How a few simple treatments can change the way you hear.

Do-it-yourself may have been adequate for building your dorm room hi-fi, but it won't suffice when planning a decent home theater, surround music or a distributed audio/video system. Today you need to work with an electronics dealer who has the ability to understand your preferences in both system performance and room decor.

One way to determine if a dealer is worthy of your business is to see if the company pays attention to how you'll feel about your media room. After the components and furnishings have been specified, the two biggest contributors to improving your cognitive experience are the lighting (see AV Insider, January 2004) and the acoustical treatments. Good lighting control, fixture selection and location set the proper cinematic mood and won't degrade the picture. And getting the acoustics right assures that you'll enjoy maximum performance from the audio and video gear you buy.

By allocating at least 10 percent of your system's budget for acoustical treatment, you'll gain benefits such as clearer dialogue, more precise sound localization and a greater sense of spaciousness in surround sounds. It's generally felt among audio experts that proper acoustical room treatments contribute to more than 50 percent of the quality in a modern hometheater or audio system.

Everyone knows good sound when they hear it; you just feel right about being in that room. This is not by accident. It's achieved by proper room design and the balance of three acoustic factors: absorption, reflection and diffusion. Research has shown that most people like the same range of reverberation time in performance spaces. These times are typically between .2 and .4 seconds. But because most homes come with smooth, straight walls and ceilings, achieving this ideal reverberation time can be a challenge. With the proper combination of these three treatments, this challenge can be met in a new construction or retrofit space.

Absorption and Reflection

Absorption is used to help reduce room reflections and echoes and to create the ideal reverberation time. Absorption is most economically addressed by covering either fiberglass or man-made wool panels with acoustically transparent fabric. These panels are typically hung directly on the wall or hidden behind a floor-to-ceiling fabric wall treatment. If the absorptive panel is thick enough—3.5 to 4 inches for proper midrange attenuation—the sonic energy passes through the fabric and into the panel and is returned to the room as heat. Some absorption can also be achieved with well-placed drapery and certain types of ceiling tiles.

In systems with too much absorption, the room sounds "dead" and lacking in ambience. Hearing one's own pulse in a home theater should never be a performance objective. With too little acoustical treatment, you'll hear long reverberation times and more reflected than direct sounds, resulting in a lack of dialogue clarity when watching movies, for instance.

The proper amount of reflection in a room can be achieved by not treating a certain amount of existing drywall and ceiling surfaces, or by using panels similar in appearance to the absorption panels but containing an underlying reflective material.

Deliberate Diffusion

A sound diffuser removes the negative effects of acoustic glare that is created by flat wall and ceiling surfaces. Acoustic diffusion is intended to distribute the sound generated in a space uniformly. To use a light analogy, if you take a pinpoint light source and shine it into a frosted glass, you diffuse the light into many directions. The overall amount of light is not reduced; it is uniformly distributed. In large concert halls, the irregular surfaces of the statuary, relief ornamentation, columns, coffered ceilings, and balconies actually create diffusion by scattering the sound.

A good diffuser allows sound to be scattered in uniform directions. In a residential diffuser, this can take a number of form factors that until recently have been borrowed largely from the professional sound recording studio industry. These devices typically have the design aesthetics of science-fair projects. Fortunately, several companies now offer diffusers that are relatively thin and unobtrusive, so they can be covered in fabrics similar to the other types of acoustic panels. An authorized dealer/installer who carries acoustical treatments such as these is likely to be schooled in applying the proper ratio and placement of all three of these treatments.

With the advent of multichannel audio and movie soundtracks, the need for proper acoustic treatment has never been more important.

There are other acoustical-treatment challenges such as standing waves, rattles, sound isolation and background noises from heating and ventilation systems. Many of these issues can be addressed by utilizing proper design and construction techniques when you are building your new home or media room. If you are planning a new home, seek a qualified dealer/installer to learn more about proper building and acoustic-treatment techniques. A little bit of time and money invested here will yield enjoyable dividends for years to come.

What is the cutting edge of residential acoustical treatment? "Shape optimization" allows architects and acousticians to enter the room's dimensions and the acoustician's performance specifications into a computer model that then details acoustic treatment criteria so the dealer knows where to apply the various types of acoustical treatments. This program also allows you to "listen" to your room before it's built, via a model set of loudspeakers or headphones. Pretty cool stuff indeed!

John Caldwell is president and founding partner of CEBIZ, a marketing development and consulting agency for manufacturers, dealers and reps. www.cebiz.net.

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