Eight-foot pitch

[1] For example, the A above middle C in eight-foot pitch would be sounded at 440 Hz (or at some similar value, depending on how concert pitch was set at the time and place the organ or harpsichord was made).

These lengths can all be obtained by successive doubling because, all else being equal, a pipe or string that is double the length of another will vibrate at a pitch one octave lower.

The particular length "eight feet" is based on the approximate length of an organ pipe sounding the pitch two octaves below middle C, the bottom note on an organ keyboard.

If a pipe is open at both ends, as is true of most organ pipes, its fundamental frequency f can be calculated (approximately) as follows: where If v is assumed to be 343 m/s (the speed of sound at sea level, with temperature of 20 °C), and the pipe length l is assumed to be eight feet (2.44 m), then the formula yields the value of 70.4 hertz (Hz; cycles per second).

The discrepancy may be related to various factors, including effects of pipe diameter, the historical differing definitions of the length of the foot, and variations in tuning prior to the setting of A = 440 Hz as the standard pitch in the 20th century.