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  • Omnimatrix: low budget, big sound?

    Though I'm not sure what the name of this desig will be, I had to put something in the title!

    This is a project based upon the Raal Solaja's speaker that had a prototype shown at RMAF 2009, I believe. That speaker is suspected to go for about $4000/pair, I believe all active. http://blog.stereophile.com/rmaf2009...festyle_bliss/
    My intent is to try and produce a low budget version of this omni speaker, probably using all buyout drivers and a passive XO. It is a full range omni 3-way with a total of at least 14 to 16 drivers between the pair!

    The design uses two 4" dia tubes, about 8" long that are mounted side by side, about 1/8" apart. Each tube has a sealed 3-1/2"+- driver up and down firing in it, making for 4 mids per side to up the sensitivity and power handling. The midrange is set, from some Vifa buyouts ($8ea.), here:
    http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-223


    The woofers are still undecided. It is currently betweeb dual 12" sealed woofers in a 40L+-, 12.5" dia tube front and rear firing per side, or two Peerless 831735 6-1/2" HDS buyout woofers (picked up 4 for $30ea. The 12"ers were PE buyouts from about 2 years ago. In a sealed 40 liters, a parallel pair will get down to around an F3 in the mid 30's, f10 around 21hz and will take more power than I'd ever give them and not get close to Xmax. The drawback is these would have a qtc of around 1.0 with a sensitivity of around 88db/2.83V. The Peerless alternatives could be done sealed or ported. In undersized and unconventional 40L ported enclosures they can get to around and F3 of 44hz, F6 of 32 and F10 or around 24hz. Since both drivers will be located near the floor and typically near one room boundary wall, there should be enough boundary gain to fill in the lowest octave.

    The tweeter will be the biggest challenge. The concept is to fire the tweeter from inside on of the tubes, into the side of the adjacent tube. The closeness of the two tubes will be the key as they form the sides of front and rear firing horn. This is probably not full range omni since the tube diameter will begin to make directional to some degree. This was RAAL's concept in the Solaja. Of course they used a side mounted ribbon tweeter, which is probably ideal and may be where I end up. I will start testing with 4" dia. pvc tubes for prototyping and the Vifa OX20SC00-04 3/4" neo dome tweeter.
    http://www.parts-express.com/pe/show...%20ox20sc00-04
    The domes spherical output, as compared to a ribbons more horizontal cylinder output, could be a problem, but I think it is worth testing and I have some ideas for controlling the vertical dispersion that I will go into later. The intial test will be with a single tweeter, centered in the side of one tube firing into the other tube, but I will probably test opposing, but offset tweeters to increase power handling and perhaps use the vertical off axis comb filtering to reduce the vertical dispersion.

    If the domes prove problematic and I may be forced to try and find a narrow ribbon, which could inflate the budget a significant amount. One potential ribbon would be this one:
    https://www.madisound.com/store/manu...s/ft7rprev.pdf
    Because of difficulty in fitting to the curved surface and wavguide, the tweeter body needs to be pretty narrow and becaue of the small volume in the tubes, it has to take up a small volum also. This Fostex has both a narrow body and ribbon, small volume and a curved waveguide-like face plate that might work well fitting with the tube curve. Of course, the cost increase is significant, since these are $93 each as compared to $16 for the Vifa's.

    Below is a mock up of what it might look like with an aluminum finish on the tubes. Crossing the woofers low, around 200-250hz, placing them near the floor and pushing the woofers off to the side of the mid and tweeter allows both the front and back firing woofers to be closer to the room boundaries while keeping the omni midrange and tweeter further from the wall, which omni's usually prefer. There should be no bsc needed in this design.


    Dan N.

  • #2
    Attached Files
    Dan N.

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    • #3
      Re: Omnimatrix: low budget, big sound?

      I love the idea! Something smaller, with say a 6.5-7" woofer for actual surrounds would probably be a good fit for me since I need some sort of small surround to go in the corners on either side of my sofa. My wife even loves the look! Hummm...

      Comment


      • #4
        Re: Omnimatrix: low budget, big sound?

