Simon Price
As in the title this article explains the difference between passive and active speakers. I explain matters not only in the sense of the crossovers used, but whether the speakers are themselves powered or not.
Crossover types – Active v Passive
With a conventional two way PASSIVE speaker (high frequency tweeter and mid/bass unit) or three way PASSIVE speaker (high frequency tweeter, mid driver and bass driver) a Crossover splits the frequencies of the analogue power amplifier** or integrated amp (pre and power amp in one**) into bands of frequencies which are fed to the relevant driver. Lower frequencies to the bass unit and high frequencies to the tweeter. The crossover consists of resistors, coils, and capacitors to do this job.
If a speaker has one driver, which is of course very rare, then it doesn’t need a Crossover. The full range signal is just sent to the speakers single driver.
Note : **An integrated obviously is both a pre amp and power amp in one, and separated pre and power amps exist as separate boxes. Power amps are often called ‘mono-blocks’ if separated to right and left power amps, as distinct boxes for the same stereo job. Effectively it’s all done in the analogue domain in the sense the source amplifier is spitting out an analogue signal.
The signal path from source to speaker – passive speaker
With an Active Crossover the frequency split is done before power amplification. So in an active speaker the various frequency signals for the required drivers are sent to the power amplifier(s) for then sending to the drivers.
This process with the active crossover can be done in the analogue domain i.e an analogue sound signal is sent from a pre-amp or integrated to the Active Crossover. Alternatively it can be done in the digital domain where a digital signal of 1s and 0s is sent to the amplifiers, which can involve DSP (digital signal processing)
The signal path from source to speaker – active crossover & active (powered) speaker
The use of an active crossover in a speaker means that you can use that active crossover to send the signal to seperate power amps in the speaker.
In a passive speaker when the signal goes through the crossover after being amplified, some of that power dissipates in the crossover and never makes it to the drivers. This is not the case with an Active Crossover since the signal is amplified after it goes through the Crossover. This too can account differences in sonic capability between the two designs.
So what’s an Active speaker?
When we refer to an ‘Active speaker’ we mean one which contains amplification internally, as opposed to the passive type which requires speaker cable from the power amp or integrated amp.
Active speakers are commonly seen in pro audio firms (eg ATC , PMC) for recording studio monitors, but also are used in consumer audio for subwoofers, Bluetooth speakers as well as sound-bars.
Obviously you can’t often upgrade active speakers since amplification is built in, but a passive set up allows you to upgrade your integrated or pre and power amps later. So you can follow this route or the active speaker one.
With an Active Crossover in the active or passive domain, it allows speaker designers to design the active speaker to use different power amps. Using different specs for the power amps and power requirements for each amp suited to each driver, as well as different power supplies for the power amps, allows further tailoring of the sound. Further, the Active Crossover can be tailored to the respective power amps. Very often why the active model of a similar passive speaker can sound *better*. This is true of lots of peoples opinions of the passive KEF LS50 versus its active relation – the LS50W, for example.
Designers often argue that keeping the signal short in an active design means that the longer paths of traditional passive set ups with an amp and passive speakers, are minimised. A direct path to the music in other words. Why you perhaps, often find manufacturers rating their active speaker model over the passive version.
ATC’s SCM40A (‘A’ for active) is a 3 way active speaker comprising a bass driver, high frequency driver and mid range driver, hence 3 way. It is an active powered speaker with an Active Crossover in the analogue domain which uses separated power amps for each of the drivers. Each amp module is of different power handling ability.
On the other hand, Totem’s Kin Play 2 way speakers (tweeter and bass/mid unit), for example, uses an active power amp with a passive crossover.
Just to confuse, in discussing Passive and Active Speakers, some articles refer to active speakers interchangeably with Active Crossovers. As with the Totem’s mentioned, you have an active speaker with a passive crossover. Some articles refer to these active speakers as *powered speakers*. The use of ‘active speakers’ and a separate meaning of ‘active crossover’, is commonplace usage. But be careful not to confuse the two, as this article explains.
The ATC SCM40’s I mentioned use Class A/B power amps to drive all drivers, whereas you sometimes find some active speakers use higher efficiency Class D designs which produce less heat so you can use high power amplifiers in tight spaces with little cooling or cooling fins etc. For example KEF LS50W use Class A/B amplification for the tweeter and Class D amplification for the bass/midrange driver.
To check out the differences between Class A, A/B, and Class D, click here.
Or have a look at what ATC have to say here.
