Re: Coaxial Wedge Collaboration
Thank you to all for an excellent thread. I hope that it will be revisited by all that were interested. I followed this thread during the height of activity hoping that it would guide me in my own coaxial wedge monitor development. My project monitors, designed as dual purpose small venue front of house and monitors for Fractal Axe-FX guitar rig, are approaching completion.
I read this online forum and others extensively. I studied designs. Read white papers. Spoke with experts, and I sought the advice of Jack Arnott. He provided excellent advice and even put me in contact with Curtis List and John Halliburton to help engineer crossovers and cabinets. And to their credit, the recommendations they provided did not necessarily center on buying products and services from them. Curtis List, helped me find alternatives to custom engineered (read very expensive for a one-off build) passive crossovers. Despite not clearly being significant commercial customer, Jack offered to send me a BMS coaxial floor monitor to test with my Axe-FX rig.
My build ended up using the BMS 12CN860 triaxial point source driver. This project is not unconstrained by costs. In fact, I have a wife that must never know how much I spent on the drivers…or the plywood, or for that matter the Fractal. In order to save a little money, decided to become my own design engineer and cabinet builder. It turned out to be a fun, frustrating, educational, and time consuming endeavor. Now that I’m done, I’m sure paying an experienced cabinet builder is a good investment. However, if I had it to do over, I would do it again.
I wanted my floor monitor to have three potential placement options. That would be two angles firing up from the floor and one as a stacked or pole mounted main front of house type placement. I’ve noted many floor monitors are designed to provide a 60 degree or 30 degree (to the floor) play angle. I looked at several configurations and decided to use a less pronounced 50 and 40 degree angles. For the sake of simplicity in cutting and joining the cabinet sides, all of the angles, except those that establish the baffle board’s angle to the floor, were made to be 90 degrees.
The nature of the 12CN860 favored a ported cabinet. I made my first draft blueprints using a big role of Post-It Notes graph paper. I was able to draw an end view to scale to make sure my design and driver placement would accommodate the driver’s depth. I even made a big Post-it cut out of the driver’s profile to move around on my drawing. Once satisfied with my basic design, I moved it into Sketchup. I used Kristian Ougaard’s Unified Box (Unibox) Model spreadsheet to estimate ideal volume and port length. Ideally, I would have built several test cabinets and measured the drivers’ behavior to optimize my results. Time and money constraints prohibited real-world prototypes, so I trusted that Unibox predictions would be better than my uninformed guesses.
I used 25mm Baltic birch for the baffle board and constructed the remainder of the cabinet out of 18mm. Most of my joints are simple butt joints. I did use a biscuit (or plate) joiner for the end pieces but more for alignment purposed than anything else. To minimize the number of bar clamps needed, I drilled slightly oversize screw holes in the flat side, and pilot holes in the edges sides of my butt joints. I could then glue and screw the joints together, with a little play to adjust alignment. I made 45 degree cleats to reinforce my right angle butt joints, which I again used screws to pull in tight while the glue was drying. I ran the angled edge of the backs into the opposite cuts of the doubled sides. This gave me a offset v-shaped channel, to create a joint with a lot of surface area. I over extended my butt joints so the grain end edges could be sanded or trimmed with a router flush with the flat sides. Finally, I used a half inch round over bit to finish off the edges.
I lined the cabinet with 2 inch poly fill from a set of old JBL studio monitors. It was nicely dyed black on one side. I installed a prefabricated jack plate with two Speakon connectors, paralleled to a pair of ¼ inch phone jacks. The plate has room for another, “full range”, Speakon jack and a switch, which will be used if/when Curtis List designs some crossovers for the 12CN860. The 4 inch ports are from a set of Klipsch subwoofers. They are made of flared plastic fittings at both ends and cardboard tube in between. I was able to cut them down to an appropriate length and re-glue the ends. I bought the poly fill, jack plates, and ports on eBay.
I’m still doing some testing but so far, they are vastly superior to the RCF 12” two-ways they are replacing. The sound jaw-droppingly good. Easily EQ flat. And their smoothness, camouflages how loud they are. I can listen to them at higher volumes than the RCFs, for extended periods, without ear fatigue.
