Troels Gravesen's PMS (Poor Man's Strad) DIY build

[THOMO]

One of the more interesting kit designs around with them having a very benign  impedance and reasonable efficiency so that opens the door to using simple valve amps and minimalist Class A type amps.

[The Mad Scientist]

Front baffles assembly completed (I should have taken some photos) and additional Hawaphon added in the gaps.

 

 

The curved section of the front baffles was more or less the same process as the rear panels. Sections of kerf bent plywood sandwiching a sheet of DodoMat MLV. The ends of the flat portion of the baffle and the beginning of the curved section were mitred (16°) to get the best fit at the transition. Mitres were glued up by lining up with masking tape, then applying 2 part mitre fix to the joint and folding them together with the tape acting as the hinge.

 

Dodo Mat was applied after slapping on a big layer of vinyl adhesive, then the top section was placed with masking tape hinges, another layer of vinyl adhesive and then 2 part mitre adhesive applied along the joint before folding over and then strapping down with ratchet straps.

 

Working quickly with lots of tape, 3 adhesive components and gloves, I forgot to take photos!

Incidentally, the curved sections of the front baffles are not made  from Baltic Birch ply. It's almost completely unavailable in the UK, due to the Russian invasion of Ukraine.

 

My local branch of a nationwide timber supplier now stocks their newly developed "Stretek". Essentially a product made in China to the same ISO glueline spec as Baltic Birch, but using Poplar. It's not as well made - edges don't cut as cleanly on my tracksaw, there's the odd internal void and it's only ~82% as dense as Baltic Birch. Beggars can't be choosers, so it's all I have to work with at the moment.

 

Felt applied to Hawaphon on the front layer.

 

 

 

I've taken a bit of a diversion with the cabling. Fitting the crossovers inside the cabinet was always going to be tight, and they would have been completely inaccessible once fitted, so I'm going down my initially rejected route of external crossovers. Initially suggested by a member of the Roon Community by using a single run of 4-core, but I've decided to do it properly with a single 4-core Starquad to each driver. Going to make up a couple of carbon fibre wrapped Baltic Birch boxes (from my last remaining piece) for them with lots of Neutrik Speakon connectors.

 

I'll have short runs of Canare 4S11 to the boxes from the AHB2s, then 3 runs to the speakers, one for each driver. Another 15 metres of 4S11 ordered and delivered from BJC within 48 hours!

 

One of the challenges was how to drill in holes for the Neutrik sockets on a curved rear panel.

 

I have a really nice UJK drill guide, so a mod with a few button head hex screws (to clear the base from the curve) and some Blu-Tack dots enabled me to drill holes radially, so the connectors would sit flush with the curved panel.

 

7 mm pilot hole first:

 

 

Then hole saw:

 

Finishing the last 10% from the inside to prevent break-out:

 

Finished holes (the shiny stuff is mitre bond spread around outside where the hole would be cut to prevent the surface ripping out with the holesaw):

 

 

And with the Speakons test fitted. Nice snug fit:

 

 

To keep the holes clear of resin from the carbon wrapping, they're plugged with plasticine:

 

 

Internal wiring installed. Nothing fancy, just 14 AWG, silicone insulated, tinned OFC:

 

 

Prior to installing the acoustic wadding, I polished the area around the ports and fitted the ports with epoxy:

 

 

The wadding around the ports had to be fitted before the front baffle was fitted, so ports had to go in first:

 

 

Mirror polishing is quite a process. 120 grit flap disc, followed by Norton Vortex Rapid Blend disc, followed by Norton Rapid Blend 2SF/3SF, followed by felt flap discs with black, green and white polishing compounds, then a final, low speed polish with Autosol. As a frequent welder/metalworker, I have lots of grinders (3 x 4 1/2" and 3 x 5"). Cordless due to variable speed and portability. My pair of nine inchers are still mains powered:

 

 

I keep the felt flap discs and their respective compounds separated in Ziploc bags.

