Another enclosure building thread...

[scorpio]

Since I have started building new cabs, I thought I could start a new thread as well, since it would describe another building process, and I could share all my mistakes as well (since it's the first time I'm trying this approach).

One thing first, I'm not trying to 'clone' exisiting models or even designs from JBL, so the final product will look a little different to what is most commonly shown here, I hope you won't mind.

Attached pictures are not in the right order, so the second picture below should show my current speakers, product of about 3 yrs of tinckering. They sound good enough (to me) to think that I really want to keep them, but they look shall I say 'industrial'. In the pic below, I'm experimenting with the port tuning, which got me a 'dad, why did you put exhaust pipes on your speakers?...' question.... Time to change this... My target is to have enclosures of the same volume but less visually intrusive, with more fluid forms. I also plan to experiment with building a radial horn, as I believe that those look nicer than the round ones (will have to hear if they sound as good) and might be better adapted to my relatively close listening distance by being less directive.

Since I wanted something more rigid, and with limited parallel faces, I decided for a curved enclosure, like a simplified B&W 800 type. I also selected to build a (simplified again) matrix type framework to limit side walls vibrations. The approach I tried is best described in the first pic below. With this, I will end up with only very small unsupported areas, none of them being of the same size since I purposefully placed the risers in a random manner.

Third and fourth pics are showing the enclosures with the first layer of scarfed MDF cover. This is a feisty material to work with, I did not expect that it would be that difficult to bbend while ensuring good contact point with the framework. In fact, if the first of the two enclosure, I have some areas where contact was not good, and I had to fill some gaps with thickende epoxy - that was mistake Nr1 . Then it's also tricky to cut to exact shape with breaking the individual ribs, which I did when I tried to true the connection with the top panel using a router (mistake nr2). How well, the second cab ended better that the first, as I did not repeated those two minor screw ups.

That's as far as I am today. A second layer of scarfed MDF (both layers are 9 mm thick) will be bound to the first using Sikaflex type floorboard adhesive. I've used it to stick and oak floor over tiles in my living room, it has fantastic adhesive properties, but remain slightly elastic. It's also quite dense, so I think that it will allow the making of a pretty good 'constrained layer'. It's going to be messy though, I'm not looking forward to that... I'll probably make the first of the two cabs later this week. I'll keep posting pictures as I go along, but I'm kinda slow, so it may take a little while.

Cheers from Belgium,

[Hoerninger]

I tried to true the connection with the top panel using a router (mistake nr2)

You are building an interesting furniture/curvature. Good luck!

I do not know whether questions are welcome.

Could you explain the difficulties of mistake2? I would not have expected any problems as I do not have any experience.
What kind of horn do you have, the white one? Is it a tractrix-horn or a Kugelwellen-Horn?
____________
Peter

[scorpio]

You are building an interesting furniture/curvature. Good luck!

I do not know whether questions are wellcome.

Could you explain the difficulties of mistake2? I would not have expected any problems as I do not have any experience.
What kind of horn do you have, the white one? Is it a tractrix-horn or a Kugelwellen-Horn?
____________
Peter

Questions are certainly welcome! In mistake 2, while trying to level the MDF using a router, even going very slowly, the 'ribs' of the scrafed MDF broke and got loose from the backing panel, this on almost 1/2 of their length. Thankfully they did not break away completely, so I stuck them back in place using some PVA glue. In the end, this will have no real impact as the adhesive that I'll use to stick the two panels together will give enough structural strenght, but still, it p****d me off!

The horn is almost a tractrix curve, it follow JM Le Cleach' model (Jean-Michel does post on this forum). This I built out of MDF layers and bondo... It tends to be a little beamy at high freq, and I build it for a 800 Hz cut off (it has roughly a 420Hz acoustical cutoff), yet I use it a 600 HZ for now, and would like to go further down in crossover point. If the radial type doesn't do the trick, I'll probably just buy a larger horn (300 Hz) of the same type at musique concrete (http://www.musique-concrete.com)

[macaroonie]

I have done lots of bendy shapes for my work and the one and only time I tried using slotted mdf was a total disaster. This stuff is not strong it is only meant for people who want arch ways in their houses. Try using multi layers of 4mm Birch ply. It bends easily as long as you use the long grain to your advantage. Build it up to the thickness you need using contact adhesive.

[scorpio]

I agree that it's a lousy material to work with, if you apply any effort across the ribs. Along their length it is however no different to unslotted material.

What I am counting on is the combination of the MDF plus the interlayer adhesive, like a macro composite. The MDF is strong along the length of the ribs but has no resistance whatsoever across them, once the gaps will have been filled with the adhesive, this should change. I hesitate to use the flexible ply, but I shied away as I don't want to use solvent based adhesives for such large surfaces, too much stink and hassle. I hope I won't be disapointed, we'll see.

Completed the first layer on the second cabinet yesterday, hopefully will lay the first cab with the second layer of MDF tomorrow night.

[macaroonie]

I referred to just plain 4mm sheets. The trouble with the MDF as you have found is that the ribs can just break off. The 4mm ply will bend round your shape easy. I built a kitchen island with a very similar shape to your cabinet using 4mm. Use ratchet web straps to hold it in place and you can use your router to trim off without fear. Good luck