The unit may also have other pieces such as microphones and {HEAD ~ speakers} in {TAIL ~ order} to allow communication in difficult circumstances to be facilitated 
The unit may also have other pieces such as microphones and { HEAD ~ speakers } in { TAIL ~ order } to allow communication in difficult circumstances to be facilitated
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH