100 Hz: transformer hum at 50 Hz mains

Transformers and fluorescent-light ballasts on 50 Hz mains buzz at 100 Hz, twice the mains frequency, because their cores flex on both halves of each cycle. It is also a common bass test tone.

Which note 100 Hz is at other reference pitches

“In tune” depends on what A4 is tuned to, so the same frequency is a slightly different distance from the nearest note in each tuning.

Octaves of 100 Hz

Doubling a frequency raises it an octave and halving lowers it one, so these all have the same note name and the same offset from it.

• 25.00 Hz · G0
• 50.00 Hz · G1
• 200.00 Hz · G3
• 400.00 Hz · G4
• 800.00 Hz · G5

Harmonics of 100 Hz

A real instrument playing 100 Hz also sounds whole-number multiples of it. The first eight, and the notes they fall nearest:

Period and wavelength

One cycle of 100 Hz lasts 10.000 milliseconds; in air at 20 °C, where sound travels at about 343 metres a second, one wavelength is 3.43 metres.

Convert another frequency

Or hold 100 Hz as a steady tone, sweep from it, or beat it against a second tone in the tone generator. The note frequency chart lists every note from C0 to B8.

Frequently asked questions

Related frequencies

• 50 Hz — mains hum in Europe and most of the world
• 120 Hz — transformer hum at 60 Hz mains
• 60 Hz — mains hum in North America