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!
|10-200 Hz Sweep
+ Voice Over
A -6 dbFS sweeping sine tone, from 10 Hz (supposedly inaudible) to 200 Hz (supposedly played back by all sound systems, including those smallish laptop speakers). On the top of the test tone, a voiceover tells you which frequency is currently playing.
Play back the file until you start hearing the underlying sweeping tone as it rises. The voiceover tells you the frequency you have reached. This frequency more or less represents the lowest limit of your audio system.
Frequencies lower than 20 Hz are beyond our frequency hearing range: our low frequency response test - which starts as low as 10 Hz - should remain inaudible until it reaches 20 Hz. If you hear frequencies below 20 Hz, suspect this test to be corrupted by Harmonic Distortion generated from your speaker or subwoofer.
Harmonic distortion can happen at any frequency, but is obvious at frequencies that are supposedly inaudible.
Check your subwoofer for Harmonic Distortion here.
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