Thanks to everyone for the responses. So it seems like a narrow dip in spl at one point in the range is relatively inconsequential, at least in this instance. That's good to know.
@roadcykler, your post is surprising on an audiophile forum. Whay do I want to hear the dip? Because I want to be able to correlate the measurements with my listening experience. Or in this case, to learn that the the dip has little effect on what I'm hearing. If none of this was important, I'd just buy some old Pioneers at the goodwill and be done with it. I like learning about audio almost as much as I like listening to music -- it's how I put together a system that presents the music at its best.