KRK KNS 6400 On-Ear Closed Back Circumaural Studio Monitor Headphones Voiced to remain true to the character of KRKs class leading studio monitors, developed with 25 years of years of experience in studio sound. The latest reference quality frequency response for closed-back, circum-aural dynamic headphones. Newly developed headphone acoustical system bringing a new level of headphone performance for the first time. A new standard in headphone comfort, even over extended periods of use, designed to avoid feeling uncomfortable especially during long periods of use. The special foam conforms to the ear to help ensure an improved fit. Exceedingly accurate natural and wide frequency response. The latest reference quality frequency response for closed-back, circum-aural dynamic headphones. Newly developed headphone acoustical system bringing a new level of headphone performance for the first time. Exceedingly accurate natural and wide frequency response.