The Focus 160 is a fairly tiny mini-monitor:
86 dB/W sensitivity (moderately low efficiency)
7.9 x 13.8 x 11.6 inch (fits on even modest bookshelves)
17 cm LF driver (6.5 inch)
My dynamic range estimator gives the following results:
Freq,Hz Max SPL, DB
These speakers are capable of producing a moderately loud output (100 dB) only down to 60 Hz.
Below 70 Hz, even a 50 wpc power amp could possibly overdrive them.
If you wanted to use them with a 100 wpc (typical AVR) WPC amplifier you would have to cross them over around 80 Hz to protect them from excessive power and audible distortion.
In all seriousness, unless these are only for night time use, or use in a tiny apartment or dormitory with thin walls, they would need a subwoofer to be able to cover even just the narrowest possible view of the musical frequency spectrum (down to 43 Hz) at fairly tame sound levels (100 dB SPL).
Edited by planetpaul - 12/6/13 at 5:47am