Pensil Series for Mark Audio Drivers

[simon dart]

I think as the curve is quite gentle I'd have a go at laminating four plies of 4mm birch ply. I think you'd have to laminate them in place to avoid misalignment, then trim the edges. I'm thinking a circumferential brace scheme to act as a former is probably the safest and easiest way to do it.

As Dave points out though its not the optimum way to brace, but a longitudal brace scheme might work. I'll model it to see if its possible when I get time.

[planet10]

Originally Posted by simon dart

I'm thinking a circumferential brace scheme

The spaces in-between the circumferentail braces would need to be filled so that the cross-sectional area was continuous. In a TL, bracing should always run in the same direction as the line.

dave

[simon dart]

Hi Dave,

I've kept it as longitudinal as possible, but you have to space the stringers at some points if you are going to laminate the sides in place.

My initial thought is that the brace dimensions in this kind of scheme are teeny compared with the wavelength at the tuning frequency and so wont have much influence. In your experience the circumferential braces would interfere with the tuning?

[planet10]

Originally Posted by simon dart

Hi Dave,

I've kept it as longitudinal as possible, but you have to space the stringers at some points if you are going to laminate the sides in place.

My initial thought is that the brace dimensions in this kind of scheme are teeny compared with the wavelength at the tuning frequency and so wont have much influence. In your experience the circumferential braces would interfere with the tuning?

Perhaps not a whole lot as you have drawn them (even thou you are violating the "keep xsection the same" rule). bit unless you have some sort of temporary infrastructure in place bending the panels over that superstructure is likely to "squash" the superstructure

dave

[simon dart]

Its not straightforward and would require some test pieces... ermm ...I think the pensil 10.2 is a bit too big for translam :-D

[chrisb]

Originally Posted by simon dart

Its not straightforward and would require some test pieces... ermm ...I think the pensil 10.2 is a bit too big for translam :-D

I built something rather like this a few years ago - it's not as simple to fabricate in one piece as you'd think. It was a rather tight radius elliptical shape that after several unsuccessful permutations of drivers and XO was abandoned for sonic reasons.

Even unfinished, it had a elegance to the design that was hard to ignore, and I'd certainly not want to discourage the project, but if you've never done something like this before, you can find out too late that your construction methods interfere with the design's operating principle(s).


I work in a commercial millwork shop that builds rather a lot of curved reception walls, bulkheads etc. For structurally rigid curved panels, we laminate several layers of rubber ply with yellow wood glue and vacuum bag / cold press. It takes more material, and discounting the time for glue to set, longer to fabricate the jig than to lay up material.

Something you might want to consider is to fabricate each of the curved side panels separately as torsion boxes ( skinned both sides ) then add extra external layers after assembly of top/bottom / front/ back. A single layer of rubber ply (2 layers of soft luan veneer over synthetic rubber) is rather lossy, which could be very helpful for the inside layer. Damping the void cavities with loose fill would rather tricky - rock wool etc might be a good idea.

Your mention of translam suggests access to a CNC machine, which would be invaluable in accurate cutting of the multitude of curved ribs require whichever method you follow. While the translam method does provide some amazing aesthetic possibilities, I personally consider it criminally wasteful of material, and in a shop were machine time is money, very costly. It also has some limitations in terms of the bracing scheme more suitable to this type of design.

Of course, you could always try to rent some spare time on one of these:



B&W

[murio]

Originally Posted by mac1963

Hi all
Finally found the time to post some pictures of the final result. Solid Sucupira (sliced up and rejoined to avoid warping) was used, and the sound is AMazing! Thanks again, guys, for the info and support that made these possible.

One question Mac! That stand is attached to the port of the box! Thoes it have any side efects for the bass because the stand is a bit longer, so the port is not like the original?