To get your scene to talk you can use WAV, MP3 and OGG for sound sources. All UA should support WAV. If you would like to use compressed formats (e.g. MP3 or OGG) provide alternative encodings in your AudioClip node.
<AudioClip url='"myAudio.wav", "myAudio.ogg","myAudioSource.mp3"' loop='true' enabled='true' />
For further informations take a look in the x3d documentation