   
Sound DesignApril-2004, Home Entertainment and Design Magazine Making home theaters look and sound good requires a delicate balance of form and function. The blockbuster movies based on J.R.R. Tolkien’s The Lord of the Rings trilogy manage to keep even the most cynical moviegoers on the edges of their seats. Likable characters, elaborate costumes and gorgeous cinematography are obviously at the heart of the trilogy’s success. But what draws us into the story is not just how the movies look, but how they sound. Just admit it: The ominous thump of the Orks’ footfalls as they run through the forest captures audiences just as much as the creepy visuals do. Incorporating dark fabrics into a home theater’s design helps prevent light from reflecting off walls and washing out the screen image. Filmmakers spend millions on the best equipment to capture, edit and mix audio. Watching movies may seem primarily a visual experience, but what we see is definitely affected by what we hear. This applies not only to the tools that go into movie making, but also to those used to play movies at home. A home theater is more than just a room with technology. This space does not simply exist—it performs. And how well a home theater sound system performs is determined in large part by the acoustics of the space. Defined as the science of sound, acoustics are affected by the room’s shape and dimensions and by the building materials. The acoustical behavior of a space may also be affected by furniture, artwork and products added specifically to enhance the acoustics. The effects of poor acoustics are familiar to everyone. We’ve all eaten in a restaurant where the voices of the other patrons echo all over the room, drowning out our conversation. And we’ve all attended concerts in environments so reverberant that it is impossible to hear the musicians clearly. Acoustic treatment can be concealed behind fabric to improve the sound of a room without impinging on the room’s appearance. In home theaters, such unfavorable effects are even more pronounced. With too much reverberation, dialogue becomes difficult to understand and sound effects may be obscured. Conversely, too little reverberance can make music and movie soundtracks seem lifeless. A poorly designed room may produce annoying, booming bass in one seat—and almost no bass in another. But in many home theaters, acoustical analysis is conducted only after the room is designed and the audiovisual system is installed. And some home theaters receive no acoustic consideration at all. I think that acoustics is probably the most overlooked element in a home theater. You can’t ignore acoustics unless you listen to your DVDs through headphones. The room—and what sound is bouncing around it—is part of the whole experience. Most homeowners are driven by what they can initially see, so they spend a lot of money on architectural finishes and interior design. Unfortunately, they don’t always understand the ramifications of not having a properly treated room and how that affects the sound quality of the space. Making Good Sound Look Right One key aspect of creating a great-looking and great-sounding room is employing a professional acoustical consultant at the outset of a construction project. You can do it afterwards, but it’s kind of like building the Hoover Dam and then doing the engineering after you are done. At that point, you have what can be a monumental disaster that costs a lot of money to correct. You are much better off doing the engineering before you start the building because if you get the engineering done in the first place, you can often completely integrate it and make it invisible. Behind the fabric are the speakers and a variety of acoustical treatment devices that control and direct sonic reflections If you deal with acoustics at the beginning, you can actually integrate the acoustical solutions into building’s look. If you do it at the end, it’s like a Band-Aid on top of the room, and it just looks terrible. The majority of elements that lead to a good-sounding room really have to be fundamentally built into the design at the outset. New Dimensions in Sound Perhaps the most important part of the acoustic design process is choosing the right room dimensions. Rooms act as resonators, amplifying or attenuating certain frequencies of sound depending on the distances between the walls. Every rectangular room has three fundamental resonances, which are based on the width, length and ceiling height. Any one resonance is not significantly troublesome, but problems occur when resonances overlap. For example, if your room is 15 feet wide and 15 feet deep, you double the resonance and end up with boomy bass at 75 hertz. That means every time the bassist on your favorite CD plays a D, the note will sound extremely loud. Another option is to install acoustic panels that are designed to blend in with a room's overall decor Poorly chosen room dimensions can also cause certain frequencies of sound to cancel each other out. The difference between resonance peaks and dips as you move around a room can be as much as 40 decibels. That’s similar to the variation between soft conversation and a scream. The goal in a listening space is to adjust length, width and height so the room resonances are spaced in frequency by five percent or more. That’s great for