Ear simulator
Type 4157 Bruel and Kjaer

The Ear Simulator consists of a main housing into which are assembled a number of rings whose shapes form annular air volumes connected to the main volume of the housing by air passages. The main ear canal volume is of a similar shape and volume to that of the actual human ear and provides a similar acoustic impedance to the insert earphone being tested. A 1/2-inch microphone is mounted in the housing of the Ear Simulator, terminating the main ear canal volume. Preamplifier Type 2669 is supplied with the set.
To ensure that measurements are reproducible, a reference measurement plane is defined, see Fig. 1. This is perpendicular to the ear canal axis at the normal position of the tip of the ear mould.

Type 4157 is delivered in a mahogany case with an individual calibration chart giving all parameters for its correct use (see Fig. 3).