 

Front baffle glued up and strapped down:

 

 

Still a long way to go, bit they're beginning to resemble speaker cabinets. And at 42 kg each now, every workshop session is becoming a workout!

Edited May 30, 2023 by The Mad Scientist
typo

[The Mad Scientist]

The astutely safety conscious amongst you may notice that the grinders are guardless. I only use them like this for polishing. Nothing worse than getting almost to the end of a mirror polish and sctratching your workpiece with the guard. For grinding, I use the standard guard, and for cutting, the additional auxiliary clip-on guard. I also wear a full-face visor. Never, ever, ever, ever, ever work with cutting discs without a full-facer, or wear loose clothing, or anything with a hood that has a drawstring.  I've seen lots of accidents with grinders, including one within our company where a guy in a hooded waterproof coverall, got the drawstring caught in a grinder he was using. I'll leave the rest to your imagination. He survived, but his injuries were not insignificant.

[kiwilistener]

9 hours ago, The Mad Scientist said:

Front baffles assembly completed (I should have taken some photos) and additional Hawaphon added in the gaps.

 

 

The curved section of the front baffles was more or less the same process as the rear panels. Sections of kerf bent plywood sandwiching a sheet of DodoMat MLV. The ends of the flat portion of the baffle and the beginning of the curved section were mitred (16°) to get the best fit at the transition. Mitres were glued up by lining up with masking tape, then applying 2 part mitre fix to the joint and folding them together with the tape acting as the hinge.

 

Dodo Mat was applied after slapping on a big layer of vinyl adhesive, then the top section was placed with masking tape hinges, another layer of vinyl adhesive and then 2 part mitre adhesive applied along the joint before folding over and then strapping down with ratchet straps.

 

Working quickly with lots of tape, 3 adhesive components and gloves, I forgot to take photos!

Incidentally, the curved sections of the front baffles are not made  from Baltic Birch ply. It's almost completely unavailable in the UK, due to the Russian invasion of Ukraine.

 

My local branch of a nationwide timber supplier now stocks their newly developed "Stretek". Essentially a product made in China to the same ISO glueline spec as Baltic Birch, but using Poplar. It's not as well made - edges don't cut as cleanly on my tracksaw, there's the odd internal void and it's only ~82% as dense as Baltic Birch. Beggars can't be choosers, so it's all I have to work with at the moment.

 

Felt applied to Hawaphon on the front layer.

 

 

 

I've taken a bit of a diversion with the cabling. Fitting the crossovers inside the cabinet was always going to be tight, and they would have been completely inaccessible once fitted, so I'm going down my initially rejected route of external crossovers. Initially suggested by a member of the Roon Community by using a single run of 4-core, but I've decided to do it properly with a single 4-core Starquad to each driver. Going to make up a couple of carbon fibre wrapped Baltic Birch boxes (from my last remaining piece) for them with lots of Neutrik Speakon connectors.

 

I'll have short runs of Canare 4S11 to the boxes from the AHB2s, then 3 runs to the speakers, one for each driver. Another 15 metres of 4S11 ordered and delivered from BJC within 48 hours!

 

One of the challenges was how to drill in holes for the Neutrik sockets on a curved rear panel.

 

I have a really nice UJK drill guide, so a mod with a few button head hex screws (to clear the base from the curve) and some Blu-Tack dots enabled me to drill holes radially, so the connectors would sit flush with the curved panel.

