How much of your music are you hearing?

Preface: this page describes an all-analogue, multi-amplifier speaker system, including a 'line level' crossover instead of the usual 'speaker level' crossover. A crossover can also be made using digital technology. Without getting into the debate about digital versus analogue, I can confirm that digitizing a musical signal then reconverting back to analogue does result in a different listening experience to that obtained from an entirely analogue system.

I offer bespoke solutions for those who prefer the fully analogue approach.

Regarding definitions: most 'active speakers' (as advertised) are NOT the same thing as the system described here. Specifically, they mostly lack the line level crossover and frequency band dedicated amplifiers described here.

Passive crossover issues

In almost any multi-way speaker there is a filtration device, or 'crossover,' which ensures that the correct frequency band is sent to the corresponding drive unit - highs to the tweeter, lows to the woofer, etc. The crossover is made up of power tolerant inductors, capacitors, and sometimes resistors. Even assuming that top quality components are used, their presence between amplifiers and speaker none-the-less takes a toll on signal integrity - degrading and morphing pitch, time, and transients (all these being the building blocks of music itself) as well as degrading non-musical aspects such as 'soundstage' (focus, stability) and the old 'audiophile' chestnut 'transparency'. As documented elsewhere, the deleterious effects of conventional crossovers are partly due to the behaviour of the constituent components, and partly due to their location - interrupting the electrical relationship between the amplifier and the speaker drive units. This barrier or damping effect makes matters difficult for any amplifier; preventing it from delivering its best performance.

Enter the active crossover...

In a fully active, multi-amplifier speaker system, the crossover function is performed at line level, schematically located between the control unit or 'pre-amp' and an array of power amplifiers. If a signal must be manipulated, as in this case, then it's almost always better to do it at line level using active circuit design (IE 'with gain'). In other words, perform the crossover filtering concurrent to the existing process of amplification.

After exiting the crossover, each frequency band is sent to its own, dedicated power amplifier. This is a major departure from conventional topology and is responsible for much of the sound quality benefit - each power amplifier in the array only handles one part of the frequency spectrum. No matter how good or expensive an amplifier might be, it will perform (sound) better when it is dedicated to just one part of the frequency range instead of having to cope with all of it. BTW, this is not the same as 'bandwidth limitation' discussed elsewhere; in this case we are sharing the original, full bandwidth across an array of amplifiers (at this point, some readers will already see the benefit of matching amplifiers, IE using the same model of amplifier throughout).

Another advantage: because the amplifier is now connected directly to its corresponding drive unit, the two act almost as a combined circuit; movements of the cone, or dome, more closely mirror the amplifier output. The improvement in control, clarity, and pitch fidelity is matched by a reduction in distortion (both transient and time based smearing).

Now that the passive crossover, with its sometimes multiple ohms of parasitic resistance(!!) has been bypassed, all that remains is the tiny fraction of an ohm inherent to the connecting cable (for perspective, even cheap 'bell wire' is kinder to a complex musical signal than are the inductors and capacitors found in a passive crossover).

Sound quality result? Increased resolution of detail, improved pitch fidelity, more clearly defined and solid timing, greater tonal gradation/nuance, and a sense of less strain at higher volumes. If all is done well, the music becomes more intelligible and involving; more like music, and less like sound. Regarding the non-musical factors, these too are greatly improved. In particular, performers' sonic images emerge more clearly from the space between the speakers (focus, definition), and image stability is also improved (although room acoustics are often the main contributor to image stability).

So why isn't everyone using an active system?

High cost, and a reputation for poor sound quality(!) Here is what I think went wrong regarding reputation. Domestic active systems became popular in the early to mid eighties as a spin off from what had become (and remains) standard for studio monitoring systems. Two manufacturers in particular, Linn Products and Naim Audio, staged impressive demonstration of what was possible in a domestic context, and subsequently offered excellent products, albeit at high prices. They helped create a new market for home active systems (also highly influential was Meridian). However, due to the cost of multiple high quality amplifiers, there soon began a consumer/retailer led trend toward using different qualities of amplifier for the various frequency bands (a common assumption was/is that one can 'get away with' a cheaper amp for a tweeter, and that woofers only need lots of power in order to sound good). Then the 'audiophile gurus' pounced, and the ensuing discourse seems to have muddied the waters further. Before long there were all kinds of hybridised recipes for 'audiophile grade' active systems, and most of the results were a significant compromise of the initial concept. Many of these systems were very expensive, yet sounded poor even compared a well configured passive system, let alone a by-the-book active system. [Note: avoid mixing amplifiers - stick to the same make, model, and version throughout - consecutive serial numbers help assure this. And avoid using bottom of the range amps - the load sharing advantage only goes so far...]

To make matters worse, manufacturers past and present have squandered the main benefit of a line level crossover (cleaner signal path) by adding various quality sapping knobs and switches, including circuitry to allow the user to manipulate the crossover points and relative levels (btw, there are valid reasons why these features are needed in a crossover built for studio or stage, but those features none-the-less have a cost in terms of signal integrity). In any case, the sound quality result is poor compared to the approach used at Naim, and Linn (and emulated here).

Many owners of compromised active systems eventually heard a well configured passive system with a single high quality amplifier, and found it sounded much better than their own, and was cheaper... Today, if you read anecdotes on the internet, you will find a wide disparity of experiences; it should come as no surprise given the above.

Anyway, this type of system has never been, and perhaps never will be, mainstream because there are so many ways to inadvertently spoil the end result and render the exercise a waste of time and money.

Another caveat: a well setup, excellent turntable/arm/cartridge, combined with a modest amplifier and passive speakers will, all being well, sound better than a mediocre player coupled to a 'no-expense-spared' active system. An active system cannot improve the source signal it receives ("Garbage in, garbage out").

I'll close with an abridged description of the conversion or design process:

1) I first measure the speaker 'as is' (acoustic conditions) and isolate its true acoustic crossover point. 2) The crossover component values are calculated with respect to the measured, or desired, crossover point. 3) The crossover is assembled. 4) The speaker is remeasured, post conversion, to ensure that the target crossover point has been achieved, and that the crossover and speaker are performing as predicted. Adjustments are made as needed. Naturally, a sound test with music is also performed.

Above, these are passive, or 'speaker level,' crossovers.

BTW, on the internet one sees many adverts for 'active speakers,' but that term is often used to describe a passive speaker (IE passive crossover) that has an amplifier (1 amplifier) included within the speaker cabinet. Some of these products sound excellent, but they are not the same proposition as described here. Meanwhile, studio monitors described as 'active' are more likely to have the configuration described here - housed within the speaker cabinets for convenience (and with some loss of resolution likely).

A number of measurements are made from different angles and distances, and from all drive units.

Here a prototype has been made using a blank PCB from a third party (I can refer interested persons to that vendor). In some cases, an entirely bespoke circuit is required. BTW, despite appearances there are no DSP chips here(!)

Prior to assembly components are measured individually; where applicable, I match components to within 1% (emulating what is done at the better audio makers).