Why does the volume become low during or after swimming

Why does the volume become low during or after swimming?

The sound quality may deteriorate if water gets inside the headphone sections (A). When you use your Walkman in the pool, be sure to choose the size of earbud carefully so that it fits fully into your ear and then insert the headphone sections firmly into your ears, so that there is no gap to allow water to get in.



If water gets inside the headphone sections, hold your Walkman as illustrated and shake it about 5 times to remove the water.
However, if there is still water is in the headphones, remove the earbud, put a dry cloth over the aperture of the headphone, and shake the headphones about 5 to 10 times.

The volume level is becoming low. Is this a defect? 

You may experience this phenomenon while swimming and water gets into your ear. The human eardrum detects sound by air vibration created by the headphones. It therefore becomes hard to hear the sound when water enters somewhere between the eardrum and headphones part.
 
The size of the ear is different by person, the original installed earpiece may not fit to each ear.
It is advised to use the bigger size (most suitable size) of earpiece to prevent water entering into the headphones.