Talk Composites - The Forum for Advanced Composites

Enclosure

http://www.talkcomposites.com/Topic11490.aspx

By Valkrym - 5/27/2014 9:25:40 PM

I have searched through the threads but haven't seen this particular subject. I'm looking at fabricating a complete composite subwoofer enclosure within the spare tire well of a 98 Saab. There will be a dividing wall in the center creating two seperate chambers. Considering that aspect I believe that I'm going to make 2 different foam plugs and wrap them individually with resin infusion. Then I will cut out the holes for the subs and extract all of the plug material. Then glue them together with polyurethane adhesive to install them into the well. I would like to use a combination of carbon(exterior), glass fiber(center filler), and aramid(interior shell). This will be my first use of this resin infusion. 1: What thickness would you recommend making the walls and what layers of the above materials would be best? I would rather it be too thick than be subject to cracking considering the amount of pressure and vibration from the subwoofers. 2: Can you see any problem areas with this process?
I have attached a picture of the tire well.
By Dravis - 6/3/2014 8:55:51 AM

What kind of upper frequency cut-off are you looking at on the Sub?   A CF/Glassfibre composite "box" will have rather high frequency "ring" to the walls because of the stiffness of the composite materials.

If you are going for a low (below 80 Hz) cutoff (which I would, considering the placement of the sub) then it will probably not be a problem for the sound, but ALL the "home-built" composite Sub-enclosures, bar a few, that I have heard were "buzzy" as heck...Crazy

I once made an enclosure for a spare-wheel well for an Audi, I made it as a two part construction, one "bucket" with a dividing wall and perforated extra walls to add stiffness to the "bucket", this was made from hand layup glassfibre and laminating resin, i covered the inside of the wheel-well with a 15 mm layer of selv-adhesive foam "sound-mat" and put a plastic bag (Bin-liner) on top using a little bit of spray adhesive.
The I built the "bucket directly in the "well" I used pieces of flat laminate, already finished and cured to support the dividing wall and the supports.

I made a "lid" for the bucket as a CF/ glass sandwich construction. Since I I already had the Sub-speaker, I made a "ring" from solid CF tape to fit the flange of the speaker,with laminated in M6 aluminium studs.
This ring was made directly on the speaker (a bit risky -- i know ... but judicious use of vac-bag film and wax made sure that nothing got stuck to the speaker.. Rolleyes )

The ring was laminated into the "lid" which was made as a vac bagged hand layup.. two layers of 200 g twill on the top ... layup was done on a glass plate ... I made up a thick "paste" of heavy Zircon-sand (the stuff used for sandblasting) and put down a thick layer of that on the back of the lid, to make a "dead" material, the same stuff was added to the inside of the "bucket"  (all after the layup had fully cured and the peel-ply was removed.

The sound was very good, no "buzzing" and the guy who now owns the car, is very happy with it :-)