I came up with this:- I measured the depth of the inner steel panel of the body (to which the speaker bolts) to the outer skin at the 12, 3, 6 and 9 'o' clock positions. Then I measured the diameter of the speaker aperture of the inner metal body skin from plastic screw insert across to it's opposite...This determines the diameter required, and simple math will give you the circumference using Pi.
I cut some stiff cardboard (2mm thick) to the circumference length x the widest measured depth of the void...that widest point is at the 6 'o' clock position - the narrowest is at the 12'o' clock position - I created a tube by joining the two ends of the cardboard and marked the 12, 3, and 9 'o' clock measurements I had made. Then, undoing and laying the cardboard out flat again I joined the dots so to speak....when the cardboard was cut along the line of the joined dots and re-joined as a tube it forms what can be called a tube that has been cut across at an angle on one end...or for those that understand...a truncated tube.
The cardboard tube when fitted in the aperture rests it's outer edge against the 4 plastic screw inserts which extend about 10mm in through the metal skin, and this maintains it's correct circular curvature.
I then lined the inner face of the cardboard with "Builders Flashing". This is a 2mm thick layer of butyl with a thin aluminium foil stuck on one face and a peel off paper on the other, which when removed exposes the butyl which is seriously sticky stuff. The sticky face was bonded to the flat layed out cardboard so that the aluminium faced inwards into the tube.
Because the final fitted item is a larger circle than the aperture, the ends cannot be joined until it has been inserted into the body void...I left a 10mm overlap of cardboard only to provide a fixing face for the two ends of the now flashing laminated cardboard...Once inserted, the cut edges of the flashing top and bottom of the tube, stick to the inner and outer metal skins, creating a sealed aluminium lined tube into which the speaker will be housed when replaced. I cut and stuck a flat disc of the same flashing to fit inside the tube and against the outer body skin, thus providing more sound dampening there, and sealing off the tube completely with the exception of the end where the speaker fits. I then used some foam weather-strip..( foam rubber with one face which has a peel off paper strip and a sticky surface under the paper.) I used a 30mm wide strip and stuck it to the outer face of the inner skin in a circle, so that when the plastic footwell trim is replaced, it would create a seal between the plastic trim and the body, thus elliminating excessive access for dust etc. I replaced the speakers and trim, and repeated the fitting on the opposite footwell speaker. The second speaker was a doddle and took about 20 minutes including stripping out the trim and completeing the job...simply because I now had a template for the cardboard and it was quick to duplicate the first side.
The end result is my footwell speakers are now housed in aluminium lined tubes where the sound insulation properties of the flashing keeps the output inside the cockpit, and a speaker housing which keeps out the dust....
The entire job took an hour and a half..but only because the first side required the measuring and cutting etc etc to make the first tube.
The benefit is immediately perceivable with a 70% + increase in output discernable from the footwell speakers.
