. The skinny baffle radiates nothing in the way of sound, but it is SUPER clean looking. I wished that it sounded remotely decent (yes I know that I am missing a bunch of high-frequency drivers in this design). I just took that photo after grabbing the 1 speaker I ever made from of the garage so, yeah, it's been a dead project for several years.

    This all brings me to where I am today and I think it's time to resurrect my "Golden Unicorn" of speaker designs. I call it that because I think it's a thing of fantasy and would be a beautiful thing if it existed. What my unicorn loudspeaker would look like is in the first picture. I drew up my Ikea Hemnes home theater furniture and added in the 60inch Samsung LCD for reference. I want them on the wall and super shallow so they match the slim lines of the TV. Looking at all the DIY loudspeaker design design information on the internet and beyond, I decided that the most important design feature was going to be the size and shape. Then, of course, it needs to be pretty for my wife.

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    So, I went looking for midbass drivers that were in the 4 inch range and came across the very nice looking HiVi M4N. With an overall TV height of 31" I can mirror that with my enclosure and still manage to shove in 4 of these with a Dayton DC28F-8 for the central tweeter. I'm sure there are many many MANY things wrong with my baffle layout, but looks were the primary design criterion. Currently the design has an internal depth of only 2.5" and an outer depth of only 3.5". This was because I was going to wall mount my TV with a super flat bracket. I've since decided that a fully adjustable tilting swiveling wall mount makes more sense. So, I think my overall depth can be as much as 5" without being too stocky on the wall. I am trying to avoid having a 31" tall bookshelf speaker on my walls.

    At this point I don't even know what to ask about power handling and crossovers because I know enough that I have to have my drivers selected and the enclosure designed to really start looking at frequencies, so I'll put some other design possibilities up here and let you throw some comments on the board.

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    Thanks!

    PS - The 2.1 spec in the title is for the future sub to go with this system and also the custom amplifier to drive it all. The idea is to hide the electronics as much as I can...maybe even hang the amp behind the TV so the cables are virtually invisible.
    Attached Files

  • #2
    I like them! The MMTMM arrangement should be fine vertically aligned like that, any odd lobing will be in the vertical axis instead of the more critical horizontal axis. How much volume is in there? My only concern would be bass response with what looks like small internal volume, so that sub-woofer will be very important.

    For your MTM drawings, the center to center distance is far too large. You'd want to tighten those drivers up toward the middle, which may loose the aesthetic you're going for.
    Electronics engineer, woofer enthusiast, and musician.
    Wogg Music

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    • #3
      Ideally you want the tweeter at "seated ear-level". Also it's a bad idea ("lobing" issues) to spread the midbasses apart (like in your lower pics).
      The B4N can go deeper than the M4N (similar look). If you made a pair of "Overnight Sensations" (the MTM style - dual woofers), kept the drivers as close together as possible, and modded the crossover to reduce "baffle step compensation", you'd be very close to your ideal. Also (vented), you might not need the sub w/the OSes (unless you like it LOUD) as they'll reach down to 50Hz or better.

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      • #4
        There's this, a kit is available, w/o cabinet.

        Overnight Sensation Center Channel... Bipole... What? When? - undefinition

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        • #5
          Originally posted by wogg View Post
          I like them! The MMTMM arrangement should be fine vertically aligned like that, any odd lobing will be in the vertical axis instead of the more critical horizontal axis. How much volume is in there? My only concern would be bass response with what looks like small internal volume, so that sub-woofer will be very important.

          For your MTM drawings, the center to center distance is far too large. You'd want to tighten those drivers up toward the middle, which may loose the aesthetic you're going for.
          I really liked the MMTMM look, but if I can get away with an MTM 'bringing da bass' a bit more, I'm fine with switching. The internal volume would be 0.303cf before subtracting for driver volume and internal bracing, so I estimate that the total volume is going to be roughly 0.20-0.25cf when it's all done. Not much at all for good extension which is why I was leaning towards a sealed enclosure. Also, I should mention that I don't have an issue putting up an oversized grille that would hide the empty space at the top and bottom of a setup like this: (NOTE: the topmost and bottom most braces are not solid)

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          • #6
            Originally posted by Chris Roemer View Post
            Ideally you want the tweeter at "seated ear-level". Also it's a bad idea ("lobing" issues) to spread the midbasses apart (like in your lower pics).
            The B4N can go deeper than the M4N (similar look). If you made a pair of "Overnight Sensations" (the MTM style - dual woofers), kept the drivers as close together as possible, and modded the crossover to reduce "baffle step compensation", you'd be very close to your ideal. Also (vented), you might not need the sub w/the OSes (unless you like it LOUD) as they'll reach down to 50Hz or better.
            The tweeter will sit at just about 42" off the floor which is just about perfect in my livingroom. Yeah, I'm aware of the lobing issues that occur when the crossover frequency is being traversed, but I was hoping that I was the only one who would care. Though, like I said in my previous response, I'm not opposed to squashing the drivers together in the center (notice the clipped baffle plate on the Dayton tweeter) and covering the whole thing with a sleek grille. More to your point of deeper bass response, I forgot about the B4N's having a minute sealed enclosure volume (0.08cf) versus the M4n's (0.17cf). This means I should be able to get two properly sized chambers in my tiny overall box that should still punch out explosions from bad action movies.
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            If I manage to get my box volume perfect for these mid-bass drivers (neglecting all other factors of speaker inconsistencies) do you think my cutoff point to drop down into the sub would be low enough? I have an old 5.1 PC setup that I believe allows you to cross the sub at a very high (in my opinion) 250Hz. Makes action scenes very boomy and not tight at all. The satellites are minute, which I think is why they went with this high crossover. I don't want that to happen with this system.

