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Sennheiser CX 400 BT (Black 508900)
Model: CX 400 BT · US configuration
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An assessment scenario for the earlier Black 508900 CX 400 BT: sealed-tip true wireless, no active ANC, with AAC/SBC/aptX support and one active Bluetooth source connection. The model is end-of-life on Sennheiser U.S.; this is not a claim that a matching offer or healthy battery is available.
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Assessment scenario: Earlier sealed in-ear earbuds without ANC
An editorial assessment scenario for an earlier, sealed in-ear model documented without active noise cancellation. Check the actual seller package and condition; this is not a statement of visitor intent or current stock.
Explore this buying guide ↗Why consider this model?
- The exact-model manual identifies closed-back ear-canal coupling and lists XS/S/M/L silicone adapters; that establishes a tip-based design, not a personal seal or comfort guarantee.
- Sennheiser describes the model noise reduction as passive, not active ANC. The checked U.S. page marks the family end-of-life, so this landing is an earlier-model assessment.
- The manual lists aptX, AAC and SBC and says playback is possible from one device at a time. Its approximately seven-hour figure is an AAC example under stated source, distance, volume and EQ conditions, not a test.
Tradeoffs to weigh
- It does not satisfy a must-have active-ANC or two-simultaneous-source requirement.
- The checked documentation does not establish an IP water rating, a water-rated case or wireless charging for the exact case; unknown is not treated as support.
- A case-combined figure of about 20 hours is a manufacturer maximum; battery capacity in an older or used unit is unknown.
- Sennheiser marks the model end-of-life. No present retailer stock, seller condition, warranty or returns are asserted.
Check these before ordering
- Match U.S. Black article 508900 and variant 45465086918939; do not confuse White 508901, CX True Wireless 508973, CX 150BT or CX 350BT.
- Check that the offer is a complete pair with the exact compatible case, both charging contacts working, suitable ear adapters and the listed cable; the manual contents are not proof of what a reseller includes.
- Ask about battery behavior and charging, the seller return policy and warranty before relying on an older unit; no individual offer was checked.
- Confirm the source device supports the chosen codec and accept one active source connection at a time.
- Do not assume IP protection or Qi charging from the product name or a case photograph; consult documentation for the exact unit.