Thanks for all your replies. I think I'll be using 18 mm plywood and 2x2'' timber for internal bracing.
There's a couple more things I'm wondering about. I would like to build the subwoofer like a perfect cube, because I like things to be symmetrical. Or should I avoid this? I've read about golden and acoustic ratio, but some people say it doesn't matter for a small subwoofer. Also, does baffle size matter? I'm building a down-firing subwoofer, so I'd like the baffle to be small, so the subwoofer doesn't take up too much space.
There's a couple more things I'm wondering about. I would like to build the subwoofer like a perfect cube, because I like things to be symmetrical. Or should I avoid this? I've read about golden and acoustic ratio, but some people say it doesn't matter for a small subwoofer. Also, does baffle size matter? I'm building a down-firing subwoofer, so I'd like the baffle to be small, so the subwoofer doesn't take up too much space.
Hi HumbleDeer,
The damping factor of materials only matters if the first mode of any of the enclosure panels sits within the bandpass, which is usually not the case for MDF or plywood as building material for a subwoofer. Nonetheless, you last remark is perhaps too often overlooked in the diy world...
Regards,
Djim
The damping factor of materials only matters if the first mode of any of the enclosure panels sits within the bandpass, which is usually not the case for MDF or plywood as building material for a subwoofer. Nonetheless, you last remark is perhaps too often overlooked in the diy world...
Regards,
Djim
All depends on the shape (span) and bracing. A cilinder like a bucket or pcv pipe will not bow out even if they are very thin.
Take a look at how boats are build; you can use 3mm/ 1/8" ply for a canoe if you brace it well. 1/2 or 3/8 ply is often used for 30-40 foot catamaran hulls. (with catamarans weight matters a lot, not so much for mono hulls)
Bracing takes more time so commercial speaker builders opt for thicker wood instead. Other ply like okoume can also be a lot lighter as it is only 5/7 the weight of birch ply. That makes a 25lbs box instead of 35lbs with the same thickness ply.
Glueing a box is much stronger then screwing it and makes it airtight.
Take a look at how boats are build; you can use 3mm/ 1/8" ply for a canoe if you brace it well. 1/2 or 3/8 ply is often used for 30-40 foot catamaran hulls. (with catamarans weight matters a lot, not so much for mono hulls)
Bracing takes more time so commercial speaker builders opt for thicker wood instead. Other ply like okoume can also be a lot lighter as it is only 5/7 the weight of birch ply. That makes a 25lbs box instead of 35lbs with the same thickness ply.
Glueing a box is much stronger then screwing it and makes it airtight.
I usually use the 15mm vrs ¾” equivalence. In quality plywoods vrs MDF of the same thickness, the plywood is lighter.
dave
As long as the woofer does not go higher than a quarter wavelength of any internal dimension box dimension ratios do not matter. This is usually the case with a small subwoofer. A subwoofer radiates in an omnidirectional matter so baffle size and the side you put the woofer on is also moot unless it is loaded by a nearby surface.
dave
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dave
dave
Until post #25, it's one of those "my box is stiffer than your box" threads, taken as Article of Faith without good rationale.
Nobody seems to notice or to care that the OP box is one of the ridiculously tiny boxes for a large driver, about 9-inches to the nearest edge worst-case. Not that anybody can actually depict what the problem would be if the box wasn't infinitely stiff.
I thought the rap-your-knuckles test was just an old (but actually meaningless) habit us old guys have?
B.
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I think doubling the baffle is good - you can chamfer or step the inside to negate any problems a too-thick panel will bring though unlikely much problem on a sub. watch your plywood isn't really cheap stuff with lots of cavities, or that the inner sandwich material is rubbish. good bracing probably just as important as ridged sides.
A place in Minnesota took over,and continue sale. Before this 12's weren't available but they will be, later if not now.
VG woofers. I know where there are some open box sdx 15" if your interested in looking at them.
+1. Chamfer baffle back after determining height of your speaker flange, and countersinking that depth. Careful not to chamfer the baffle thinner than you'd like it. Use threaded claws to mount the sub. Those are great and wont strip on ya. But avoid removing material where they seat on the inner baffle.
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Bracing is not bad, but...
it will impact the sound due to "turbulences", especially in ported designs.
What differential stresses are you talking about?
Depending on the driver, the hole is reinforced with a rigid metal structure.
Some testing would be very interesting to see if the facts confirm the speculation/intuition. Reading threads where Geddes has contributed taught me that a lot of the intuitions people have are simply not borne out in testing, or more advanced theory.
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