I guess I ought to preface this rack design post by stating: Although I currently enjoy my music played back multi-channel style and the same "Big Rig" performs cinema duties, I'm still very much a hair shirt wearing, "everything-makes-a-difference" audio dweeb.
My current predominantly digital signal path and the mostly Meridian gear which play host to it does seem less
affected by audiophile tweaks than the tube two-channel gear I once owned. However, I still find attention to S/PDIF cabling, power conditioning, and mechanical vibration isolation all make audibly positive differences. The mix of audio and video in my present Big Rig with video's competing formats requires much more extensive racking. I am happy with some of my gear support elements. The custom Corian sand-box "shelves" and Black Diamond Racing isolation cones and pucks all work brilliantly. However, the row of low welded Target tables under the very heavy "sand box" isolation shelves leave something to be desired in rigidity, but also in effective use of space and aesthetics.
These complaints with my existing racking have driven my interest in finding something better. Unfortunately even the tweak-iest high end "audiophile approved" rack manufacturers failed to address all my requirements. In this case my decision to go DIY was totally about function rather than saving money. My steadily refined rack design was far beyond my DIY skills, but owning a high-end bicycle shop provides access to craftsmen with the abilities and tools to realize my vision. Thus this is more of a Design I
ourself rather than a Do It Yourself project. My actual build thread progress can be found here on the CAM Forum
. For this post I'll stick to a Coles Notes version of the build.
The above renderings and drawings are the original rack concept and despite some last minute material changes are still a pretty accurate representation of how the finished product will look. The plan was to build the rack frame from powder coat finished high strength thin-wall steel tubing. The frame would use 3" square for the main posts and a combination of 1"x2" and 1" square for the framework. The all the smaller diameter tubing will be filled with low expansion foam to damp the steel's tendency to ring while the 4 main posts are filled almost to their open tops with sand. A BDR (Black Diamond Racing) isolation Puck "floats" atop each sand-filled pillar and provides a footer for the BDR cones which interface with the corners of the 6' wide upper shelf. The long upper shelf was originally to have been CNC milled from a 3" thick lamination of ApplePly. The milled plywood shelf would have been reinforced with a pair of inset 2" cro-mo "angle iron" stiffening ribs running almost the entire length of the shelf. This would have ensure adequate stiffness under load. The top shelf features 3 milled out wells, each to be partially filled with sand which would then float a Corian slab which in turn the component would rest upon. All the individual lower shelves are Corian sandboxes as well. Each of the six lower sandbox shelves rests on 3 point levelling set screws inset into the frame. By this point you've worked out that I'm a fan of "BrightStar"-style sand filled isolation!
Over time the design evolved some. Ultimately I chose to go with brushed thin-wall stainless steel for the frame. A gifted local custom bicycle frame builder, Hugh at True North Cycles
, has almost completed the frame with just the final finishing work left to go. Below are pictures of the almost completed rack with close-ups of some of the detail work. Other than the material and finish change, the rack frame remained true to the original design.
The top shelf was a tricky proposition from the start. Aesthetically I was stuck on it being a single long span which under the weight of the shelf, sand, and components- had the potential to create rigidity problems. Well Gerry of Apex Composites, the only nearby CNC house with the a large enough mill, suggested that rather than a steel reinforced plywood shelf, we should make it from carbon composites. A shelf made from carbon wrapped structural foam would be a fraction of the wooden shelf's weight- sub-10 pounds vs 100 pounds! A composite shelf could be stiffer. Finally the composite construct of bonded foam, uni-direct carbon, and woven carbon with a "dress layer" lamination would be self damping. The three matching "floating" isolation shelves would also be made from structural foam and carbon. Well what wasn't to like with that! Yeah it drove the price up significantly but its only money. Full speed ahead! Below are the CNC-ready CAD drawings for the top and floating shelves.
Summer holidays have hampered the progress of my shelf somewhat as its a side project for Gerry at Apex but we are getting there. Two slabs of dense structural foam were laminated and then CNC milled to the desired shape. Lengthwise recesses were milled top and bottom to accommodate layers of unidirectional carbon which provides the strength stiffness. Then the entire thing was sheathed in regular woven carbon and "Peel-Ply", which when removed leaves a rough finish carbon which doesn't require sanding for subsequent laminations. Below are bottom view photos of the shelf. You can clearly see the underlaying strips of unidirectional carbon in the photos but it will be invisible upon completion.
At this point we performed a deflection test on the shelf. We supported the shelf on BDR cones and pucks at the outside corners and then distributed a 230 pound load of Olympic weight plates over the component sand wells. A dial micrometer device measured just over 1mm of deflection under that load. The in-house engineer at Apex had predicted under 1mm for 180 pounds so he was dead on. Wow at the moment the shelf weighs about 7 pounds! So with the core construction and testing complete, I'm now in hurry-up-and-wait mode for the shelf and three matching isolation slabs to be finished.
I'll update this post with further pictures upon the rack's completion later this Summer.