There are many ways that loudspeakers can be categorised – two-way or three-way, floorstanding or stand-mount and so on. But one way that’s relatively uncommon in the high-fidelity area is passive versus active speakers. That’s because almost all loudspeakers used in high fidelity have traditionally been passive. In professional audio, by contrast, studio monitors are very frequently active.
Passive or Active loudspeakers … what’s the difference
The difference between passive and active loudspeakers boils down to one single thing. Active loudspeakers have an amplifier – or amplifiers – built in. Passive speakers don’t. Simple, eh?
(Although, of course, things are never quite that simple. There are some speakers which are a bit of both, typically with an active bass driver built into an otherwise passive loudspeaker.)
So, passive loudspeakers need to be driven by amplifiers. In the home, that has long been the norm for high fidelity and home theatre sound systems. Speaker cables carry the powerful signal from the amplifiers to the loudspeakers.
With active loudspeakers, all you need is the signal cable running from a pre-amplifier to each speaker. Traditionally, most active loudspeakers require an analogue signal, but some have in-built digital to analogue converters and work with a digital audio feed.
These days there are lots of network or Bluetooth-enabled loudspeakers which do indeed pack amplifiers into loudspeaker enclosures. The great majority of these are, while technically stereo, effectively mono due to both loudspeakers being packed into one compact box. That said, there are certainly some rather high quality two-box stereo network/Bluetooth speakers available. But here we’re focusing on traditional two channel stereo delivered from several sources, controlled by a preamplifier or integrated amplifier.
The Pros and Cons of Passive and Active speakers
Let’s pretend for the moment that the myriad of other differences between loudspeakers that might affect sound – driver quality, enclosure design and construction, build, size, efficiency – don’t exist, and consider the advantages and disadvantages of each approach.
You can expect active loudspeakers to be more expensive because you’re also paying for the amplifier or amplifiers. But, on the other hand, you save in not having to pay for separate amps.
Since the voltage delivered to passive loudspeakers is fairly high, and their own impedance is low, their cables are pretty much impervious to noise generated by electrical fields in your room. You will get no electrical interference in your sound that way. Active loudspeakers are fed a low-level signal into a quite high impedance, so any noise that is inserted into long cable runs will be more likely to get through into the sound. In pro audio this is recognised and dealt with by active loudspeakers typically being fed their signal with XLR balanced cable connections. Some active loudspeakers also provide XLR connections. To take advantage of these you’ll need a preamplifier with XLR outputs, and they are typically quite expensive.
One major advantage of passive loudspeakers is that you get to choose which amplifier to use with which set of speakers. With active speakers, amplifier and loudspeaker are bundled. Choose one and you get the other.
But against that, with quality models the makers of active loudspeakers have the opportunity to select amplifiers well-suited to, even optimised for, their loudspeakers.
Which brings us to the advantages of active loudspeakers.
The first, and perhaps most consequential, is that many active designs employ active crossovers and multiple amplifiers, one for each driver. One of the trickiest parts of passive loudspeakers design is developing an effective crossover network. You want the bass sounds to go to the large woofer, the high treble sounds to the tweeter, and in many cases, the mid-range frequencies to go to a midrange driver. Sometimes there are even more divisions. Loudspeakers are called two-way if they have only tweeter and woofer, three-way if they have those plus a midrange, and four-way if they have a tweeter, a woofer, and two midrange drivers handling different frequency bands.
To send these frequencies to the correct drivers, a passive loudspeaker requires a crossover network employing hefty capacitors, resistors and coils with thick wire, all of which are expensive and can potentially degrade the signal. And then there are decisions required about the cut-offs. Sharper cut-offs – perhaps 18dB per octave – reduce interference between the drivers but add phase shifts. All this is hard, technical work and the solutions are expensive compromises. Perhaps unsurprisingly, performance-compromising shortcuts are frequently taken.
This kind of crossover is also used in some active loudspeakers, but those which use a separate amplifier for each driver can employ an active crossover to divide the frequencies between the different drivers.
Active crossovers work at the line level. They can be less expensive and easier to design because the components aren’t handling large currents. And while similar kinds of careful judgements have to be made in choosing things like crossover frequencies and filter slopes, it’s all round easier because of the lighter-weight components and the ability to build more complex circuits. Increasingly DSP-based crossovers are being employed. These filters, which are implemented in the digital domain, can be much more flexible and don’t necessarily induce the same kinds of phase shifts.
Of course, you could rightly point out that a lot of passive loudspeakers employ multiple sets of terminals for bi-wiring and potentially bi-amping. Couldn’t you just use extra amplifiers and an active crossover for them? And indeed you can … but you should first be prepared to perform surgery upon your loudspeakers. If the speakers are two-way, you will need to disconnect the passive crossover and wire the input terminals directly to the relevant drivers. If they’re three-way, you will need to bypass the crossover with the bass driver’s connections – and be aware that thereby changing the loading may have unpredictable effects on the operation of the crossover for the midrange driver.
One final performance difference has to do with amplifier control over the loudspeakers, especially the bass drivers. I think this is perhaps the biggest difference when it comes to sound quality.
Amplifiers tend to control non-linear behaviour in loudspeaker drivers. This is a fairly technical subject, which we’ve explained here, but in short, the lower the resistance of the whole circuit, outside of the loudspeaker drivers themselves, the better that control. Some quality amplifiers specify that resistance in the form of a “damping factor”. But it’s the whole circuit that matters, and that includes the connecting cables between the amplifier and the actual speaker driver (including the crossover components, if any, and the wiring to the driver inside the speaker. If the amplifier has a damping factor of, say, 100 – the higher the better, and that’s a middling kind of measure – and the additional wiring adds a further 0.1 ohms of resistance, the total damping factor is more than halved. If you pay a lot of money for a very expensive amplifier with a damping factor of 500, all that careful design and componentry will largely go to waste if the cables reduce this to a damping factor of just 70.
What has all this to do with passive and active loudspeakers? Simple, one major advantage of active loudspeakers is that the amplifiers are mere centimetres from the drivers, whereas with passive loudspeakers, they are metres away. In active loudspeakers the resistance of the wiring can be almost insignificant. And if the active speakers have multiple amplifiers, thus eliminating the passive crossover, the control is even better.
It has certainly been my experience that quality active loudspeakers typically have a level of bass tightness and control that goes beyond all but the very best passive systems.
So all that covers the potential performance differences between passive and active loudspeakers. But there are two practicalities that should be taken into account. The first is quite mundane, but do remember that you will need power points for active loudspeakers. Passive loudspeakers require only the audio feed.
Finally, remember that you have a much, much greater choice of options with passive loudspeakers. There are many, many more passive models available, and of course you can choose from many, many more amplifiers. Active loudspeakers occupy only a small segment of the market, so choice is limited, and you are entirely in the hands of the loudspeaker maker as the quality of the built-in amplifiers.Just remember, while it’s useful to have all this background knowledge, in the end you should judge on results. If you are choosing between passive and active loudspeakers, take your favourite music with you to the stores featuring them and have a thorough listen. Then let your ears do the choosing.