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

Setting Speaker Distances (Delays) and Levels

Once a subwoofer crossover point is selected, it is time to set speaker distances (or delay times); this adjustment ensures that sounds arrive at your listening position with the exact timing that soundtrack designers intended. Almost all AVRs and controllers provide menus where you can specify the distance between your listening position and each speaker in the system, including the subwoofer. Use a tape measure to determine those distances and enter them in the appropriate set-up menu. For best accuracy, measure from one common point in the center of your listening position to the center of each speaker’s grille. Once distances are set, you’re ready for the enjoyable process of setting speaker levels (where you’ll finally get to hear your speakers in action). Virtually all AVRs and controllers provide “pink noise” test tones that slowly shift from channel to channel in your system. Use caution when listening to these tones, taking care not to play them too loudly. Your mission is to use the set-up menu to adjust the volume levels of each individual channel until all channels are evenly balanced in output. With practice you can do this by ear, but for greater precision and more reliable results a smart alternative is to use a good, inexpensive sound pressure level (SPL) meter such as those sold by RadioShack. Skip the digital SPL meter and choose the more accurate and less expensive analog model (catalog #33- 2050.) Set the meter to C-WEIGHTED position, SLOW RESPONSE, and set the sensitivity knob to 70. Using the centerchannel speaker as your reference, listen to the test-tone pattern and determine which channels need more or less volume to match the level of the center channel. As you make volume adjustments, try first to balance the output of the L/R main speakers with the center channel (since these three speakers carry the bulk of the sonic workload), then balance the surround speakers to the front speakers, and finally match output from the subwoofer to the rest of the system. Hint: If you are using an SPL meter, try pointing it toward the ceiling, and positioning the meter so that its built-in microphone is in roughly the same position as a seated listener’s head would be.

Fine-Tuning the Subwoofer

You are nearly ready to test your speaker setup using soundtracks and movies, but before doing so I recommend performing a few subwoofer-specific tests and adjustments. Your objective is to have the bass output of your main speakers and the subwoofer blend seamlessly, and to achieve this result you’ll need to adjust the phase control of the subwoofer to “synchronize” its output with that of the main speaker. Try listening to recordings with repetitive low-bass content (e.g., a concert bass drum that is struck again and again throughout a song), and then adjust the subwoofer’s phase control until the best overall combination of bass output and bass clarity is achieved. If you have residual problems with boomy bass, try positioning the subwoofer farther away from the wall to improve clarity. (It may take several tries before you get good results.) Once you’ve adjusted the subwoofer’s position and phase controls to your satisfaction, you may need to reset distance settings (if necessary) and re-adjust subwoofer volume levels.

Listening Tests

Your final system “sound check” should involve listening to music (using your AVR or controller’s surround- sound modes) and to wellrecorded Dolby Digital or DTS film soundtracks (but remember, music is usually the tougher and more revealing test). Normally, the set-up steps above will get you very close to optimal sound, but don’t be surprised if it takes some fine-tuning to get surround imaging to gel. Your goal is to achieve a smooth, seamless “ring” of sound that surrounds your listening position. Don’t be afraid to make small “tweaks” to achieve a more perfect blend; it’s part of the fun. When in doubt, let your ears be your guide.