[Sursound] horizontal-only decoder design for line sources
hi *! if i were to use a dual-band (aka shelf-filtered) third-order octagonal decoder with line arrays instead of point sources, are there any optimisations that should be applied to the decoding matrix? i guess there will be some error in the W component, at least in the hi-mid band where the line array emits something close to a cylindrical wave. my conjecture is that line arrays will let you create larger setups, since they suffer from less level drop across the diameter of the listening area, thus you can get further away from a source before the auditory event collapses into the opposite speaker. as mentioned before, we have run some tests with such a rig last year, the results have been very promising, and i'm currently writing it up. numbers show it shouldn't work, but it does. can anyone point me to papers that look at phantom imaging in the ambisonic case? the classic two-source experiments dealing with summing localisation and the "law of the first wavefront" seem to suggest that large-scale ambisonics with humongous time errors can't work at all. and the rV/rE metrics seem to focus on the sweet spot, i.e. an area where all speaker signals are coincident. in large-scale systems, this is obviously no longer the case: for an array of 20m diameter, not only are the speaker signals outside the summing localisation window of <1ms, they even begin to move out of the "haas window" of 30ms, where distinct echoes should become audible... best, jörn -- Jörn Nettingsmeier Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487 Meister für Veranstaltungstechnik (Bühne/Studio) Tonmeister VDT http://stackingdwarves.net ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
[Sursound] 1. Re: Ambisonics setup overview
Thanks for all your info: I looked into the basic /// max eternal ambipanning~ /// by www,icst.net It says " ambisonic equivalent panning (without intermediate B-format) I opened the help file and looks like it might work quite well thanks for all your support Darren ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] 1. Re: Ambisonics setup overview
On 03/17/2011 06:25 PM, Darren - Bradley wrote: Thanks for all your info: I looked into the basic /// max eternal ambipanning~ /// by www,icst.net It says " ambisonic equivalent panning (without intermediate B-format) I opened the help file and looks like it might work quite well thanks for all your support but you will lose all flexibility wrt speaker layout, and as other people have remarked, four speakers is not really good for larger audiences... i'd recommend six, and possibly second order. -- Jörn Nettingsmeier Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487 Meister für Veranstaltungstechnik (Bühne/Studio) Tonmeister VDT http://stackingdwarves.net ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] horizontal-only decoder design for line sources
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Dear Jörn, Jörn Nettingsmeier wrote: > hi *! > > > if i were to use a dual-band (aka shelf-filtered) third-order octagonal > decoder with line arrays instead of point sources, are there any 2D? A horizontal ring? I think it shouldn't matter then. "2 cents" P. -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.10 (GNU/Linux) iEYEARECAAYFAk2CktYACgkQrE8mG1pMpRo7JQCdH5LL9pccPDSxHflfnmhoAVfX oBUAn0jvEclqDB6iR01wTUPM2ltLNFqG =uVXr -END PGP SIGNATURE- ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] horizontal-only decoder design for line sources
On Thu, Mar 17, 2011 at 03:20:38PM +0100, Jörn Nettingsmeier wrote: > if i were to use a dual-band (aka shelf-filtered) third-order octagonal > decoder with line arrays instead of point sources, are there any > optimisations that should be applied to the decoding matrix? > i guess there will be some error in the W component, at least in the > hi-mid band where the line array emits something close to a cylindrical > wave. > > my conjecture is that line arrays will let you create larger setups, > since they suffer from less level drop across the diameter of the > listening area, thus you can get further away from a source before the > auditory event collapses into the opposite speaker. > as mentioned before, we have run some tests with such a rig last year, > the results have been very promising, and i'm currently writing it up. > numbers show it shouldn't work, but it does. > > can anyone point me to papers that look at phantom imaging in the > ambisonic case? the classic two-source experiments dealing with summing > localisation and the "law of the first wavefront" seem to suggest that > large-scale ambisonics with humongous time errors can't work at all. > and the rV/rE metrics seem to focus on the sweet spot, i.e. an area > where all speaker signals are coincident. in large-scale systems, this > is obviously no longer the case: for an array of 20m diameter, not only > are the speaker signals outside the summing localisation window of <1ms, > they even begin to move out of the "haas window" of 30ms, where distinct > echoes should become audible... I don't see any reason why it shouldn't work well unless you make the array even larger. Practical PA arrays do not behave like the theoretical infinite line source, their main purpose is to provide controlled directionality in the vertical plane. To behave as a line source rather than a point, they have to be larger than the wavelength, this imposes a lower frequency limit. On the other side, once the wavelenght is comparable to the distance between the drivers they will start to appear as a collection of discrete sources, and this limits the range at the high end. Combining these two limits results in a rather narrow frequency range for any practical array. And anyway the extent of the near field is proportional to the array size - once you are far enough they will again appear as a point source. It's not exactly true that rV/rE 'focus on the sweet spot', they are metrics that can be applied anywhere, and that apparently map well to perception (respectively for low and mid/high frequencies). rV is a property of the field that can be expressed directly in terms of the zero and first order components (i.e. it does not depend on how the field was generated). It's probably not very interesting in this case as it makes sense only in the 'area of reconstruction' and will have erratic values outside it. But for a large array you would use max rE, or at least a very low crossover frequency to max rV. rE can't be expressed easily in field components, it is a measure of how 'wide' the contributions from each speaker to the total power are spread. It will increase for higher order since more power is concentrated in the speakers corresponding to the intended source direction. In fact rE makes sense only if you _don't_ have field reconstruction and the only option is to add powers. In case you have a 'pre-echo' not corresponding to the source direction, you could still apply the rE metric to each of the 'pre-echo' and the 'main' part separately - I guess this would be the first step in analysing such a situation. How much 'pre-echo' can be tolerated in function of its relative timing, level and direction will probably depend very much on the nature of the source material. Anything with distinct envelope transients will probably reveal it more than more steady signals. As far as I know there is little definitive material about this, except for some simple cases. Ciao, -- FA ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] horizontal-only decoder design for line sources
Meyer Sound has a technical report on their site that is relevant to this discussion: "Can Line Arrays Form Cylindrical Waves? A Line Array Theory Q&A" http://meyersound.com/support/papers/line_array_theory.htm -- basically what Fons says, but with some nice pictures and a bit of theory. Aaron Heller Menlo Park, CA US ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
