Any speaker that can get down to 20HZ would not need a sub.
I would respectfully disagree on a few grounds. Placement and the effect on midbass from the woofer being two of them. Even if we get past the second (say McIntosh XRT2k or Infinity RSI) we still have the first (though in those cases bass is a separate tower so...)
This is the conundrum for audiophiles, almost everything that can get that low is very expensive.
I'm not sure I agree there either. They are just (generally) not brands we gravitate towards.
There certainly is a price to be paid having two 20Hz cabinets compared to one; but it needed be overbearing.
Now let me contradict myself and also agree with you: They generally are. I think this is a matter of the fact that audiophiles aren't generally emphasizing a desire to get LF response, instead prioritizing all the other frequencies, because they plan to use subs. Only when speakers are getting expensive does the company "throw in the kitchen sink" and build down to 20Hz.
Another problem that raises costs is that it takes a lot more power to run lower frequencies than higher ones; so your crossovers (assuming they are't active) start having to bleed off much more energy to the top-end if the speakers are expected to operation down to 20Hz; and adding more drivers makes the crossovers more complex (compared to the relatively easy active crossover in your AVR)
Heck: My complaint is more often with speakers that try to be as full range as possible when I would prefer they try to be the best they can be above 60-80hz... speakers that, for example, give up efficiency to be flat to 50 when I'm going to cross them at 80; but YMMV
That being said, the majority of full range tower systems are in the 35 and 30 HZ region and many owners of such designs do not incorporate a sub. For what they listen to they get low enough.
Here we do agree.
A 20 HZ bookshelf design is virtually non-existent. I am sure there is some sort of esoteric, super high end, bookshelf being produced out there. However, I expect it would be some sort cost no object statement piece, like this one.
https://pmc-speakers.com/products/consumer/se-series/mb2-se Which is not a bookshelf but a stand mounted speaker.
I agree. Such designs are uncommon at best. Even in nearfield monitors (which are designed with the intended use of running sans sub) generally only go down to 50hz or so.
Creating one would mostly be a matter of using the crossover to lower the >20Hz sound down until their flat. Sensitivity would be terrible; but it could certainly be done.
I have active 4-way towers. They are calibrated to drop-off around 35Hz. This is to maximize clean SPL. Because they use an active crossover, I have a second configuration that makes them flat to 20Hz at the cost of volume.