 

7 mm pilot hole first:

 

 

Then hole saw:

 

Finishing the last 10% from the inside to prevent break-out:

 

Finished holes (the shiny stuff is mitre bond spread around outside where the hole would be cut to prevent the surface ripping out with the holesaw):

 

 

And with the Speakons test fitted. Nice snug fit:

 

 

To keep the holes clear of resin from the carbon wrapping, they're plugged with plasticine:

 

 

Internal wiring installed. Nothing fancy, just 14 AWG, silicone insulated, tinned OFC:

 

 

Prior to installing the acoustic wadding, I polished the area around the ports and fitted the ports with epoxy:

 

 

The wadding around the ports had to be fitted before the front baffle was fitted, so ports had to go in first:

 

 

Mirror polishing is quite a process. 120 grit flap disc, followed by Norton Vortex Rapid Blend disc, followed by Norton Rapid Blend 2SF/3SF, followed by felt flap discs with black, green and white polishing compounds, then a final, low speed polish with Autosol. As a frequent welder/metalworker, I have lots of grinders (3 x 4 1/2" and 3 x 5"). Cordless due to variable speed and portability. My pair of nine inchers are still mains powered:

 

 

I keep the felt flap discs and their respective compounds separated in Ziploc bags.

 

Front baffle glued up and strapped down:

 

 

Still a long way to go, bit they're beginning to resemble speaker cabinets. And at 42 kg each now, every workshop session is becoming a workout!

I feel yah mate. By the time you get them all together, put the crossovers and drivers in and mount them to their plinths they will probably weigh as much as mine did. Keep at it I want to see what you think of them once you have them going.

Edited May 31, 2023 by kiwilistener

[The Mad Scientist]

A bit more progress. Trimming off the edges of the front baffles. Stainless flat bar (I keep various lumps around for backing aluminium parts when welding) provides a straight edge, a stable base and allows me to set the height of the router cutter. Use a brass guide bush just a little bigger than the cutter. Running a bearing guided cutter was "nibbling" the edge of the stainless bar.

 

 

 

I'm pausing on the cabinets for now. The next stages get into the carbon wrap and I want to get a feel for it (no doubt there will be learnings and refinements!) before I embark on wrapping the cabinets, so I'm getting onto the crossover boxes first.

 

Mitred sections for the boxes lined up and masking taped ready to glue up:

 

 

The masking tape makes it dead easy. Glue up, fold over and everything is aligned, only the last join really needs clamping.

 

Flipped over, ready for the glue:

 

 

Glued, and the open corner clamped up. The additional clamp was to check for squareness:

 

 

I overcut mitres by about 0.5°, this ensures the external corner closes fully and allows room for the glue at the inside corner:

 

 

Bottom panel glued in. Fit up isn't quite as precise as I would like, but it's not furniture and as it's being carbon wrapped, I'm not stressing over it:

 

 

 

 

I'll start on the carbon fibre next.

 

Edited June 5, 2023 by The Mad Scientist
typos

[The Mad Scientist]

Now things are getting a little more exciting!

 

Black epoxy base coat painted onto the bottom of the crossover boxes:

 

 

Once it reaches the "tack" stage (1.5 - 2.5 hours), it's time for the carbon fibre overlay:

 

 

After a further couple of hours, wetting out the fibre with the first coat of clear epoxy:

 

 

Despite being only ~0.2mm thick, the carbon fibre is starting to take on that really nice 3-Dimensional appearance:

 

 

 

[Keith_W]

Wow, this is truly next level. I can't wait to see it finished. How much of this have you done before? Did you have to learn new skills along the way? 

[The Mad Scientist]

6 hours ago, Keith_W said:

Wow, this is truly next level. I can't wait to see it finished. How much of this have you done before? Did you have to learn new skills along the way? 

 

Thank you.

 

This whole project has been quite challenging in terms of figuring whether stuff will work and then finding the best way to do it.  I've built speakers before and done raw veneering, but they were simple boxes.

 

This is the first time I've done a curved cabinet, used kerf bending and a constrained layer construction. It's also the first time I've gone big with stainless steel.  The anniversary present for the my wife gave me the confidence that I could tackle the stainless successfully.

 

The carbon fibre skinning is completely new to me too, but there are loads of online video tutorials that show how it's done. It takes time and patience and there are no shortcuts! Hence,  starting with the easy bits to get a good feel for it before tackling the main cabinets.