new construction, but what if you want to build a home theater into an existing space? There are four ways an acoustical consultant can improve a room’s sound. One method is to use resilient construction—springy walls, floors and ceilings—to dampen the resonances. Another method is to install tuned absorber devices, such as diaphragms and resonant cavities, that will absorb individual room resonances without affecting the rest of the sound spectrum. A third method is to locate speakers and subwoofers where they actually cancel the room resonances. The fourth method is to use an electronic equalizer to counteract the boost from room resonances. However, an equalizer cannot correct the dips from room resonances; you would burn up amplifiers and blow speakers if you tried it. The Treatment and the Wrap Once the room dimensions are chosen, the acoustician “treats” the room with products designed to diffuse, reflect or absorb sound. Usually, the front of the room—the area near the video screen—is treated with absorptive products to keep the all-important dialogue sounding clear and focused. The back of the room is most often treated with reflective or diffusive products, which help maintain realistic sonic ambience. You may have seen acoustic-treatment products in photos of recording studios. Some look almost like small models of New York City, with square columns of varying heights jutting up like skyscrapers. Others employ creatively shaped foam or curved wood panels. A few companies have attempted to style their acoustic treatment products to avoid making your living room look like Aerosmith’s weekend hideaway. Yet acoustic treatment products retain a bad reputation among interior designers. To make acoustic treatment invisible, acousticians usually design a room within a room. The outer shell, framed with studs and drywall, holds the bulk of the acoustical treatment. The inner shell, usually made at least partly of fabric, hides the acoustic treatment and, usually, the speakers. It also incorporates the video screen and interior design elements. In these rooms, the fabric itself is critical to the success of the acoustical design. Much to the dismay of interior designers, not all fabric is created equal, and some may affect the way acoustic treatment products work. Fabrics may act as a filter through which the sound passes, changing the timbre of the sound and diminishing its intensity. If the sound is unable to pass easily through the fabric into the acoustical treatments installed behind the walls, the acoustical design is compromised. That is why acousticians request that an interior designer submit fabric samples for testing. Acoustic treatment can also be incorporated into a home theater’s ceiling as in this picture. Many fabrics have a negative effect on sound transparency or even on the natural acoustics of a space. When assessing fabric, an acoustician analyzes its weave pattern, density and consistency. Appliques and tightly woven upholstery are notorious for creating uneven sound transparency. Fabrics used should be fireproof, or at least fire-retardant. Interior designers should also avoid light-colored fabrics. The fabric should be darkish in tone, especially for rooms where a video projection screen is used. If it’s a light-colored fabric, it will reflect light from the screen and wash it out. Highly reflective fabrics are a bad idea, too. Not all acoustically excellent rooms are shrouded in fabric, though. Sometimes, acoustical treatments are used as visible design elements. There are creative ways to make acoustic treatment less obtrusive. For example, acoustical panels can be cut into artful shapes and sizes; some are made to look like paintings. Microperforated wood pieces and plasters are sometimes applied on top of acoustic treatments for aesthetics. Working in Isolation It can be just as important to keep sounds inside the theater from escaping, or sounds originating outside the theater from entering. You don’t want to hear traffic outside or people walking above if you are in a home theater because it takes away from the experience and pulls you out of that magic. And if you have family members who are studying or reading, the last thing they want to hear is an explosion from a DVD soundtrack. However, some clients opt out of implementing sound isolation. Ultimately, it depends on what the client’s expectations are. With sound isolation, they may not really care if they are making noise in the home theater and the rest of the house hears it. There are grades of acoustical design and treatment. With all of the acoustical panels, paints, sprays and fabrics on the market, some homeowners may wonder how much is too much. Certainly there have been cases of going overboard. In fact, a space that has been over treated may wind up sounding dead. The question is not how much treatment to use in total, but what proportion of treated versus untreated surfaces you need to create a balance. While gear heads may not want to hear it, sometimes your money is better spent on acoustics than on equipment. If you are spending $50,000 on equipment and putting it in a room with hardwood floors and drywall, you are going to get radically better sound if you put $35,000 into the equipment and $15,000 into the acoustics. -->
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