KEF UNIQ - where to place the microphone for Near Field Measurements?

[Waveform Fidelity]

According to Keele’s AES paper, the near field SPL measurement can provide a good estimate of the FF SPL. He derived this theoretically and verified it practically on a number of loudspeaker drivers with cone diaphragms. He also showed that the SPL across the flat piston is uniform and tapers to the edge.

The assumptions:

-flat rigid piston
-infinite baffle

Measurement conditions

Place microphone within <0.11X of the diaphragm dimension and symmetrically on-axis.

Question: In the case of the UniQ driver (or generally with drivers with phase plugs), when measuring the mid-frequency driver, the center is occupied by the tweeter and phase plug, so where should the microphone be placed?

Anyone done any measurements or simulations to share?

 

[Head_Unit]

It should work right in front of the woofer part of the cone. I do not believe the microphone has to be placed symmetrically on-axis if I remember Mark Gander's paper correctly. I did not always have it like that. The velocity of the cone is the same across the cone (maybe not by the surround) assuming it is rigid, so the sound pressure should be the same as well.

Of course any placement is assuming a kind of pistonic motion-if the cone is breaking up or the dust cap out of phase or something then it won't be valid. Really a low frequency measurement was my impression. I remember being SO SO happy when a full LEAP simulation would actually look like my nearfield measurements! AES E-library is down again, I can't look up Gander's paper. Which was Keele's paper?