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Hi Troels,
Way back in 2018, I decided to build your Poor Man's Stradivari.
I had a notion to skin the cabinets with carbon fibre. I read all of the
details on your website, ordered the kit from Jantzen Audio, made a
template for the horizontal cabinet pieces, cut the pieces, ordered the
carbon fibre, resin etc. then never found the time to actually get on
with it.
This year, I decided that enough was enough; it was time to stop
procrastinating and to get on with the build.
I wanted a very heavy, very well damped cabinet, free of unwanted
resonances, so I decided that a sandwich of 2 layers of 12mm Baltic
Birch ply separated by a layer of 3 mm DodoMat (mass loaded vinyl) in a
sort of "constrained layer" construction was the way to go. I also had
some spare pieces of Korff Hawaphon laying around, which I decided to
add to key areas to further dampen and minimise resonance. After using
what I had to hand, I decided to buy some more. I also added lots of
pieces of DodoMat and 8 mm felt damping to the internal surfaces.
In terms of construction, I followed the outline cabinet drawing you
provided, with the addition of lots of vertical braces. Other than the
centre section of the front baffle where the drivers are mounted, I
wanted smooth curves, so the plywood was kerf-bent using a track saw.
For the ends of the cabinet, I decided to sandwich in a sheet of 3 mm
aluminium before adding the final rounded end cap. This presented
numerous challenges, however, in the end, I think the results are worth
the effort.
Top and bottom panels are made from 3mm 1.4301 (304 grade) stainless
steel and I will be fabricating 25mm deep plinths from the same
material, filled with steel shot. There were lots of challenges around
attaching the stainless panels and then finally trimming them to fit the
cabinet. A jigsaw with carbide blades for the roughing cutting out,
followed by a low speed cordless router with a carbide spiral cutter
worked well.
Fitting the crossovers within the cabinets was challenging and would
have limited future access, so in the end, I decided to mount them in
matching external carbon fibre skinned boxes, with everything connected
via Canare 4S11 starquad speaker cable and Neutrik Speakon connectors.
I've used Neutrik Speakons for years. They're robust, reliable, have a
very low contact resistance and a very high current rating. After all,
they're the standard equipment for stage and studio the world
over!
I still have some way to go in terms of final finishing. The first
cabinet is ready for final flatting and polishing and fitting of the
drive units, the second cabinet has its drive unit cutouts completed and
is ready for stainless trimming.
When both cabinets are completed, I'll begin fabrication of the plinths.
In the interim, here are the photos of the construction so far. I will
update with further photos as the build progresses.
I ought to weigh the cabinets again. At last weigh-in before addition of
the carbon fibre, resin and drive units, I was up to 42 kg per cabinet.
I reckon current mass is ~46 kg and the plinths will add a further ~20
kg to the build.
I've been a fan of your website and speaker designs for years. I built a
pair of SP 83s a good number of years ago (18W8531 and D2604/830000) and
I'd like to thank you for you enormous contributions to the DIY audio
community.
If you have any questions, please ask. I'll be more than happy to
answer.
Best Regards,
Graeme Finlayson
https://www.dropbox.com/sh/l1vhy6k7uadkrsv/AAAPiIDyETdTKxU5ukH5_4tya?dl=0
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