Not all projectors have onboard audio, and for those that do, the audio is sometimes all but useless—particularly with highly portable models. If you need sound for your presentations or for watching video, make sure that the projector has built-in audio that’s clear enough and loud enough to meet your needs. If not, consider using a separate sound system—often a good idea for home theater or home entertainment in any case—or powered external speakers. If you already have Bluetooth speakers, check whether the projector supports Bluetooth. Then there's 3D. Showing images in 3D for educational, business, and home applications seems well past the boomlet it enjoyed a few years ago. But if you're a fan of 3D movies or have an application that requires 3D, it's still easy to find projectors that support it.  Several 3D technologies are available, so make sure any 3D projector you consider will work with the 3D source you want to use. A “3D-ready” designation usually means it will work only with 3D generated by a computer. If you have a collection of 3D Blu-ray discs, the designation to look for is usually "full HD 3D." And before you go shopping for 3D glasses, be sure to check which kind the projector supports. There are several types, including some proprietary versions.