Audio Equipment

Microphones/Transducers: Overview

Along with a recorder you will need a microphone or transducer. The scope of this document is limited to four basic sound categories: audible range (20 Hz- 20 kHz), ultrasonic (30 kHz and higher), infrasonic (below 15 Hz), and underwater sounds.

In the audible range category there are many brands of high-quality microphones available, Sennheiser, Shure, and Audio Technica, just to name a few. We have tested, and are currently using, the Sennheiser line of microphones. They have proven to be extremely durable, exhibit very low self-noise figures, offer high output, and depending on the particular model selected, are almost completely immune to high humidity related problems.

Capturing ultra-high frequency sounds such as those created by bats requires the use of a specialized transducer known as a bat detector. These devices convert the ultra-high frequency sounds down to a frequency range that can be heard as well as recorded. Capturing underwater sounds also requires the use of another specialized transducer type, the hydrophone. These specialized devices are covered in detail in later sections.

There are two types of microphones that are directional enough for natural sound recording at a distance: the shotgun microphone and the parabolic reflector microphone. To better understand the relative utility of different microphones and parabolas we have compared their beam-width (angle of acceptance) to the field-of-view of lenses commonly used on 35mm cameras. This comparison is approximate and assumes that the frequency of interest is around 2500 Hz. If the frequency of the sound is lower, a larger parabola is required for equal performance.