Prepared and reviewed by the JRT Audio OEM/ODM team · Updated 27 October 2026.
1. Turn the approved sample into a controlled reference
An approved sample should be linked to the final driver configuration, acoustic filters, damping materials, nozzle, vent, housing, cable, ear tips and firmware or DAC settings where applicable. Store the measurement curve and physical sample together with the approved artwork and bill of materials.
- Approved left and right reference units
- Measurement fixture and test conditions
- Driver and acoustic-material version
- Cable, connector and plug configuration
- Housing color, faceplate and logo artwork
- Accessory and packaging specification
2. Define frequency-response tolerance and channel matching
A target curve alone is incomplete. The buyer and manufacturer should agree on the frequency range reviewed, smoothing, fixture, insertion method and acceptable variation. Channel matching matters because an imbalance between left and right can shift vocals and imaging even when each side looks broadly similar.
3. Check electrical and distortion performance
Impedance, sensitivity direction, continuity, polarity and distortion checks help detect assembly, driver or soldering problems. Test conditions and limits must match the product design; copying another model's limits can create meaningless acceptance criteria.
4. Inspect nozzles, vents, filters and sealing
Small changes in acoustic filters, glue, vent openings, nozzle mesh or shell sealing can change the sound. Visual inspection should therefore be connected to acoustic results. Buyers should also confirm that left/right markings and nozzle dimensions match the approved sample.
5. Verify connectors and cables
For detachable designs, inspect connector retention, polarity, repeated insertion, intermittent contact and left/right cable identification. Review plug type, microphone or remote functions, strain relief and cable finish. A premium-looking cable that intermittently disconnects is a critical customer-experience failure.
6. Review fit, cosmetics and accessories
Check shell seams, faceplate alignment, scratches, bubbles, color variation, logo position, ear-tip fit and accessory completeness. Cosmetic limits should use clear photos or physical defect samples instead of subjective descriptions such as good or acceptable.
7. Plan batch sampling and traceability
Define the inspection level, critical/major/minor defect classes and the action taken after a failed lot. Keep production date, component lot and inspection records so any field complaint can be traced and contained.
- Acoustic measurement record
- Electrical and functional test
- Connector and cable check
- Cosmetic reference standard
- Accessory and packaging check
- Batch code and inspection disposition
Related OEM buyer resources
9 current HiFi IEM OEM models 9-model comparison guide IEM customization guide
Buyer questions
What causes sound variation between IEM production units?
Variation can come from drivers, acoustic filters, damping, vent dimensions, sealing, nozzle mesh, assembly and measurement setup. The control plan should address both components and process.
What is IEM channel matching?
Channel matching compares the left and right earpieces under the same conditions. It helps prevent audible imbalance and unstable stereo imaging.
Can an approved frequency-response graph replace a golden sample?
No. The graph records part of the acoustic result, while the golden sample also provides a physical reference for fit, finish, cable, accessories and the complete listening direction.
What should an IEM pre-shipment inspection include?
It should include model and batch identification, acoustic and electrical results, functional checks, connector and cable inspection, cosmetic review, accessory count, packaging and disposition.