IEMs can leak sound. How noticeable it is depends on their construction, fit, playback level, the material being played and the surrounding noise. “In-ear” does not mean that nobody beside you can hear anything.
A useful answer is specific to a situation: a quiet bedroom, a shared office and a train are very different environments.
Leakage and isolation are different questions
Isolation describes how outside sound is reduced at the listener’s ear. Leakage describes sound escaping from the earphone to the surroundings.
The two can be related, but an isolation figure is not a measurement of what your colleague hears. Do not turn a manufacturer’s attenuation claim into a leakage claim.
For example, Etymotic publishes isolation information for its ER4 earphones. That describes the stated behavior of those products, not the outward leakage of every IEM.
What changes the result?
- Listening level: turning the source up can make escaping sound more noticeable.
- Fit: a poorly seated tip changes the acoustic seal and may change the level you choose.
- Construction: a vented design and a more closed design need not behave identically.
- Room and distance: faint sound can stand out in a quiet room but disappear into background noise.
- Program material: a voice or bright percussion may be easier to recognize than a different passage at the same setting.
A practical courtesy check
In the room where you plan to listen, wear the earphones normally and use your usual low listening level. Ask someone at the relevant distance whether they can hear or identify the audio. Keep the setting and passage the same when comparing another pair.
This is a practical check, not a calibrated laboratory measurement. A phone recording can change the apparent result through automatic gain and noise reduction. A single recording does not establish a universal leakage rating.
Do not increase the volume just to make a demonstration dramatic.
Do you need another pair?
First check the fit and reduce the level if comfortable. If a particular setting demands near-silence, a design trial in that setting is more useful than relying on the term “noise isolating.”
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