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            • #7
              Just noticed this morning that someone used the B4N's in an MMTMM center channel that wasn't the MS kit....posted pics and a review:

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              I'm more of a stickler on looks so I certainly won't be rushing through the build process, but this looks like it's essentially a slightly larger volume version of what I was looking to do. I suspect that there's a bit of lobing going on here.

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              • #8
                He makes designing speakers look really easy.

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                • #9
                  At about 4" in.depth, I think you'd be near 0.3cf. Boxes this small don't really need any internal bracing (if walls are at least 5/8" thick). The OS MTM likes 0.3cf, and (like I said) should get into the 45-50Hz range (vented). I think you'd be amazed at the bass output (w/out a sub - not that you couldn't always add one later).

                  The design you linked to most likely is not very good. "Textbook" XOs almost never work well (or even well enough). There are MANY "projects" out there (even here on PE's own Showcase) that really can't sound all that great - the thing is, the guy who designs/builds a "bad" speaker almost always thinks they sound pretty great.

                  That said, most projects that have advanced to a PE "kit" stage are extremely high quality/value. As are others you can find writeups of here in TT. You can model how low woofers will go yourself (in any given box) using something like (free) WinISD from linearteam.org .

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                  • #10
                    Originally posted by Chris Roemer View Post
                    At about 4" in.depth, I think you'd be near 0.3cf. Boxes this small don't really need any internal bracing (if walls are at least 5/8" thick). The OS MTM likes 0.3cf, and (like I said) should get into the 45-50Hz range (vented). I think you'd be amazed at the bass output (w/out a sub - not that you couldn't always add one later).

                    The design you linked to most likely is not very good. "Textbook" XOs almost never work well (or even well enough). There are MANY "projects" out there (even here on PE's own Showcase) that really can't sound all that great - the thing is, the guy who designs/builds a "bad" speaker almost always thinks they sound pretty great.

                    That said, most projects that have advanced to a PE "kit" stage are extremely high quality/value. As are others you can find writeups of here in TT. You can model how low woofers will go yourself (in any given box) using something like (free) WinISD from linearteam.org .
                    Awesome insight, Chris. I agree....think of the random time you cooked something totally from scratch and it actually tasted pretty good. you go around telling everyone who didn't taste it that it was Michelin star amazing! I plan on selecting the components and building the custom crossover for my specific design, so I hope it won't end up sounding too poopy (yes, that's a technical term I use as an engineer). Also, I was planning on using 1/2" MDF to shrink the exterior dimensions as much as possible which is why I chose to brace the box a bit. I was assuming that the thinner wall would need the bracing if I dip into the lower frequencies. Is there any way to model how the box will respond to frequencies, or is that the whole point of WinISD is to figure out the response of the entire system?

                    A design thought I was having is with what I should do right behind the drivers on the back wall? I was going to just put 1/2" acoustic foam all inside the enclosure except for the rear side of the front baffle. Another thought was to put an angled bit of wood to deflect the sound off angle, but I figured that would eat up more CF where the foam 'fakes' more CF. I assume this will be a tiny port if I decide to port these bad boys....bottom firing?

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                    • #11
                      Ok...Played with WinISD a bit....forgot how picky it is with adding custom driver information. I landed at some kind of nice response curve (I think) using a 1st order high-pass Butterworth filter at 75Hz in a vented box tuned to 55Hz. Sure I've done this all sorts of wrong, but hey, that's what the first try is for, right?

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                      • #12
                        Finally stepped into Solidworks for a quick 3D design. I've included the inner supports, port tubes, terminal cup cutout, front baffle cutouts, and the B4Ns. Still need to model in the terminal cup and tweeter. Then I can move on to grill design. I like traditional rectangles, but I have the chance to go edgy and put some angles on them. I'll throw some ideas out for comments and recommendations as I'm not sure what will affect the sound.

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                        • #13
                          So (just for a double-check) you've got each B4N in how much space? using what dia. ports? and their lengths?

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                          • #14
                            Originally posted by Chris Roemer View Post
                            So (just for a double-check) you've got each B4N in how much space? using what dia. ports? and their lengths?
                            Chris,

                            It looks like when I subtract the drivers, tubes, and inner bracing from the volume I am left with roughly 3.6L (0.14cf) per end. I went with the pair of 1.25" PVC for port tubes as were described on the OS MTM site, but now I'm realizing that I should be designing these enclosures as a pair of regular OS MTs joined together and sharing a tweeter. This would mean a single port tube at either end of the enclosure. Would it make more sense to leave out the middle solid braces and allow the entire volume to work together like the actual MTM would?

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                            • #15
                              Well, since both woofers will get the same signal, they COULD be in the same space.
                              Paul's (orig) OS TM is spec'd at 0.16cf tuned to 53Hz (1.25"id x 6" long port).
                              To put a pair of woofers in a box, you could double the volume AND use 2 port tubes (same id and length).
                              It doesn't matter whether the box is one interior volume (w/2 ports), or 2 separate volumes (each w/its own port).

                              By making your box smaller (0.13-0.14cf, there's 28.3L/cu.ft.) you need longer ports to reach the same tuning. 8" would look about right.
                              You should put ONE 8" long port on each box end. You CAN make the interior one airspace, it's optional.
                              What you ended up with (assuming that those are a pair of 1.25" x 6" long ports - you didn't tell me the length, even though I asked for it) is a box tuned into the mid 80's ! Y!KES!
                              You should be validating this stuff in WinISD.
                              To enter data into the "Pro" version, just enter (in this order): Qes, Qms (NOT Qts - let ISD calc that), Fs, Vas (be sure it's in the proper "units"), Re, Le (sort of optional), Sd (in sq.cm. - typically), Xmax, and Pe (RMS watts).

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