How the test reaches your subwoofer
A browser plays two channels, left and right, and has no separate subwoofer channel. Your sub gets its share of the tones through bass management, which splits the low bass off the main channels:
- AV receiver. Set the main speakers to Small so bass below the crossover goes to the sub; THX recommends Small for all speakers. With the fronts on Large, a stereo source may not reach the sub until you set Subwoofer Mode to LFE+Main on a Denon receiver, or switch on Extra Bass on a Yamaha.
- Soundbar with a sub. The soundbar splits the bass for you. If the sub stays quiet, check that it is paired and that its level isn’t turned down in the soundbar’s settings.
- Sub connected to a stereo amplifier. The sub’s own crossover (low-pass) knob decides where it takes over from your speakers.
Check the sub works and how deep it goes
- Keep the volume low and press 50 Hz. You should hear a steady hum from the sub, and feel the cabinet vibrate if you touch it.
- Work down through the tones. The lowest one you still hear or feel as a steady tone, not a flutter or a rattle, is roughly where your sub runs out in your room.
- Stop at once if the cone makes a slapping or clicking noise: that is the driver hitting its mechanical limit.
Set the phase control
The phase switch (0° or 180°) or dial lines the sub up with your main speakers where both play, around the crossover. Klipsch’s manual says to choose the position in which your subwoofer has more output at the listening position, and REL gives the same rule: whichever setting is louder.
- Sit in your usual seat and press the tone closest to your crossover frequency. If you are not sure what yours is, 80 Hz is the value THX requires in its certified receivers.
- Have someone flip the switch, or turn the dial in steps, while you listen.
- Keep the setting where the tone is loudest. REL notes that the difference can seem subtle at first, and that if the sub is turned up so high that it swamps the speakers, you should turn it down a little so the two blend.
Check the blend with the crossover sweep
Bass sweep 200 → 20 Hz glides slowly down through the crossover region, from where your main speakers play the bass to where only the sub does. A good blend sounds even on the way down. A clear hole around the crossover points to the phase setting (or, on a receiver, the sub’s distance setting, which shifts its timing), while a big boom at one pitch is usually the room.
Movie soundtracks carry their own bass channel, the LFE. Dolby’s encoder low-pass filters it at 120 Hz by default (the filter can be switched off), and the tones on this page go a little higher, to 150 Hz, to cover crossovers set above that. For an exact frequency, use the tone generator. To set a car amplifier’s gain with a multimeter, you need full-level amp gain test tones, not these. Check your main speakers are wired the same way round with the speaker polarity test.