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Symposium Clone - Part I

Posted by pburant (A) on April 24, 2003 at 04:00:07

I am currently working on building a Symposium Clone shelf and thought I'd share my results thus far. First, the design (from top to bottom):

.125" Sheet of 6061 Aluminum
.25" Oak plywood
.5" MDF
1" Polyethylene foam (2 - .5" layers)
.5" MDF
.25" Oak plywood
.08" Sheet of 6061 Aluminum

This design is derived from both the details on the Symposium web site and from other inmates. There are several deviations from published designs, but the overall design philosphy was followed - to make a sandwich of materials of differing hardness/density, with the hardest layers on the outside. I purchased .5" PE foam, hoping to keep the overall height of the sandwich down, but I decided it would be better to err on the side of too much foam rather than too little.

I used high strength epoxy to bond the wood together (which I'll also use for the aluminum-wood bonds), and used simple craft spray glue for the foam-wood and foam-foam bonds. I had bought a small can of the 3M Super 77 adhesive for the foam, but I found it harder to work with than the less expensive spray glue, and since the foam is PE, I couldn't see the regular spray glue doing any harm (so far, so good). I would be concerned with glue damage if the foam was anything except PE.

Although I am still waiting for my aluminum to show up (it's due today), I have all the other layers bonded together and currently supporting my CDP. The not-quite-complete sandwich is replacing a single .75" piece of MDF, which was part of an isolation system. The MDF sat on a barely inflated bicycle innertube, and I had a set of DIY roller bearings between the MDF and CDP. With the only change to the system being the substitution of the sandwich for the MDF, the changes have been all positive, and to a greater degree than I had predicted.

Since I already had a reasonably effective isolation system, I didn't expect huge changes from the sandwich, but I was wrong. The changes were as big, and of the same character as going from no isolation to roller bearings for a CDP - there was a braodband reduction in noise, allowing more detail to emerge, and the pitch of bass notes now seems more neutral (the tonal changes seem to have been confined to bass, as opposed to the noise cleanup).

As for the sound settling in, I haven't noticed that happening to a large degree. While my foam layers were bonding together, I was careful to place the equivalent of my CDP's weight atop the sandwich, hoping to 'break in' the foam to that load. I did notice upon receiving my foam that it is very slow to fully spring back to it's original shape once deformed, so I was careful to not put too much weight on the sandwich while bonding the foam. The foam is relatively stiff, however, and didn't defrom to a visible degree under a 40lb. load (the shelf size is 15"x17").

Hopefully I will recieve my aluminum tonight and will be able to report back later this weekend about the sound of the finished product. At this point, it sounds so good already that I'm having trouble imagining the aluminum has much room for improvement, but probably the most important thing I've learned in all my tweaking is that no matter how good your system sounds, there is probably a way to make it sound better by tweaking the current hardware, often for little or no money.

-Pete

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