A sound generating object for worn by a user, includes: a first accelerometer; and a second accelerometer; wherein when the sound generating object is at an operative position, a line extending through the first and second accelerometers intersects an axis at right angle, the axis extending in an up-and-down direction, the first and second accelerometers being spaced by a known distance; wherein the first accelerometer is configured to determine a first acceleration component having a first value, and the second accelerometer is configured to determine a second acceleration component having a second value; and wherein the sound generating object is configured to determine a distance between ears of the user based on the first value of the first acceleration component determined by the first accelerometer, the second value of the second acceleration component determined by the second accelerometer, and the known distance between the first accelerometer and the second accelerometer.