[LAD] what does "full range" mean with regard to ambisonics and speakers?

[Jörn Nettingsmeier]

On 07/31/2010 04:40 AM, "Bearcat M. Şandor" wrote:
> Folks,
>
> I'm a recovering audiophile.

:-]

> I have read that speakers in an ambisonic set up should be "full range".
> I'd like to set up a ambisonic speaker system (8 channel to start), and
> the prospect of 8 full range channels is daunting.  Since it seems they
> would be stand or wall mounted (at least some of them) that means
> monitors and subwoofers. Since all channels must be the same, that means
> 8 subwoofers...somewhere in the room.
>
> So what does "full range" mean usually and what does it mean in terms of
> talk on this list?

first, as initial shock therapy to the (ex-?) audiophile: ambisonics is 
not full-range in the usual sense. its localisation mechanism only works 
in a very limited frequency range. the idea is to use that small range 
to produce such good cues to the brain that it conveniently ignores that 
the rest is garbage ;)
i'm taking localisation only - timbre reproduction must of course happen 
from 20 to 20k...

if you want eight speakers, that would fix you up for up to third order. 
since i assume you're not much into computer-generated music (which 
would provide some source material), and since i know that higher-than 
1st-order recordings are rare (because i've personally made at least 1% 
of them...), it could make sense to go for 6 speakers initially. very 
good for first-order replay, very good for "super-stereo", easily 
accommodates 5.1 content with only minor placement errors, easier to 
place, and 25% cheaper. unless you choose a very exotic brand and model, 
it should be no problem to extend this setup to eight or more later.

it's no problem (and in fact customary) to use subwoofers with 
ambisonics for low-range extension. you can either forego localisation 
in that band and just use a mono sub (perfectly ok), use 2 and have some 
l/r signal in ithem, or you can use 4 subs in the corners of the room 
and drive them with a special horizontal decode. that's pretty awesome, 
because you can do a decode such that one speaker pushes while the 
opposite speaker pulls. of course that wastes quite some amp power, but 
it makes your room effectively infinite volume, which means you can fit 
very long waves into it without weird effects, and you will win a nice 
trouser-flapping effect without boominess and that obnoxious pressure on 
the ears.

if you're going to use ambdec for decoding, i can show you how to create 
two separate configurations for the full-range speakers and the subs, 
and to combine them into a single matrix (that's assuming that the subs 
themselves do their own low-pass filtering - if not, you'd need to do 
that with a plugin, but that means you will have to use another 
application in addition to ambdec).

best,

jörn