THX insists on a high level of quality in the products that we endorse. For a home theater system to carry the THX logo, the products must pass a stringent THX Certification process. Although in 5.1 sound systems there is a discrete channel for the low frequencies – LFE (subwoofer), low frequencies can still exist in the left, center, and right channels, depending on the soundtrack. Depending on how your receiver is set-up, these low frequencies will crossover into the subwoofer channel. Some systems may have problems in a seamless crossover from the Left-Center-Right channels to the subwoofer. As this may affect system set-up and adjustments, it is best to know how your system is performing.
A tone, which starts at 200Hz and transitions down to 20Hz, is generated in the left, center and right channels during this test. The purpose of the test is to alert you to any frequencies that might drop out or not be faithfully reproduced as your Left-Center-Right speakers crossover to the subwoofer. Listen for a drop in volume level during the transition. A high quality system will reproduce the tone sweep smoothly and without volume level fluctuations as the frequency decreases. Systems that appear to vary in audible levels may need further diagnosis. Although any problems maybe inherent in the system, it is important to know what your sound system is capable of reproducing. Faults may be due to a variety of reasons, but the best resource would be your local home theater salesperson. They may suggest a variety of options for you to try. Don’t forget to check out the THX recommended list of home products!