Are there any single-driver bookshelf speakers from budget to very high-end that have a frequency response range from ~100Hz to 20KHz and above for home Hi-Fi use? That could be paired with a sub-woofer and accordingly adjust the frequency cut-off at the sub-woofer end that match the bookshelf speaker's starting frequency. Like the ones without any crossovers or coaxial speakers, just one single speaker driver with a sensitivity of at least 85db SPL. Most of them can be built as a DIY project, but those single-driver speakers are mostly for professional sound environment settings like recording or live venues.