12″ Ported Bass Cabinet. Tolex covering, and fixture fitting.

Before covering the cabinet – I want to rout out a few recesses in the carcass. This is so the fixtures can fit over the tolex, but sit down, flush with the surface. I’ve got hold of a pair of reclaimed bass cabinet handles off an old Ashdown 4 x 10″ cabinet. To be honest – they’re a bit overkill for a cabinet this size, but I don’t want to see them go to waste. The jack plug socket is a plain, circular, 1/4 inch Marshall type. I’m going to mount that on the side of the cabinet – adjacent to the speaker, towards the rear, so it’s out of the way – but easy to access. It’ll also keep me from having to chop the back panel about.

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The handles go pretty much dead centre in each side of the cabinet, but mounting them a  little higher than centre, gives a better visual balance. After tracing the handles onto the carcass, by drawing round each, in turn – I fit a straight cutting bit to the router, and set the plunge depth to about 1.5mm. Using a combination of an edge following attachment, and a bit of careful freehand – I remove a portion of each, marked cut-out. I’m aiming to get the routed area to be approximately 2mm larger than the handles, all round. It’s important to keep an area intact in the centre while the outline is cut – so that the router always stays level.

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The handles have a deep recess. After calculating how much of a cut-out will be required for each handle – I mark the area to be cut, and drill through at the corners, using a 10mm drill bit. This marks the edge of the cut-out area, where the handle recess will sit. It’s repeated for both sides, and then the recesses are cut out with a jig-saw. The internal transitions on the handles – from flange to recess – are slightly eased. To help with the overall fitting of each handle, I round over each of the cut-outs with a rounding over router bit.

The jack plug socket is marked out in the same way – checking that the cut-out is positioned so that the socket does not clash with any of the sides or reinforcing battens, and so that the connecting wires can easily reach the area where the speaker will sit. The cutout is routed to a depth of 1.5mm to accomodate the socket flange, and a central area drilled through the carcass with a spade bit – big enough to accommodate the jack plug mechanism. Once again – the edges of the opening are rounded, to ensure that the socket sits properly within the opening.

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With all three of the cut-outs complete, I spend a good while checking the cabinet over for any rough areas, or faults which require filling. I don’t want to leave any imperfections in the finish which may be large enough to telegraph through the Tolex covering – so any super rough areas are sanded flat, and any places where the plywood has torn, or where the dowel posts have been exposed when rounding over the edges, are filled with a two-part filler. The whole carcass is then given a final check over, and a good brushing and vaccuming out.

Because I need an air-tight box when the project is complete, I also run a bead of sealant around the junction of each batten, with the outside carcass. These joins are already glued and screwed – so a silicon bead should act as belt and braces. I wouldn’t necessarily go out and buy sealant, if I didn’t have any in – but I’ve got some suitable bathroom sealant left over from a DIY job. Now, I’m possibly the world’s worst person when it comes to applying a neat silicon bead – but no-one’s going to see this. (I find that if you dip a gloved finger in white spirit, and then push and form the bead as you pull your finger along the junction – you push the silicon into the angle of the joint, simultaneously remove any excess silicon, and make an air-tight seal – all at the same time). But that isn’t how the pros do it, of course. It’s a messy business – but once done, it should ensure that the speaker and ports work as they are intended.

The silicon will take a while to cure – so, after cleaning down the workshop, (I don’t want sawdust all over the place while I’m sticking the Tolex on), I leave everything overnight, so I’m ready to move on, first thing in the morning.

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Next day – fresh coffee. I’m using a Marshall type, “Levant” Tolex for the cabinet. I was after “Elephant” Tolex, which would have been an almost perfect match – but my supplier was out of stock. Even so – the “Levant” should match pretty well with the the covering of the Ashdown bass amplifier I’ll be using with this cab. I’ve got hold of a 2 metre length of the Tolex, Which should give me two, separate, 2 metre lengths – wide enough to easily cover a cabinet of this size, with some spare left over.

No matter how you cover a cabinet – there will be joins in the Tolex, and although every attempt can be made to disguise the seams – they’re unavoidable. The idea seems to be to locate them on the base of the cabinet, so having identified and clearly marked the top side of the cabinet, the Tolex is measured and cut to provide two pieces of material, wide enough to wrap the box. One smaller piece is cut to cover most of the base of the cabinet – a second piece covers the other three sides, with enough spare at each end to overlap.

