SR1a Headphone + HSA-1b AmpReturns are not accepted on Discounted items. The World's First Earfield Headphone Monitor The SR1a by RAAL requisite is the world's first Earfield headphone monitor. Experience mixing, mastering, and home listening with unparalleled accuracy and realism in a soundfield devoid of room acoustics and comb filtering caused by work surface reflections. Earfield technology delivers unheard of program accuracy and a speaker like soundfield experience.