Microphone Placement for Recording Bats

Where you position the Song Meter Mini Bat 2 (or any other recorder) can have a significant impact on the quality of your ultrasonic recordings. In most cases, the ideal placement is on a narrow pole, several meters above the ground and away from reflective surfaces.

The small wavelengths of bat echolocation calls mean a microphone can pick up reflections of these calls in more situations than when recording audible-range sound. Prominent reflections can result in recordings that are more difficult to identify manually or algorithmically.

Note:

Recording quality is far from the only consideration when positioning a microphone. In many situations, you may be limited in where you can mount equipment, or you may need to keep your recorder out of view or locked to a fixed structure.

These factors may take priority over capturing the highest-quality recordings possible. However, the following recommendations, when practical, will improve the quality of your recordings for later analysis.

Distance from Reflective Surfaces

To avoid prominent echoes in your recordings, you should ideally position the microphone away from reflective surfaces. Some common examples of reflective surfaces include the following:

  • The ground

  • Bodies of water

  • Buildings

  • Rock faces

Surfaces that are less flat or more discontinuous than these examples can still reflect ultrasound, but the reflections will tend to be less prominent. For example, a microphone positioned near the foliage of a tree will produce cleaner recordings than one positioned the same distance from a brick wall.

Avoid Placing the Microphone Against a Hard Surface

When possible, fastening the recorder to a narrow pole or similar object is preferable to mounting directly to a large object like a tree trunk. When the microphone is very close to a solid surface like a tree trunk, sound reflecting off of the tree can interfere with incoming sound, depending on the sound's frequency and direction of travel. This destructive interference can create small gaps in the recorded echolocation call.

These gaps are usually small enough that a human reviewer can still easily recognize the shape of a recorded call, but they may cause problems for algorithmic bat identification.