Tannoy I9 user manual Voltage and Power Selection Distributed Line Operation

Cable choice consists mainly of selecting the correct cross sectional area in relation to the cable length and the load impedance. A small cross sectional area would increase the cables’ series resistance, inducing power loss and response variations (damping factor).

Connectors should be wired with a minimum of 2.5 mm2 (13 gauge) cable. This will be perfectly satisfactory under normal conditions. In the case of very long cable runs the wire size should exceed this, refer to the following table for guidance: -

		C.S.A. OF				CABLE		% POWER		dB LOSS		% POWER		dB LOSS
CABLE		EACH						LOSS				LOSS
				AWG		RESISTANCE				INTO 4Ω				INTO 8Ω
RUN (m)		CONDUCTOR						INTO 4Ω				INTO 8Ω
						Ω				LOAD				LOAD
		(mm2)						LOAD				LOAD
10	2.5		13		0.13		3.9		0.17		2.0		0.09
	4		11		0.08		2.5		0.11		1.3		0.06
	6		9		0.05		1.6		0.07		0.8		0.04
25	2.5		13		0.33		9.3		0.42		4.9		0.22
	4		11		0.21		6.1		0.27		3.1		0.14
	6		9		0.13		3.9		0.17		2.0		0.09
50	2.5		13		0.66		17.0		0.81		9.3		0.42
	4		11		0.41		11.4		0.53		6.1		0.27
	6		9		0.26		7.5		0.34		3.9		0.17
100	2.5		13		1.31		29.1		1.49		17.0		0.81
	4		11		0.83		20.5		1.00		11.4		0.53
	6		9		0.52		14.0		0.65		7.5		0.34

5. Voltage and Power Selection (Distributed Line Operation)

When using 70.7V or 100V distributed-line systems, the transformer can be tapped at 60W, 30W and 15W, with an extra 7.5W tapping for 70.7V line systems. The taps are selected via the rotary switch shown in Figure 4a.

When the relevant voltage tappings have been selected, add the individual power in Watts at all speakers and select and amplifier with a rating equal to or exceeding the total power in Watts. All of the transformer primaries should be connected in parallel to the output of this amplifier. If for example, you select the 7.5-watt transformer tap, it means that at full rated amplifier output the speaker will receive the full 7.5 watts. If the amplifier gain is reduced, each speaker will receive a proportional amount of power, maintaining the overall system balance.

It is recommended that a generous power safety margin (3dB of headroom) be left so that the system does not have to operate continuously at its full rated output power

In order to comply with relevant fire safety regulations (i.e. BS 5839:1998), it is required that in the event of fire, that failure of the circuit to which the loudspeaker is connected does not occur before evacuation of the building is complete. Suitable measures include:

a)use of terminal blocks (for connection to primary) with a melting point of not less

than 650°C, for example constructed from ceramic materials;

c)use of terminal blocks of a lower melting point but protected with thermal insulation;

d)use of terminal blocks such that, on melting, an open-circuit or a short-circuit does not occur.

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