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



 

Hi Troels,
Just a quick update. The second speaker is finished and they’re now in the lounge, albeit on temporary plinths made from laminated plywood. I will start work on the stainless-steel plinths this weekend (if I can tear myself away from the sofa). I’ve updated the DropBox folder with some more photos.
 
I’ve set up the positioning and toe-in and re-measured and implemented a new set of REW room corrections. It seems my layout measurements were pretty good. According to REW’s step response, both speakers were within 1 mm of the measurement microphone position!
 
The WAF was looking a little dubious at first. I knew I was taking a substantial gamble with the PMS, which is why I really had to pull out all the stops with the looks and go for something really modern and professional looking. It seems the gamble has paid off. There were a couple of initial grumbles about the size of them, however, it seems my wife is beginning to appreciate both the sound and the aesthetics!
 
As to the sound, all I can say is WOW! These sound nothing like any other speaker I have ever heard. There’s a huge cohesive soundstage the width and height of the room and everything just sounds “right”. From the bass through the midrange all the way to the treble. Bass is fast and articulate and strikes a perfect balance between quality and quantity. The midrange is just sublime. The MCA15RCY is a truly exceptional driver. Even the treble has impressed me. The 27TFFC’s performance truly belies its price (I did make your suggested mods though). I’m really not convinced the D3004/660000s in my previous stand mounts is much better, despite being nearly 4 x the cost. How Seas can make such a good tweeter so cheaply is beyond me! I guess everything is helped by the cabinet being very heavy and inert. Even with an ear pressed against the front baffle, there’s no hint of cabinet resonance.
 
The ambience the PMS delivers on live recordings is simply staggering. I now fully understand your comment that this speaker “comes with a room”!
 
Compared to my previous speakers (231 mm baffle width), my PMS has an effective baffle width of somewhere nearer 600 mm. Mine came out slightly wider (approximately 550 mm wide) than the 520 mm of the drawing, though it doesn’t seem to make any appreciable difference to the in-room response.
 
This is purely intuitive thinking on my part – baffle-step f3 for my previous speaker would be somewhere around 500 Hz, for my PMS, it’s nearer 200 Hz. There’s a huge difference in energy distribution between 2pi and 4pi space between 200 and 500 Hz for the 2 speakers. The PMS has much more direct and much less reflected energy in this range. Is that why the wide baffle sounds so different and why there’s so much more ambience?
 
Best Regards,
Graeme