That’s something I’ve been thinking about for my next upgrade. Towers or bookshelves. If I went with bookshelves I’d potentially have more budget for even better subs. I have my towers crossed at 60hz as it is, so I may better off with higher quality bookshelves anyway.
Here's my take (which not everyone will agree with):
1. Any decent bookshelf will be capable of delivering sound down to 80 Hz without much of a reduction of spl. Any decent sub has the ability to reach 200 Hz, though one may wish to adjust the cut off well below that.
2. A really good tower can get down to about 40 Hz. After that spl drops, so a sub is still required.
3. The cost savings accrued through buying bookshelves can be considerable, leaving enough money for a better sub or more subs.
4. Bass quality improves with two or more subs. This is important because low frequency modes are notoriously difficult (some would say impossible in practical terms) to tame when one sub is used in anything but a free space or anechoic chamber.
6. A low reaching tower can reduce modes, but only up to the point of cut off. 40-50 Hz modes are common for most medium sized listening spaces, so a tower can still work here. But modal reduction at 40-50 Hz means nothing for modes or bass quality at lower frequencies.
6. It makes more sense to have a bookshelf based 2.2 or 3.2 set up rather than a comparably priced tower-based 2.1 or 3.1 set up, assuming that you're operating with a fixed budget.
May have skipped a logic step or two... it's been a long day!
