HD 620S

Tonal Profile

Sennheiser's closed answer to its own open 6xx line: 150 Ω, closed cups, and a published THD of «<0,05 % (1kHz/90 db SPL)» — a tenth of what the open models quote at the same level.

Amplification Warning

110 dB per volt means roughly 0.2 V for 100 dB — high efficiency for 150 Ω, so this is a closed 150 Ω headphone that a laptop genuinely drives. The impedance still argues for a low-output-impedance source if you care about the bass staying where it was tuned.