THE SENNHEISER HD 4 SERIES - Let Everyday Sound Great. The HD 4 SERIES, the complete Sennheiser quality package in a range of durable, closed-back over-ear headsets that fulfill your everyday aural needs. It speaks of dynamic yet puristic and timeless design. Featuring a robust and foldable headband for easy storage on the go, the HD 4.20s ensure good attenuation of ambient noise and great wearing comfort even during extra-long listening sessions. The HD 4.30 features the power and quality of the Sennheiser sound anytime, anywhere and creates an exceptional soundscape with precise acoustic response and a rich dynamic bass.