Thứ Tư, 5 tháng 10, 2011

Insider secrets for getting the best sound from your home-theater system

Insider secrets for getting the best sound from your home-theater system

A home-theater audio system begins with the commitment not to skimp on equipment. We suggest devoting roughly half of your overall budget to audio gear and urge you to look beyond published specifications in choosing components. Instead, rely on your own listening tests to determine which units sound best. (There’s no substitute for careful listening.) If you follow our suggestions, we’re confident you’ll have a better-balanced and more satisfying system in the long run.
For the purpose of this article, we assume you’ve chosen a good AVR or controller/amplifier combo, a DVD player, a surround-speaker system with powered subwoofer, and appropriate digital, interconnect, and speaker cables.

Speaker Placement

After arranging your room’s furnishings and layout for home theater and unpacking components and making basic cable connections, the first major step in audio-system setup is speaker placement. Hint: Hold off on making final speaker cable connections until you know exactly where you want your speakers to go. Begin by placing the centerchannel speaker just above or below the center of your display, with the front of the speaker in approximately the same plane as the screen, facing toward the listening area. Avoid placing the center-channel speaker near reflective surfaces (e.g., shelves) that could muddy the sound.
Next, position the left and right main speakers symmetrically to the sides of your display; if you imagine the listener is seated in the center of a big protractor whose centerline points toward the center of the screen, then the main speakers should be placed about 30º left and right of the center, with the midrange driver at ear level. Hint: Place the front three speakers in an arc—not a straight line—so that they are the same distance away from your listening position (use a tape measure to check this). If the speakers are angled-in toward the listening position (as opposed to pointing straight ahead parallel with the sidewalls), be sure the amount of angle (called “toe-in”) is the same for both speakers.
Next, position left and right surround speakers symmetrically to the sides of and slightly above and behind your listening position—about 110º left and right of center. For 7.1-channel systems, the left and right back surround speakers would be placed symmetrically above and behind the listening area, about 150º degrees left and right of center. Hint: When using dipolar surround speakers, be sure to aim the null axis of the speaker toward the listening area. (This gives desirably diffuse surround sound.) The rule of thumb is that the surround speakers should be positioned at least three feet above the seated listeners’ heads.
Finally, position your subwoofer in accordance with the manufacturer’s instructions; some models are designed for use in corners or against walls, while others are not. Remember that the goal is bass quality—not bass quantity. If you encounter problems with indistinct, boomy bass, try pulling the subwoofer out into the room, making sure that the distances from the side and back walls differ (this helps fight boom-inducing resonance).
Once you are satisfied with speaker placement, you can make final loudspeaker cable connections. Hint: Leave some
slack in your speaker cables so that you can adjust speaker positions later if necessary, and, where necessary, conceal cables inside molded rubber cable-protector channels that rest flat on the floor. (These are available in most office supply stores, and improve system aesthetics while preventing guests from tripping over cables.) This is also the time to install the spikes that couple the speaker to the floor.

Defining Speaker Configurations and Sizes

Most AVRs and controllers feature speaker set-up menus in which the first order of business is to define the speaker configuration you are using (where numbers such as “5.1” denote five main speakers plus a “.1” subwoofer). Start by selecting the menu item that corresponds to your overall configuration, and then make additional menu selections to indicate what sizes of speakers you are using in each position and whether or not the system includes a subwoofer. By convention, full-range speakers are considered LARGE, while speakers that need bass reinforcement from a subwoofer are considered SMALL.

Setting Subwoofer Crossover Frequency

Your next task is to select an appropriate subwoofer crossover frequency— that is, the frequency below which the subwoofer will take over the bass workload from the rest of your speakers. Since most AVR/controller menus allow you to choose just one subwoofer crossover frequency that applies for all SMALL speakers in the system, the best strategy is to pick a frequency which provides adequate bass support for those speakers that produce the least bass of their own. For example, if your main speakers extend down to 65Hz, but your surround center-channel speakers reach only to 80Hz, it would be best to choose 80Hz as the system subwoofer crossover point, because this allows smooth, gapfree bass support for all speakers in the system. Use the frequency-response specifications for your speakers as a guide in selecting a crossover frequency. Note that some AVRs and controllers let you set multiple crossover points on a channelby- channel basis; where this is the case, match crossover points to fit the requirements of your individual speakers.