Sound is basically a form of wave., the ECE guys, and specifically people in for EM and related stuff LOOOVVEEEEEEEEE waves (those of you being extra picky - yes every wave is a quanta and every quanta has wave component, for now for the sake of his question, I am leaving Quantum mechanics aside) Sound is basically when anything is moving to and fro in a media....

So snswer is so broad: Sound engineering is used in communication. SAW filters are one of the most precise filters for many applications.

Understanding of sound and noise that surrounds sound in acoustic spectrum is also very important when developing mobile and landline phones.

Then comes energy conversion from sound waves. Compressed sound waves can make sustained highly viable energy source

To decrease vibrations and sound proofing is age old mechanical engineering concept, but needs all that can be obtained from ECE on that front as well. Dampers, actuators, feedback control are all ECE.

And the list goes on. In nut shell knowing: how: to use something for optimal results is engineering [I think...]