Superlux
HD668B
headphones
$45
Used market: $35*
Specifications
3 of 7 values have a recorded sourceExpert Audio Engineering Commentary
Tonal Profile
Semi-open, 56 Ohms, and the one Superlux with a detachable cable at both supplied lengths — which is why it outlives its own price class. The 56-Ohm load is the useful detail: it is nearly double the 32 Ohms of the HD681, so a source with a high output impedance loses less grip here, while a 250 mW-into-32-Ohm phone output has 2.6 dB less headroom in voltage terms.
* Estimated with the depreciation fallback (~78% retained value). · checked on 8/5/2026