FINE-TUNING the Placement of Your Subwoofer

THX subwoofers	page 12

Here are two methods of setting the correct phase with your subwoofer.

PHASING TEST METHOD ONE

Set the switch labelled "SUBWOOFER PHASE" to the "+" position. Then, play a familiar CD, LP, laserdisc or tape with steady, consistent bass content. Listen carefully to the "mid-bass" region of 70 - 125 Hz. This is the part of the spectrum where electric or string basses and drums predominate.

Then, reverse the position of the "SUBWOOFER PHASE" switch. If it is set to the "+" position, set it to the "-" position. If it was set to the "-" position, set it to the "+" position. The best way is to have a partner work the switch while you sit in the main listening position and listen.

Now listen to the same music, concentrating on the mid-bass. If you hear less bass, set the "SUBWOOFER PHASE" switch to the opposite position. If you hear more bass, leave the switch where it is; the new position is correct.

PHASING TEST METHOD TWO

First, set the toggle switch labelled "SUBWOOFER PHASE" to the "+" position. Then, feed wideband pink noise (found on test CDs, the "Wow" disc, or a pink noise generator) through your front channel speakers and your subwoofer. You can do this test by listening, but it is best to use a spectrum analyzer and look at its display in the "mid-bass" region of 70 - 125 Hz.

Now, listen to the same wideband pink noise or look at the spectrum analyzer output in the mid- bass region. If you hear/measure less bass, set the "SUBWOOFER PHASE" switch to the opposite position. If you hear/measure more bass, leave the switch alone; the new position is correct.

This test is necessary because the different distances from each speaker to your ears mean that it is possible that the Subwoofer's output may arrive at your ears out of phase with the Satellites' output. When this happens, the midbass is cancelled. Re-do this test any time you move any of your speakers or the listening position.

If you want to experiment, move the main speakers or subwoofer towards or away from your listening position, in small increments. When you hear the best combination of stereo image localization and focus with solid midbass impact and output, you have the ideal location.

If you have two subwoofers, perform one test for each subwoofer. When you perform each test, make sure the other subwoofer is not operating by either unplugging its input cable or its power cord.

8. FINE-TUNING THE PLACEMENT OF YOUR SUBWOOFER

Experimenting with the placement of the subwoofer can significantly improve its sound. Once the subwoofer is hooked up, listen to it with a familiar CD, Laserdisc, LP, etc. with good bass content. As you move the subwoofer, listen carefully for changes in the amount and quality of the system's bass reproduction.