Here's an FR plot from a measure I did. This is taken with the driver mounted in an Altec 816 bass horn, 1' from the horn front, on axis.

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As good as this plot looks, the driver sounds even better. It has quite an extended range; and the mid-bass sounds absolutely gorgeous.
Next up is to put one into a 1.5CF test box to zero in on the Vas number, then build a ported cabinet for it. I'll probably start with a 2-way waveguide design.