Wiring low impedance loudspeakers & sound systems

Warning – Do not connect low impedance, low Z or 8 ohm loudspeakers to 100v line outputs on public address PA amplifiers

Please note that all diagrams are for one channel only – for stereo you will need two sets of speakers

  • Plan your loudspeaker layout and locations together with your cable routes
  • Use cable with a minimum specification of 10a twin sheathed two core flex for the loudspeakers – this means that there is a blue and a brown wire inside a white outer (for instance)
  • Install the loudspeaker cable – remember with low impedance PA sound systems all loudspeakers are usually connected in parallel – this means that the cable starts at the amplifier and goes to the first loudspeaker and from there to the second loudspeaker – there is normally no more than two loudspeakers on each amplifier output channel
  • Remember that the total wattage of all of your loudspeakers added together should be higher than the rated wattage of your amplifier
  • All loudspeakers must be connected in the same phase – it is likely that your cable and your loudspeakers do not have the same coloured wires – choose an obvious convention such as brown cable to red or + on loudspeaker and blue cable to black (for instance) and stick to it throughout your installation
  • Once you have installed and connected all of your loudspeakers and you are happy that there are no short circuits or other problems with the installation you can connect the other end of your cable to your amplifier’s low impedance or 8 ohm outputs
  • Your amplifier may have both low impedance (low Z or 8 ohm) and 100v line connections – you must never use both at the same time or connect low impedance speakers to the 100v terminals
  • Connect your wires to the ‘8 ohm’ and ‘com’ on the amplifier
  • Your amplifier should ideally sit on top of your CD player or other units so that there is adequate ventilation and airflow to keep the amplifier cool
  • Turn all volume controls to minimum and set all bass and treble controls to midway
  • Connect your microphone to the amplifier and switch your amplifier on
  • Turn your master volume to around midway and gradually turn the microphone volume (or input volume) up while speaking into the microphone
  • Adjust to the volume level that is required

It is important to match the speaker load with your amplifier’s output impedance so that you get maximum transfer of power and that you avoid dangerous amplifier conditions by using an incorrect load impedance. If you are unsure it is safer to use a higher impedance speaker load to help protect the amplifier. The manner in which your speakers (in a multi-speaker system) are wired together determines the overall impedance

Wiring 2 Speakers in Parallel
Two 4 ohm speakers = 2 ohm load to amplifier
Two 8 ohm speakers = 4 ohm load to amplifier
Two 16 ohm speakers = 8 ohm load to amplifier

Alternative ways to wire low impedance loudspeakers

Wiring 2 Speakers in Series
Two 4 ohm speakers = 8 ohm load to amplifier
Two 8 ohm speakers = 16 ohm load to amplifier

Wiring 4 Speakers in Series/Parallel
Four 4 ohm speakers = 4 ohm load to amplifier
Four 8 ohm speakers = 8 ohm load to amplifier
Four 16 ohm speakers = 16 ohm load to amplifier

Wiring 4 Speakers in Parallelthis should be avoided if you are unsure of the amplifier’s minimum load impedance
Four 8 ohm speakers = 2 ohm load to amplifier – this can damage many amplifiers
Four 16 ohm speakers = 4 ohm load to amplifier
Four 32 ohm speakers = 8 ohm load to amplifier

E&OE