 

I've done a few little trials with stuff here and there to test the ideas out before committing and so far it seems to be working out OK.

 

I'm never satisfied unless I keep pushing and trying/learning new things.

 

I've also grown more patient with age - I'd never have coped with a project like this 20, or even 10 years ago.

Edited June 6, 2023 by The Mad Scientist

[ICUToo]

36 minutes ago, The Mad Scientist said:

I've also grown more patient with age

Yers, that's the real thing, isn't it?

You can do a step, then leave it for a day and come back.

As a youth, I tried to finish projects stat- didn't work out so well...

Edited June 6, 2023 by ICUToo
selling

[ENIGMA]

Us DIY people here appreciate the work.

 

Looking forward to seeing the wrapped finish, i used CF on my Sophera speakers and  when yo see the light shine on it the effort is justified. These are large panels and the CF is a smart choice as the dark grey look is not so imposing.

[The Mad Scientist]

A bit more progress.

Lids for xover boxes roughed out on the table saw and then routed with a flush trim bit. New router's first time out of the box. Didn't want to do any critical stuff with it until I have a proper feel for it

 

 

 

 

 

Pilot drilling for the threaded inserts:

 

 

Drilling out the holes for the threaded inserts:

 

 

Threaded inserts in and ground flush and aluminium inserts in the screw holes on the lid

 

 

With the fasteners before carbon skinning:

 

 

I've also set about making the pieces to close the cabinet ends off. 3 layers of 12 mm "Stretek" plywood laminated up and glued with Titebond 2. First two pieces clamped up:

 

 

Trimmed up on the tablesaw:

 

 

Curve marked out and a good few passes on the table saw:

 

 

 

Ready to start sanding:

 

 

First curve taking shape:

 

 

I treated myself to a new sander in preparation for this project. A Mirka Deros 5650CV. Completely dustless and the Abranet abrasives are just superb. Most expensive sander I've ever bought, but I suspect it'll be the last one I'll ever need to buy.

I'm thinking to add a strip of 3 mm aluminium between the cabinet and the ends. Rather than just big, black monoliths, the strip of Al might help to break up the outline a little.

[The Mad Scientist]

Second set of cabinet ends glued up:

 

 

First carbon layer added to the xover box lids and top and bottoms flatted out with 120 grit ready for the next parts of the carbon wrap:

 

 

[The Mad Scientist]

I'm long overdue an update.

 

Apart from progressing with the carbon, I’ve tidied the ends of the cabinets, and cut the remaining end pieces:

 

 

From the scorching it’s clear my table saw blade is overdue a clean!  Aluminium pieces cut out too:

 

 

 

Very messy with the table saw.  For safety, I use an aluminium specific blade which has a very different tooth profile and different rake from a wood cutting blade:

 

 

 

A fair bit of sanding needed to pull it all together, but it’s getting there:

 

 

 

 

On with the xover boxes. Once the initial ‘wetting’ coat of resin is applied, it is left to fully cure before sanding with 120 grit to key the surface. Then 3 to 4 coats are applied in succession, roughly 2 hours apart while the previous layer is ‘set’ but still soft.

 

 

 

 

 

The pros make this stuff look so easy. In fact, it’s not that easy at all. The base coat is the same as the top coats with the exception of a black filler material. This prevents the base material from showing through the carbon fibre, especially if it is light in colour. It is applied and left to reach the ‘B’ stage (roughly 2 hours after initial application) before sticking the carbon fibre layer on.  If it’s not at quite the right stage, you get some bleed-through which is visible in the final finish:

 

Despite being thin (~0.2 mm) and flexible, the carbon fibre doesn’t really like to go around 90° corners. Three of the box corners are slightly rounded, the end corner is square:

 

 

