Back about 15-20 years ago or more there was what seemed like a significant design change in speakers. especially floor standers, in which they went from the large woofers and wide cabinets to what we see today in speakers that have cabinets that are relatively tall, narrow and deep,and not much wider than the drivers themselves. Apparently, it was determined through measurements that a significant amount of "diffraction" was occurring and sound was being lost along the width of these wider boxes, especially with sound from the tweeter, thus, considerable inaccuracy in what the listener was hearing.
Comparatively speaking, in most of today's models, you don't see drivers much bigger than 6 and a half inches, yet they still get as much or more bass than these older designs with the giant woofers. It seems more scientific fine tuning has been done between the cabinets and drivers to get the superior efficiency in sound. Ian could certainly give a much better description than me of design philosophy and the changes that have occurred over the years.
Probably not the best example, but I have an old set of speakers from Radio Shack with 12 inch woofers and giant cabinets, yet, in all sound categories, they don't even come close to my M80s.
