IER-M9 vs IER-Z1R

Sensitivity tells you how much volume a transducer produces per unit of input power. A 100 dB/mW headphone hits 100 dB SPL with 1 mW; an 85 dB/mW headphone needs ~32× more power for the same volume.

Comfortable listening

• Conversation / background music — 60–70 dB.
• Engaged listening — 75–85 dB.
• Loud / hearing-damage zone (sustained) — 90+ dB.

Pairing with sources

A phone's headphone-jack DAC outputs ~25 mW into 32 Ω. With a 100 dB/mW headphone, that's 114 dB peak — plenty. With an 85 dB/mW, you might only get peaks around 99 dB — comfortable max, no headroom for transients.