550Hz

550 Hz (hertz) is a frequency that corresponds to 550 oscillations per second, a purely numerical value usable across many fields. In physics, it lies squarely within the audible range for humans, which extends from roughly 20 Hz to 20 000 Hz. At this frequency the wavelength of sound in air at standard temperature and pressure is about 0.623 meters, calculated from the speed of sound roughly 343 meters per second.

The frequency is frequently employed in audio engineering as a test tone for balancing audio equipment. It is one of the standard reference levels defined in many calibration procedures, especially in high‑fidelity audio and broadcasting. It also has practical utility in hearing aid testing and acoustic research, because the human ear has a heightened sensitivity at frequencies around 500 Hz, which translates to a lower threshold for quiet sounds in that band. Engineers therefore choose 550 Hz to provide a stable, perceptible tone that can be used to monitor device performance or to check room acoustics.

In music, a tone close to 550 Hz lies between the notes of a C major scale; it is slightly higher than the note A4 (440 Hz) and lower than C5 (523 Hz), placing it near an A‑sharp or B‑flat in standard tuning. Some sound synthesis applications use 550 Hz as a fundamental frequency for electronic pads or for creating subtle melodic motifs. The frequency also appears in scientific data sets where a narrow‑band analysis is required, such as vibration tests or resonant mode characterisation of mechanical structures.