My open baffles are fitted with vintage alnico Altec 416B 8 ohm 15" drivers - rightly highly desirable in the 2nd hand market.
When I bought the speakers they crossed at 400Hz to the midrange, but I have now changed the midrange drivers to ones that can happily crossover at 100Hz, so the quality of the 15" driver is no longer exploited at these 'higher' frequencies. This makes the need for a high quality bass driver slightly less of an issue.
My overall impression of the current Altec bass drivers is that they are not pulling their weight and sound a bit quiet (quite normal with OB cancellations) compared to the midrange and tweeters. There is no way I will correct things by attenuating those.
The Altecs have a Qts of 0.25 and I am going to experiment with the ubiquitous Eminence Alpha drivers which have very similar sensitivity but a Qts of 1.25. Should be interesting.
So we will see what happens when they arrive and are fitted.
