Hertz is a unit of measurement for oscillations per second or cycles per second and can be used to measure sound frequencies. The higher the rate of Hertz (Hz) the higher the frequency. The lower the rate of Hertz, the lower the frequency. Human hearing ranges from 20Hz, the lowest frequencies humans can hear, up to 20KHz, which would be the upper limit of human hearing and considered shrill and piercing. This is also the frequency range where most home audio speakers are rated for frequency response. Some powered home theater subwoofers play down to 15Hz or lower, which energizes a room with acoustic energy that can be felt in your extremities, chest and elsewhere throughout the body.