"Do-It-Yourself … That's the choice I did and the reason you'll find several schematics, mainly for tube electronics, but also some formulas for loudspeakers"
Audio Hi-Fi DIY - Claudio Bonavolta
Measures Conversion, Electronics, Loudspeakers, RIAA preamps, Solid state MC preamps, Solid state preamps and Solid state amps.
(Proper Loudspeaker Design is more complex than Launching Rockets into the Ocean )
Tapered Quarter Wave TubeFirst described by Paul Voigt in 1930, TQWTs allow a good quality-to-price ratio. They are also easy to build.Similar to transmission lines, the TQWT is different by its shape, a kind of horn is used as back load but the driver is not placed at the beginning of the cone as usual but on its side.
In closed boxes, the back wave of the speaker should be completely absorbed (= converted in heat) by the damping material.As the speaker is nearly transparent to sonic waves, if a back wave returns after a reflection on the back wall, some part will also come out through the speaker with some delay giving a not very clean sound.