Once upon a time, audio power amplifiers were necessarily made using thermionic valves (vacuum tubes). So they were necessarily large, expensive, dissipated loads of heat and needed expensive and sophisticated output transformers to cover the full audio range.
It was also realised during those ancient times that it was very difficult, if not impossible, to cover the entire audio range in a satisfactory way with just one loudspeaker unit. It therefore became necessary to divide the signal into separate bands of frequencies, to be handled by specialised low, high and often intermediate (mid) frequency range loudspeaker units.
Dividing the signal before the amplifier would make more than one large and expensive valve amplifier necessary. This did not deter some manufacturters - at least one very expensive mono loudspeaker unit using a specialised preamplifier and crossover, with two separate power amplifiers for the low and high frequencies, was listed the 1957 Hi-Fi Yearbook published by the British magazine Hi-Fi News. This was one early example of what we would today call an active loudspeaker system.
Most loudspeaker system designers, however, had to be content with hanging a power-sapping, signal-distorting mess of passive components between the power amplifier and the loudspeaker units.
And then stereo came along. Any designer thinking of placing his crossover network before the amplifiers would now have to double the number of amplifiers required. That, of course, ruled out active system design almost completely.
And then Solid State Made Activation Possible
Sometime in the mid to late 1960's, transistors powerful and reliable enough for heavy-duty audio amplifier use became widely available and by the early 1970's audio amplifiers using thermionic valves became all but extinct.
At the same time, small-signal audio circuits could be built using transistors and used to perform analog signal processing - such as filtering, equalisation and time delay as required for loudspeaker crossovers - much more easily and cheaply than with valves.
Since the mid-1970's, an active crossover could be designed using the new solid state electronics to divide, equalise and phase-compensate the response of a loudspeaker system much more effectively than a passive network. At the same time this would allow each drive unit to be interfaced directly to the power amplifier output, with obvious advantages in efficiency, distortion, damping and just about every other parameter of any importance in the interface between amplifier and loudspeaker unit. An added bonus is that each power amplifier also works into a much simpler load and handles a less complex, narrower-band signal.
The mini-monitor enclosures used the same drive units as the passive BBC LS3/5a introduced a couple of years earlier, and which is still being made and still has a very active following among audiophiles today. The Linkwitz units, however, enjoy the benefits of an active crossover, equalisation and time alignment circuit. High-quality mini monitors of this type, but in passive form, became popular with audiophile manufacturers and buyers in the 1980's.
That system also included an active subwoofer - a device which, once again, eventually found popularity in the next decade, and then only in compromised architectures as an add-on to passive main loudspeakers, not in a fully integrated and optimised active system.
Given these developments, one would have thought that those in the audio community most concerned with quality would, since the 1970's, have increasingly abandoned passive loudspeaker systems in favour of active systems. And this did happen in some quality-conscious sectors of the industry. Most high-quality professional sound reinforcement equipment, and most of the highest-quality professional monitor loudspeakers used in recording studios, broadcasting and other stringent applications, have been designed as active systems since then.
At Last, it was Possible - But Audiophiles were not Interested
The consumer market, however, was side-tracked into entirely different directions altogether.
First there was the quadrasonics fiasco of the early 1970's. No sooner was greater signal processing sophistication by means of solid state electronics available, than it was put to the dicey task of squeezing an additional two channels into the two that can be physically recorded onto the two sides of a phonograph record groove, for the sake of the dubious merits of achieving "all-around sound".
Unlike the transition from mono to stereo, where the benefit of going from boxed-in sound to a wide and deep image could not be doubted, and the technical basis for the implementation was sound and well understood, the transition to quadraphonics was plagued by much less clarity of purpose, far shakier technical foundation, and - the killing blow - differing implementations by different manufacturers of both equipment and records. Less than half a decade later, quadrasonics had died the death and by 1980 four-channel sound was largely forgotten.
