There are two main factors that set how easy or difficult a speaker is to drive, these are Speaker Sensitivity and Impedance. A speaker rated lower Ohms requires more current than a higher Ohm speaker. Similarly, a speaker with lower sensitivity requires more power to reach the same volume as a speaker with higher sensitivity.
Sonus Sonetto II's nominal impedance level is 4 Ohms . 8 Ohms is pretty much the standard impedance amongst stereo speakers and amplifiers so Sonus Faber Sonetto II is not considered a difficult to drive speaker from Impedance perspective.
Sonus Sonetto II has a sensitivity of 87 dB. With a sensitivity level of only 8 dB, Sonus Faber Sonetto II is a difficult to drive speaker from Sensitivity perspective, so make sure to choose an amplifier with high power if you like listening to your music at high volume levels.
Read our detailed Sonus Faber Sonetto II Review