If employed in a less-than 1:1 diaphragm-to-throat ratio, the front chamber would act as a low-pass filter by attenuating higher frequencies. In essence, the front chamber is an acoustic filter by its physical dimensions and could give a -6db rolloff on the upper frequency bandpass.

A horn that lacks a front-chamber (1:1) PER SE would be limited in its upper band pass as a result of foldings (if any), and the mass rolloff, electrical impedance, etc., of the driver, amongst other considerations.

DM