When I finally had gotten my un-orthodox speakers in working order, I decided never again to build a pair of speakers.
But the came my mind up with the idea of building a pair of small speakers in concrete, just because ...
So small speakers had to be ... 3-4" full-range drivers?! Like Dayton Audio PS95-8??
They happened to be on sale right now and a pair cost med less than USD 50. The 3 and half inch seemed to be a pretty good compromise.
First plan was to make a simple mold out of fiber boards, but switched to special paper tubes meant for casting conrete. Picking a 19 cm tube (outer) and a 15 cm (inner) would give me a speaker of reasonable size - 7,7 litres ported box.
However, I am not sure about that volume as it seems to be rather big for that driver. I did see a project where a similar driver and a passive radiator was placed in a 3 litre box (2,7 litres actualle - see links below.)
Started off with ideas to use the kind of goo used to level out concrete floors, but when I heard you could dye concrete I went for fine cement, but have to find out a way to reinforce the concrete. The floor goo came with reinforcing fibres, but I picked up an idea that fiberglass, sipped in pieces and added to the concrete could do the job. I am not building a building the SF Millennium Tower.
My very first sketch, just to undersatand myself how to make the mold. It is all about thinking in reverse - what is
to be cavities and openings must be solid and what is to be solid cast concrete must be cavities ...
A long threaded rod will hold the inner parts in place as it may tend to float.
Some fiddling in Illustrator to see if I can fit the driver and the BR tube on the front.
Done my shopping, one tube inside the other, 20 kg och cement, dye, paraffine oil, all loaded in my French armoured car.
Some pics uploaded for friends on Swedish audio forum. At least I got some loose screws ....
These T-nuts are a menace when working with MDF and I fear the will be a menace when working with concrete so I will fit them onto pieces of sheet metal that will be cast in the concrete, hoping that will fix all problems. Greased bolts will secure the nuts until the concrete has cured.