[LAD] A Cathedral in your backyard

Joern Nettingsmeier nettings at folkwang-hochschule.de
Wed Apr 25 07:51:09 UTC 2007

Jens M Andreasen wrote:
> What I think would be possible as an experiment though (without
> involving a budget the size of the Pope or TU-Berlin), is to place a
> large amount of uniform speakers in a circle and then feed them with the
> same monophonic signal. If everything works as expected, it should then
> appear like the sound emerges from the center of the circular array of
> speakers.
> * The speakers could be a collection of ghettoblasters and kitchen
> radioes with fresh batteries. 
> * The signal could be a local radiostation (hey, this
> is /wireless/ :-). 
> * The location could be a park or a stadium in your city.
> Would that work? 

no :-D

you might indeed get a "standing" wavefield that looks the same, but the 
problem is it's not a standing wave. :) listeners outside of the focal 
point would hear the speakers nearer to them first, leading to phantom 
images. generally, in large auditoriums, you have to be very careful 
with the signals coming from the opposite direction... for instance, 
"proper" ambisonics decoding calls for antiphase signals from opposite 
speakers, but that falls apart outside the "sweet spot". that's why 
malham et al. came up with their "controlled opposite" rendering, which 
basically means that the speakers opposite a sound source are quiet.

i got a chance to listen to the wavefield synthesis system at tu berlin 
for several hours (thanks torben for a late-night session!), and i found 
that virtual sound sources inside the speaker array work very well for 
low and mid frequencies (torben had me step inside a techno bass drum, 
and it was quite astonishing), but it only works for higher frequencies 
as long as you're not in between the speakers and the virtual sound 
source (due to dampening i guess, and because the virtual source has not 
converged correctly yet).

jörn nettingsmeier

home://germany/45128 essen/lortzingstr. 11/

Kurt is up in Heaven now.

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