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Thread: Another enclosure building thread...

  1. #1
    Senior Member scorpio's Avatar
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    Another enclosure building thread...

    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,
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    Quote Originally Posted by scorpio View Post
    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

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    Senior Member scorpio's Avatar
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    Quote Originally Posted by Hoerninger View Post
    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)

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    Senior Member macaroonie's Avatar
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    Input

    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.

  5. #5
    Senior Member scorpio's Avatar
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    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.

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    Senior Member macaroonie's Avatar
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    Not slotted ply

    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

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    Senior Member scorpio's Avatar
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    A short update

    Just a quick update on my slow progress. First thing was to test the strength of the adhesive I planned to use. First picture shows a test piece, result is pretty good, there is no 'springing' back when I removed the straps holding it in place, it kept the exact shape, that's good, no tension in the final piece.

    Is it strong?, not too bad according to the 2nd picture (I'm close to 180lbs), there's no cheating here, it held without any problem! The piece of wood is just there as I used it to see if I could screw through this material combination. That's one drawback, the materials is not strong enough to hold real thight screws, better count on the adhesive!

    Other pics are one of the cab getting it's second layer of sheeting and finally the two cabs as they are today, with a coat of primer just to judge the outer surface. After much hesitation, I've decided to paint these instead of trying to veneer them. I'd really love to have a wood finish, but have never done any veneering, I don't think that this is a good first projet for that (there's close to 2sqm surface per cabinet...).

    More later, hopefully, with a few days of holidays coming, I should be able to make some progress a little more quickly,

    Cheers
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    Senior Member richluvsound's Avatar
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    nice work,

    Hi Scorpio,

    Welcome to Sikaflex anonymous. Iv'e been toying with idea of floating the baffle on this brilliant Sika product.

    Rich

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    Damn I'm jealous. If I could just think of a way to make cabinets using unistrut.

  10. #10
    Senior Member scorpio's Avatar
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    Quote Originally Posted by richluvsound View Post
    Hi Scorpio,

    Welcome to Sikaflex anonymous. Iv'e been toying with idea of floating the baffle on this brilliant Sika product.

    Rich
    I thought about that, I am planning to add a second layer of hardwood to bolt the speaker on the front plate, but in the end, I'm going to hold this second layer using screws, not sikaflex. This is only because I want to keep it removable so that I can change port tuning if I want to change driver in the future. Otherwise, I'd definitely use Sika!

  11. #11
    Senior Member scorpio's Avatar
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    progress updates

    Quote Originally Posted by scorpio View Post
    I thought about that, I am planning to add a second layer of hardwood to bolt the speaker on the front plate, but in the end, I'm going to hold this second layer using screws, not sikaflex. This is only because I want to keep it removable so that I can change port tuning if I want to change driver in the future. Otherwise, I'd definitely use Sika!
    Well, I changed my mind and used a fixed front baffle inthe end. Here are the final cabs in the room, and after installation of the speakers. The actual color is a deep brown, not a dark grey as it kinda looks here.

    Verdict? Bass is slighlyt deeper (bigger volume) and is tighter, the pannels definitely hardly vibrate even when driven hard, and vibrate only is small portions, as expected from the build. The biggest improvement however is int he lower mid, more details and focus, better integration with the horn - surprisingly that's where most of the improvements are taking place.

    There is still fine tuning to do, I'm sure I can extract more from the bass still, and I have a 5235 X-over waiting as well, which should bring even more kick to the lower mids,

    It's also a lot better visually (more obvious 'in the flesh' than in pictures), takes a lot less visual space in the room - for me it was worth it!

    Next is to experiment with some other (radial) horns and possibly build grilles when that's done, but it will take me certainly well into spring 2008.

    Anyone needs a set of bass cabs? I have 2 empty ones cluttering my garage...

    Thanks for reading this far, even it this is very remote from 'heritage' stuff, besides the components used.
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    Congratulations , with all the curves it harmonizes much better.
    BTW which compression driver are you using?
    __________
    Peter

  13. #13
    Senior Member scorpio's Avatar
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    Quote Originally Posted by Hoerninger View Post
    Congratulations , with all the curves it harmonizes much better.
    BTW which compression driver are you using?
    __________
    Peter
    Thanks!

    I'm using 2450 with aluminum diaphragm, which I believe were intended for 2440, but I'm not sure about that. I don't have the exact references.

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    looks nice allmost like my ones what bas unit do you use.

    http://bildarkiv.hififorum.nu/classe/jbl%20classes.jpg

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    Senior Member scorpio's Avatar
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    Quote Originally Posted by classe sundh View Post
    looks nice allmost like my ones what bas unit do you use.

    http://bildarkiv.hififorum.nu/classe/jbl%20classes.jpg
    Yes, but you use real wood to finish yours I did not dare trying that!!
    I'm using LE15A right now.

    I'd be interested in more details about your system it looks not only splendid but very interesting, would you have a link to more details?

    Cheers

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