On Mon, May 2, 2011 at 4:25 PM, Stefan Schreiber <st...@mail.telepac.pt> wrote: > Jörn Nettingsmeier wrote: > >> >> for larger audiences, the game seems to be a bit different, although i >> don't quite understand why. i find 1st order over eight speakers covers >> a larger area more easily and uniformly than six, but the theory says it >> shouldn't, because outside the sweet spot, rV reconstruction is mostly >> not happening and everything relies on rE, which is degraded by using >> more speakers than necessary...
r_E is not degraded. r_E remains the same for any uniform layout with more than the minimum number of speakers. > But < why > ? > > It is important for theoretical reasons to discuss this a bit more. This is > not anything "evident", I would think. > I believe the reasoning is that when there are many speakers producing almost the same signal, you get more comb filtering effects when moving out of the sweet spot. This is discussed in Solvang, Audun. "Spectral Impairment of Two-Dimensional Higher Order Ambisonics" JAES Volume 56 Issue 4 pp. 267-279; April 2008. however the paper doesn't specify the decoder used. I've seen many reports of comb-filter effects and then found that "matching" (aka velocity, basic) decoders were being used at HF. (we discuss this in BLaH3). In fact, the only time I've ever heard comb filtering in Ambi playback is with incorrect decoders. I will say that when Eric, Richard, and I set up a demo during the 2008 AES in San Francisco, using the 24-speaker hemisphere array at "the Bubble", there was a distinct HF dip at the sweet spot, but we didn't have precise info about the locations of the speakers and didn't have a lot of time to make measurements or tweak the decoder before the demo. Moving 10-20cm away from the sweet spot in any direction restored the HF response, but there were no comb filtering effects. The configuration was 3 rings of eight speakers, with some of the speaker behind a projection screen. For the informal listening tests reported in our papers, the speaker location error is less than 1 cm. This is verified by placing an omni microphone at the listening spot and driving the speakers with impulses. Since the topic is domestic speaker layouts, I have a permanent four speaker rectangle set up in our living room, with two more speakers on stands that can be put in place to make a hexagon. I've also experimented with an eight-speaker bi-rectangle for 1st-order periphony, but that stretched the limits of domestic acceptability. Aaron Heller <hel...@ai.sri.com> Menlo Park, CA US _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
