Meridian Audio Speaker - Manual (Page 2)

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.
page 2 Meridian Loudspeakers: The DSP Path The Meridian Papers - 1
LINE LEVEL IN LOUDSPEAKER
ENCLOSURE
LF DRIVER
HF DRIVER HF POWER
AMPLIFIER
LF POWER
AMPLIFIER
ELECTRONIC
CROSSOVER
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.
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.