You’ve spent a considerable amount of money on a handsome new home theater, complete with comfy theater chairs, a bright, vivid video projector, huge screen, powerful surround-sound system, and all of the of the complementary audio/video components. So when you touch Play, why doesn’t your system sound out-of-this-world amazing? It could be because one of the biggest factors in a room’s audio performance is the room itself; if it isn’t designed and treated for proper acoustics, it won’t perform like a champ no matter how much high-performance gear you buy.
When building the theater or media room of your dreams, you need to devote a percentage of your budget to the acoustical design, treatment, and calibration. The design of the room is the first step on the path to great sound. It’s much easier to create the ideal acoustic situation for your home theater if you talk to an acoustician or professional home theater installer before the room is built. According to Nyal Mellor, owner of Acoustic Frontiers, of Fairfax, Calif., a company that does residential acoustical design and calibration work, a typical budget for acoustics might be 10 to 15 percent of your overall home theater budget. The design portion of this would include creating a sound-isolated shell for the theater, determining how many speakers and subwoofers will be necessary and where to put them, locating acoustical treatments, specifying equipment, and even planning for things like heating and cooling ducts—which can introduce unwanted noise into the home theater space.
After the room is properly laid out and constructed, the equipment will be installed along with acoustical treatments, which are available in two basic types—diffusors and absorbers, usually made from fiberglass, molded plastic, or wood. Like their names imply, diffusors diffuse sound and absorbers absorb sound. An overly absorptive or “dead” room is one in which too much sound is absorbed, making the room feel uncomfortable and overly quiet. An overly reflective or “live” room is one in which audio reflections bounce all over the place, like on a basketball court or in a house without furniture. At a very basic level, an acoustician or a knowledgeable home theater designer will employ a combination of diffusive and absorptive materials to create the ideal acoustical environment that is comfortable and sounds fantastic. “It’s a bit like Goldilocks’s porridge: You have to use a combination of treatments to create a room that is just right,” says Mellor.
Acoustics can be incredibly complex, so instead of delving into complicated science that would make most readers’ eyes glaze over, we geeked out for an hour or two with two acousticians to report back the following nine things you need to know about home theater acoustics.
1. Your home theater is like an aquarium. The first issue addressed in acoustic design is the room structure itself. “Imagine an aquarium with a hole in it. It doesn’t matter where the hole is; all the water is still going to leak out,” says Dennis Erskine, an architectural acoustician and owner of Erskine Group, of Marietta, Ga. “Your theater is the same. The sound isolation is only as good as the weakest leak. You can have isolation clips, a HAT channel (also called a resilient channel, which is a thin metal channel that isolates drywall from the framing studwork), and two layers of drywall with damping material, but cut a hole for a light switch with a drywall saw, and all the money you spent on sound isolation is pretty well wasted.”
According to Erskine, a properly isolated room is completely sealed and mechanically isolated from the structure of your home. This is accomplished via a combination of damping and mass to reduce the amount of sound entering the room.
2. Your home is louder than you think. The average background noise level in a really quiet home is 33 to 35 decibels. However, the softest sound on a movie soundtrack is 22 decibels. This means that at normal volume levels, you can’t hear those soft sounds. “Whispers, the rustle of grass, leaves in the wind…those sounds disappear,” says Erskine. “Turn the volume up, and now the people on the screen are yelling at you. When a train wreck occurs, everyone will get up and leave the room. This is the sort of thing that makes theaters fall into disuse.” Sound isolation is imperative to keep sound out of the theater and the noise floor low enough so that you can hear those quiet passages without having to adjust the volume.
3. It’s nearly impossible not to wake the baby. The common misconception about sound isolation in home theaters is that it is used to prevent sound from leaving the room. “The public has been told that you need sound isolation so that you don’t wake the baby, but to achieve this will cost you more than it will cost to build your home,” Erskine says. That’s because the loudest sounds from a home theater are up to 115 decibels, a massive amount of sound energy to prevent from leaving the room. “It’s nearly impossible to achieve completely.” While sound isolation certainly helps, it’s primary objective is keeping sound out of the room and not the other way around.
