Control buttons can be selected and installed by the customer or system integrator. Optical and functional aspects play an important role for the selection of an external button. It is essential that the button operates silently. For microphone units beyerdynamic recommends the use of a piezo button with integrated dual colour ring. Furthermore, for chairman microphone units there are two piezo buttons available without illuminated ring, but with ”Clear” and ”Prior” description. Piezo buttons have no mechanical parts to avoid noise or abrasion. The rugged metal housing avoids damage through rough handling and is completely sealed so that no dust, dirt or liquid can enter the housing. The buttons are easy to clean with usual cleansers. Piezo buttons must not be used for the Push-To-Talk function (PTT) of a microphone unit.