The Microsoft HoloLens Developer Edition has built-in speakers to provide a 3D sound experience. These speakers are designed to project the sound to your ears so a 3D app or game can give you a fully immersive sounding experience. However, if you’re hearing impaired or just want the audio from the HoloLens to be private then these built-in speakers may not be ideal. Is there another option for HoloLens audio, such as connecting headphones or earbuds?
If you look in the manual booklet that comes with the Microsoft HoloLens, it doesn’t mention anything about using wired headphones with the device. It would normally be assumed that you cannot and the device doesn’t support it. Even though it is not mentioned, the device does have a port opposite to the power plug that looks remarkably like a standard headphone jack.

This headphone looking plug isn’t mentioned in the HoloLens “Let’s get started” booklet that comes in the box. It seems to be an undocumented feature. What is it? Is it a headphone jack?
Yes, yes it is! Just plug in some headphones and the Microsoft HoloLens will seamlessly switch to using those for the audio output rather than the built-in speakers. You’ll probably want to use some earbuds as standard headphones may not fit very well over the top of the Microsoft HoloLens. Plus, having two huge things strapped to your head may not be all that comfortable.

One of the benefits of using headphones or earbuds with the Microsoft HoloLens is the sound is more directed into your ears. As a result it’ll likely sound a little louder at the same volume level. This should help those who are either hearing impaired or in an environment where it may be difficult to hear the built-in speakers.`