Active, Passive, Bi-amped Speakers Explained
This article has been drafted to clarify one of the most widely and incorrectly used phrases in audio today - 'Active'.
Parts of a sound System
First let's define the parts of a sound system:
- Amplifier - the electronic device that changes a small signal to make it more powerful
- Crossover - the electronic device which splits an audio signal into separate frequency ranges "“ such as high frequencies (treble) and low frequencies (bass)
- Driver - the component within a loudspeaker of which there may be several. These are sometimes referred to as "woofers" and "tweeters"
- Loudspeaker - the box from which the sound comes from. These can include one of more drivers and numerous electronics
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" or "4-way active" (5-way systems are rare but do exist). This refers to how many bands the audio signal is split into, therefore each requiring a different amplifier channel.
Active crossovers are usually part of a Digital Signal Processing (DSP) unit and are commonly stored in racks with the amplifiers, although this does vary from company to company.
Passive means that a crossover (the "passive crossover") exists between the amplifier and drivers. Such a system could be "2-way passive", "3-way passive" etc., which refers to how many bands the already-amplified signal is divided and fed into each driver. Passive crossovers are typically circuit board mounted within the loudspeaker and have components such as resistors, capacitors, and transformers
This means that the loudspeaker has the amplifier(s) within it to make it work.
What about "active" speakers?
People refer to products such as Mackie SRM450s, JBL Eons and RCF Art500A as "active" speakers because the amplifiers are built into the speaker. In these examples the products do have "active" electronics as they have separate amplifiers for the low frequency and high frequency drivers. The fact that the amplifiers are within the loudspeakers does not make them "active"
The correct phrase for these products is "2-way active self-powered". So people use the word "active" when they actually mean "self-powered" "“ which are different concepts.
Am I being pedantic?
No, I am not. The reason is that there are many self-powered speakers that are passive. The distinction is important as it suggests a level of electronic complexity and audio quality.
Active & Passive
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 then 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 good 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 "“ neither is "better" or "worse" but each has situations for which it is appropriate.
Active systems allow each amplifier to only work on a specific frequency range. This can be of benefit as a high current drain on a sub-bass will have no impact on the power and clarity for the high-frequencies. Active also breaks up the power requirements of a system which can allow for greater overall power performance in larger applications. This can also help to increase "headroom" (spare power which helps achieve a cleaner sound). Headroom is a concept that is very important to us as this is what helps create sound with big impact but without distorting or being painful.
As each element is controlled separately a greater level of project-specific customisation of each element is possible without colouring the sound. This is important for larger audio applications where high performance is required.
The downside to active systems is that they require considerable processing equipment, many more amplifiers, more complex cabling and distribution networks. This makes them significantly more expensive. Most professional concert systems contain active elements.
Passive systems tend to allow for lower maximum power levels due to fundamental limitations within the electronics of the passive crossover networks (although these limitations have reduced considerably in recent years). Passive systems require lessprocessing and fewer amplifiers which make them cheaper but less flexible.
Modern concert sound systems (including the Martin W8LM and D&B Q1 systems) can run in passive or active mode as they have highly sophisticated passive crossover networks which present minimal performance limitations.
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