BB vs NB detection ranges?

[MarkShot]

I am reading a book on naval warfare. The text states that BB detections (general non-specific noise) occur before NB detections (specific harmonics associated with various ship sub-systems). It sounded fairly reasonable.

In the meantime, as an SC/DW player NB detections are always possible prior to BB detections. In particular, those very faint lines (with high gama settings) or even shadow lines at 50Hz and 60Hz frequencies being the very first indication of a contact. The text did note that low frequency sound is the least subject to attenuation over distance and thus is the most detectable; although high frequency sound is mainly used for active sonar, since the high frequency is needed to distinguish metallic object returns compared other naturally occurring reflectors.

So, which is the more sensitive passive system BB or NB? If BB, then why does it seem reversed in SC and DW?

Thanks.