I have also thought a lot about most cars which made prior to the early ’80s in the context of installing hands-free kits. These cars typically had a single speaker built in to the doasboard for use with a (typically AM-only) mono radio and if I was fitting a hands-free kit to one of these cars and this kit was primarily a communications kit without music playback functionality, I would use that speaker for the hands-free kit. The cars are still relevant now, especially in Australia which has natural conditions and a legal environment that lends itself to older cars still being on the road.

Another factor is that the hands-free kit being illustrated in the PDF is primarly a communications kit without any music playback functionality i.e. iPod control, MP3 playback from attached media or Bluetooth A2DP / AVRCP functionality.