Webaudio API is still a working draft. See here for a support list.
Apparently not all Android devices are ready for it ... yet. See here for an example. As with any of those new (exciting) features you need to test support before using them on a device:
var contextClass = (window.AudioContext ||
window.webkitAudioContext ||
window.mozAudioContext ||
window.oAudioContext ||
window.msAudioContext);
if (contextClass) {
// Web Audio API is available.
var context = new contextClass();
} else {
// Web Audio API is not available. Fallback
}