100 volt Public Address System Information Website

100v Public Address Basics

Installing a PA System

Audio Principles & Theory

Miscellaneous

Public Address Information - 5

100V Line Public Address

As most commercial tannoy speakers come with adjustable wattage settings (multi-tapped transformer) it is possible to adjust a speaker to suit its location. More often than not, a speaker only needs a small amount of power in a quiet location such as an office and a moderate amount in a warehouse. Always try to keep back as much power as you can by keeping tappings as low as you can in order to do the job, then if you need to adjust one speaker “UP” there is headroom in the system to do it without problem.

Suggested starter wattage settings for speakers, these are not correct for every application but will get you going in the right direction.

	Quiet room/area	Average area	Noisy area
Ceiling speaker	0.75 – 1.5 w	3w	6w
Wall cabinet speaker	0.75 – 1.5w	3w	6w
Small projection spkr	2.5w	5w	10w
Large projection spkr	5w	10w	15w
Horn speaker	2.5w	5	10w
Pendant	5w	10w	20w

Public Address loudspeaker wiring can be done best with a double insulated twin flexible cable such as 2182Y available from most electrical wholesalers and RS Components etc. It is important to wire all the speakers in the same polarity to ensure correct phasing. Failure to do this will result in some speaker cones moving out, whilst others move in, this results in a thin sound, lacking quality, level and tonal response. Please refer to the table below for recommended sizes of cable and their maximum distances

	0.75mm 2	1.0mm 2	1.5mm 2
30 watt load	800m	1066m	1600m
60 watt load	400m	533m	800m
120 watt load	200m	266m	400m

It is industry practice to wire the 100v common output as the negative conductor within the cabling. Keeping this arrangement throughout ensures all connections to speakers are made in phase. Ensure all speaker connections are well made (particularly those where there may be disturbance in a ceiling) and secure, this will reduce the risk of a cable being pulled, connection broken and ultimately creating a short circuit on a speaker line which can result in a damaged amplifier. A short can be detected audibly if there is low volume and a distorted output.