In every corner of life there are guilty secrets, ancient truths that are never discussed, arcane knowledge that must be kept hidden, heresies that must never be spoken. And every now and then someone decides that the time has come to bring one of these things back out in the open; that the world has surely grown wiser and sufficiently mature to be able to re-consider such matters in an informed and dispassionate manner. But in the end they are always beaten back, bruised and battered, to lick their wounds and ruminate on the irrationality and perfidy of their fellow man. Thus it always was, and ever shall be.
We have our own share of dark secrets in the world of audiophilia. Things we mostly know to be truths, yet we conspire to consign them to the darkest corners, lest they disturb our carefully nurtured equilibrium. Including what, for many, may be the most profound wisdom of all, the thing whose name may not be spoken. The active loudspeaker.
There. I’ve said it [… looks furtively over shoulder …].
An active loudspeaker is simply a speaker with its own amplifier(s), which are typically (but not necessarily) built-in. There can be many reasons for doing this, which include:
- Matching of the amplifier characteristics to the loudspeaker’s needs, and being able to optimizing them without concern for compatibility issues when using it with another manufacturer’s product.
- Being able to use an active instead of a passive crossover.
- Simplicity for the consumer, who no longer needs separate amplifiers, preamplifiers, and all the cables and cords that connect them together.
The first of these reasons – designing dedicated amplifier(s) specific to the loudspeaker – is one that exercises much debate among audiophiles. It is all due to the nature of the status quo. We are accustomed to buying our speakers, amplifiers, and even the connecting cables, according to the specific sonic properties of each. We understand that a special part of curating a very personal system is being able to fine-tune our amplifier and speaker selections according to our needs and desires. We have become accustomed to this paradigm, and have developed not just a degree of comfort with it, but a certain expectation that this is how it should be. Yet at the same time, as a community, we tend to acknowledge certain truisms. That manufacturer A’s amplifiers tend to be a good match with manufacturer B’s speakers. Or conversely, that manufacturer C’s amplifiers are usually a bad match with manufacturer D’s speakers. In any case, we understand that identifying and developing system synergy is an important part of the process, and moreover, we have come to expect that we should be in control of that bit ourselves. And maybe we fear we are giving up something vital when we allow the manufacturer to make those choices for us.
But manufacturers are doing that all the time. Whether they are designing speakers or amplifiers, they are making choices that govern how the product sounds, and are usually making those choices with the aim of making it sound as good as they possibly can, even if their different results each end up with their own unique sound signatures. How often do we read about how this amplifier has great bass, but that amplifier has a better top end? Meanwhile this third amplifier has the sweetest midrange. This just cries out for someone to wire the first of these to the woofer, the second to the tweeter, and the third to the midrange. Such an ad hoc approach may not in practice deliver the desired synergies straight out of the box, and I am not familiar with any results that may have been obtained by anyone actually going out and trying it. But as a guiding principle for a design philosophy, I think it has a lot going for it.
Already, anybody who uses modern high-end subwoofers in their system is dipping a toe in the active speaker pond, because those subwoofers can be counted on to contain class-D amplifiers tightly optimized for use in that very specific application. In fact these amplifiers will have been so tightly optimized that I guarantee if you were to strip them out of the subwoofer and use them to power the rest of your full-range system it would sound like crap. Or, at best, crap with awesome bass.
Additionally, besides the frequency content, the requirements for driving the three frequency ranges would be different. For one thing, there is less energy in the treble, and so the tweeter amplifier would not need as much power as the bass amplifier. You could even use entirely different amplifier topologies for the three drivers – for example, a Class-D for the bass, a SET for the midrange, and a pure Class-A JFET for the treble (although, for clarity, I am not attempting to advocate such a jumbled configuration). You could use drive units with different efficiencies, and compensate for those in the gains of the associated amplifiers, or use drive units with radically different impedances (although modern loudspeaker designers seem content to adopt a totally cavalier approach to both impedance and efficiency these days, given the inherent robustness and power delivery of most modern amplifier designs). The point is, many of the design constraints passive loudspeaker designers are obligated to adhere to might no longer apply in an active design.
The use of an active crossover is probably the single most important design tool available to the active speaker designer, although it is likely that consumers will ultimately pay it the same attention they do to passive crossover design in conventional loudspeakers – i.e. virtually none. The technical reasons are quite simple to state, but would require a lot of discussion to do it full justice, and I don’t have room for that here. Basically, a normal loudspeaker crossover network operates in the low-impedance environment of the loudspeaker itself – nominally 8Ω – whereas an active crossover will work in whatever high-impedance environment the designer prefers. Low-impedance crossovers require enormous values of capacitance and inductance, and low values of resistance. Such components can be prohibitively expensive (even by high-end audio standards) when chosen solely on their sonic merits, whereas a high-impedance crossover can be constructed using component values that can be easily and inexpensively sourced even on the basis of audiophile grade quality. This alone can mean that just moving from a conventional low-impedance passive crossover to a high-impedance active crossover can result in major sonic gains, regardless of the impact of the amplifiers themselves.
