More than any other vocal ensemble, the barbershop chorus requires total unity of voices. As the First Violins of a chamber orchestra must sound like one instrument and not vie amongst each other with individual ‘soloist’ character, so each voice part must be of one voice.
This means, of course, that soloist traits such as vibrato, ‘chest’ pressure on the sound, and spontaneous interpretive embellishments (altered timing, vocal inflections, dynamics, breath plan) are not present. The greater the skill of the chorus, the more of these expressive elements they can execute AS A GROUP. The artistry is in the ear of the director, not in the individual singers. Theirs is the skill of unit delivery and 100% commitment to the artistic plan from the director.