Where they actually differ
The most decisive specs, ranked by how much they matter — before the full spec table.
| Spec | Moondrop - Aria 2 | Sony - IER-M9 |
|---|---|---|
| Sensitivity | 122 dB | 103 dB |
| Impedance | 32 Ω | 18 Ω |
| Driver count | 1 | 5 |
Between the Aria 2 and IER-M9, the Aria 2 comes out ahead in sensitivity, while the IER-M9 wins on impedance / driver count. Overall, the Aria 2 scores 65.4 and the IER-M9 scores 54.5 on our Mars Score.
Which should you buy?
The Aria 2 is the clear pick on raw spec strength, leading by 10.9 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 Aria 2 if you care most about sensitivity. The biggest gaps in its favor are sensitivity. The single most decisive one: Sensitivity — 18.45% more. 122 dB vs 103 dB.
Pick the IER-M9 if you care most about impedance / driver count. Its strongest claims are impedance, driver count. The single most decisive one: Impedance — 14.00 Ω less. 18 vs 32.
Both ship with comparable detachable cable, so those specs do not separate the two — focus on the differences below.
Bottom line: the Aria 2 is the safer default. The other model is the right choice only when its specific advantages line up with your priorities.
Which should you buy: Moondrop - Aria 2 or Sony - IER-M9?
Moondrop - Aria 2 leads the current Mars Score by 10.9 points.The more useful decision is the trade-off behind that result: compare driver count, impedance, sensitivity against the way you will actually use the product.
Choose Moondrop - Aria 2 if…
Moondrop - Aria 2 has the measurable edge on sensitivity db.
Choose Sony - IER-M9 if…
Sony - IER-M9 has the measurable edge on impedance ohm, driver count.
This is a structured comparison of the published catalog values. It is not a claim of identical real-world performance across every workload; use the linked spec drill-downs and methodology page to inspect the inputs.
Why Moondrop - Aria 2 wins
- ▲Sensitivity — 18.45% more. 122 dB vs 103 dB.
Why Sony - IER-M9 wins
- ▲Impedance — 14.00 Ω less. 18 vs 32.
- ▲Driver count — 4.00 more. 5 vs 1.
Spec comparison
Drivers
| Spec | Moondrop - Aria 2 | Sony - IER-M9 |
|---|---|---|
| Driver count | 1 | 5lead |
| Driver types | Dynamic | 5 Balanced Armature |
| Impedanceⓘ | 32 Ω | 18 Ωlead |
| Sensitivityⓘ | 122 dBlead | 103 dB |
Build
| Spec | Moondrop - Aria 2 | Sony - IER-M9 |
|---|---|---|
| Detachable cable | true | true |
| Connector | 0.78mm 2-pinlead | MMCX |