Sound And Torsion









Musical Instruments & Airframes
Part of the idea of "settling" for the Wine Crate strategy was that even though it's rather weak and contrarian at the outset, there were a myriad of ways to add strength and rigidity after the fact.  So a two-part recipe where you throw the first part away after reaching the second phase.  And if the fact was unavoidable --ie, the winecrates had to be used in order to correctly form the basic structure--  then the search was on to find methods that would add these qualities without adding enormous weight and mass. 
There are basically two fields here that are donating methodology, one is musical instruments, with which I was familiar if not awfully knowledgeable.  Experience, however, was there : in music projects I've had several electric guitars and a full acoustic piano taken down to small parts in my travels, and had the occasional expoded view --literally-- of an overtuned acoustic guitar.  Ribs, fan-braces, struts, corner & cross-braces were at least things I'd known in several contexts.  The other field is aeronautics, about which, of course, I know nothing at all.
The original plan ---discarded in this present version-- the idea of doing real cabinetry around the form of assembled winecrates, and then knocking them apart from within and removing the evidence...  was what gave rise to the Torsion Box concept.   Which arose from the thought that maybe some parts of the winecrates, spines, corners, etc that had subsequently been perfed for mass relief ... could stay on in the finished product.  What would be added would be a rigid exoskeleton of plywood to strengthen and stiffen the enclosures. 
So if there were to be an outer layer or skin of veneer-ply to be added to the outsides of the winecrate assembly, why not utilize a specific structural approach that was known for it's strength, low mass, and resistance to vibration ..? 
Well, you can check the links below for a start, but the idea of a Torsion Box is simple :  adhere outer skin materials above and below an inner grid or framework.   With the resulting structure being considerably stronger than the sum of the parts in a straight stack or layered construction.  And of course being lighter than solid materials of the same dimension.  In acoustic terms, I reasoned that the grid-core would be much less inclined to resonate at any one fixed rate, and present a complex target for vibration.
This general idea of the Torsion Box is honed to an excrutiating, nano-precise extent in Airframe Technology for aircraft, but is also in universal usage in nearly every "solid" element in furniture from Ikea and other low-cost manufacturers.   Ever notice those thick, sturdy looking tables and furniture that don't weigh anything at all as compared to what they look like ?   Ever wonder how hollow doors stand up to repeated use ?
Torsion boxing.  Think internal I-Beam, but taken further, in both length and width directions, like a chessboard of sorts.... the grid of crossed beams becomes its own plane.    In addition to forming flat panels, any wavy or complex curve can be accomodated with torsion-box strategies, given appropriate core design and flexible enough outer skin materials. 
So, a wonder of modern engineering, a sleight-of-hand trick with light materials doing heavy-duty service.  Right up my alley, maybe.  Does it suit speaker cabinetry ?  
On this particular point, I really have no idea.  Hence, Sound & Torsion
And make no mistake, what we learn here will forever influence the way sound is heard in ...  my living room.  Or at least until exotic & beautiful cabinets from real speaker builders appear ...
For more on the Torsion Box concept, have a look at the links.











James Donahue 2011


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