Sennheiser HD 400 PRO Studio Reference HeadphoneIts all in the mix. When working at home or in the studio, you need your mix to sound as it does when your listeners hear it. The HD 400 PRO reference headphones are your everyday tool to get the job done. Its open back design provides a natural and accurate listening experience for fine tuning your signature sound. The core of the HD 400 PRO is the 120 ohm transducer developed by Sennheiser engineers, featuring a specialized polymer blend in its