Ignore the curve at the bottom, that’s lens distortion from my phone’s camera.  For future projects with square corners, I’ll work it like a veneer project where you veneer each face separately and trim before applying the veneer to the adjacent side.  Even at ‘B’ stage, the base coat isn’t actually all that sticky, so the resin doesn’t “glue” the carbon fibre in place. One of the end corners opened and needed a repair. Carbon fibre seems to be reasonably forgiving in this respect. If the weave is lined up and glued properly, the overlap seam is only visible when inspected close-up:

 

 

I take my hat off to anyone who makes proper carbon fibre components with resin infusion. Whilst it may look easy on video, it takes a great deal of skill!  I’m glad I retained the patience to start with the xover boxes. The learnings will be very useful when it comes to the cabinets.

 

Taking in the learnings from the boxes, I took a different approach with the lids.

Applied the base coat to just the top surface, and then used FusionFix to stick down the edges. It’s a resin compatible thermoplastic adhesive which holds down the carbon fibre but still allows the resin to flow and adhere. It’s also great for stabilising cut edges. Even though the fibre weave I have is resin impregnated for better handling, it still tends to fray a little and shed fibres at the edges. The FusionFix holds it together for much cleaner cuts:

 

 

Edges folded over and trimmed ready for the “wetting” coat:

 

 

Wetting coat applied :

 

No “mistakes” to correct this time around

 

Remember those aluminium inserts in the lid? Time to find them again:  A quick measurement:

 

 

Followed by a pilot drill with a Dremel:

 

 

Bullseye! Plasticine

 

 

A quick switch to a spiral router bit and a clean hole with the plasticine removed:

 

 

 

And then drilled through with a nice brad point bit:

 

 

 

 

Flatted down with 240 grit and holes for Neutrik Speakons drilled out:

 

 

320, 400, 800, 1200 and 2000 grits followed by cutting compound on a sponge pad. Internals sprayed with matt black paint:

 

 

Competed box with stainless fasteners:

 

 

 

 

Both boxes completed, crossovers fitted and everything wired up:

 

 

 

Right speaker cable partially completed:

 

 

Edited July 2, 2023 by The Mad Scientist

[El Tel]

Very impressive, Graeme. Looking quite special.

[Janus77]

Great job!

[Ian McP]

Jeez, with those skills you'll be building a WW2 Mosquito next!

 

 

[ENIGMA]

4 minutes ago, Ian McP said:

Jeez, with those skills you'll be building a WW2 Mosquito next!

 

 

Out of carbon fiber would certainly be amazing.

[The Mad Scientist]

A few very hectic work weeks, followed by a much needed week off to de-stress, decompress and recuperate  whilst engaging in creative pursuits.

 

Second speaker cabinet. 1st  end cap and aluminium insert sanded flush.

 

 

My "apprentice" keeping a watchful eye on progress:

 

 

The plywood piece has locating pins to ensure alignment with the aluminium after carbon skinning. Cabinet and end pieces with be skinned separately then glued together with the aluminium sandwich. The aluminium will then be embedded in the intermediate resin coats:

 

 

Making the end caps out of laminated plywood has an added bonus. The layers, when sanded, provide a "contour map" which enables a quick visual check of evenness of the curve:

 

 

I picked up a box of Mirka 40 grit Abranet HD sanding discs to speed the process up. Gloves are a must with these - the edges are lethal. Each end cap ears 2 x 40 grit pads just for the roughing out.

 

On flat surfaces, the sander is dustless, but on contours, it tends to throw a fair amount of debris, so my trusty air-powered respirator is needed. One of the best investments in my health and safety ever.  Rechargeable battery on the back, has replaceable carrtridge filters and disposable visor films:

 

 

Achieving a seamless blend between the main cabinet, the aluminium fillet and the end cap is a laborious and time-consuming process. 40, 80 and 120 grit, filing of the aluminium and hand sanding the plywood at the ends where the sander can’t reach. Even with a belt sander to rip the excess aluminium back to speed up the process, it was still nearly four hours per edge, ~16 hours for both cabinets.

