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Author: Gan Weimin

Parabolic microphones are widely used in field bird surveys, monitoring and recording.

What is a parabola?

A parabola is a geometric curve: when a straight line (Q) strikes any point (P) on its inner surface, the inclined plane at these points will reflect the incoming straight line to the "focal point" (F) of the parabola. Therefore, when countless parallel lines are shot onto a parabolic surface, each of them will be reflected to the focused "focal point" (F).

How does a parabolic disc-shaped cover amplify sound?

When you make a sound, for example, speak, the sound travels through the air in the form of sound waves. Sound waves travel around you in a circular form that gradually expands and weakens. However, no matter in which direction sound travels, sound waves convey the same audible audio information. When sound waves encounter a hard surface, that surface can cause the sound waves to be reflected in the opposite direction. This reflected sound wave can cause echoes and reverberation, etc.

If a distant sound wave reaches the parabolic dish-shaped cover, the sound wave will be reflected away from the collision point due to the Angle of the surface. However, since this is a parabolic mask, as we know from the above, sound waves will be reflected to a very special position: the focus point. If a weak sound wave strikes a parabolic surface with countless different points, all the sound waves at these points will be reflected back to the focus point. The sound waves at all points contain the same audio data, and a consistent, amplified sound signal will be generated at this focus point.

The use of parabolic microphones

Although the sound is amplified at the focus point, the user cannot simply place his ears at the focus point, as the rest of his head will prevent the sound waves from reaching the parabolic surface. Instead, the parabolic microphone places a small audio receiver at the focus point, which is fixed on a plastic arm. The audio receiver is connected to the amplifier circuit through wires. Users can listen to the sound by plugging a pair of headphones into the amplifier and also connect it to a tape recorder for recording.

In the wild, since birds are often far from people, using a parabolic microphone to record their chirping is a good choice. When you see a distant target, directly aim the parabolic microphone at the target (the direction of the bird). However, due to the long distance, even a slight rotation of the parabolic microphone can cause it to deviate from the target by tens of centimeters. Therefore, the user must use his own listening skills as a guide to determine whether the microphone has correctly locked onto the bird target to be recorded