Sound And Torsion


Guesswork & Woodwork

Introduction : The Fortress Of Solitude

The classic profile of a high-end speaker system is at heart a multi-driver, complex-crossover, low-efficiency brick--  nestled protectively in blankets of damping and reinforced silence.  To reconcile the complex behaviors of the differing drivers and to minimize resonance and reflection, the cabinet is usually constructed of of massively thick, super strong materials.  The system is assembled with all possible build overkill, and lots of internal layering, all in an effort to be a neutral source of sound, free of cabinet influences or colorations. 
The sleeping, blanketed  brick is thus constrained in every direction, acoustically isolated, mechanically cushioned, and electrically locked into submission, and consequently, must be awakened with a strong kick from powerful amplification.  So a few hundred watts of feedback-controlled power amplifier may not even be enough.  It may take totals of a thousand watts of bi- or tri-amplification, to awaken some of the sleepier overgrown bricks.
Anyone with trained or experienced ears can tell you that virtually any music playback construction has its own sound -- whether a messy euphonic color-generator, or an overdamped lockdown from which lifelike sounds can never bloom.
It would be false to claim that my approach here to speaker systems is 1oo%  a refutation of the 'locked-down-brick' school of high end loudspeaker.  Because the truth is that this level of build overkill and coffin-like cabinet-making is very much beyond my skills and resources anyway.  Because half the approach here is that of necessity, there will be no huge table-saws, cnc-cutting, routering, vacuum-clamping stations or ovenbaked finishes;  there will be no eight-foot sheets of materials, no inch-and-a-half thicknesses of anything.  Because I have no experience with those procedures, no real competence with those materials, and just don't have any of that on hand. 
But there should be no mistake-- fifty percent of the approach is still is the idea that amplifiers with full harmonic qualities but lower wattages should be able to drive reasonably efficient speaker systems, in well-thought-out cabinetry that is light and rigid.   Like a cello's sound box, strutted and braced with numerous site-specific ribs and crosspieces each designed to their own purpose, each reinforcing the overall integrity of the whole.

The Dull Glow Of Limited Success
Since I knew that these wouldn't be the last enclosures for my new/old Tannoy dual concentrics, I had the idea that the first efforts might just be the right time to try something adventurous.  I had the idea that lightweight construction-- but with fairly sophisticated bracing -- might be an approach to good sound that wouldn't deaden the harmonic bloom, or discourage lively pacing & poise in the time domain.  Perhaps I could sidestep the curse of the hibernating bricks.
As a first look into the world of the Tannoy renaissance, I had read the indispensible TannoyMania by Harvey Rosenberg.  My thought was that soon enough, my Tannoys would evolve into a Transmission Line effort, and eventually, a Back-loaded Horn enclosure, but like any completely new project with its own learning curve it might be best to start with something simpler.  So why not first try some simple boxes with walls intact, as with 'infinite baffle' types, and live with those for awhile.  Not too further down the road, 'bass reflex' ported boxes could be the next effort.
Well on the way by now, I ran into an article on the Hans Hilberink Tannoy Monitor Gold site, that mentioned the phrase 'torsion box' ...  an interesting approach that accomplishes a large, braced enclosure that isn't life-threateningly overweight.  But this version apparently required a serious wood shop.  So I promptly looked elsewhere, in that such cabinet work was beyond my resources here.   My "resources" in the woodworking department, it should be mentioned, are best described as budging the needle just beyond zero.  I knew for a fact, for example, that building any rectilinear box of 12" speaker scale with perpendicular walls and accurate joinery was pretty much beyond my range of capability.  But that really couldn't be the end of the story.
Because the storyline I'm sticking with is that you should extend all of your budget into the part of the system you can't manufacture yourself, ie the raw speaker drivers -- and moving along in time you'll be able to build cabinets of increasing sophistication and/ or eventually settle on original Tannoy or custom carpentry.  This should ensure an ongoing baseline of playback integrity, with each new level enlarging the frame, validating that those expensive drivers are expanding their capabilities. 
So, I'd have to do a bit of range-finding, taking various stabs at under- and over-building some small-box woodworking, like transformer or powersupply boxes and chassis projects, and I did just that.
The dull glow of limited success illuminated a path, a way in through the kitchen door,  just for me.  If I couldn't reliably make razor-straight cuts or mitered edges or ninety-degree corners, I'd just have to order some in from the outside world. 
Since purchasing custom-cut panels of virtually any woods or plys was an expensive invitation to fouling the joinery (I knew without trying),  I hit on the hollywooden idea of using stand-ins for the real thing.  All that was required, really, were inexpensive, uniform, and relatively square wooden forms around which I could construct my cabinetry.
Before I go on, it should be apparent that I had absolutely no qualm or uncertainty that my Tannoys might sound their best in a matched set of Westminster Royals -- or Canterburys -- or Churchills or Glenairs, for that matter.  It's just that the raw drivers are so ridiculously expensive these days, and the first couple of cabinet renditions to house them would have to be conscious of my budget.  As in: no budget at all for cabinets, due to the budget having been spent entirely on the perfect vintage speaker drivers.
A long road to get to this, but that's the way some of this do-it-yourself audio goes;  a couple of eventual days of execution, preceded by months of figuring out your own peculiar strategy.  And that road came to a halt outside my local wine-merchant's premises.  Not the shop, exactly, which was also a help in its own way, but outside, at the Dumpster.
Where I found stacked, higgledy-piggledy,  a dozen or so average wine crates. It was the holidays, and they were moving a lot of product.  The crates are made of low-grade boxwood but displayed exactly what I didn't  have -- reasonably square ninety-degree corners, clean edges, and a workable, building-block size & scale appropriate to speaker cabs.  These could be tacked together to obtain the shape, used to build the cabinet forms around, and then knocked apart from within and discarded.
As I thought further about the idea, I noted that these stand-ins were themselves capable of transporting twelve bottles each, somewhere between thirty and forty pounds in total, across international distances, and had proven themselves over hundreds of years and still counting.  Although they were in many respects contrary to loudspeaker objectives (resonant and flexy, non-rigid) they might endure the trial run to provide more than just temporary forms, and could be used as skeletal frames, once glued, strutted, braced and then mass-relieved via cutouts, to create an internal bone-structure on which to build outwards ...  
So at least there was something of a roadmap, an itinerary of maybe-yes maybe-no experiments to make, none of which involved completely closing the door on future versions, and none of which required much in the way of expenditure.
We were on our way toward a landing.  We know you have many choices of  speaker enclosure strategies, and we congratulate you on choosing the cheapest seats in the house.
Next, let's revisit that Torsion Box idea ....

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Sound And Torsion
tannoy loudspeaker project