30 Hz test tone: check how low and how clean your subwoofer plays

A 30 Hz wave goes through 30 cycles each second, and one cycle takes 33.33 ms. Wikipedia's Subwoofer article says the typical range for a subwoofer is 20 to 200 Hz, which puts this tone near the bottom of that range. Wikipedia's bass guitar article says five-string basses add a low B, which works out to 30.87 Hz, just above this tone.

One wave is 38 feet (11.4 meters) long in air. A wave that long won't fit inside a 13-foot (4-meter) room. How a room builds up and cancels bass is covered on the room resonance page, so this page stays on the tone.

Once the tone is playing, listen for three kinds of trouble. A rattle from the cabinet, a grille or the room can mean something is loose or moving that shouldn't be. Distortion adds copies of the tone at whole number multiples, the 2nd and 3rd harmonics, which sit at 60 Hz and 90 Hz here. A distorted low tone can also sound rougher, and higher, than a clean one. A tone that turns rough as you turn it up can be a sign the sub has hit its limit.

The Subwoofer article states the basic idea: "Subwoofer output level can be increased by increasing cone surface area or by increasing cone excursion." Large drivers need large cabinets, so most subwoofer drivers have large excursions, and high excursion at high power tends to add distortion. That distortion is the trouble you're listening for.

A silent result doesn't mean the tone failed. Small speakers can't play the lowest tones, and the speakers in phones and laptops are much smaller than a subwoofer driver, so expect little or nothing at this pitch. Sensitivity also varies with frequency. According to the Equal-loudness contour article, the ear is most sensitive between 2 and 5 kHz, so a quiet bass tone can slip past unnoticed.

On the bass scale, 30 Hz sits above the 20 Hz tone and below the 40 Hz tone. Sixty Hz is one octave above it. The subwoofer test tones page plays 30, 40 and 60 Hz together, and the 20 Hz page shows how far down your gear goes.