I have *very* limited experience with DAF. I used it twice in speech therapy. Just for proof of my fluency potential. So, please take my answer with a grain of salt. I wouldn't think DAF would work in only one ear. My understanding of DAF is that it works by stopping you from hearing what you're saying, as you are saying it. If one ear is 'open', I'm not sure how effective DAF would be. I'd think it would be quite distracting to hear real time and the delay fractions of a second after. Hopefully someone else can provide a better answer.