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To build Pi2 Towers you recommend to use panel of 5/8" (that is almost 16mm). But if I want to cover them with a foil of 4mm plywood, must I use panels of 12mm? Or have I better to use panels of 14mm (for example), making a little larger port? And what about mdf for panels? Is it a good solution?
MDF is wonderful material for these speakers. Since the port length of the two π tower is set by its rear panel thickness, the Helmholtz frequency is a function of the thickness of the wood. Here are some recommended hole sizes for various panel thicknesses: 1" thick panel => 4-3/4" diameter port cutout 3/4" panel thickness => 4-5/8" diameter port cutout 5/8" panel thickness => 4-1/2" diameter port cutout.
Many thanks! But are there remarkable differences in "sound" between 5/8" and 3/4" thick panels (for example)?
No differences in measurements or subjectively (at least to my ears) between various wood thicknesses, provided the braces are installed. You should have an internal cross-brace one-third the way up from the bottom and another one-third the way down from the top, just under the woofer. Those are what really prevent the panels from vibrating. Don't forget to put insulation on the braces too, spanning the cross-section of the cabinet.
Thank you again! I think I'll choose the 3/4", due to the foils of plywood. Otherwise the inner panels would have been to thin and hard to assemble...
Cut these "window panes" with the same saw seting, at the same time, as the top and bottom pieces. They help square the cabinet during glue-up and then function as braces.
Bill Epstein wrote on Thu, 09 December 2010 22:02 ... Cut these "window panes" with the same saw seting, at the same time, as the top and bottom pieces. They help square the cabinet during glue-up and then function as braces. That's a good tip, thank you! And what about using screws (with abundant glue of course) to assemble? Would it be wrong? After I'll cover all with plywood...
Quote: And what about using screws (with abundant glue of course) to assemble? Would it be wrong? Not "wrong" just something I no longer use. I never liked having to fill the screw holes but worst of all, even when clamped, sometimes the torque of the screw would move the pieces. I also gave up on 18ga. nail gun nails, especially in MDF because they bend going in and come out all over the place. Eschewing fasteners, once mastered, is easier and faster. The latest bar clamps from Bessey and Jorgensen with their square jaws really help, too.
No screws, then... I wanted to economize on clamps... Thank you.