Design and features:These headphones can be used wirelessly with Bluetooth devices or can be cord connected. When cord connected they have medium-high sensitivity so they can provide satisfying volume levels when used with home audio equipment and even lower-powered portable audio devices. The HD 4.40BT has an integrated microphone and volume, music player function, and call connect/disconnect controls for use with paired Bluetooth devices. Additional features include NFC Bluetooth pairing and earcups that fold for ease of storage. The free Sennheiser Cap Tune app download for Apple or Android smartphones acts as a audio playback app, provides various types of tonal adjustments, and Airplay (for Apple devices) and DLNA (for Android devices) audio WiFi network streaming. This model comes with a detachable 56-inch long standard audio cable, a USB charging cable, and a carrying bag.
Sound quality: We found the HD 4.40BT delivers sound quality that falls in the very good range - it reproduces music and voice very well although it does have some noticeable sonic quirks. The overall sound can be summarized as somewhat hazy and a bit congested. Bass (as in bass drums, bass guitars, stand-up bass, etc.) has decent impact and goes deep, but the lower bass is a bit boomy while the mid- through upper bass is a bit subdued. The midrange (voices, guitars, horns, etc.) is a bit thin and congested and somewhat hazy. The treble (cymbals, the upper range of violins, etc.) is a bit subdued and sizzly (sounds that should have a delicate shimmer have a sound a bit reminiscent of bacon frying), and the upper treble is muted. The sound has a good sense of liveliness and is somewhat open -- sound-wise it almost seems like you don't have anything covering your ears. There was no significant difference between Bluetooth and wired sound quality.
Comfort: We found that these headphones produce a sense of moderate pressure around the ears. Users with larger ears may find the over-the-ear fit of the ear pads feel cramped, or that the ear pads sit on, rather than around their ears. Users with smaller heads may find they can't get a good earpad seal around the ears which affects the sound quality: the bass becomes a bit subdued. As typical of over-ear models the ear pads might feel hot and/or sticky after prolonged use.
