The answer lies in an innate sense of music; I call the great ‘vocal’ actors “singers in speech”. John Gielgud and Judi Dench are virtuoso examples from older generations; Ralph Fiennes is today’s supreme inheritor of this tradition. The architectural skills he uses to place each syllable according to its weight and purpose turns verse into music, and enables the meaning of the verse to travel through and with the music, so that musical phrasing is not an embellishment, but the essential channel to reality.
It can be thrilling to hear, and shocking to feel, for the audience is sometimes unprepared for the brightness of truth which suddenly hits them through the musicality of his voice - it is as if they have been ambushed. The words carry unanticipated punch and anguish. No wonder audiences sometimes feel seduced by Fiennes; it is not a matter of sexual allure, but of vocal enchantment.
Thunder in the Air: Great Actors in Great Roles by Brian Masters