Principals of Audio: Active Speakers


There are no good small passive speakers.

The opening years of the new millennium witnessed a minor revolution in the pro audio marketplace: the rise of the active nearfield speaker. We can perhaps even pinpoint the moment: in 2001 Yamaha discontinued the seminal (passive) NS10 monitor. Four years earlier, Mackie had launched the active HR824: a blunter tool for dissection of a mix, but radically more powerful-sounding. No external amplification was required, and for many, neither was a subwoofer. Behold the future.

Yamaha never released a direct successor to the NS10 (if you discount the second generation NS10M). From 2004 on, all Yamaha’s near-field monitors were active: the HS80M was perceived to be an activated NS10 (though it wasn’t). No passive option was offered in their MSP range. The HS80 was replaced by the even-more-NS10-like HS8 and smaller variants – all active.

In 2005, ADAM Audio launched the hugely successful A7 – another active design. Although ADAM offered a passive version, it sold it very small numbers. The industry moved to active speakers and hasn’t looked back. A similar shift took place within a few years in the live and PA arena: although passive speakers occupy an important place in large-scale applications where very high SPLs are required, the big sellers of the past decade have undoubtedly been active 2-way speakers or, currently, portable column speakers in the image of the Bose L1 – many of which are active designs.

Everywhere, then (apart from the domestic market) active speakers predominate – especially in a small form-factor. Two questions therefore merit consideration:

  1. Does the ubiquity of active speakers in the professional domain derive from technical superiority and practical benefit, or is it just a passing fad? and
  2. Why have active speakers not penetrated the consciousness or influenced the buying decisions of the average audiophile?

ACTIVE IS BETTER . . .

In a passive design, the amplifier drives a high-level, full-frequency mono signal down a speaker cable, through a series of connectors, into a crossover that splits the signal into different frequency bands: in the case of a two-way speaker, high- and low-pass circuits ensure that a tweeter receives only high-frequency information (for instance, above 2KHz) and a bass driver only receives information below the crossover point.

Many powered speakers from manufacturers such as Logitech, Creative and Audioengine, and baby studio monitors such as the Fostex PM0.3 are in fact not active, although they may be advertised as such. They typically have one mains-powered speaker and an unpowered ‘slave’ companion. Internally, they follow the same architecture as the passive system described above, with a stereo amplifier hidden in one speaker. Soundbars rarely advertise whether they have passive or active XOs, but there’s no good reason for them to be passive.

Active speakers are different.

Active speakers dedicate an amplifier to each driver. In the case of an active studio speaker like the ADAM S3H, there are eight amplifiers per stereo pair – each specified for its application: a 50W Class A/B amplifier for the AMT tweeter, a 300W Class D amplifier for the 4-inch midrange driver, and a different 500W Class D amplifier for each of its two 7-inch bass drivers. The advantage of such an approach is obvious.

Active designs typically close-couple each amplifier to its driver, without lossy connectors or the losses involved in long, high-level cable runs. Cabling is matched appropriately to each transducer: bass drivers tend to be wired with heavier gauge material than HF units.

Active crossovers operate on line-level signals, and are located ahead of amplification. Each amplifier therefore only receives input appropriate to its output – which unburdens them from having to reproduce the whole frequency range.

The net result is a speaker that is – technically and sonically – hugely more free-revving.

The shift to active speakers at the turn of the millennium derived largely from the realisation that little active speakers do bass like passive ones can’t. If you consider the measured frequency response from the NS10M below, you’ll see how the LF rolls off at 100Hz. Yamaha nominally rate this speaker at 60Hz, but we have to generously allow ±10dB to arrive at this figure. And it doesn’t really matter how powerful an amplifier you use, bass performance is fundamentally constrained. Contrast that with the similarly sized Genelec 8050 which is only 2dB down at 38Hz, or the rather smaller ADAM S2H which is ruler flat to 50Hz and nominally rated at 35Hz ±6dB.

