FINIS Duo MP3 player specially design for swimmer or under water diver . It is popular for good quality sound without the use of ear buds. But how it is possible. As they said :

Bone Conduction audio transmission to deliver crystal clear audio through cheekbones to the inner ear. An integrated clip design secures the Duo™ to goggle straps to rest on the cheekbones for a comfortable and streamlined fit.

Link

https://www.finisswim.com/Duo