Most projectors you're likely to consider for backyard movies today have a built-in speaker or speakers. But with the exception of room-to-room portables, which offer good audio systems by definition, and the growing category of laser UST projectors that are often advertised as laser TVs (and aren't suitable for lugging to the backyard), you'll want an external audio system in most cases, or at least external speakers. The reason: It's difficult to deliver good-quality audio at high volume levels from the small spaces most projector chassis leave for the sound system. Room-to-room portables offer extra-wide or taller, nearly cubic shapes than traditional projectors, and fill the extra space with low- and high-frequency speakers (technically, "drivers," in audio terminology), which are often chamber speakers. They usually boast plenty of wattage to provide sufficient volume even for outdoor use. (Laser UST projectors are much wider than traditional projector designs, and many use the side facing the seating area for what amounts to a soundbar.) Of course, regardless of how good the audio quality and volume are for the projector you pick, you might want even more robust audio. If so, consider getting outdoor speakers, and look for analog or digital audio-out ports or Bluetooth speaker support in the projector. Bluetooth can be especially handy if you already own a robust Bluetooth speaker set, but with a caveat we'll get to in a moment. Many home theater projectors don't offer even a pass-through audio port, however. They're designed with the assumption that you'll use a separate audio system connected directly to your video source. As for Bluetooth speakers: Because of the vagaries of both video and audio processing, losing sync between the image on the screen and the sound from a Bluetooth speaker is a common issue. To avoid it, look for audio-delay adjustments for Bluetooth speakers in projectors and in external audio systems. Note also that most room-to-room portables, and many smaller portables, offer a Bluetooth speaker mode themselves, so you can use them with other audio sources. One last thing: A booming audio system might be great within the confines of your own backyard, but consider your neighbors' comfort when you set the volume. (Or make sure to skewer extra shrimp, pop extra popcorn, and invite them over.)