The lowpass filter on most subwoofer amplifiers can be adjusted between roughly 40 and 160 Hz. As an example of what it is doing, if we set the filter to 80 Hz, it will produce everything lower than 80 Hz. It is called a "lowpass" crossover because it allows all frequencies lower than the crossover point to pass. Most home stereo speakers can work at their best down to 60-100 Hz, so we would like our subwoofer to begin making sound right about where the main speakers stop. To find this setting, get the system up and playing music that has a good bass component. Adjust the subwoofer's volume so you can hear its output clearly. Adjust the crossover knob back and forth through its full range. As you increase the cutoff frequency to the point where it begins to overlap the main speakers, you'll hear the system begin to "boom". (If you have trouble hearing this change while standing very close to the subwoofer, go to the area where you would normally listen and have someone else adjust the knob for you.) Turn the knob back until the boom just falls away. Leave the knob set there. Optimize the volume of the subwoofer so it matches the main speakers, and you're done. Once optimally set, your active subwoofer will require no further adjustment if used exclusively for either music or home theater. You may find that different settings work better for each situation, so take note of these. Because of this, often a remote-controlled plate amplifier is used, or the enthusiast will have a separate system for music and home theatre.
How is the crossover properly adjusted?
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