I live in the States (Missouri), and I'm having trouble finding these tubes in any decent size. Settled for a 12" tube from Lowes to try out this design with my 10" Sub. It sounds decent, but I think the sub needs more breathing room.
I'm new here, and I have never played with PR's before, but heres a little idea I just had regarding the sub standing upright and the PR sag. I would also think that the PR is going to have a sag value that may make it "bottom out" with the in stroke durring the really low notes if the PR is used in the top half. With mass added this would be even more so. Has anyone ever thought of incorporating a spring system under the PR? I think there are calculators you can use to figure the correct spring strength needed and compression for the wieght. If you could find the correct length needed for just the right amount of compression, I would think you could make the PR sit right mid-way when not used, and the spring would limit the in stroke. If this sounds useless please let me know. Just an idea lol.