o determine the role of intraoperative electroco- chleography to optimize the fitting of the floating mass transdu- cer of the Vibrant Soundbridge on the round window membrane in patients with conductive and mixed hearing loss. Improved round window vibroplasty outcomes are observed when the surgeon is promptly informed of the compound action potential changes induced by the floating mass transducer round window membrane vibroplasty and alters surgery accordingly. The key point for optimal coupling is a floating mass transducer in full contact with the round window membrane, free to vibrate without any contact with the surrounding bony structures and mobile footplate.