[. . . ] The headset is supplied with open-ended cable so that the user can choose the connector most suitable for the application. [. . . ] Some manufacturers use a headphone symbol for it, others the designation , , 121 TR 9-5". Connect the cable of your HME 45 telcom headset to this socket (see fig. You need it as a , , switch" at the beginning and the end of your phone call. Please note for the HME 45 telcom If your telephone has a headset socket not corresponding to the 121 TR 9-5 standard of the German Telekom, you have to have an adaptor made, or you have to use a new plug. Some telephones (especially from German manufacturers) have a receiver socket suitable for the headset. In particular, this socket is able to supply the necessary operating voltage for the condenser microphone. [. . . ] Microphone Transducer principle Frequency response (2 cm distance between mic and corner of mouth) Output voltage Impedance Other Contact pressure Weight (without cable) Cable Connector [. . . ]