15" bass box - with a difference ...

Id use a thick epoxy to bond (basically glue) the 90 degree edges and let it set. Id then us glassfibre reinforcing tape (like chopmat but on rolls) and do the internal corners. 

Should then be strong enough that all you need on the outside is a cosmetic capping. 

Just make sure you key and prep the faces well and it should be really strong. 

Thanks for the input guys ...

Well I got around to digging up the HC stuff from the shed ... and it seems my memory of what I have is a bit screwed up ..... I don't have a complete 8 x 4 sheet of HC. but I have 2 pieces :-

hexalite 14mm thickness

1) 38" x 41.5" 965mm x 1055mm - few small holes (weighs 3.3Kg)
2) 34" x 52"   863mm x 1320mm - covered with material/foam underneath + timber edging.

Altogether thats about 1.5 sheets :-)  .... but may not be optimal in terms of making a cut sheet.

Should be plenty to make a compact 15" box though.

The 1st piece with holes - the holes can be easily gummed up with something (the holes don't go right through - just one layer of the GF).

The 2nd piece needs a bit of attention re removing the material covering, foam and timber edging, but should be in good nick apart from a few holes like above.

I'm pleased with the weight - its about 30% of the weight of 18mm birch ply I think. My proposed 5-sided box should come in at about 5Kg I think - but thats without front baffle, bracing, grill etc.

I've been using this beyma plan (with cut list) as an example/rough guide for size/shape etc.

I'd use cylindrical port(s) (plumbers plastic pipe - 50mm or so ? )instead of the triangular ones.

I'd likely bleat for help a bit with WinISD/box tuning etc. .... some TS params I don't understand properly.

The B&C 15CL76 looks like a little honey for this - thanks for that heads up - and yes of course you're right about using neo .... was hoping to get the driver for <100 quid - but not _too_ expensive.

I'm guessing these are probably meant for stage wedges etc. - so likely designed as bass/mid really rather than specific bass, but should work well for about 40Hz-80Hz or so ... no ?

Actually, my FBT Maxx4 uses B&C neo drivers - so thats kinda nice and neat :-)

I'll almost certainly come back for tips on type(s) of glue/epoxy etc. and stuff like order of assembly of the panels.

Got a bit more of a clue (I think) on how to deal with the edges. Will come back with my proposed details and sketches etc. .... but this ain't gonna be a next week type of schedule ... I'll probably be relying on a mate over the road for tools etc., but ATM he's very covid wary so can't do anything for a while anyway. Can't use the box till summer time anyway, so now is the time to start planning it.

Your best bet would be to use a 90 degree extrusion such as this http://https://www.pennelcomonline.com/en/gb/Penn-Elcom-Double-Angle-Extrusion-Priced-As-A-2M-Length-E22652000/m-9913.aspx?PartnerID=10&utm_source=google&utm_medium=cpc&utm_campaign=UnitedKingdom&gclid=Cj0KCQiA3NX_BRDQARIsALA3fIJRb7wp6zSZGKHaUzWv9Ho75TVk7nPAAKJ1eFxsnD1mpK5XUChqZu0aAsPOEALw_wcB

Alongside a suitable epoxy. I can't remember which we used, but it was 3m and really not cheap. I'm sure RS do a slightly more reasonable equivalent. It could be worth getting one with gap set glass beads (~150um) if the 90 degree angle doesn't support this by geometry. Also, primer if needed and clean the joints properly with IPA and very fine grit before even thinking of gluing.

Bear in mind you have to have continuous adhesion along the full length of both sides (inside and out). Not following this will just result in the composite tearing itself apart quickly. Your edges need to be completely rigid in every plane.

Another alternative is to use two 90 degree aluminium angles inside and out. Getting the correct single extrusion (as linked above) is a bit of a challenge in itself.. Rivets can be used but purely to help keep in position during cure. They must be within the glued area to prevent point loads.

Bracing, you can use the same composite, but at 90 degrees. 

Baffle wise, you can use the same material, but have a tapped ring (ideal for load spread) or separate nuts with washers for the woofer bolts. Unless you want to swap woofers about, no reason to have MDF (ugh)

The alu ones have very poor damping, don't know about GF. It could be worth adding some small squares of bitumen to the centre of the panels to see if it makes a difference. This can be done to the outside, and will of course start to weigh quite a bit. Hopefully they will made naff all difference.

Oh, and go Neo if you're making this. Worth extending the weight savings if you're using such a fancy material. I'm a big fan of the B&C Neo drivers and the CL series are hilariously light (and cheap!), with really respectable BL/QTS.