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Helix Dome MT. A Jeff Bagby design.

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  • Helix Dome MT. A Jeff Bagby design.

    Earlier This month I purchased a new Helix dome MT kit from DIY Sound Group. As always the packing was more than up to the task of protecting the drivers and the CNC MDF baffles. I will warn that you need to be prepared for a box well stuffed with packing peanuts or similar. Fresh out of box, the mid-woofers had a very classy and stout cast frame. They are a custom driver for Denovo. A quote from the site.
    "It uses a custom high end woofer with a 3 layer cone. The middle layer is a hexagon matrix similar to a honeycomb that gets 'sandwiched' between the two other layers to make for a strong light weight cone."
    The SB29ASDAC tweeters were very impressive and had a very substantial and handsome aluminum face plate. Both sets of drivers were a step above what I had used in the other kit builds I have had to date. Granted they were quite a jump in price as well.

    There is an earlier thread here. http://techtalk.parts-express.com/fo...-helix-dome-mt
    Last edited by Waltzilla; 09-30-2018, 05:45 PM.

  • #2
    I built the boxes to spec out of MDF. They were my second attempt at mitered corners. Not perfect but I was satisfied with the results. The plans call for a window pane brace. I opted to use a shelf of MDF and routed out holes to allow airflow between the two chambers. I planned from the start to veneer the boxes. Once I had them glued and rough sanded, I gave them a heavy coat of shellac. I let the shellac dry overnight and then sanded everything again down to 120 grit. I then spray painted the insides of the boxes and the bottoms flat black.

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    • #3
      Next it was time to glue on the baffles. My boxes were a very close match to the pre-cut baffles. I then used wood filler to even out the gaps. I let them dry and then sanded everything back with more 120 grit.

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      • #4
        Once the filler had cured it was time to make my first attempts at veneer. I opted for the main body of the cabinet to be red oak and a contrasting cherry baffle. The oak was Band-it brand iron on as was the edge banding. I made a trip to the local WoodCrafters for the cherry. A mere 45 minute drive (not that bad by Oklahoma standards). I found some sequence cut unbacked veneer with some nice curly figuring and some iron on cherry edge banding. I chose to use a vinegar and iron stain for the oak but I wanted to leave the cherry with a natural finish. I glued the oak on first and stained it before I proceeded to do the baffles. To glue the fascia veneer on I opted for the PVA/hot iron method. The center seam line could be cleaner, but it's done and I am not unhappy with the results. Everything was then lightly sanded to 220 grit.

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        • #5
          Looks good! I like the vinegar/iron stain, very dark and unlike ordinary red oak. Looking forward to hearing how they sound.
          If life were fair, Elvis would still be alive today and all the impersonators would be dead.
          ~ Johnny Carson

          Bungelow Ed's Photo Album http://techtalk.parts-express.com/album.php?u=8594

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          • #6
            For now I am powering them with my old trusty A450 amp in the bedroom. I am very happy with these speakers. They have a very smooth sound to my ears. Specs list a range of 40hz-20khz at 88db 2.83v/1m. The bass is very clean and nice. More than enough for the mix of music I enjoy without a sub. A pretty wide mix, classic rock, R&B, jazz, bluegrass, even the occasional disco song. Gangster rap (I will listen to some hip hop) and Nashville machine country are about the only exclusions. The tweeters are very pleasing not overpowering. I won't try to use esoteric terms I can't really quantify. For imaging and sound stage, I can separate the instruments and their placement in nice recordings. The sound feels bigger than the placement of the speakers but my room is FAR from ideal and I haven't spent a lot of time yet getting them where I want them.

            A friend wanted to hear them so I took them over to his house for a test run. He was surprised and quite pleased with them as well. He said he would be happy to run them in his living room. It's an apples and oranges comparison but they held their own against his B&W's. I found the big 3 ways overly bright but they definitely were more at ease filling the room with sound.

            Walter

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            • #7
              Some addendum. The boxes were finished with one coat of boiled linseed oil, then touched up every few days with some Howard Feed-N-Wax until I feel happy with the look. I originally intended to fill in the back panel with cherry veneer as well, but decided flat enamel would suffice. I only used a little poly stuffing behind the woofer. In the past I have lined all my boxes with egg crate foam and then light stuffed with poly.

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              • #8
                Can you compare them to any previous kits you built?

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                • #9
                  Nice project. Please consider leaving a review at DIYSG. Erich H says nobody is doing reviews and he doesn't know which designs to restock.

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                  • #10
                    Originally posted by djg View Post
                    Nice project. Please consider leaving a review at DIYSG. Erich H says nobody is doing reviews and he doesn't know which designs to restock.
                    I left a review that was basically the first and fifth posts of this thread and sent this link to Erich. I sent a couple of pictures and told him to use any of this he wanted and let me know if he needed more or better pictures. I want to support him in any way I can.

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                    • #11
                      Originally posted by Jake View Post
                      Can you compare them to any previous kits you built?
                      To date, I have built the C-notes, Overnight Sensations, OS MTM (as a center) and the OS TMM towers.

                      The TMM towers are the mains in my HT setup. They are impressive for the cost, effort and footprint. If I push the volume a little too far I think I am too close to Xmax and they get sloppy. I very rarely push them that hard. The MTM is run as my center channel. In the future I plan to make a TV stand with the OS center incorporated. I don't know what I will wind up doing with the MTM. Buy another ND 20 and make some MT's for my wife or buy anther MTM kit and give those to my wife. Or give my wife the current MT's and move the MTM's to the back channel of the home theater. A decision for a later date.

                      The Overnight Sensation MT punch way above their weight class. A friend of mine loaned me a pair of "spare" Von Schweikert VR's for my wedding. He's no stranger to audiophile. He heard them (OS) at the wedding and was amazed. http://techtalk.parts-express.com/fo...ed-ot-somewhat

                      The C-notes are something special. For the cost the sound is amazing. I found the bass a little lacking and a sub necessary. I think if there was a way to use something like Jeff Bagby's semi-universal woofer with them they would be beyond great, but then they would be a $600-800 kit and not $100. I've heard rumors of an MTM version and I would be near the front of the line for one of those. I gave my pair to one of my best friends.

                      The Helix Domes MTs are head and shoulders above all of those. I think that's to be expected though. Much nicer drivers, more money spent. I don't have an amp at the moment that can max them out. I plan to remedy that soon.

                      I wouldn't hesitate to recommend any of these kits to a friend.

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