Signal cabling with an impedance measurement is a variant of the spur line. The main difference with a spur line is that the speakers do not have a condenser and are placed in the network parallel. It is also possible to wire star-shaped with an impedance system, to connect different branches in a zone.
Because all speakers are measured, it is possible to detect failure of a speaker.
Finally, by using a Bridge of Wheatstone you can detect a slight difference in an impedance flawlessly. There are manufacturers who use this technique and it will probably work well. From practice, in other electronic applications, it is well known that a small instability in the network, like aging of the cable, will cause imbalance and a false alarm will be generated.
A cable for impedance line should always be performed in functional integrity. This is costly as to installation proceedings and use of materials, and therefore an impedance measurement line has its limitations. In addition, in case of a wire break the system will work no longer or only partially. In case of a short circuit in the cable this part of the system will not work at all and this may cause problems in the amplifier, with all its consequences.
‘However, this can be solved by choosing a different technique: Loop wiring’
An evacuation central with impedance measurement is interesting in acquisition, but when the costs of the installation are added, a system with loop wiring will eventually be cheaper. The big differences with loop wiring are the following:
-By loop wiring the use of a functional integrity cable is not necessary, so the price of the cable is lower:
-When using loop wiring the cable does not have to be braced every 30 cm, so the cost of the installation is lower.
Therefore, it is important to take a critical look at the total investment of the type of cabling and the proceedings.