But component quality is not the only advantage of active crossovers. By moving to an active crossover, we can expand our design horizons dramatically, and consider crossover architectures that would be either impractical or prohibitively expensive to implement passively, or that would be sonically compromised by the components that were used. This affords us opportunities to correct for flaws that we might otherwise be forced to accept as part of our final design compromise. Crossover behavior is such an underappreciated aspect of the loudspeaker design art, as it impacts not just the nominal frequency response of the speaker, but also the phase response, and by extension aspects of the polar dispersion pattern which is a key factor governing how the speaker will end up sounding in your actual room.
Yet more design freedom is introduced if we implement the crossover in the digital domain. Digital crossovers allow us to access performance regimes that would be either out-of-the-question in an analog circuit, or would require a complex implementation that might in and of itself introduce unacceptable sonic compromises. Digital crossovers have the advantage that, if done correctly, their performance is exact and deterministic, and they don’t suffer anything analogous to the real-world sonic signatures of analog capacitors and inductors. However, digital crossovers require that the incoming signal be in the digital domain, or be converted to the digital domain, and many consumers will want to take issue with that. At the end of the day, it is something else that wannabe active loudspeaker designers are just going to have to juggle with. For what it’s worth, my own expectation is that a statement-grade active loudspeaker based on a digital crossover will be able to correct for so many of the design limitations of a conventional passive loudspeaker that it would be an impossible product to dismiss out of hand. Even so, some people can be relied upon to do just that.
Unlike the technical arguments around active loudspeakers, which on the whole are fairly objective, gauging the market response is a different and harder thing. You are asking the customer to dispense entirely with his amplifier – and maybe even with more of his audio food chain, depending on just far you want to go down the integration path. I would contend that, if the designer does his job properly, he can present a product to the customer whose performance would make a sufficiently compelling argument in its favor. And I would also contend that customers would be willing to purchase such a product – particularly if it is skillfully positioned.
The economics of active loudspeakers will also come into play. Since they integrate an amplifier with a loudspeaker, there will perhaps be some sort of expectation of a cost benefit that would inherently arise. But in general, that isn’t going to be the case. There will still be as much electronic gear in an active speaker as a passive one – and probably more, given that there will be multiple amplifiers (and multiple DACs in a digital design). The business model will also come into play, since the traditional markup on loudspeakers tends to be larger than that on electronics. All these factors will conspire to ensure that an active loudspeaker is not going to be cheaper than a nominally equivalent passive speaker/amplifier combo, all else being equal. This will give rise to a significant marketing challenge, because customers will look at an active loudspeaker and just see a loudspeaker. And a loudspeaker-sized price point will pop unbidden into their heads. Even if they understand at an intellectual level that it also contains a bunch of seriously high-end amplifiers.
But customer acceptance is not the biggest problem we face. No, the problem is more insidious. As things stand, life is tough for high-end audio dealers. A decent stereo no longer holds the cachet it once did, and new customers are increasingly difficult to attract. Then there’s the internet effect, where people come into the store ‘knowing’ more about a product they’ve never heard than the salesman who has been selling it for years. It’s tough out there. So dealers are generally not at all receptive to anything that looks like it is going to rock their boats. And active loudspeakers can really rock the HMS Status Quo. What the dealer fears is that active loudspeakers effectively remove from the market the customer who wants to upgrade his system component by component. This has always been the lifeblood of the dealer – the customer who comes in to upgrade his amplifier one year and his speakers the next – and the customer he sells an active loudspeaker to isn’t going to be doing that any more. So dealer resistance is probably going to be the biggest obstacle a potential active loudspeaker manufacturers will face – followed closely by established amplifier manufacturers who won’t want to see their dealers selling a competitive line of active loudspeakers.
But maybe I’m wrong. Maybe active and passive loudspeakers can co-exist after all. Dynaudio are now happily selling a mixture of both active and passive speakers, and doing a fair job of positioning their product range. [And their active speakers are all digital.] PMC sells a nice range of active speakers that they position as rather industrial-looking studio monitors. Meridian have made high-end active loudspeakers for as long as I can remember, and their latest flagship offering, the DSP8000 Special Edition, is also a digital model. And B&W’s absurdly expensive (but absurdly gorgeous) Nautilus has only ever been sold with an external active crossover for use in a (4-way) active configuration where the customer supplies his own amplifiers. So active loudspeakers are out there, although they still aren’t making anything remotely like a splash. But it’s a situation I’d be keeping an eye on.