Cancellation can be an issue, what I did to help resolve the cancellation is us a open baffle bandpass design. This helps with several problems associated with O-B designs.
1. Using the band pass increases spl at the tuning frequency.
2. Having the bandpass port loads the driver thus having better control and increased power handling.
3. The band pass port being far smaller than the driver is similar to using a much larger baffle on the same driver. - As I understand it, and reduces cancelling effects.
4. This one is only a guess and difficult to explain. I think possibly because on the band pass port the waves are shaped differently and delayed enough to reduce cancellation. This is just a theory, and I have nothing to back it up. Other than my original non band pass designs were not very good.
5. The woofers need to have relatively high QTS or higher to be used in open baffle (low dampening). In totally open baffle the woofer has little load and moves large amounts to get to the lowest frequencies.
Dave Harris.....What I don't know is a lot. - amateur advice giver.
www.FastlaneAudio.com "Home of the Fastrac"