AVR 4550 (serv.man14) - Harman Kardon Audio User Guide / Operation Manual. Page 10

10 REAR PANEL CONNECTIONS

negative (–) connections and the tan and black
terminals are the surround back right positive
(+) and negative (–) terminals.
For multiroom use, connect the brown and black
SBL terminals to the red and black connections
on the left remote zone speaker and connect the
tan and black SBR terminals to the red and black
terminals on the right remote zone speaker.

 RS-232 Port: This jack is used to enable the
AVR 4550 to be controlled by an external
computer or programmable remote system that
uses RS-232 commands. Due to the complexity
of RS-232 connections, we recommend that they
be made by a trained and qualified custom
installer. See page 18 for more information on
the RS-232 control port.

 Fan Vents: These ventilation holes are the
output of the AVR 4550’s airflow system. To
ensure proper operation of the unit and to avoid
possible damage to delicate surfaces, make
certain that these holes are not blocked and that
there is at least three inches of open space
between the vent holes and any wooden or
fabric surface.