e. the need for careful positioning of the microphone in close proximity to the lips of the Figure 58.15 On-the-ear headset user. of headsets places suppliers and communication managers in an 58.13.2 Earphones unnecessarily inadequate position. The acoustic and electrical performance of the headset clearly is Handsets normally have a high acoustic impedance and high gain also fundamental to its design. In particular, the microphone and output. Most headsets cannot achieve the same acoustic impedance earphone transducers must be matched correctly, both to interface and gain without amplification. With close coupled earphones, as with the system being used and to suit user requirements. Ideally, used on over the head style and under the chin style headsets, this the microphone and earphone transducers in the headset need to can be achieved easily either with or without an amplifier, according operate to the same electrical and acoustic performance as the to the system specification with which they are interfacing. How- handset. This is not always easy to achieve mainly due to size and ever, to overcome the use of unhygienic eartips on single sided weight considerations, and often sound pressure levels need to be headsets, an acoustic low impedance earphone is used which has compensated for by automatic gain control and adjustable volume been specifically designed to work with an acoustic leak between control. the earphone diaphragm and the ear canal. The first headset to employ this principle is GN Netcom's Profile which has an adju- 58.13.1 Microphones stable earphone to provide users with maximum comfort combined with optimum sound pressure output from the earphone. Most headsets use either standard electret or electromagnetic micro- phones. Both types can be boom mounted in miniature form, but the electret type is generally most popular. Acoustic tubes are used on 58.14 The growing need for headsets some headsets but these generally provide poorer transmission quality than boom mounted microphones and are subjec