The Trike (From HiFi News & Record Review 50 years ago!)
The inner diameter of the outer pipe (M) should be 1.5 times the effective cone diameter of the driver. The driver is a Phillips AD3701M a 6.5" driver with a cone diameter of about 130mm so 1.5 times that is 195mm and the pipe is 200 mm. Height of the outer pipe should be about 4 times its inner diameter or in this case 800 mm and that it what it is. The inner pipe inner diameter should be 0.6 M-wall thickness of inner-pipe so that is 200mm times 0.6 minus 4mm wall thickness = 116mm. As far as I can tell it is 118-120mm close enough. The average lenght of the inner pipe is 0.6 of the length of the outer pipe, in this case 480 mm.
M=1.5 cone diameter, T=0.6M-t (keep it above 0.5 and below 0.7)
H= 4M and d=0.6h
The building material. Going right to left: The pipes from Bauhaus, in the US it would be Home Depot and such. The drivers are from old Philips speakers bought at a thrift store at a very low cost. The plate and the bowl have the right diameter for marking the cutouts. Never use the cardboard tubes to trace the cuts as they are not truly circular. The outer tube is fine as it is the inner has to be cut to the right lenght and slant. Cables and connectors is needed. The inner tube will get some bonded acetate fiber (I do not like to work with fiber glass. The green felt to the left may come in handy if I need to add some more damping material in the pipe. The pine board will be material for the baffle of the driver and blocking the end of the inner pipe. Missing is some kind of feet to lift the pipe up from the floor to a hight of M/10. The feet will depend on how I finish the tubes, cover with a nice fabric, painting it, wall paper perhaps. I think I will build it first and if I like the sound I will work on the looks ;)