One-sentence answer: The body of a bone conduction headphone must work normally under sweating and rain. The acoustic breather membrane of the transducer cavity, buttons, magnetic charging contacts and silicone-overmold joint surfaces form multiple sealing paths. Using a CTS Sentinel C28WE (C28) leak detector with vacuum decay for complete-unit air tightness testing can intercept water ingress defects before shipment.
The transducer cavity must both transmit sound and resist water. The membrane material itself and the bonding ring are both leak-sensitive points, and testing must avoid crushing or detaching the membrane.
The body mostly uses silicone overmolding on a plastic frame. The two have different coefficients of linear expansion, so micro-gaps tend to appear at the joint surface after long-term wear. This is a typical path that passes at the factory but leaks water after use.
Magnetic charging contacts, buttons and microphone holes are distributed on different curved surfaces. The fixture must conform to the curved surfaces, making plugging more difficult than on a flat housing.
Sealing locations: acoustic breather membrane bonding ring, magnetic charging contact area, button seals, microphone hole, silicone overmold and frame joint surface, rear cavity cover seam.Consequences of leakage: after sweat and rain water seep in, they corrode the transducer and mainboard, causing reduced volume, distortion or no sound on one side; contact corrosion causes charging abnormalities; moisture in the vibration unit also brings abnormal resonance, which users can directly perceive.
Yes. The breather membrane itself has a controlled air permeability, which appears as a continuous slow pressure change during testing. Therefore, the criteria should be set according to the membrane's inherent air permeability characteristics, and the test differential pressure and rate should be limited in the program to avoid misjudgment or damage to the membrane material.
Use a custom-formed soft silicone pad to cover the contact area and apply uniform pressure, avoiding damage to the metal contacts by hard tooling. The contacts are also a transition surface between metal and plastic, and inadequate plugging is the main source of misjudgment at this location.
Pay attention to the fit state of the joint surface and the fixture compression. Silicone is highly elastic; too little clamping force causes sealing leakage, while too much changes the state of the joint surface. It is recommended to include clamping force and daily check in the work standard.
It is possible, and this is a common fixture risk for curved-surface parts. Silicone has a critical point of permanent deformation under compression. Once the clamping force exceeds it, it cannot be seen at shipment, but after a period of use micro-gaps appear at the joint surface, which instead become a new water ingress path. The approach is to validate the compression and judgment window separately with known-good and known-bad samples, and freeze the clamping force into the work standard.
The difficulty of air tightness testing for bone conduction headphone bodies lies in coexisting breather membrane, scattered openings on curved surfaces, and silicone joint surfaces. The CTS C28WE, with vacuum decay and controllable test differential pressure, ambient drift correction and 32 programs for multiple models on one line, together with custom-formed soft silicone tooling, forms a stable interception for factory water resistance.
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