Is it all about the BASS? Subwoofer Build

THE BUILD: LOTS OF CLAMPS!!!

The next challenge was the gluing together of all 18 layers.  I have seen other build threads of laminated designs and the glue up didn't always go well...!!!  Some people had problems with the layers drifting slightly and this would create a skewed, non-square cabinet.  I needed to plan well and couldn't risk a big mistake at this stage.  Some laminated constructions use continuous dowels (wood) or long steel rods to align and tie all the layers together, however, these were sometimes problematic and skewed.  After some thought, I decided to use short dowels and ensure each layer has some degree of interlock - this would further enhance strength, but would allow me to tweak the alignment of the layers as the glue up progressed.

I decided to use 4 dowels per layer.  The weakest point is the intersection between the horizontal and vertical braces - this is only a 16mm x 16mm square and I wanted to ensure a very strong bond here. The orange arrows show the dowel points:



I decided to use 6mm diameter and 40mm long wooden dowels.  Each layer is 24mm thick, so a dowel centred through one layer would protrude by 8mm into each neighbouring layer.  Therefore, I would put a 40mm dowel into every other layer.  This is quite difficult to explain so here is a sketch:



You can see that everything is tied together nicely, and (crucially) there will be some adjustment to correct any drift/skew during the gluing process.

The next challenge was to drill holes very precisely... The holes had to be in exactly the same place on every layer and the holes had to be perfectly perpendicular to the layer.  Even a tiny error would be magnified with each layer.  I made a jig which would fit snuggly over a layer.  This jig had 10mm holes so the router guide collet would slot in and align each hole perfectly.



NB: the (top) outer holes are for a slightly different dowel position on 3 of the rear (hypex) layers.  Here the braces have been cut to allow clearance for the passive radiator basket and the dowels have shifted outboard very slightly.

I gathered all of clamps and began the glue up process...  I started at the back (rear baffle) and worked up.  I used a good quality, waterproof PVA glue - this was applied liberally and consistently to one surface.  Once glued the layers are easily repositionable for about 30mins, so I had to work fast and did about 5 or 6 layers in a gluing session.  As feared, the layers did drift easily - it may only be 0.2mm between two layers, however, this became 1mm over 5 layers - EEK!  This would equate to 3-4mm skew over the full 18 layers!  NOT GOOD!!!



Fortunately, I had anticipated the drift, so after gluing 5-6 layers I got a set square and used the clamps to force the layers into a perfectly square alignment.  The glue had not cured, so it was relatively easy to get a handful of layers in perfect alignment.  Once aligned I could clamp all of the layers together with considerable force - the rear baffle was protected from the clamps with pieces of scrap wood.



Each gluing session took about 45mins and around 5 or 6 layers were clamped (depending on drift).  Those layers were left to cure for 24 hours before the next 5-6 layers were glued into the stack.  After 3 days (only about 1 hour per day) the stack was 17 layers high:



Just the front baffle remained!  That would be glued into place once it had been routed for the inset veneer.  Routing for the veneer was a massive challenge and did NOT go perfectly to plan (some stressful times ahead...).  The veneering is covered in the next instalment - stay tuned folks!

Can they be 'upgraded'  

*edit - no idea what happened there;

I love a good plot twist. What happened next!?

This is where a wide metal scraper and plastic wood/body stopper comes in handy to get rid of imperfections.

Do you mean to lay smoked chestnut in the centre of the baffle with a 20mm border and then fit a 20mm frame of birch veneer around?

Edit: The Birch ply veneers are 1.4mm thick, so I'd need to match that with 0.6mm thick Chestnut?  Perhaps sand the birch veneer to match?

yep you can do that,why are they so thick? perhaps look around at different suppliers?

I did consider that, but wasn't sure if the veneer would bond consistently to filler.  I was also worried about perfectly flatting the filler...

The devil's always in the detail.

Very true, the top veneer thickness is lost in a small roundover anyway. Your comments are much appreciated - always good to learn new skills and gather other good ideas and tricks.

That is flippin' stunning.

It's a beauty!

Thank you, that's a good tip. There may be a second sub one day, so I'll probably do that on the next one.

THE BUILD: SANDING, VARNISH AND FINISHING!

All of the awkward and potentially difficult work was now completed, just the finishing remained...

I sanded the sub with belt and orbital sanders, and then finished it by hand.  Sanding was relatively quick as the parts were routed pretty close to finished size.  The birch ply layers came up pretty well:





I varnished the sub with a water based floor varnish.  I have used this varnish before and it works really well on speakers - it gives a great finish and is extremely tough.  The varnish was applied in very thin layers with a foam roller and later coats with a cloth.  I used wet and dry paper to lightly sand between each coat.  In all 10 coats were applied and the sanding was done with progressively smoother wet and dry paper.  Between coats 1-3 was 400 grit, coats 4 and 5 was 800 grit, coats 6 and 7 was 1200 grit, coats 8 and 9 2000 grit.  The final coat was finished with 3000 grit and finally smoothed with a car polish.  This is method advised by a bodyshop (where my speakers were painted - that's the next build thread!  ).  My Father (a carpenter) was also consulted on the best finishing method.  It worked extremely well and gave a very smooth satin finish (photos don't do it justice):




It was now time for final fit out and wiring.  Here is the Hypex and passive radiator in place:



The feet are cones made from 24 birch ply offcuts.  They are height adjustable and attached to 6mm threaded inserts in the base. 

This is the finished sub:







Thanks so much for following the thread to this point.  There will be a few further posts where I cover the break in, setup, integration and sound quality.  

The next thread will be my speakers so stay tuned if you like some DIY woodworking...

Thank you!  .  SWMBO is actually pretty chilled about my HiFi obsession!  I am fortunate enough to have a separate room, so have relative freedom on what goes in there (as long as I don't spend too much!!!).  She does really like them and was consulted a lot on the design.  I am probably more particular than her and wanted them to look pretty.  A sub is often a bit of a brute, and I wanted a sub and a good looking piece of furniture.  

I will mention the sound soon.  <SPOILER ALERT>  I don't miss the stereo pair of REL t7i's it replaces!