Loudspeakers come in many different sizes and variations. Choosing the right equipment for your needs, requires a bit of understanding of what’s available. This article will look at how a loudspeaker gets its power and explain the differences between Passive and Active speakers.
For many applications, full range speakers are all that is required. These will contain a low frequency driver to handle the bass and midrange, plus a high frequency driver to handle the treble. Some applications also require subwoofers and these will typically have only one type and size of low frequency driver.
A passive loudspeaker requires a separate power amplifier, which is not included in the speaker itself. With a passive speaker system, a power amplifier receives a signal from a pre amp source (eg. mixing desk or DJ mixer) then increases the amplitude of this signal and provides enough electrical current to drive the speaker effectively.
If the speaker is a full range or mid-high unit, it will have at least one bass driver and one high frequency driver. As these components are designed for their specific bands, they must be sent the correct part of the audio spectrum. If a bass driver is sent treble, it will almost certainly sound poor, but if a tweeter is sent bass, it will be destroyed in no time at all. To separate the audio, there will be a passive crossover inside the speaker, which splits the incoming audio into high and low frequencies for the specific drivers.
Signal Flow For A Passive System
If the speaker is a subwoofer, it is unlikely to have a crossover inside as there is usually only one type of driver. In the case of a passive subwoofer, an external crossover would be needed. Some amplifiers have electronic crossovers built-in.
When picking components for a passive sound system it is important to choose an amplifier with appropriate power output for the power of the passive speaker. Too large an amplifier will blow the speaker up. An amplifier which is too small will probably force the user to drive the amplifier into clipping which will also blow the speaker up.
Whether it is a subwoofer or full range/mid-high speaker, if it is an active speaker (sometimes referred to as powered), it has a built-in power amplifier. This makes active speakers very portable and easy to set-up and takes away the worry of choosing the individual components correctly. Active speakers are available in different sizes, from small studio monitors to large touring systems for concerts and festival. A well-designed active speaker has amplifier modules which are designed for the drivers in that particular speaker. This allows the manufacturers to optimise audio quality because the amplifier’s power and output impedance is matched to the speaker drivers. The crossovers required to split the audio signal up for the different drivers are built into the amplifier modules and in many cases are carried out with in-built digital processing. This can help to make it a simple plug and play set up which is perfect for studio monitors and portable PA systems.
Signal Routing For An Active System
Many mid-sized speakers aimed at bands, mobile DJs and corporate events are increasingly available with on-board DSP (digital signal processing) to provide the user with more control and features such as proper limiters to prevent damage from being over driven. They may also have presets to make the speaker behave as full range, or for live or dance music or as part of a larger system which may include subwoofers.
Which one is right for you?
This depends on what the speakers will be used for and who will be using them. If a system is needed which is easy to set up and is to be used for similar sizes of audience, an active system is usually the best option. Most portable active PA speakers have microphone and instrument inputs which make it easy for public address or small live artists where a separate mixing desk would be unnecessary hassle.
For some users who already have existing amplifier racks and particularly if the speakers might be used outdoors, passive speakers can be more appropriate. For the more experienced user, being able to choose the amplifier and system processing to drive them with, can sometimes offer better results than using active speakers. Passive systems are also very sensible options for installed systems in commercial applications such as bars or venues. Often, running separate power and signal to speakers can be problematic and in the event of an amplifier failure for an active speaker which is installed twenty feet in the air, it can be rendered out of action for possibly weeks. With a passive system, if the amplifier fails in a rack in an equipment room, an amplifier can be swapped out in minutes while the original one goes off for repair.