Under controlled conditions, we assessed acoustically (long-term average spectra) and perceptually (singer survey, listener survey) six performances of an soprano, alto, tenor, and bass (SATB) choir ("N" = 27) as it sang the same musical excerpt on two portable riser units (standard riser step height, taller riser step height) with varied dimensions of largely horizontal space (close spacing, lateral spacing, circumambient spacing) between singers. Given previous research that suggested horizontally spread spacing between choristers contributes to chorister perceptions of more efficient vocal production and audience preferences for choral sound, we wondered: (1) if spectra analyses might point to a possible acoustical explanation for auditor preferences; and (2) if increasing the height of riser steps to add more vertical space between rows of singers would affect choir sound. Statistical analyses of spectra data acquired from an audience position microphone found significant differences (p < 0.001) in mean signal amplitudes among the various performances. The taller riser unit appeared to enhance modestly the contributions of horizontally spread lateral and circumambient singer spacing. These effects were most robust (c.2-4dB) in diffusion of higher frequency partials in the 2.4-3.7kHz range in and around the "singer's formant" frequency region on both riser units, and in 4.7-7.1kHz partials on the tall riser unit. All choristers (100%) thought horizontal singer spacing influenced choir sound; 92.59% of singers described this perceived influence as "moderate" or "much." Most choristers (96.29%) thought riser step height influenced choral sound, with 62.95% of singers perceiving this influence as "moderate" or "much." Singers thought spread spacing contributed to most comfortable vocal production, better hearing of self and ensemble, and best overall choir sound. Listener ("N" = 21) survey results indicated significant preference for the overall sound of the spread singer conditions in close versus spread comparisons.