4. With the introduction of new spatial surround-sound formats like DTS:X and Dolby Atmos come new acoustical considerations. Traditional surround “channel” speaker systems, like 5.1- or 7.2-channel arrays are different than new “object-based” spatial surround-sound formats like Dolby Atmos and DTS:X, and therefore require slightly different acoustical design considerations. “In my opinion, the acoustical treatment design for reflection control is different for the new spatial audio formats. With a traditional 5- or 7-channel system we believe that the ceiling should not be overly absorptive. But when using discrete ceiling speakers for Atmos and DTS.X we advise keeping the ceiling more absorptive so as to not corrupt the spatial cues in the surround field,” says Mellor. Of course, some Atmos and DTS:X speakers are designed to reflect off the ceiling, so it’s important to talk to your acoustician to determine the right treatments for your ceiling based on the speakers you are using in your Dolby Atmos or DTS:X surround setup.
5. Acoustics make expensive gear perform like it should. While some homeowners may not want to devote money to acoustical treatments and design, it’s important to know that they essentially enable your expensive speakers and components to operate to their maximum performance potential. “When you consider that 80 percent of sound in a home theater is a reflection and not coming directly from the speakers, you can understand why acoustics are so important. They will have a greater impact on the sound quality in the room than a better surround-sound processor, cables, or speakers,” says Erskine. “With the proper acoustics, $40,000 worth of gear will sound like $400,000 worth of gear.”
6. Acoustics make your bass sound tight. Bass energy from subwoofers can be especially tricky to manage, with uneven bass response across a home theater noted as a very common problem. Bass traps are super-thick absorbers designed to absorb longer low-frequency audio wavelengths. “Controlling the bass in the room and having the bass decay at the same rate as the rest of the sound in the room is important,” says Mellor. “Home theaters that have bass issues will have big bumps and dips in the frequency. Bass trapping is always required, but should be complemented by multiple subwoofers to reduce seat-to-seat variability, as well as DSP equalization.”
7. You can hide acoustical treatments or use them as design elements. If you are thinking an acoustically treated theater will look unattractive, think again. Generally, you can hide absorptive products behind an acoustically transparent fabric wall. Absorptive panels themselves are usually finished in fabric, so they can also be designed to match the room and simply hung on the wall surface. There are also paintable panels that can match the room’s shade exactly. Meanwhile, a ceiling can double as both a design element and an acoustical element. Erskine’s breathtaking ceiling millwork diffuses sound, while a fabric-stretched star ceiling with fiber optic lighting functions as a great faÃƒ:§ade behind which to hide acoustical absorption materials. Some diffusors—those made from wood especially—are so beautiful, they can be left exposed like artwork.
8. Acoustics aren’t just for theaters. Did you know that acoustical treatments can help with taming noise in other areas of the home? For example, treatments can help reduce air-conditioning compressor noise by directing sound away from the home. They can also help minimize the sound generated by equipment inside a utility room from seeping into bedrooms above. “Look at what Frank Lloyd Wright does in his homes. He puts carpets on the floor, uses soft furniture and decorative tapestries, and designs cantilevered bookcases at strange angles to either absorb or diffuse sound,” says Erskine.
9. You need an expert. When you are embarking on a new home theater project, make sure that your home theater design firm has acousticians on-staff or has the necessary experience to properly design your room. Many companies outsource this part of the home theater design. “Acoustics are an engineering problem; you can’t read a book or simply Google it. To get it right, it’s a four-year degree plus experience in the field,” says Erskine.
To find a find a professional who specializes in acoustical design check out our list of home systems integrators, the Acoustical Society of America website or the CEDIA (Custom Electronic Design and Installation Association) website. Your ears will thank you for it. EH
Krissy Rushing is an A/V publishing industry veteran whose experience spans more 15 years. From her early days as executive editor of Home Theater magazine, Ultimate AV, and Audio Video Interiors, to her more recent work as a freelance writer, Krissy specializes in making technology understandable to anyone.