Examining the Hi-Fi press of the early solid-state era tends to show that, in terms of prices, quadrasonic equipment had occupied the middle-to-high sectors of the market, and by and large, the very highest end of the market remained resolutely stereophonic, preferring two high-quality channels to four doubtful ones.
So what were the manufacturers of really high quality stereophonic equipment leveraging the new solid state technology for? And what were the customers sold on? Did they, like the professional sector, finally plump for active loudspeaker system designs? Did that kludge of passive components between power amplifier and loudspeaker unit finally become, in the highest sector of the market at least, a thing of the past?
We all know that the answer is no. In the early 1970's, audio electronics manufacturers trying to attract customers at the highest end of the audio amplifier market did not attempt to market active systems. Instead, they offered their customers amplifiers of ever higher power, with ever lower measured static distortion. And their customers bought these new super-amps and connected them to the same kludge of passive components that fed the loudspeaker units in the audiophile-grade passive loudspeaker systems they bought.
In the quest for ever greater accuracy, the passive crosovers in those systems became ever more complex, which made the load on the amplifier ever more diffficult to drive, which placed ever greater demands on the amplifier. This became the motive power behind an equipment-churn cycle to which audiophiles are supposed to be regularly subjected, and which the industry calls "upgrading". In short, higher quality loudspeaker means more difficult load, means bigger and better amplifier is required - and so on, all to the benefit of manufacturers' and retailers' bank balances. More on this below.
Fast forward to today. Today's audiophile may be buying a large, sophisticated, high-power solid state power amplifier, of much the same concept - if not the same performance, one hopes at least - as the 1970's super-amps. Or they might be buying an amplifier using valves, whether push-pull, single-ended, directly heated, triode or pentode. In any case, they will be doing their level best to buy the very "best" amplifier that they can afford - only, in the vast majority of cases, to connect it to the same kludge of passive components that come before the drive units in a passive loudspeaker system.
Why have active loudspeaker systems, with their undisputed advantages, not become the rule, rather than the exception, at even the highest segment of the market?
The answer, and it is the same today as it was in the early 1970's, is marketing.
Marketing, Equipment Churn, the Audio Industry - and Active Loudspeakers
The audio industry, from manufacturers to retailers to magazines and the reviewers that write in them has cultivated in most audiophiles the conviction that a process of continuous and frequent equipment changes (I call it equipment churn, the industry calls it upgrades) is a necessary part of enjoying music reproduced with a high level of quality in the comfort of one's home.
There is, of course, an attendant truism. In all areas of technology, there is a continuous advance. Engineers in all fileds are constantly finding ways of achieving the same, or better, results for a smaller outlay in cost, size and power consumption. This is, of course, great for the consumer as well as for the manufacturer.
But in the area of high end audio, things are not so simple.
First, comparison of a high-quality circa-1960's stereo system, playing high-quality circa 1960's stereo records, with a modern high-quality setup playing modern source material, digital or analogue, costing about the same in real terms today as the 1960's system did in its day, will prove that the state of the art as far as the musical results achieved are concerned, has not advanced so much in the intervening four decades, let alone since last year.
Second, and perhaps even more important, it seems that today, in high-end audio, the aim appears, in many cases, to be to actually achieve the same or slightly different - not necessarily better - results, but with a much higher outlay in bulk, power dissipation and, most importantly, it would seem, cost to the customer. In other words, to sell customers the same or slightly different (not necessarily better) performance, for more money. And the process of constant, costly equipment churn audiophiles seem to be all to eager to indulge themselves in - or subject themselves to - and which process much of the industry seems to be encouraging audiophiles to consider an indispensable part of enjoying high quality music reproduction in the home - obviously generates sales for manufacturers.
In that context, active loudspeakers, in which the electronic crossover and the amplifiers are an integral part of the loudspeaker system, are anathema because the loudspeaker and amplifier cannot be "upgraded" independently, which of course means the vicious circle of equipment churn is broken. Audiophiles conditioned by retailers and the press are very resistant to buying a loudspeaker that comes with its own amplifiers. Retailers will not sell an active loudspeaker system in preference to a passive system which will bring the customer back for an amplifier "upgrade" next month, next quarter or next year, which will probably bring the customer back for a loudspeaker upgrade - and so on.
