This study numerically investigates the spatio-spectral sound transmission properties of a sonic crystal flat lens and presents a discussion on the effects of negative refraction on the spatio-spectral selectivity of sonic crystals. For this propose, pulse response analyses are carried out to demonstrate the spatio-spectral acoustic transmission features of a triangular lattice two-dimensional sonic crystal flat lens at the bottom edge of the second frequency band. The spectral analysis indicates the existence of a spatial filtering effect resulting from the wave focalization of the negative refracted wave beams emitted from a point source. We theoretically demonstrate that this effect can be utilized in the implementation of highly frequency-selective spatial sound filters by using sonic crystal flat lenses from point type acoustic sources. (C) 2016 The Physical Society of the Republic of China (Taiwan). Published by Elsevier B.V. All rights reserved.