Figure 1: Typical laboratory
standard microphones

IEC 61094 'Measurement Microphones' gives specifications and defines calibration methods for various types of microphone used for making measurements. It also introduces a nomenclature which is designed so that microphones may be specified without referring to specific manufacturers models or using terms like 'one-inch' and 'half-inch' microphone.

Measurement microphones are classified as laboratory standard microphones or working standard microphones, though any that meet the laboratory standard requirements will also meet the the working standard requirements.

A laboratory standard microphone is a condenser microphone capable of being calibrated to a very high accuracy by a primary method such as the closed coupler reciprocity method. Consequently it is required to have an exposed diaphragm surrounded by a ring which allows it to be mated to a small coupler without disturbing the diaphragm. Figure 1 shows typical laboratory standard microphones.

Figure 2. Typical working
standard microphones

The first part of IEC 61094 establishes a system for classifying laboratory standard microphones into a number of types according to their dimensions and properties. Laboratory standard microphones are described by a mnemonic system consisting of the letters LS (for Laboratory Standard) followed by a number representing the mechanical configuration and a third letter representing the electroacoustical characteristic. The third letter may be either P or F representing, respectively, microphones having a pressure- or free-field sensitivity which is approximately independent of frequency in the widest possible frequency range. The designation LS2P thus refers to a laboratory standard microphone of mechanical configuration 2 having a nearly constant pressure sensitivity as a function of frequency. 'Mechanical configuration 1' is equivalent to a 'one-inch' microphone and 'mechanical configuration 2' is equivalent to a 'half-inch' microphone, so the Brüel & Kjær microphone type 4180 is an IEC type LS2P, and the Brüel & Kjær type 4160 microphone is an IEC type LS1P.

Figure 2 shows typical working standard microphones. They normally have a protection grid, though this is not required by the Standard. The Standard does state that the pressure sensitivity of the microphone can only be determined if any grid is removable.

Part 4 of IEC 61094 extends the nomenclature to working standard microphones and adds 'Mechanical configuration 3' for 'quarter-inch' microphones and D to the options for the third letter (for microphones having a diffuse-field sensitivity which is approximately independent of frequency in the widest possible frequency range). So the Brüel & Kjær microphone type 4144 is an IEC type WS1P, and the Brüel & Kjær type 4165 or 4133 microphones are IEC type WS2F. A quarter-inch diffuse field microphone would be a WS3D.