The smaller piece is then glued and stuck to the base of the box. I’m using a spray, contact adhesive. It’s messy stuff – so I need to get organised and spend a bit of time covering over the workbench, and anywhere that might get accidentally oversprayed. Both the Tolex and the cabinet needs to be sprayed, and then the glue has to be left for a while to “tack up” properly. Once the material is bonded to the side of the cabinet, I use a roller to make sure there are no air bubbles, and to ensure the glue is well bonded.

The larger piece of Tolex is then stuck to the body, in exactly the same manner – the roller working from the middle of the top side, outwards – down each side in turn – until the cabinet is lying on its’ back again. The joins between the two pieces of Tolex are then cut using a sharp knife along lines, equidistant from each edge. It’s easy to use the width of the straight-edge, as a convenient measure. Each cut is done through both pieces of Tolex, and then the excess is taken from each, so that there’s a straight butt joint between each piece. The glue stays “open” for about 20 minutes – so the join can be pushed about and manipulated until the join disappears. The whole area is then well rolled all over – to make sure the bond is the best it can be.

At least, that’s the theory. In practice, the material is quite stretchy – so you have to get the tension right before making the overlapping cut. Let’s just say – I’m new at this and I’m clearly not the world’s best upholsterer. Not on the basis of these joins, anyway. But then maybe they’re not so bad. It’s just a question of technique., and it’s not exactly rocket science. The joins are functional – they’re on the bottom of the cabinet, and I’ll be able to hide the worst of it all by attaching the rubber feet over the joins.

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Did I mention how messy this spray glue is? Inevitably – there’s some overspray, and glue contamination from the joins, and it’s all over my hands, and I’m trying to be tidy and precise. Cellulose thinners is supposed to be the solvent for the glue – but it also appears to soften the Tolex vinyl. A little goes a very long way – so be warned. And put a mask on. Open the windows.

Also – now that the sides of the cabinet are covered – the material which is stretched over the cut-outs can be cut away using a sharp knife.

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The material is then squared in each corner, and cut – so that each side is released. There’s a particular way in which the mitres can be cut, so that the seam is invisible, and so that each corner is well wrapped. I’ve watched it a hundred times on YouTube, and it looks easy – but it isn’t. It isn’t easy at all, and I’ve wrapped hundreds of canvases in my time. (The process of wrapping canvases has a similar technique, which helps get the corners crisp). I’m not going to describe how I fitted my corners. I can’t honestly say I’m anywhere near mastering it. Needless to say – my approach was based on the recommended procedure – but things went a bit awry here and there. You might want to make sure you cut away the correct pieces of material, and properly mask off the areas where you spray. It helps to wait until the glue on each face is left to properly “tack-up” before sticking down, and then to stretch and burnish down each piece, especially into the corners, so that the bond is good. It seems to help if you gently warm each roundover edge with a heat gun, once the fabric has been stretched into place. This seems to help the Tolex conform to the correct shape  – but beware. Too much heat seems to soften the glue again.

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After a bit of a struggle – maybe the result isn’t too bad, after all. Fortunately – the worst of each mitre join is hidden by the subsequent attachment of the metal corner brackets. Each is held in place by two wood screws. The handles and jack plug socket can also be attached at this stage – the fitting of each one pulls the fabric in, and over the edge of the routed areas, to provide neat, narrow reveals all around each fixture.

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Once the glue has dried I mitre, and stick a length of rubber, door sealing gasket around the inside face of the rear panel opening. It’s another left over from DIY around the house – but won’t go to waste in making sure the box remains air tight, once the rear panel has been fitted and covered with its’ own tolex covering.

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Four rubber feet are screwed into position on the base of the cabinet – right over the seams I had so much trouble with. Actually – the more I look at the finished result – the more I can see that the worst mistakes are (mostly) hidden from view. Get a grip man – it’s just a Tolex box, after all. Most of the “difficult” areas are on the inner corners, and will be hidden once the baffle and rear panels are in place. Because the rear panel has been cut to exactly match the sides of the cabinet, the fit is incredibly tight. To allow for a snug fit with the addition of a few layers of Tolex – I’ll have to re-measure and trim a few millimeters off each side. I’ll wait until the glue is dry everywhere else before I cover and fit the back panel. It’ll give me a chance to track down some screw head cups, and some suitable wood screws to finish off the job.

Next on the job list for the cabinet, will be the fitting of some sound-deadening foam inserts – to line the box, before I get to the critical stage of finishing the baffle board, and fitting the speaker and sound ports.

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