On Sat, Mar 19, 2011 at 05:50:15PM +0100, Jörn Nettingsmeier wrote: > well, with a 3.5m array (which is quite a standard length), you're down > to 100 hz, which is Pretty Darn Good.
You won't have much directivity for 1 wavelenght - first zero at 90 degrees. > as for the upper limit, with some intelligent waveguiding and other > magic fairy dust, you can get the individual elements to emit something > close to a plane wavefront already. The question is _how_ close compared to the wavelenght. Simple fact is this: a source that produces vertical cylindrical waves does not have any vertical directivity and has a frequency response going down by 3 dB/oct compared to the elementary sources is it composed of. PA arrays do not behave like that at all. > true, but there is still great potential. line arrays can be made to > work ok'ish over more than a hundred meters. Yes, but they are just point sources at that sort of distance. > * you don't necessarily have to resort to a "controlled opposites", > strict cardioid decode, in order to avoid the collapsing of the image > into the opposite speaker(s) for listeners close to those speakers, > because the "good speakers" retain more level close to the "bad > speakers". this will improve localisation in the inner listening area > considerably. This is *always* the case, even for point-source speakers. In-phase decoding optimizes in one direction - the one opposite to the source. Max-rE provides a more global optimisation. For example it will do a better job for a listener close to a left or right speaker for a front source. Also consider that even at just 3rd order, the 'back lobe' for max-rE is down something like 28 dB, and this only improves as order goes up. > * with more uniform coverage over distance, we can create larger > listening areas where speakers still contribute evenly to the sound > field in terms of energy. > > * we can reach listening area sizes where all perceptual assumptions > that hold for usual ambisonic reproduction break down completely, > because while the speakers contribute evenly in terms of energy, they no > longer do so with respect to time. Again, the extended cover is the result of carefully shaping the vertical polar pattern of the array over the range where it intersects with the the part of the horizontal plane where the listeners are. It is possible because 'close' listeners are in a differenct direction (as seen from the array) compared to 'distant' ones. It is not the result of of any 'near field' effect, or cylindrical waves. Ciao, -- FA _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