 

Beginning to resemble a speaker cabinet now:

 

 

3.2 mm locating pins (short lengths of spare welding Tungsten) glued into the baffle ready for my Jasper circle jig to cut out the holes for the drive units.  I’m taking a slightly different approach to the cabinets than I did for the xover enclosures. There were a few imperfections due to base layer bleed through and inadequate coverage with the black base coat resin.  This time, I’m going all out. Black water-based dye coat first:

 

 

Next, I’m applying the black base coat, but allowing it to fully cure, followed by keying with 120 grit abrasive:

 

 

Cleaned up, ready for a clear “basecoat” to adhere the carbon fibre skin:

 

This way if there’s any bleed through, it’ll be clear resin and invisible once the wetting out and build coats are applied.

There was a little movement at the edges of the base panels, despite being glued on with polyurethane adhesive, so I’ve added additional stainless screws to tighten everything up:

 

 

Drilling stainless and countersinking the holes is easy with a drill press or a suitably anchored mag drill. Drilling it by hand is a whole different ballgame - exerting enough downward pressure on the bit to get it to bite into the stainless is nigh on impossible. Took me 2 hours to drill and countersink 4 holes. 

For the second one, I’m breaking out the magdrill! I have a couple of long ratchet straps in the car for the roof bars which should be long enough to tie it down.

First piece of carbon fibre for the rear of the first cabinet cut, edges bonded ready for final trimming and cutout to fit around the router pin for the midrange port:

 

 

First pieces of carbon fibre in place:

 

 

Prepping the remaining carbon fibre for the main cabinets:

 

 

Locations of router pins marked out, glued up with FusionFix and drying out ready for the cutouts:

 

 

 

First baffle skinned in carbon!:

 

 

The "wetting” coat has been applied to all of the first cabinet, allowed to cure and “keyed” with 120 grit. First aluminium insert and end cap in place:

 

 

After keying, degreasing and applying a substantial bead of Araldite Ultra, the aluminium was laid in place and then held down by 7 stainless steel screws. A further bead of Araldite was applied to the top of the aluminium insert and then the carbon-wrapped end cap was fitted with its locating pins and then clamped down with ratchet straps. I went with Ultra rather than Rapid as it has a longer open time to allow for positioning. The only downside is that it takes 8 hours to reach handleability and 14 hours to cure to full strength.

 

Edited July 25, 2023 by The Mad Scientist
extra image removed

[Mr 57]

Looking through your progress pics, that is SERIOUS, serious commitment.

The time you have taken, the fantastic finishes you are achieving, blows me away ! 
I was going to say I “hope” they turn out well, but that’s undercutting it, there is  no doubt they WILL be fantastic!!

[The Mad Scientist]

Thank you!

 

When I kicked off this project, I seriously underestimated the scale of what I was taking on and the time and commitment it would require!

 

It has forced my skillset to entirely new levels and tested my ingenuity like nothing before.

 

I'm looking forward to the finished article, but at the same time I will definitely miss the journey.

 

 

[kiwilistener]

2 hours ago, The Mad Scientist said:

Thank you!

 

When I kicked off this project, I seriously underestimated the scale of what I was taking on and the time and commitment it would require!

 

It has forced my skillset to entirely new levels and tested my ingenuity like nothing before.

 

I'm looking forward to the finished article, but at the same time I will definitely miss the journey.

 

 

Yes indeed, large projects have a habit of demanding your time and attention to detail, as well as having to learn to improvise on the run. When I built my pair of "Strads" I ran into all sorts of tricky situations. Would I build a pair again today? Not a chance. While the result was rewarding, I found that I was not truly happy with their performance. Wide baffle speakers have a sound of their own and truth be told the room I had them in wasn't sufficiently big enough to hear them at their best.

