hi joseph,
On 03/02/2012 08:02 PM, [email protected] wrote:
Hi All,
A few naive HOA Qs I'm hoping to gain some insight on...
1) Order (M) is related to minimum number of loudspeakers by:
(M + 1)^2 for 3D
2M + 1 for 2D
Is there a similar relationship for order and loudspeaker array radius?
not really. only in the sense that you need higher orders for larger
listening areas, in the general case.
there is a similar formula mentioned in one of franz zotter et al.'s
papers which tells you for any given order for how many zero crossings
of a wave the reconstruction will be correct (obviously
frequency-dependant). sorry i don't have the paper around right now...
The practical question comes down to, does my room (or installation)
size end up limiting the order I can successfully synthesise?
no. but you might find there is little benefit in going much higher than
third order if your desired listening area is only for a few people.
no matter how small your room or listening area, source sharpness and
stability will improve with higher orders. only you might find yourself
way up the diminishing returns curve pretty quickly.
but if you have to play back lower order material as well (such as a
native soundfield recording), i found it is advisable to have a separate
low-order decoder which uses fewer speakers, for better clarity and less
phasing.
aaron heller disputes this, he claims to have observed no detrimental
effects in vastly over-specified systems, and if you look at simulations
where N->oo, he should be right, but in practice i have found systems
with many more speakers than strictly necessary to be significantly
worse in terms of phasiness... maybe others can comment and clarify.
As an
example, if I'd like to try 5th order, do I need to make sure my room is
at least minimum size? (Yeah, there are problems regarding loudspeaker
positioning, etc., but let's disregard that for now.)
2) And a related question.... For HOA do I prefer a narrow dispersion
loudspeaker over a wide dispersion loudspeaker?
you must make sure that all speakers cover your desired listening area
completely, without significant loss of HF.
other than that, the directivity of the speaker governs how much diffuse
sound in relation to direct sound will be generated. so as a very rough
guide, for a very live room and large speaker distance, more directive
speakers might be beneficial. vice versa, in a small and quite dead
room, widely dispersing speakers might be more pleasant to listen to,
since they will excite more diffuse sound, which helps gloss over
phasing problems.
a matter of taste, and your mileage may vary.
best,
jörn
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
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