Fons Adriaensen wrote (Thu, October 15, 2015 6:47 pm) : > On Thu, Oct 15, 2015 at 03:59:46PM +0200, Jörn Nettingsmeier wrote: > >> We've seen all those outlandish claims of magical waveguides that >> are just fractions of the wavelength in diameter and yet shape the >> sound so wonderfully that a 20Hz beam will travel all the way to the >> moon (using the revolutionary VacuProof™ technology that will >> finally bring cinema-friendly space battles). The problem is, this >> waveshaping is not physically possible. > > Yes, it's a simple as that - not physically possible. > > If you think in ambisonic (spherical harmonic) terms it's > easy to see why. Orders zero and one correspond to physical > quantities, pressure and velocity, so these can be generated > directly at any point. Higher order SH can't. > > Which means that you can have cardioid subs, or even > supercardioid ones, but anything expected to create more > directional beams will need to be of a size comparable > to wavelenght. > > Can be (and is) done for open-air PA systems using very big > arrays. But not in any normal room, there simply isn't the > space to do it. >
There's something I've missed here ... for several years (as Feynman commented <https://www.youtube.com/watch?v=hTRVlUT665U> there's a point when it's too late to ask idiot questions, but here goes;-)> : If X,Y,Z correspond to velocity then does W correspond to some displacement of (a notional membrane say in) the aether in Jorn's vacuum of space;-)> If so ... by extension (always dangerous) ... then don't the next five (second order) components relate to acceleration ? To rephrase the question with no idiot presumptions: Why, in ambisonics, do we repeatedly refer to velcocity but never acceleration? (If one exists, then so must the other.) I feel an idiot even asking, so harsh replies accepted ;-)> Michael _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit account or options, view archives and so on.
