The HE-400 headphones offer remarkable bass clarity and depth, with a "black background" effect that enhances the perception of bass onset in tracks like "Angel" by Massive Attack.

It's mentioned that these headphones have a tonal balance, but their resolving ability is considered lacking for a planar.

Users recommend modding the earpads, such as using Jergpads, to address treble balance and improve comfort, especially for those who find the original pads too small.

It's been suggested to drive the HE-400s with an O2+ODAC combo for optimal performance.

Removing the grills on the non-stealth version can open up the sound, but this modification doesn't help the stealth version.

Switching the Audinst HUD MX1 to high gain can significantly boost output, making it more effective for driving the HE-400s with a clearer and louder sound.

The HE-400se is hard to drive, requiring a powerful amp for optimal sound, even though it’s an entry-level planar model.

Owners note that the HE-400s are better suited for rock than classical, contrasting with the HD600 and HD650 which offer a more open soundstage.

A user felt the HE-400se lacked life compared to the dynamic AKG headphones, despite the latter's bass roll-off.

The HE-400s are praised for handling a wide range of music styles, from singer-songwriter to Nine Inch Nails, with a warm and forward sound.

Some users find the HE-400s lacking in bass compared to personal benchmarks like Beats IEMs and HTC One, though overall sound quality is satisfactory.

Some owners find the earpads cause itchiness, which is a notable comfort issue for longer listening sessions.

The stock cable is criticized for being too short, rubbery, and inflexible, detracting from the overall usability of the headphones.