        I did some prototyping today and thought I'd pass some photo's along. As I mentioned above, I found some pvc coupling hubs at Lowe's and decided to use them for the prototype. I also did some thinking about how to make the tweeter front to back position adjustable and came up with a way to do that as well.

        As will be made clearer in the photo's, I used a smaller diam. pvc tube (1-1/4"id) to create a tube the tweeter can slide in and out of. It turns out that the ID of the 1-1/4" pvc is a little bigger than 1-1/4". I decided to use 1-1/4" hardwood dowell to slide in an out of the tube to provide the back for the tweeter. It turns out it is just a little smaller than 1-1/4" od. I had some 1/2" width UHMW adhesive back tape that turned out the provide the perfect spacer for a snug fit between the dowell and the ID of the pvc tube. For prototyping, I'm going to simply try double sided masking tape to hold the tweeter against the dowell and I still have to come up with a way to get the wires into the tweeter.

        Once the 1-1/4" pvc tube is inserted into the side of the pcv coupling hub, the outside of the protruding sections of the 1-1/4" tube were sanded flush with an upright belt sander. Then I used a chamfer bit on the router table to create a chamfer around the ID of the tube and then sanded the sharp edges to create a bit of a roundover. I will probably try the opposing, offset dome tweeter option previsously discussed as well, in which case the location of the 1-1/4" tubes will shift up and/or down on the opposing tubes, to create the offset.

        Each larger woofer tube is made from 3 sections of the pcv coupling hub. The center one holds the tweeter and the top and bottom ones are cut down so that the internal flange on the hub can act as a backer for the baffle. For prototyping, I'm simply going to use 1/4" plywood as the baffle.

        I think the photo's below will make this all much clearer.

        If anyone has any ideas for a better name for this project, shout them out!

        Prototype photos:













        Dan N.

        Comment


        • #5
          Re: Omnimatrix: low budget, big sound?

          The RAAL's have had some pretty impressive comments made about them. I believe Jon Marsh, over at HTGuide, put them in his top 10-12 at the show, at any cost, and he has no axe to grind like some magazine reviewers might.

          I don't know if I can pull that level of quality off here, especially passively and with budget/buyout drivers, but it should be fun trying! Of course they are said to throw and impressive soundstage, so using this concept for surrounds might be a perfect use.

          One could certainly go higher end with the drivers. I suspect this would be much easier to do actively as well. If this one works out passively, I might have to try the active/miniDSP route with some higher end drivers. I suspect the real challenge here will be getting the tweeters to work and once that is accomplished, it won't be much different than my other omni designs.
          Dan N.

          Comment


          • #6
            Re: Omnimatrix: low budget, big sound?

            Dan,

            diggin' the concept, and know (from other's comments) that you do great work. I've been thinking a lot about omnis - and was planning to clone your sound-round design with some buyouts I've got on hand. If this design's drivers are still available, I'd be very interested in building a set. Price is right.

            I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
            "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

            High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
            SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
            My Voxel min sub Yet-another-Voxel-build

            Tangband W6-sub

            Comment


            • #7
              Re: Omnimatrix: low budget, big sound?

              Hi Don,

              The current dome tweeters and midranges are still available, as is the Peerless HDS 6.5", if I end up going that way, which I suspect I will, since the 12" woofers in a pair have a sensitivity of only about 87db 2.83/m, whereas the mid combo is up around 93db. Using the 12"ers would probably demand an active element to the design and bi-amping, which begins to be a totally different project.

              You can't go wrong with the SoundRounds concept either. They have a great soundstage and excellent imaging as well, IMO. That said, they would be much more spl limited as compared to this design.
              Dan N.

              Comment


              • #8
                Re: Omnimatrix: low budget, big sound?

                How about;
                Cyliness (silliness)
                Cylilamps (since they look like lamps)
                Canisters
                Cantrois (for 3 French cans)
                Kanntrois (french/German hybrid)
                Cartesian Poles
                Lateral Radii
                Cylindricalus
                Acoustic Origins (acoustic emanation from center points)

                How's that?
                Wolf
                "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                *InDIYana event website*

                Photobucket pages:
                http://photobucket.com/Wolf-Speakers_and_more

                My blog/writeups/thoughts here at PE:
                http://techtalk.parts-express.com/blog.php?u=4102

                Comment


                • #9
                  Re: Omnimatrix: low budget, big sound?

