I observed a slight caveat with the felt backwave damping modification ONLY if one uses the stiffened felt, that is somehow because it is so rigid, it acts as a waveguide too well especially for the treble region, and so the end sound might sound a bit more stringent around 10kHz.The simple solution to this, I found, has been to taper off the right angles of the felt strips that line the grid of the drivers. Easiest way to do it is to use your fingernails and pass through between each two strips of felt a dozen times. So basically the aim is to round off the outer corners of the stiffened felt strips to reduce the "waveguide" effect (imagine reshaping the cross-section of the felt strips so that it is now a half-circle instead of a rectangle).Of course some of you might not note these differences, but I tend to be extremely picky about sound signatures, especially minor changes in sound signatures, as they bug me a lot as soon as I notice them. So just take the above with a grain of salt and only try it if the situation fits yours and you yourself experienced a similar phenomenon.
I'm looking at the magnet plate as a diffraction effect. Maybe I'm off the ball, but I dunno... You've got a (in theory) planar wavefront from the driver, which then passes through the magnet plate and essentially becomes a multipoint (multi-line?) array. It's no longer a planar front, so you have a diffraction pattern. Variables: size, thickness, and spacing of the holes/slits. If I may veer tangentially into fluid dynamics, the edge of the holes plays a role in "flow" (assuming we're going for laminar flow instead of turbulent). Whether or not that's applicable to acoustics since we're dealing with energy propagation not bulk flow, I dunno, but I wonder what properties transfer over. Or maybe this all does have some effect, but the magnitude is inconsequential compared to the reflections/resonances/etc.Eh, too much thinking and blathering.
hehe Laminar vs turbulent flow. We engineers think alike.I'm also curious about the need to taper the felt. I would say that cutting the felt to match the zig-zag pattern that's on the grill would be very helpful. A straight cut should have slight obstruction to waves coming off the driver.
