Abstract: Signalling apparatus for a sound system, the signalling apparatus being configured for communicating with a processor, the signalling apparatus comprising: an identifier comprising a unique parameter value for identifying a sound property associated with the signalling apparatus; and an electrical contact configured to electrically connect with an electrical contact associated with the processor to communicate the parameter value with the processor, wherein the signalling apparatus is configured such that the electrical contact of the signalling apparatus is substantially fixed with respect to the electrical contact associated with the processor during activation of the sound system and/or signalling apparatus.