Fully powered, or “active” loudspeakers have a lot of very real advantages. Here’s a punch-list of the top 5:
• Lower distortion
• Better dynamic potential
• Extended response
• Managed phase and other time-domain characteristics
• Packaging efficiency and cost advantages
I’m going to go into each of these a bit deeper, but first, by way of a counterbalance, here’s a list of all the serious-performance active loudspeakers that have made real commercial successes in the broader consumer electronics market over the past thirty years or so:
Impressive, inn’it? Yeah; there haven’t been any. Which is strange, since any audio engineer much past freshman year would agree that packaging together the power amplifier and transducer components (the drivers) of any audio “b-chain” is by far the most logical, and cost-effective way to ensure optimal reproduction. And that’s true even if we look only at my five key advantages, ignoring the dozens of others we could name.
Lower distortion: Since an active speaker has the luxury of dividing and directing tweeter-signal and midrange- and/or woofer-signals at line level, before reaching the power amplifiers, it does not require the passive, high-power-dissipating (and phase-mangling) dividing network (crossover) found in virtually every conventional passive speaker. And crossovers are notorious power sinks, introducers of substantial harmonic distortion (both the familiar total-harmonic, and some more arcane types), and are limited to just a few practicable choices of filter-slope, none of which is wholly ideal.
Better dynamics: In passive speakers the crossover network inevitably absorbs some measure of power-amp juice (dissipating it as heat) before this ever reaches any transducer’s terminals, and some degree of non-linearity in doing so is all but unavoidable. This contributes to dynamic compression. Perhaps more important still, in an active-speaker design the engineer knows precisely how much power each driver can successfully exploit, and can design its individual amplifier accordingly, while adding instantaneous, non-invasive “Smart” driver-protection instead of relying on old fashioned, slow, and arguably sonics-sucking fuses.
Extended response: This one’s no-brainer. To take the simplest example, if you’re designing a dedicated amplifier for a known woofer, with a known roll-off in your chosen enclosure alignment, you can easily “cheat” an extra half-octave or so of bass extension by adding in reverse EQ to the woofer amp. More subtly, you can “shape” midrange and/or tweeter responses in an effort to complement each transducer, yielding idealized driver-to-driver integration, optimized overall system response, or both. And since all of this amplitude-domain equalizing happens at line level the consequences in terms of distortion and phase can be made very nearly nil.
Managed phase and time-domain behaviors: In today’s digital age, if we introduce DSP to the mix, a whole ‘nuther world (as we say here in New Hamp’shuh) of engineering potential opens up. Active-speaker designers can now command system directivity (to an extent), and individual and relative phase and other time-domain behavior, to achieve just the multi-driver wavefront they desire.
Packaging efficiency and cost advantages: These are almost too numerous to name. By building the power amps into the loudspeaker cabinet – which mostly is just wasted air-space anyway – you eliminate the need for a bulky external power amplifier or receiver. (And with active-EQ the speakers themselves may be made smaller at little sacrifice in extension; witness all those super-slim “power-towers.) And exploiting multiple small amplifiers, each dedicated to a finite few octaves, is more cost effective than producing a single huge, full-range one that’s able to produce enough power to drive all those transducers, and heat the crossover network. And it’s not just the cost and size of the power amp itself we save, including its enormously expensive chassis and fascia; there are its packing materials, owner’s manual, logistics costs, and the shelf on which it would have to reside – plus the differential of energy we’d have needed to power it.
So why don’t we have any active speakers in the rational-price high-performance hi-fi space? It’s pretty simple: people won’t buy them. And it has ever been thus. The classic example is probably that of the Powered Advent Loudspeaker, an active variant of the top-selling Large Advent 2-way produced by the Cambridge, MA maker back in the late 1970’s. Same basic drivers, same bulky, rectangular cosmetics, almost identical size. The Powered looked just like a Large Advent (except for a couple of pilot lights), and it sounded just like a Large Advent—one that played twice as loud, went a good half-octave deeper, and displayed dynamic punch and transient clarity and excitement that rivaled those of speakers absurdly more expensive.
Everyone in the industry who heard them agreed that the Powered Advent was a genuine tour de force. (The P.A.L. was the brainchild of Tom Holman, late of U.S.C. and Lucasfilm/THX, now chief of audio at Apple.) Yet nobody—but nobody—would buy them. And not many even remember them today. I haven’t seen or heard tell of a pair in at least 20 years. (Anybody else?)
Not much has changed today. The marketplace has quietly accepted active design as de rigeur for desktop computer speakers and Bluetooth boombox-equivalents, but for serious audio and home-theater systems we still insist on passive speakers all around, and bulky amplifiers and receivers. Hybrid, active-woofer designs from companies like Definitive Technology and GoldenEar have made a good deal of noise. But only a couple of ultra-high-end firms such as Meridian and Bang & Olufsen—brands that can, presumably, afford to do the right thing and let consumers catch up—have seriously pursued active-speaker design.
Good for them. But there’s no categorical reason why all the active goodness should be the exclusive province of those rich enough to afford these searingly expensive if admittedly brilliant designs. The benefits I’ve outlined above are all eminently scalable. And it’s about time somebody got busy and started scaling them.