Meridian Audio Speaker manual Meridian Loudspeakers The DSP Path, Hotrod or Hi-Fi?

The Meridian Papers - 1 Meridian Loudspeakers: The DSP Path page 2

Hotrod or Hi-Fi?

Consider your car for a moment. Did you buy the engine from one manufacturer, the suspension from another and the transmission from someone else? Probably not. Yet this is the way that high-priced hi-fi systems are often assem- bled. It is generally not known – and impossible to know – how such a compos- ite system will perform.

Components are chosen independently of one another and out of context with the sound of the system as a whole, often on the basis of irrelevant, anecdotal or sim- ply erroneous information.

Hardly surprising, then, that the elusive Grail of audio – ‘musicality’ – is difficult, if not impossible, to find in the traditional audiophile arena. At best, hi-fis like this are not integrated systems but hot-rods: they do one thing well. This is why expen- sive systems often only sound their best playing back one type of music.

Meridian believes in the complete, inte- grated system, and that a system should be judged on how well the entire package performs in the real world. This is why all our components explicitly speak the same electric and acoustic language. While their performance with other manufacturers’ equipment is exemplary, they positively sing when placed in chorus with equip- ment of their own pedigree.

In almost thirty years of existence, Meridian has learned not only the param- eters upon which a superb-quality total system is based: we have also refined our capability to design the individual compo- nents that comprise such a system.

Don’t forget, a Meridian system can be as simple as a CD player and a pair of DSP speakers. Because the amps and control are in the speakers, that’s all you need.

If you examine the vast majority of cur- rent – and past – hi-fi amplifiers and speakers, you will find the

same story: a single channel of amplifi- cation handles the full audible frequency range of the system. A single pair of cables carries this signal to the loud- speaker cabinet, and inside the enclo- sure the high-level audio is split into multiple bands and fed to appropriate drivers. The circuit that handles this splitting is the crossover, and it consists of a number of filters that separate out the different bands to suit the require- ments of the different drivers.

The simplest example of this traditional approach is the two-way speaker shown diagrammatically in Fig. 1, where the full-bandwidth output from the amplifi- er is fed into a passive crossover that derives signals to drive the tweeter and woofer.

This, it turns out, is one of the worst things you can do, as processing high- level analogue signals requires compo- nents to be chosen primarily for their power-handling capability and not for their audio quality. The filters require inductance, capacitance and resistance, and to operate at high levels and low impedances – in the order of a few ohms – without losing efficiency, these components are often far from perfect. Inductors are iron or ferrite cored and capacitors are non-polar electrolytics,

introducing distortion. In fact, every- thing is more difficult to manage at high power levels. Suddenly the cables that connect the amplifier outputs to the loudspeakers can impact the sound of the system, for example – something that benefits only the makers of expen- sive cables.

Even if it is practical, at great expense, to use air-cored inductors and film capacitors, it is still difficult for the designer to avoid making compromises in the frequency characteristic of the crossover without presenting unpleasant loads to the power amplifier in terms of impedance or phase angle. In addition, the relative efficiencies of the drivers have to be well matched to avoid wast- ing power and damping – this limits the designer’s choices of which units to use. Look at it another way: In a passive sys- tem, the only power available to drive the crossover components is the signal itself.

A solution, long known in the profes- sional field, is to operate the crossover at line level, ie before amplification takes place. The amplification then fol- lows the crossover instead of preceding it. In modern professional live sound installations it is extremely common to pass the line-level signal to an active, electronic crossover, then on to the amplification and finally to the actual drivers of the loudspeakers.

Fig. 2: An alternative arrangement to that shown in Figure 1, in which an electronic, line- level crossover drives a pair of amplifiers feed- ing woofer and tweeter.

LINE LEVEL IN

HF POWER

AMPLIFIER

ELECTRONIC

CROSSOVER

LOUDSPEAKER	LF POWER
ENCLOSURE	AMPLIFIER

HF DRIVER

LF DRIVER