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100V Line Public Address Systems / Tannoy Systems

How to set-up and install - wiring help. 


100V line public address systems are sometimes referred to as a "constant-voltage system". 100v line systems are perfect for commercial sound projects where lots of speakers are required at various points around the area.

Some other factors you may wish to consider when deciding whether to install a 100V line audio system are:

100V Line Speakers

100v line speakers
can be ‘daisy chained’ from one to another over long distances (unlike standard low ohm speakers) without having to run back to the amp and there is no variation in the mono sound from each speaker, (if you imagine a large area with speakers dotted around, a stereo sound would be lost). This is similar to wiring lights on a radial circuit.
Most 100v line speakers are fitted with ‘tappings’ on the back which allows the user to select the wattage. Changing the wattage from say 10 watts to 20 watts will increase the maximum volume from the speaker, selecting a lower tapping will decrease the maximum volume. This allows complete control over sound sensitive areas.


By using volume control units you can group speakers into sound zones. Inserting the volume control unit at any point ensures that each speaker after that point (in the daisy chain) will be controlled by the volume control unit which is especially good if you require quiet areas within the project. You will also need to make sure the volume control you select is capable of running the speakers thereafter, information about how to find the wattage of the speaker is above.

Correct Cable Selection

The amplifier and the square area of the internal copper conductor within the cable limits the number of speakers that can be run on any 100v line system. After you have decided how many speakers will be required on a particular cable run for your sound project, calculate their total wattage by selecting the appropriate tapping for each speaker as follows:

Example: If 5 watts has been selected on 12 speakers and 10 watts on 4 speakers then the total wattage will be 100 watts. If the total cable length is 250 metres then 1.0mm² cable should be used.

Please see the table below which will help you decide the size of cable you will need for your project.

100V Speaker Cable Size

Please note, double insulated speaker cable should be used at all times (we stock up to 2.5mm² as this is usually more than ample) as voltages can approach 100 Volts. The cable should be clipped securely along the run and should be kept away from potential sources of interference such as other power cables and data cables.

Amplifier/Mixer Selection

When a system is being installed and is going to be used for speech, we recommend not using more than 90% of the amplifiers total wattage when matching up speakers, if it is being installed for background music then we recommend not using more than 70% of the amplifiers total wattage. I.e. for background music, speakers totalling 70 watts should be used with an amplifier rated at 100 watts.

Mixers are useful for allowing more than one source to be plugged into speakers at any one time. For example a CD player could be plugged in along with a microphone. If look for a mixer with ‘VOX mic priority’, any background music playing will be muted when a particular microphone input is used and the music will reinstated after this input has finished being used, this is perfect for tannoy systems. Mixers usually have additional outputs allowing slave amplifiers to be run, this may be necessary if you have a large number of speakers that you wish to use.

Induction Loop Systems

If you wish to fit an induction loop system for people with hearing disabilities then a ‘loop amplifier’ would be required, this could also be plugged into the mixer so people with hearing disabilities can also hear any announcements. Loop cable should be run around the perimeter of the building in order for the loop system to work, our loop amplifier can cover an area of 600m² which means it is suitable for use with cable lengths of up to 98 metres. The  1mm² loop cable we supply is suitable for this length, the minimum loop length when 1mm cable is used is 12 metres.

Wiring Diagrams

The way 100V line speakers are connected together is illustrated in the diagram below;

As well as using volume controls, it is also possible to switch loudspeakers so they are completely turned off, a simple 2 way lighting switch could be used for this purpose. The wiring should be the same as the following diagram;

100V Line Transformers

Don’t make the mistake of confusing 100V line systems with standard stereo system set ups, the main differences are as follows:

Standard stereo setups are usually supplied with low-impedance speakers.

When low impedance speakers are ‘daisy chained’ together and linked in parallel the impedance drops. Usually a maximum of 4 speakers can be linked to a standard stereo system whereas with a 100V line many speakers can be linked together, the only limiting factors are the size of the cable and the power of the amplifier.

Standard low impedance 8 or 16 ohm speakers cannot be used with 100V line systems unless you buy a 100V line transformers'.

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