@ ngccglp

The T/S parameter I found in WWW showed me a low moving mass so it should really work up to 500 Hz in a front loaded horn. I've simulated the LaScala with Hornresp and it gave a good result.
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Peter

PS: The spacings are about 7,5 cm, that's 1/10th of the wavelegth at 500 Hz, so the waves should come around.