The differences are that,
* the (purported) 30 Hz model's performance will be much more stretched
* the 30Hz bookshelf may interfere with the subwoof, thereby compromising integration.
* bookshelves reproducing 50 Hz & lower, in tune & time & as loud as the rest of the spectrum, are. Go for the 70Hz model.
There are many more differences, but these seem simplest. Regards
* the (purported) 30 Hz model's performance will be much more stretched
* the 30Hz bookshelf may interfere with the subwoof, thereby compromising integration.
* bookshelves reproducing 50 Hz & lower, in tune & time & as loud as the rest of the spectrum, are. Go for the 70Hz model.
There are many more differences, but these seem simplest. Regards