i'm thinking of making a spherical enclosure for my 12" woofers... i'd start with a child's ball (a cheap one from Toys-R-Us) of the appropriate volume, then wrap it with several layers of fiber-reinforced resin (fiberglass) and attach an MDF mounting surface for the woofer. Then bondo, then lotsa sanding, then paint.
Not when it comes to the larger diameters. Boy is it pricey!
I recently went to a concrete supply place, they had cardboard forms (sonotubes) in just about every conceivable diameter in 12 foot lengths. I bought 10" diameter for a little more than $3 per lineal foot.
In Denmark some companies has recently come up with mdf wich has been routed on the one side, kind of like the type of cardboard you use around glass as rappings. Yóu the make the inner shelves in the speaker, and glue the mdf on to the shelves. Maybe you can get that kind of mdf at a lokal hardwarestore?
Thanks for your help.
I'm not looking for cylinder or all round speakers, but for a flat surface on the front, where the drivers are moúnted, and rounded face att the back, like JBL.
I am in the process of finishing up a similar project myself!
I wanted to get a 5" radius edge on my speakers to minimize diffraction effects. Indeed, it is highly effective.
I went through three methods before hitting on a successful one.
First was to use 10" PVC pipe, cut it in quarters and glue the quarter pices to the edge of a box that has been built with a "step" of sorts on the edges. Unfortunately, I found that once I cut the PVC, it curled in some to a smaller diameter, making the box I had built the wrong size.
Scratch that. Didn't seem like the best idea.
Next idea was to laminate six 4.5" wide pieces of mdf together for a billet 4.5" square. Then I drew the arc on the end of the stock and ran it through the table saw 5 degrees at a time. After that, sand with an orbital sander until it is smooth instead of faceted.
This worked pretty well, but the radius was not perfectly linear in spots, and it produces an INCREDIBLE amount of MDF dust, which is hell to work with.
Current method; and this is working quite well now... I made a box with a skeletal rib-work for the cuves on the edges. Every 5 inches or so there is a routed curved piece. (I added more ribs after the shown picture)
I then used double-stick tape to attach a plastic sheet to the ribwork (similar material to overhead transparencies) and fiberglassed it from the inside. Peel off the plastic when it dries and there you have a nice smooth form to veneer over! Also, it is very strong and will not resonate, due to it's curved shape.
I will need to do a little bondo and sanding to get it just right, but this method is workind well.
Another good possibility is to use the flexible bending plywood that can be found at good lumber stores.
Also, you could cut deep scores down the length of a piece of veneered MDF of some kind and bend that around a form as well.
Hard work, but I think it's going to be worth it...
There could be a way, if you are patient and clever in working wood!
1 - Cut MDF panels in round shapes, and cut another round hole inside
You should end up with several 'donuts' of MDF of different diameters
2 - Pile and glue them together
Now you have a kind of 'discrete' approximation of a sphere
3 - now the difficult part: find a professional with a good lathe who can profile the external part in round shape
You can also work your way with a milling machine and a smoother, but a 'serious' tool will grant you a better aesthetic!
It's a work-intensive way, but it has some good side:
a - you can also model the box in oval shapes
b - the inner area will be extremely irregular (all the steps of the 'donuts'), very good to broke resonances
c - the compound of mdf and glue is very dumped, acoustically much better than pvc or fiberglass
Another possibility would be to route numerous circles of the same external diameter and the same internal diameter, so you have severl "O's". Then, you could cut all of the O's in half, and laminate these half circles together, to get a half-cylinder (deep U) shape to use for the back end of the enclosure. This would provide better resonance control and damping than the plywood method, but would also make for some seriously heavy cabinets.
Thanks for your help,
I'm thinking of building the speakears as several layer of mdf, so each section will have the desired geomtrie.
I'm wondering what you think about it.
I think this method will provide me a very stable cabinet construction.