Yamaha TW-E7B Noise-Canceling True Wireless In-Ear Headphones (White) - Manual (Page 42)

Sound is not good or sounds strange
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You might be wearing the earbuds on the wrong sides (L/R).
Check that the left (L) and right (R) earbuds are worn on the correct sides.
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“Putting on the earbuds” (p.23)
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The eartips don’t fit my ears.
Replace the eartips with the size that match your ear shape.
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“Replacing the eartips” (p.24)
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Troubleshooting > Sound is not good or sounds strange