Apart from your rent and your ride, your television may be your priciest possession. But if you’re mounting it (or its audio equipment) in the wrong place, you’re going to sacrifice picture quality, viewing comfort, or both.

Here, experts from THX provide their top tips for selecting and positioning your home entertainment system.

Eyeing that big blank spot over your fireplace? Stop right there. Interior designers will tell you that’s a tacky look. But more importantly, mounting your flat screen more than 15 degrees above or below your line of sight can mess with its picture quality.

Photo via THX

“For optimal viewing, you want your line of sight to be more or less aligned with the center of the screen,” says Eric Gemmer, director of imaging technology for THX. He says modern TVs—especially the latest 4k or ultra-high definition (UHD) models—have various layers of LCD enhancement that focus light in specific ways. If you elevate your TV, you’re going to distort the picture quality.

Hoist that TV up over your mantel, and you’ll also have to tip your head back—an uncomfortable position if you’re binge-watching the latest Netflix fave-rave, says Steve Martz, THX’s director of global technology.

To get the most from your HD set, you can’t position it too far from where you’ll be sitting, Gemmer says. A good rule of thumb: Divide your screen size by .835. This will give you the ideal gap (in inches) between your couch and your set. (For example: If you have a 65-inch set, dividing that by .835 gives you 78 inches, or about 6.5 feet.)

If you’re wondering what size TV to buy for your space, just measure the distance between your couch and your future TV’s location, in inches. Multiple that number by .835, and you’ve got your perfect screen size.

The math gets a little trickier for 4k or UHD sets. “The nearer you sit to these models, the more detail you’ll be able to pick up,” Gemmer says. “The pixels are so small that your eyes won’t get tired even if you’re very close.” For the ideal distance, see the chart below. You can sit a bit farther away if that makes you comfortable. But you’re missing out on some of the definition you paid for, he adds.

Photo via THX

When you first set up a new television, you’ll likely be asked whether it’s for home or store use, Gemmer says. “Always select home,” he says. The store settings are configured for very bright spaces, and will seem overpowering if viewed in your pad.

Most newer televisions also come with a couple settings people ignore, he adds. One of these is “cinema” or “home theater” mode. “If you’re watching your TV at night or in dimly lit rooms, these settings will improve the picture presentation,” he explains.

There’s also a “bright room” setting that will enhance your TV’s visuals for daytime viewing. “If you’re watching sports during the day on weekends—or if you have your TV in the kitchen, which is usually brighter than other rooms—that setting may improve picture quality,” he says.

For all their advancements in picture quality, the newest TVs are so thin that very few offer decent sound quality, Martz says. A sound bar (like this wireless option from Sonos) is a major upgrade. But, as with your set, positioning matters.

Martz says you want your bar right below your TV, not above it or positioned somewhere else in the room. This will help ensure your audio exactly melds with what you’re seeing on-screen. “Also, don’t tilt the bar up or down, and try to align its face vertically with your TV screen.” Again, he says this ensures there’s no disconnect between your audio and visual components.

“You want to be immersed in your viewing experiences,” Gemmer says. “All of these steps reduce the potential for distortion and viewer fatigue.”