Many years ago we ran a group audition comparing numerous sub-7-inch two way passive speakers up to a mid-range price point. To maximise their potential, we drove them with a kilowatt pre/power combination and a high-end digital source. All cabling was exotic audiophile fare – no name-drops necessary. Having established a clear preference in six hours’ listening, before packing away, we threw on the stands some similarly-sized active 2-way studio monitors we intended to trial. The difference was shocking. At approximately one-fifth of the price of the best pre/power/small speaker combination – less if you factor in cables – the active speaker was by every metric markedly superior. Stereo separation and dynamics were in a different league. All commented on the ‘grippy’ nature of the sound – it was evidently that each driver was tightly controlled in a way the passive designs couldn’t hope to be. It was an ear-opening moment you’re free to reproduce in your own home.

The puzzle then is not why active speakers have become ubiquitous in the pro world, but why they haven’t caught on with Joe Public: better, cheaper, fewer boxes, less cable clutter. What’s not to like?

WHY ACTIVE SPEAKERS NEVER CAUGHT ON

Well, for a start: cheaper, fewer boxes and fewer cables. None of these sound at all appealing to manufacturers and retailers. If the day ever dawns when an enlightened market flocks en-masse to something like currently-available studio monitors it might decimate the business.

However, Passive speakers have been aggressively marketed for so long they’re fixed in the audiophile mindset as securely as a Neutrik Speakon – another superior piece of pro audio tech that hasn’t caught on in the domestic market.

Something in the brain of the average audiophile rebels against not being able to tweak cables and upgrade amplification. There’s a perverse unease that a design may already have reached its potential off the shelf – or, conversely, that the manufacturer may have locked the buyer into some low-rent choices of internal components that can’t easily be modded. Or maybe they remind them of powered desktop PC speakers. Perhaps it’s because you can’t stuff valves in them. However well active speakers work, they just don’t seem to fit comfortably in the world-view of prospective buyers. Which is a great shame.

It would be remiss at this point not to mention Meridian, whose 1983 M1 spawned a distnguished line of products that have tunefully banged the drum for active speakers ever since. As of 2019 they remain more well kep secret than game changers, but that says more about the market than Meridian. Long may they plug away. Meantime, it is encoraging to observe a new generation of active speakers marketed as lifestyle products…

Exceptions and an exceptional problem

As a general rule, the less efficient the speaker the stronger the argument against it having a passive crossover. It would be better if small, passive speakers didn’t exist, with one exception: compact speakers using a single full-range driver deploy no or minimal filtering have problems of their own, but a crossover ain’t one.

Any speaker with a passive crossover will be improved by converting it to an active one, providing the active XO successfully handles phase coherence and time domain accuracy. Historically we’ve maintained that high-efficiency stator and open baffle speakers can work successfully as passive designs, but Siegfried Linkwitz’ final statements on this subject (the LX series) bring us back to an axiomatic truth: inside every good passive speaker is a better active speaker trying to get out.

Several standalone active crossover products exist (eg, Behringer, miniDSP, DEQ-X) that enable modestly competent DIYers to mod speakers reversibly and hear the difference. Most multichannel DACs or audio interfaces can also be configured with software crossovers using free or inexpensive software such as JRiver. Activated speakers sound liberated: precisely more like themselves, with snappier dynamics and greater detail. Try it.

At the other end of the scale, it follows from the above that there is an all-too familiar system configuration that is simply unacceptable: a one-box multichannel processor/amplifier driving long runs of high-level, unscreened signal cable through a passive crossover to tiny, inefficient drivers – in other words, the standard surround system sold by all good retailers, and even a few high end installers who should know better. Granted, AV receivers high pass output to the satellites, but a multichannel system is only as strong as its weakest link – which we’ll discuss later – and the strain thereby imposed on an amplifier – already stretched by the extreme dynamic range of film soundtracks – invariably results in a bad outcome.

In an ideal world, there would be a wide choice of inexpensive AV processors with balanced outputs on the end of which would live a bevy of active speakers individually capable of flat response to 65Hz and convincing dynamics in the crucial 100-200Hz range. It’s possible (and recommended) to build such a system inexpensively in 2019 but you have to search off the beaten track to find what should be the industry default.

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