Where they actually differ
The most decisive specs, ranked by how much they matter — before the full spec table.
| Spec | Etymotic - ER4XR | Sony - IER-M9 |
|---|---|---|
| Impedance | 45 Ω | 18 Ω |
| Sensitivity | 98 dB | 103 dB |
| Driver count | 1 | 5 |
Between the ER4XR and IER-M9, the ER4XR comes out ahead in several specs, while the IER-M9 wins on impedance / sensitivity. Overall, the ER4XR scores 39.7 and the IER-M9 scores 54.5 on our Mars Score.
Which should you buy?
The IER-M9 is the clear pick on raw spec strength, leading by 14.8 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.
The ER4XR does not pull ahead on any single popular-comparison spec — its strengths sit in the spec-table groups rather than the headline advantages.
Pick the IER-M9 if you care most about impedance / sensitivity. Its strongest claims are impedance, sensitivity, driver count. The single most decisive one: Impedance — 27.00 Ω less. 18 vs 45.
Both ship with comparable detachable cable, so those specs do not separate the two — focus on the differences below.
Bottom line: the IER-M9 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: Etymotic - ER4XR or Sony - IER-M9?
Sony - IER-M9 leads the current Mars Score by 14.8 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 Etymotic - ER4XR if…
Etymotic - ER4XR does not lead a decisive measured field here, so choose it for price, ecosystem, design, or availability when those matter more to you.
Choose Sony - IER-M9 if…
Sony - IER-M9 has the measurable edge on impedance ohm, sensitivity db, 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 Etymotic - ER4XR wins
- No decisive advantages.
Why Sony - IER-M9 wins
- ▲Impedance — 27.00 Ω less. 18 vs 45.
- ▲Sensitivity — 5.10% more. 103 dB vs 98 dB.
- ▲Driver count — 4.00 more. 5 vs 1.
Spec comparison
Drivers
| Spec | Etymotic - ER4XR | Sony - IER-M9 |
|---|---|---|
| Driver count | 1 | 5lead |
| Driver types | Balanced Armature | 5 Balanced Armature |
| Impedanceⓘ | 45 Ω | 18 Ωlead |
| Sensitivityⓘ | 98 dB | 103 dBlead |
Build
| Spec | Etymotic - ER4XR | Sony - IER-M9 |
|---|---|---|
| Detachable cable | true | true |
| Connector | MMCX | MMCX |