Manufacturers of professional loudspeaker systems have caught onto this audiophile self-flagellation, and they offer passive versions of their high-quality active systems for audiophiles. For one example: Harbeth with their
Monitor 40.1 Active which is also available as the passive
40.1 and ATC with the passive versions of their various
Studio Control Monitors which are supplied as active systems for professional use.
These august manufacturers of some of the industry's finest monitors, that are used by some of the most respected professionals to check the quality of the best recordings, are certainly not to blame for offering customers the choice. The question here is, why are audiophiles with deep pockets not buying the active versions, but spending their money instead on expensive amplifiers to use with the passive versions - and therefore spending more money to build systems which are fudnamentally compromised in their architecture. Are audiophiles in fact deaf? Can they not hear the benefits? I think not. In most cases, audiophiles don't get to hear the active, professional version of the monitor - the audiophile retailer will not have it in stock. Are they, then, uninformed? That is probably closer to the answer. The dealer who does not stock the active version will not tell them about it. Neither will they read about it in the audiophile press - it will be the passive, "audiophile" version that is reviewed.
Indeed, whenever active systems are mentioned in audiophile circles, there is an accompaniment of dark mutterings about "unacceptable signal processing" in the crossover electronics. The mutilation that the signal suffers passing through a kludge of components in a passive crossover placed at the most critical point in the system is conveniently discounted, of course. The amplifiers chosen by the manufacturer for integration with the active system will also probably not conform to the audiophile fashion of the day - more fear, uncertainty and doubt.
As a result of all this, it could be argued that most audiophiles would consider that a choice of the passive version with an expensive audiophile amplifier will actually deliver better performance than an active system integrated by even the most respected manufacturer, despite the compromise in system architecture which they might not even acknowledge to be important.
What if I am convinced of the merits of an active loudspeaker system, but still want to choose my own amps?
The limited appeal of active systems to manufacturers of commercially available audiophile grade loudspeaker systems has forced at least one loudspeaker designer convinced of the merits of the active approach to take matters into his own hands. He has made several designs for do-it-yourself active loudspeaker systems available on a license basis to do-it-yourselfers. This designer is none other than the Siegfried Linkwitz of the aforementioned Linkwitz-Riley pair of active crossover pioneers.
The designs he offers in his corporate identity of Linkwitz Lab are known as Pluto and Orion.
Linkwitz Lab offer the possibility of starting with just the documentation and a set of circtuit boards for the active crossover/equalizer, with options to obtain also ready-built crossover-equaliser units and/or flat-pack knock-together kits for the woodwork, all the way to fully assembled and tested systems, including amplifiers if required.
With the Orion especially, Siegfried Linkwitz does not restrict himself to tapping the potential of active loudspeaker system design. He uses the signal processing potential of active systems to tailor the Orion's phase response and directional response, making it possible to design an open baffle loudspeaker system using the latest advances in conventional drive unit technology. Doing away with the box of a typical loudspeaker system, and its associated resonances and colourations, is generally considered to be a Good Thing.
Also, an open baffle design is by its nature a dipole radiator, which means that it generally emits only along one axis, thus reducing the effect of room modes. Having said that, dipoles require a very different approach to placement in a room than conventional box-type systems - generally further away from walls - which is sometimes less convenient.
Doing away with the box, and aiming for "no abrupt change of directivity with frequency" and exploiting the possibilities of dipole radiation were the advatages Peter Walker of Quad had in mind when he chose an open-frame dipole format for his original Quad Electrostatic Loudspeaker. There are few audiophiles who will deny that particular design its place in the pantheon of all-time great audio products. So to people who are familiar with the merits of open-frame electrostatics or other similar panel loudspeakers, but seek a perhaps more practical and reliable implementation of the same concept using conventional drive units, the Orion is an avenue well worth exploring - and you can bring four channels per side of your own choice of amplifier with you.
