Improvements to a public address system having zone isolator circuits

(19)

(11)

EP 1 777 988 A3

(12)	EUROPEAN PATENT APPLICATION

(88)	Date of publication A3:
	28.05.2008 Bulletin 2008/22

(43)	Date of publication A2:
	25.04.2007 Bulletin 2007/17

(21)	Application number: 06255349.0

(22)	Date of filing: 17.10.2006

(51)

International Patent Classification (IPC):

H04R 27/00^(2006.01)

(84)	Designated Contracting States:
	AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU LV MC NL PL PT RO SE SI SK TR
	Designated Extension States:
	AL BA HR MK RS

(30)

Priority:

20.10.2005 GB 0521337

(71)	Applicant: PROTEC FIRE DETECTION PLC
	Nelson, Lancashire BB9 6RT (GB)

(72)	Inventor:
	Priest, Eric, c/o Protec Fire Detection Plc Nelson Lancashire BB9 6RT (GB)

(74)	Representative: Sherrard-Smith, Hugh et al
	Appleyard Lees & Co. 15 Clare Road Halifax, HX1 2HY, West Yorkshire Halifax, HX1 2HY, West Yorkshire (GB)

(54)	Improvements to a public address system having zone isolator circuits

(57) A public address network includes a driver unit (11) that comprises a high pass circuitry pass and a low pass circuitry pass. The high pass part drives an audio signal (14) on to a pair of signal wires (12). The low pass part comprises a gyrator circuit that drives a pilot signal (15) on to the pair of signal wires (12).
The signal wires transmit the audio signal and deliver it to one or more audio output units (16). The signal wires also transmit the pilot signal and deliver it to one or more isolator circuits (20). Each isolator circuit is arranged to operatively isolate a section of the signal wires.

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