On 01/07/2011 12:44 PM, Arnold Krille wrote:
Hm, my experience is limited, my setup was only once working with 5 speakers. It aim to be a 6 speaker deformed hexagon but for the sixth speaker I don't yet have the cable and stand in place. So one position was empty that afternoon I tested. But it didn't sound too bad. Of course sound from the missing direction was very thin to say the least and sound from the opposite was to strong as the counterpart was missing. I tried to match levels but then I ended with the four speaker square:-) But when I rotated the playback so the single speaker wasn't to my right side but to the front, results became better. (*)
you can get away with such things, especially in higher orders. but as you noted, it works only when the missing speaker is in particular places wrt the sound stage. since ambisonics is about isotropic reproduction, it does not work in the general case. and for bob's sake don't tell anybody you got away with it, because then everybody will want to do the same :)
Just me memory glossing over the past or is it some valid loop-hole?
it's a dirty hack. i've done it in the past, sometimes it works, sometimes it doesn't. it depends on the source material.
in a recent experiment with 8 line arrays, we played a stereo file over 3rd order, spreading the stereo base to 120 degrees. sounded great, fantastic envelopment, yet very clear, and we blew the paint off the wall with the systems. then we figured, hey, the opposite 4 arrays are about 30 dB down, why don't we just switch them off entirely? and this we did. still sounded almost as good as before. morale: maybe you can use ambisonic panning to drive a line of line arrays in order to cover a wide area, if and only if you only want to reproduce sources from one direction. but _THIS_IS_NOT_A_RECIPE_. it sounded cool when we did it, but in some other place with other source material, it may not work at all. maybe it only worked because we were in a reverberant space...
and more importantly: this is no longer ambisonics.
(*) Of course then the bass was different and only from my left. Thats what you get with two full-range active speakers for the front pair and the rest small jbl-monitors without enough volume (as in space, not loudness) to reproduce anything<100HZ to satisfaction. But the frequency-split in ambdec and DRC for each speaker help there. I just don't know what this does to phase response of the final setup. And I don't have the ears to determine that...
yes you do. you just need a reference, which means listening experience with proper setups. i feel i'm getting more confident with these cheats, because i jump at every opportunity to build or listen to a new rig and have heard some very good ones, and i always use the same demonstrably correct software, which helps.
ambi rigs are a pain to debug, much more so if you don't have a precise idea of what they can do and what they can't do. therefore, soapbox preacher mode on: for your first ambi rig, don't mix and match speakers, don't build your own decoder, don't use source material recorded with your DIY tetrahedral mike. go the textbook way. only then start doing funny stuff, but with one component at a time, just like you would debug software.
and then, maybe, when you come into a facility where nobody knows which channel order and normalisation they're using (hi guys, you know who you are), you can fix it, with some help from major ambisonic gurus and 20 hours of trial-and-error :)
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