60 Hz test tone for hum matching and subwoofer checks

According to Wikipedia's Utility frequency article, "In large parts of the world this is 50 Hz, although in the Americas and a handful of countries in Asia it is typically 60 Hz." Japan is split, with Nagoya and the west on 60 Hz and Tokyo and the east on 50 Hz. If you're not sure which one you have, check the label on your power supply or ask your local utility.

According to Wikipedia's Mains hum article, hum is electrical noise from the mains that gets into audio systems, and you hear it from the speakers. Mains powered gear and AC fields from nearby appliances and wiring can both let it in. At a venue it's often picked up through a ground loop, such as the one between an amplifier and a mixing desk.

The hum's fundamental is usually the second harmonic of the grid frequency, so in a 60 Hz area that's 120 Hz. The article also says the sound often has heavy harmonic content above 50 or 60 Hz, and the third harmonic of 60 Hz is 180 Hz.

Start quiet and raise the level slowly, because low tones are hard to judge by ear. Pause the music, then compare the hum from your gear with this tone. Ask whether the hum sounds like this tone, like the octave above it, or like neither. This is a listening check, not a measurement, and the tone can't name the device making the noise.

A speaker pushed past its limit adds copies of a tone at whole number multiples of its frequency. The 2nd harmonic of this tone is 120 Hz, the same pitch hum usually has in a 60 Hz area, so a distorting speaker can sound like hum. Keep the level low so you don't fool yourself. Small speakers may also play 60 Hz weakly or not at all, which is a general limit and not a spec for any device.

Wikipedia's Subwoofer article gives 20 to 200 Hz as the typical range for a subwoofer, so this tone sits inside it. A 60 Hz wave is about 19 feet (5.7 meters) long, and one cycle takes 16.67 ms. For the full set of 30, 40 and 60 Hz tones, use the subwoofer test tones page.