                  Wolf,

                  Where do you get this stuff?!?!

                  I kinda like Acoustic Origins the best of those
                  Dan N.

                  Comment


                  • #10
                    Re: Omnimatrix: low budget, big sound?

                    I just think about what the design entails, and then take a route from aesthetics, shapes, combos, or things that are unique to it.

                    In yours you automatically see "Cylinders", which leads to geometry or volumes, areas, etc. Wikipedia can help you find something that makes sense to your design aesthetics and goals. Since the central point of a circle is the 'origin', and your drivers are mounted on that as the listening direct axis, it suits the design.
                    Lateral would be horizontal, and many radius becomes radii for the number of listening axes.
                    Cartesian plane is the (X,Y) graph, and your cylinders would be face on the X,Y with Z being the length. Since they are tubular and on stands; 'poles' came about.
                    The others were kind of a simple play on looks and design alone.

                    I also think 'Acoustic Origins' is the best of what I popped up there.
                    Feel free to use it...
                    Wolf
                    "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                    "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                    "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                    "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                    *InDIYana event website*

                    Photobucket pages:
                    http://photobucket.com/Wolf-Speakers_and_more

                    My blog/writeups/thoughts here at PE:
                    http://techtalk.parts-express.com/blog.php?u=4102

                    Comment


                    • #11
                      Re: Omnimatrix: low budget, big sound?

                      have you played anything through then yet? That's a pretty good way to implement the design! I had no idea how you were going to do that.

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                      • #12
                        Re: Omnimatrix: low budget, big sound?

                        Hey Dan looking good. I have a design cooked up very similar to this, although its just a single tube(they're aluminum too!) instead of twin. How do you intend to wire the drivers? So that they push/push or push/pull?
                        "If you cannot find the truth right where you are, where else do you expect to find it? - Dogen

                        "Why are you wearing that stupid human suit" - Frank

                        "We spread the time as we can, but in the end the world takes it all back" - Roland

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                        • #13
                          Re: Omnimatrix: low budget, big sound?

                          Depending, of course, on the size you need, a pipe cap might work for the tweeter cavity. Harder to access the back of it if you want to change the stuffing, though. Because of the varying acoustic center shift it's going to be interesting to see what happens to the fr and polar as it passes through crossover . . . the quasi-horn loading on the tweeter should let it cross lower than it otherwise would, and help with that. Of course as you already know working with omnis the off-axis polar isn't terribly important as long as the overall off-axis power response sums smooth, and mostly flat (or drooping).

                          I presume you use some sort of easily adjustable active crossover for design to make design adjustments easier. And given the availability (and ease of building) small "active" subwoofers I'm not sure I see the point of fighting the "sensitivity" fight on that front. It's just an unnecessary design constraint nowadays. It's not like there aren't enough other things to worry about . . . ;)

                          The wonderful "naturalness" of the "omni" sound (in most rooms) makes it all worth the effort . . . kudos to you for keeping at it . . .
                          "It suggests that there is something that is happening in the real system that is not quite captured in the models."

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                          • #14
                            Re: Omnimatrix: low budget, big sound?

                            Have you made any decisions on the woofers?
                            Coupla of thoughts - I'm not at all sure that 6.5 inch woofers
                            per side would not be a limiting factor -
                            Second, you mention a 12.5 inch cylinder for the woofers - a 40+ L
                            volume would mean a cylinder about 33 inches long, wouldn't it?

                            I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                            "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                            High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                            SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                            My Voxel min sub Yet-another-Voxel-build

                            Tangband W6-sub

                            Comment


                            • #15
                              Re: Omnimatrix: low budget, big sound?

                              Looks good Dan. You're one of the very very few still working in the world of Omni's........very refreshing and surely on the path to something really special.
                              It's really fun to repurpose stuff for DIY speakers.....to see something like this come from some PVC pipe!

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