Maybe because the model assumes the same frequency response radiation pattern front and back across the full bandwidth. Linkwitz said the rear pattern/frequency response was different from the front due to an acoustic filter created between the cone and basket. So it might not look that good above whatever frequency that filter starts to operate in a real system?
https://www.linkwitzlab.com/models.htm#D
This is the BEE0 example, 100, 400 and 800 Hz (horizontal).
The first time I find this diagram useful
The first time I find this diagram useful
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Would not produce nulls in the horizontal plane, as drivers are aligned vertically.
It is a port resonance issue, after all. Or cabinet resonance escaping through ports. Port separation is ~36 cm, deepest null frequency is 1650 Hz. I threw a quick sim in interference applet (https://www.falstad.com/interference/)
You can't input exact values, but with 34 cm separation and 1881 Hz frequency it showed nulls at +-65 degrees, which agrees with JBL measurement showing the deepest nulls at +60 and -65 degrees. In vertical plane two ports would as a single ~60 mm wide-directive source, which agrees with the +70/-100 directivity from the polar map. Sorry for digging into last year's snow, but port resonance this high and this intense (and in a $900 loudspeaker by a respectable company
:) is fascinating.The horn is, after all, blameless, and performs good for seemingly simple shape. It seems broad facets work as "good enough" termination for 100 degrees horn.
The 5" example shown earlier - here are the responses of the front and the back side of the diaphragm isolated and then combined.
FRs at 0, 90 and 180 deg horizontally.
Front, back, combined (magnitudes):
Front, back, combined (phases observed at 2m with propagation delay subtracted):
FRs at 0, 90 and 180 deg horizontally.
Front, back, combined (magnitudes):
Front, back, combined (phases observed at 2m with propagation delay subtracted):
