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12" Cab Diary Continued


stevie

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As promised, here are some details on fitting the cab out. We've already gone through the assembly process, but just before you glue the top panel in, don't forget to paint behind the port with some matt black paint. Then drill the holes for the crossover. It's much easier to do with the top off. You could also screw the crossover in now, but it fits through the horn opening - so you could do that later if you like.

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Next up is damping. I suggest you use needled felt for this.A square metre - available for a fiver on Ebay is the best damping material I've found. The photo shows what you'll need. The contact adhesive is available from Screwfix but you could also use Evostick from a can if you prefer, although the spray is much more convenient.

 

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Cut a piece of felt to fit in a U shape on the bottom up to the lower braces on each side. Spray one side of the felt, leave for 30 seconds and glue in.

Then glue a second layer on the bottom panel (but not up the walls). Carry on with the rest of the cabinet until you reach the top. Do not glue any material on the back panel above the top brace, except on the side panel as shown. There mustn't be any damping material near the port.

It's much more convenient to do all of this before glueing the top on. You could connect the wires to the crossover now if you like, but it's no real problem to do it later.

Now you can glue the top panel on and admire your work.🙂

 

 

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You can give the front baffle a coat of blackboard paint now. You could, of course use Tuffcab paint, but I prefer to have a baffle that's matt black. You don't need to paint right to the edge, as you will be fitting some batten all round the outside of the baffle later.

 

While the paint's drying, fit the top handle. It will have to come off later for painting, but it'll make it easier to carry the cab around for the time being. I stuck some bitumen damping material on the back of mine. If you have something suitable, you could do the same. This isn't the kind of touch you see in commercial cabs, but that's one of the reasons why we're building our own (isn't it?).

By the way, the handle will need foam strip. You don't need to do it now but don't forget to do it later.

I'm using woodscrews on mine, because six woodscrews into 30mm of plywood are not going anywhere - especially given the weight of the cab. You can, if you prefer, use t-nuts and machine screws. Up to you.

 

 

 

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You now need to round off the corners. To prevent sawdust getting into the cabinet, it would be best to do this before painting the baffle and installing the wadding. But we wanted to keep the top of the cab open - so we're going to have to do it now.

It would be a good idea to cut a piece of cardboard to place over the baffle. Because poplar plywood is relatively soft, you don't need a router for this job. An orbital sander is fine, finishing off by hand. You could even do it all by hand if you don't have a sander. The trick is to get the round edge of the cabinet to match your metal corners. It doesn't need to be perfect - it will look fine when it's painted, honestly. Remember to sand off each corner so that your metal corners fit.

 

 

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The final thing you need to do is to even out imperfections at the joints. I discovered a really useful, water-based wood filler from Everbuild that I used for this. It's not as tough as a two-part filler - so don't use it to fill chips in corners - but it's ideal for this kind of job. It dries in half an hour and sands really easily. Then hardens over time.

 

Now you can paint the cab.

I haven't shown the batten used for fixing the grille because I haven't got any at the moment. But it's not rocket science, and I will probably mention it when I get the grilles sorted out.

I'm leaving my cab unpainted for the moment because I have to tune the port and tweak the crossover. But your next job when the paint has dried is to wire the drive units up. Ooooooh!

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Here is the crossover with the cables connected. There is a terminal block on the crossover board with a label that shows exactly where each wire goes (it's a bit difficult to see from the photo, but trust me). Just insert the fork terminals into the appropriate connector on the terminal block and tighten the screws, as I've done here.

 

 

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The cab is now connected up to my measurement system and I'll finalise the crossover at the weekend. The preliminary design I did last week is pretty close - so that shouldn't take too long at all.

I'm also contacting CNC companies to see who can produce these kits for us at a reasonable cost. I'll report back when I have some news.

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9 minutes ago, stevie said:

I've added a parts list to the very first post in this thread - and have taken the opportunity to delete the old drawings, which are now out of date. I'll post drawings of the latest version shortly.

Thanks once again Stevie. 

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Sorry, Stew, I should have been clearer. It's bitumen damping material used for sound deadening. Dynamat is a well-known brand. I happened to have some bitumen roof flashing in my garage and used that. It's not a critical component but the more fastidious amongst us will want to damp the thin plastic of the handle.

By the way, the cab I now have is as dead as a doornail when you knuckle-rap it - a noticeable improvement on the previous one. The only difference between the two is that the braces are now inset into the panels whereas previously they just used butt joints.

I've tuned the port and finished the crossover. I won't bore anyone with more frequency response curves - but draw a line with a ruler and that's what we've got. Off axis response is also exemplary.

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34 minutes ago, stevie said:

Sorry, Stew, I should have been clearer. It's bitumen damping material used for sound deadening. Dynamat is a well-known brand. I happened to have some bitumen roof flashing in my garage and used that. It's not a critical component but the more fastidious amongst us will want to damp the thin plastic of the handle.

By the way, the cab I now have is as dead as a doornail when you knuckle-rap it - a noticeable improvement on the previous one. The only difference between the two is that the braces are now inset into the panels whereas previously they just used butt joints.

I've tuned the port and finished the crossover. I won't bore anyone with more frequency response curves - but draw a line with a ruler and that's what we've got. Off axis response is also exemplary.

I'm deeply impressed by all this - what a fantastic example of the value of this forum and a credit to you guys!!

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