Between the IER-M9 and Monarch MKIII, the IER-M9 comes out ahead in impedance, while the Monarch MKIII wins on sensitivity and driver count. Overall, the IER-M9 scores 54.5 and the Monarch MKIII scores 72.9 on our Mars Score.
Which should you buy?
The Monarch MKIII is the clear pick on raw spec strength, leading by 18.4 points on the Mars Score. The margin is wide enough that the underdog only makes sense if its individual strengths line up with what you specifically need.
Pick the IER-M9 if you care most about impedance. The biggest gaps in its favor are impedance.
Pick the Monarch MKIII if you care most about sensitivity and driver count. Its strongest claims are sensitivity, driver count.
Both ship with comparable detachable cable, so those specs don't separate the two — focus on the differences below.
Bottom line: the Monarch MKIII is the safer default. The other model is the right choice only when its specific advantages line up with your priorities.
Why Sony - IER-M9 wins
- ▲Impedance — 4.00 Ω less. 18 vs 22.
Why ThieAudio - Monarch MKIII wins
- ▲Sensitivity — 8.74% more. 112 dB vs 103 dB.
- ▲Driver count — 5.00 more. 10 vs 5.
Spec comparison
Drivers
| Spec | Sony - IER-M9 | ThieAudio - Monarch MKIII |
|---|---|---|
| Driver count | 5 | 10lead |
| Driver types | 5 Balanced Armature | 1DD + 6BA + 2EST + 1 Bone Conduction Tribrid |
| Impedanceⓘ | 18 Ωlead | 22 Ω |
| Sensitivityⓘ | 103 dB | 112 dBlead |
Build
| Spec | Sony - IER-M9 | ThieAudio - Monarch MKIII |
|---|---|---|
| Detachable cable | true | true |
| Connector | MMCX | 2-pinlead |
Spec-level deep dives
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