Direction Expressed as Angles

The direction is usually expressed in terms of angles.

Azimuth angle $\phi$

• measured in the horizontal plane passing through the center of the listener's head.
• determines the position of the source in the four quadrants surrounding the listener's head: $\phi = 0^\circ$ is situated directly in front of the listener; $\phi = 180^\circ$ is situated directly behind.

Angle of elevation $\theta$

• measured in a vertical plane bisecting the listener: $\theta = -90^\circ$ is situated directly below the listener; $\theta = +90^\circ$ is situated directly above.