Hori,
Generally the term "broadband" means that a transducer should work over a broader spectrum of frequencies. In theory, they should work equally well over that wider spectrum of frequencies, but from testing we found they do not. All transducers have a sweet spot that they like to resonate at. We tried using broadband transducers with the 585 and found that the HF side worked OK but there was a noticeable performance lost on the LF side. We found the LF side of the broadband transducer liked to resonate at 42Khz, the but 585 was transmitting at 50Khz. For this reason we don't recommend using any broadband transducer with our fixed frequency (628/588) sounders.
Snips