HD 550

Tonal Profile

150 Ω open-back with a stated SPL to one decimal place — Sennheiser is the only maker in this batch that publishes sensitivity that precisely, and it does so per volt, which is the reference that actually matches how a source is specified.

Amplification Warning

150 Ω draws little current but wants voltage: about 0.3 V for 100 dB, which a laptop jack manages and a weak phone output may not with quiet recordings. This is the impedance at which the answer stops being «anything drives it» and starts depending on the source.