About the 40 Hz tone
40 Hz sits in the deep bass, where kick drums and bass synths live. It's a useful test for subwoofers and headphones: if you can't hear it, your speakers probably can't produce it. 40 Hz has also been studied in brain research on light and sound stimulation; that research is early and not something a tone on a website can reproduce.
A 40 Hz sine wave completes 40 cycles every second; each cycle lasts 25.000 ms, and the sound wave is about 857.5 cm long in air. The nearest musical note is D♯1.
Start with the volume low and raise it slowly. Use the slider to move away from 40 Hz, or try another preset: 20 Hz · 50 Hz · 60 Hz · 100 Hz · 256 Hz · 432 Hz · 440 Hz · 528 Hz · 1,000 Hz · 8,000 Hz · 15,000 Hz · 17,400 Hz · 20,000 Hz.
Questions
How do I play a 40 Hz tone?
Press Play above. The generator starts at exactly 40 Hz as a pure sine wave; you can change the wave shape and volume.
Why can't I hear 40 Hz?
Your speakers or headphones may not reproduce it, the volume may be too low, or it may be outside your hearing range. Very low and very high tones are the hardest.
Is it safe to listen to test tones?
At a comfortable volume, yes. Start quiet, and stop if anything feels uncomfortable.
More free tools
Online tuner · Online metronome · BPM tapper · Interval ear training · Chord ear training · Tone deaf test · Vocal range test · Note frequency chart · Binaural beats generator · Frequency sweep generator · White, pink & brown noise · Tone generator · Perfect pitch test · Hearing test