Superlux HD-668Bchat_bubble_outlineFrom real comments

Bright treble dominates first impressions, but it settles with burn-in. Almost every reviewer flags the HD-668B as bright or even piercing above roughly 5-10kHz when new, with some calling the highs unbearable initially. However, a large number report that after 50 to 200 hours of burn-in the harshness fades dramatically, leaving a much more balanced, listenable sound. Rolling off treble via EQ or swapping to velour pads further tames this, and several long-term owners say there's little to no brightness left after break-in.

Soundstage and detail retrieval are the standout strengths. Multiple commenters single out the HD-668B's soundstage as wonderful, huge, or excellent, with one even noting occasional dizziness from its spaciousness. Owners describe hearing fine production details, individual instruments, and even mixing choices clearly, comparing the clarity favorably to headphones several times the price. This detail and staging is repeatedly cited as the reason people recommend them despite other shortcomings.

Cheap build and stock comfort issues are common complaints. Several users describe the plastic construction as thin or feeling cheap, and stock leatherette pads are called stiff, sweat-inducing, and uncomfortable especially for glasses wearers, with one buyer citing a cable failure after a year. Comfort also suffers for larger heads due to limited headband adjustment. Most address these issues by fitting AKG-compatible velour pads, which multiple commenters say fixes both comfort and reduces piercing highs.