I found sound stage and imaging wasn't as good as it could be and in fact my current speakers are significantly better than the "Strads" in that regard, proving the point that having the right room for speakers of this size is almost as important as the speakers themselves. I will be really interested to see what you think of the Strads. Initially I was impressed with mine, but after many months of critical listening I slowly decided to replace them. Hopefully you have a better outcome than I did.

[The Mad Scientist]

I'm hoping they'll work well in the intended room. There's a fair amount of room treatment to control reflections and to diffuse the rear reflection from the listening position which is closer to the wall than ideal. It made a huge difference to my ZRTs. Widened, deepened and increased the height of the soundstage immensely.

 

Obviously, I'll also have to redo my REW corrections too!

Edited July 26, 2023 by The Mad Scientist

[The Mad Scientist]

Sorry, I've been a bit absent with the updates of late. Work life and home life has been busy.

 

Filling in the "valleys" where the aluminium meets the baffle and the end cap was proving a challenge.

 

Initially, I jury-rigged a setup with a couple of axle stands and offcuts of ply to tilt the cabinet to the right angle:

 

 

 

Turns out this was nowhere near precise enough, so a jig was required:

 

 

 

 

 

 

 

 

 

 

 

 

 

With the jig, I can angle the cabinet precisely to keep the resin in the "valley" and avoid it running all over the place.

 

 

The masking tape helps to provide a boundary. The "lip" can be sanded down before the next coat is applied.

 

Second cabinet assembled and 3 build coats of resin applied.

 

 

 

Lubrication is essential for mechanical and, as I’ve found in my 35 years of legal imbibement, also for biomechanical systems. Some Elvis Juice lubrication from Brewdog enabling smoother progress…

 

Flatting out the first cabinet to find the low spots:

 

 

Despite having a very capable sander, this part is best done by hand. With a 120 grit Abranet on the Mirka, even at low speed, it’s all too easy to go through the resin and find the carbon fibre.  Once it’s all flatted back, I reckon a couple of more coats of resin, then a final flatten before trimming the stainless, trimming out the Neutrik Speakon holes and cutting out the port and drive unit openings.  I was almost out of clear resin, so I ordered up another 5 kg. The current resin is now v.2. Resin to catalyst ratio has changed compared to the previous one, but this stuff is so much easier to work with. It’s slightly thicker when mixed, doesn’t trap air at all (v.1 was pretty good, but this is superb), cures very quickly and sands really nicely without any clogging whatsoever.

 

 

First cabinet flatted back, keyed and a couple of light coats of resin applied:

 

 

Neutrik Socket holes trimmed out:

 

 

And cables retrieved:

 

 

Measuring up the midrange port and drive units so I can work out the router bit sizes and circle jig settings:

 

 

 

 

Drive units have a specified diameter with a tolerance of often up to +/- 0.5 mm, so it’s good to measure them to make sure the cut-outs are a good fit.

 

 

 

 

 

 

I have a couple of Jasper circle jigs, but being US made, they cut circles in 1/16" increments with a 1/4" bit, so I made a spreadsheet to convert to metric with various bit sizes to give me a good range of circle sizes. Most of the time, I can find a size within a fraction of a millimetre of what's needed.

 

 

Drive units routing and test fitting:

 

 

Testing the fit. Nice and snug, just right:

 

 

Testing the midrange for fit:

 

 
Up to the larger 200 jig for the woofer cut out:

 

 

 

 

 

Test fitting the woofer:

 

 

Now test fitting all three after trimming out the "ears" for the tweeter:

 

 

The pieces of thread enable the drive units to be lifted out again after test fitting.

 

Edit: I seem to have a random selection of repeat images at the end of this post and no amount of editing seems to remove them.....

 

 

 

 

 

 

 

 

 

Edited August 31, 2023 by The Mad Scientist

[El Tel]

Epic work, Graeme. I particularly like the Brewdog cameos throughout.

 

Seriously interesting process and a testament to your skills. You are a true Renaissance Man.

[TheBlackDisc]

These are rapidly losing any presentation of “poor man’s” to me.