This unsupported element is not recommended. Authors should generally find an alternative way to accomplish the same task while adhering to all best practices, or simply do without it if it is unimportant.
The void HTML
<sound /> element specifies an audio file to be played in the background while viewing a document. Authors are urged to provide alternate methods of accessing files referenced by this element if they are important to the content of the page (perhaps by using a hyperlink) due to support only in Mosaic - a browser which is no longer available. Instead, use