HD 650

Tonal Profile

Same 300 Ω chassis as the HD 600 and the same impedance peak near 100 Hz, so the 1/8 rule applies here too: a source above roughly 40 Ω output impedance adds bass, it does not just lower the volume. 103 dB/V means about 0.7 V for loud listening — trivial for an interface, out of reach for most phone jacks.