There are two types of loudspeaker and loudspeaker circuit that we can use when designing a sound system. One is “low impedance” and the is “constant voltage, high impedance” or more commonly known as 100v line.
Both systems have advantages and disadvantages, briefly explained below.
Low impedance - '8 ohm'
Used for domestic hi-fi systems, professional live entertainment and music systems, car hi-fi and in Pro-Sound systems where high level playback of music is required. The amplifiers within a low impedance system will generate high current at relatively low voltages; therefore cable diameter is an important factor when designing a low impedance system.
Advantages
- Will produce full range sound (depending on equipment)
- Lower cost for basic setups
Disadvantages
- Cable diameter is a limiting factor in long cable runs
- Odd and multiple numbers of loudspeakers are difficult to fit or design into a low impedance system & require complex impedance matching calculations
High impedance or constant voltage - '100v line'
Constant voltage systems are used within commercial audio & industrial public address sound systems. Best electrical practice is required when installing these types of system as the loudspeaker output from the amplifier is running at a relatively high voltage and low current compared with a low impedance system; therefore cable diameter is less of an issue, and long cable runs can be achieved without considerable loss of power.
Advantages
- Easy to fit odd and multiple numbers of loudspeaker to a single amplifier circuit
- Long loudspeaker circuits can be achieved using relatively thin cable
- The majority of 100 Volt line loudspeakers have multiple tappings to enable different volume levels to be set
Disadvantages
- Loudspeaker costs are higher than low impedance versions, especially when considering full range sound. Cheap 100v transformers within loudspeakers will saturate at bass frequencies, so to obtain equivalent sound quality to a low impedance system the loudspeaker transformer needs to be high quality.
- Not really suitable for pro-sound live applications where kilowatts of power are used and reproduction of very low frequencies required.