Originally Posted by corradizo
Can you share some info on how the bass extremists build their cabinets? Most of what I have seen are 4th order walls that produce one note and mostly have no bracing other than a metal rod or two.
What most use is irrelevant, what most winners use is steel reinforcement directly on the chassis which is then filled in with fiberglass and concrete (concrete ceilings and walls is getting popular, with internal steel mesh wired in place first its really easy to do, just lay the concrete with the car on the side or roof, no form needed and you use all the space out to the edge of the chassis panel). Steel beams you see are there in addition to this reinforcement you don't see, because the largest surfaces (roof and floor) will flap like a bird under 170db+ even if they're made of steel, fiberglass and concrete. The steel beams that cross the space will be bolted through the floor and ceiling with the same bolts as the doors. And act both as a pre-tensioned steel wire and load-bearing column depending on which way the pressure is trying to force the surfaces in that particular fraction of a second. Though the steel beams are bolted to the steel beams inside those surfaces, they aren't just bolted to bare chassis skin as surface braces like we do with mdf. If you are to use bracing on mdf, you should at least double up the mdf at the contact location, or glue real wood to the surface you are bracing (or plywood), so that the force isn't concentrated on one tiny patch of mdf. Every little unit of volume you waste with the bracing will have much greater effect then.
Back to db drag: The doors are bolted in place with 10-12 inch long 1/2 inch bolts. The windows are 3+ inch thick bolted into 1/2 inch thick steel frames.
Since the enclosure makes up about half the internal vehicle volume that they are trying to pressurize with db, most enclosures are made with the level of strength as the rest of the cabin. If the doors are bolted in place with half a dozen or more 1/2 bolts, what does that tell you about the enclosure strength? :P Db drag winners are insanely aware that db will escape through the easiest path, so they constantly improve on the weakest link in strength. And anything that isn't shaking in timing with the cones, isn't producing the db that will tick them over the world record, so they try to eliminate it.
They build enclosures like we would build an armored car, we build enclosures like they would build a bookshelf.
There are of course those here who take the step to build bunker-busting
This one is about as strong as you can make an enclosure with wood. At like page 11 you see the reinforcements and stuffing.
This enclosure is probably at the border between when it may be less work and cost to just plaster the inside with polyester and glassfiber. But this particular person knows wood-working and had all the tools for it so it was easier for that person to do it this way with complex bracing than to learn glassfiber composite techniques. If someone fixed his canoe and then built this, he would probably end up just laying a quarter inch of glassfiber and resin on the inside of the plywood like this:
black is resin and glassfiber, orange is sticks for adding thickness to the glassfiber without having to fill it completely in (a cost saving technique which costs a little time in laying the mats). Grey is the plywood.
But this guy did it right. He uses plywood not mdf, he even laminates it further, he uses evenly spaced plywood bracing, he bends two of the largest surfaces twice in an S shape. Its essentially a wooden composite enclosure, wood sheets instead of (glass)fibers, with glue holding it together (epoxy/polyester resin is just fancy names for glue). But, given the time he spent making the reinforcements it may have been as quick and easy for someone equally skilled in glassfiber, to reinforce equally much (or even more) with glassfiber. So if he was a modern boat-builder he would probably have used glassfiber, but since he knew wood-working he used (the correct) wood.
With such a driver, you could probably not make it weaker, or it would flop like a plastic bag. Don't forget, relative to the cone size, its as if we built a 10" subwoofer with something like 4mm plywood. Without all that bracing, it wouldn't work. If it was mdf, it probably wouldn't work.
EDIT: FYI, this method in the picture does strengthen the material even in the direction perpendicular to the sticks. Because the glassfiber is thicker where the sticks are and that reinforces the thin bits between the sticks. You may of course run sticks along the short length instead of the long length so that you have more reinforcement, but then you spend more time on it and may ultimately get more reinforcement in a days work by working with bigger pieces (longer sticks, larger diameter sticks, more space between the sticks, thicker glassfiber mats)(glassfiber mat thickness is proportional to the sharpness of the shapes you want to push the glassfiber into and around).