HD 4.40BT The HD 4.40 BT is about freedom of movement. Thus, no cable. Instead you get the latest wirelesstechnology and audio codec with Bluetooth 4.0 and aptX for reliable transmission and true wireless Hi-Fi sound. While Near Field Communication (NFC) ensures immediate and simple pairing with compatible devices. When you love the sound of the HD 4.40 BT, thats no coincidence at all. The closed-backed design of this headset is fitted with proprietary Sennheiser drivers that came a long way before being allowed to transmit sound to your ears. So, enjoy their well-balanced, amazingly detailed sound with dynamic bass. The HD 4.40 BT was made to go places with you and make these places more pleasurable. With its around-ear design and deep, ergonomically designed ear pads it offers unmatched comfort even during extended listening sessions. Its robust foldable headband design that can be easily and compactly stored in the supplied protective case makes for perfect portability.