PARTS OF A SOUND SYSTEM
First let's define the parts of a sound system:
- Amplifier - An electronic system that takes a low-voltage audio signal and makes it powerful enough to move a driver within a speaker.
- Crossover - the electronic device which splits an audio signal into separate frequency ranges, e.g. ‘treble’ (high frequencies) and ‘bass’ (low frequencies).
- Driver - A (usually) circular piece of material (diaphragm) connected to a large magnet and coils of wire. The driver vibrates backwards and forwards to create sound.
- Loudspeaker - the box from which the sound comes from. These can include many drivers, crossovers, and sometimes amplifiers.
It is common for people to confuse the term ‘active’ with ‘self-powered’, as many self-powered systems are often also active, and are marketed as such. Self-powered simply means that the amplifier is housed within the speaker, so no external amplifiers are required. Self-powered speakers are often preferred by consumers as they are broadly ‘plug and play’ - they don’t require any additional equipment or setting up.
In audio theory, active means that a crossover (the ‘active crossover’) exists before the amplifier. This means that multiple amplifiers are needed to power different frequency ranges. A system could be ‘2-way active’, ‘3-way active’, ‘4-way active’, or more. This refers to how many frequency ‘bands’ the audio signal is split into, with each requiring a different amplifier channel.
Active crossovers are usually part of a Digital Signal Processing (DSP) unit, which will send the various frequency bands to different amplifiers within a system.
Passive means that a crossover (the ‘passive crossover’) exists between the amplifier and drivers. This means that a single amplified signal is sent to the crossover, which then splits this amplified signal into the correct frequency bands for that speaker. Passive crossovers are typically circuit board mounted within the loudspeaker unit.
Some sound systems can be both active and passive. For example an active crossover may split the signal into sub bass and full range. The sub-bass signal then goes into a dedicated amplifier and into a sub-bass speaker - this element is ‘active’. The full range signal may then go into another amplifier which powers a loudspeaker which in turn contains a passive crossover and two drivers. This example has both active and passive elements. A definition of this system would be ‘a passive 2-way system with a separate active sub bass element’.
ACTIVE VS. PASSIVE
As with any field of technical engineering, each concept has pros and cons and may be situationally more appropriate than the other.
For example, an ‘active’ system allows greater control over the individual frequencies sent to speakers, and allows the user to ensure that elements such as high amplitude sub-bass impulses don’t detract from higher frequency clarity. However active systems are often more complex and expensive, especially when scaled up to a commercial size.
When selecting a sound system for any application, it is recommended to consult with an impartial professional. SXS have no brand affiliations or loyalties and as such can assist you with choosing the sound system that is right for you.