Environmental sensors detect user visibility proximity and collision, while 3D spatial sound sources can greatly improve user engagement in a scene.
Event-producing environmental sensor nodes include LoadSensor, ProximitySensor, and VisibilitySensor. Audio nodes include Sound for aural spatialization and AudioClip for identifying sound files. MovieTexture nodes can also be used as an audio soundtrack source.
Relevant X3D Specification resources include the Environmental sensor component, Sound component and Texturing component.
The supporting Chapter 12 slideset and course videos (NPS, YouTube) for X3D for Web Authors are available online via X3dGraphics.com.
Also available: X3D Scene Authoring Hints for Audio and URL Links.
This viewpoint slideshow is online at https://X3dGraphics.com/examples/X3dForWebAuthors/Chapter12EnvironmentSensorSound/viewpointSlideshow.html
Viewpoint image version history at https://sourceforge.net/p/x3d/code/HEAD/tree/www.web3d.org/x3d/content/examples/X3dForWebAuthors/Chapter12EnvironmentSensorSound/_viewpoints