On Fri, 05 Aug 2011 21:25:11 +0100, Eiron
wrote:

On 05/08/2011 17:36, Jim Lesurf wrote:

The behaviour breaks down about 5kHz because you are now just using the
central element of the array (the center disc) and so the angles then fall
with frequency in the usual way.

I thought the annuli were fed from a delay line rather than a crossover....

They are. Jim is referring to the fact that the central portion
doesn't get any smaller with rising frequency, and at 5kHz its size is
starting to become appreciable.

d