The effects of wall diffusing elements on sound-field diffuseness were investigated in a tenth-scale model hall and in a real recital hall. Acoustical measurements were carried out in both halls to measure the surface diffusivity of the lateral walls. In the scale model, the surfaces of the lateral walls and the soffits were covered with diffusers; in the recital hall, the front halves of both lateral walls were treated using reflective panels and absorptive materials. Objective characteristics were investigated using conventional room acoustic parameters and the number of peaks (Np) computed for the measured impulse responses, which were recorded under diffusive, reflective, and absorptive conditions. In addition, as a measure of the diffuse sound fields, the relative standard deviations (RSDs) of the acoustical parameters were investigated. The diffusive surfaces caused a decrease in the standard deviation of the early decay time and an increase in the Np at higher frequency bands. Auditory experiments using a paired comparison method revealed that the perception of subjective diffuseness could be quantified by using Np. In addition, one listener group's preference was correlated with Np and varied depending on different wall surface treatments.