Background

Humans hear frequencies from 20 Hz up to 20,000 Hz. The lowest bound, 20 Hz, with a wavelength of nearly 20 meters, is a frequency we feel rather than actually hear. This test helps you benchmark the lowest limit of your audio system's frequency extension.

Because of their increased wavelength (nearly 20 meters at 20 Hz), achieving high output at low frequencies usually requires large drivers (subwoofers). Headphones or earbuds, have less trouble playing back those low frequencies despite their small size: by sealing your ear canal, they create a volume that acts as a pressure chamber. This phenomenon is totally different from what you hear when listening to a speaker playing in the open air. Without the cabin effect — another name for the same phenomenon — earbuds would produce hardly any bass.

A sealed space, or pressure chamber, lifts the low frequencies by 12 dB/octave below a frequency related to the dimensions of the enclosed volume. With an ear canal that is approximately 2 cm long, this magical frequency is located at about 5 kHz. With more than five octaves separating the bass range from this frequency, imagine the bass boost!