Meridian Audio Speaker - Manual (Page 3)

However, such an approach – “bi-amp-
ing” or “tri-amping” the system – is far
too complex and prone to error to be a
very practical approach in the consumer
field.
The Active Loudspeaker
Back in the mid-1970s, multi-amping
was almost unknown. Even more
unconventional was Meridian’s first
product, the M1 Active Speaker, which
placed both active crossover and ampli-
fication, plus the associated power unit,
in the same enclosure as the loudspeak-
er drive units. The principle is illustrated
in simple form in Fig. 2.
This method delivers a number of
important benefits. First, there is a sim-
ple line-level connection between the
preamplifier and the loudspeakers: a
large, heavy box and associated cabling
disappears at a stroke.
Second, the crossover is operating at
line level, so the considerations as far as
components are concerned are the
same as with, say, a preamplifier, and
the quality delivered by such a crossover
should be equivalent. The highest quali-
ty components can be employed, such
as metal-film resistors and plastic capaci-
tors, for example.
But there are not simply benefits on the
component side. The designer of an
active crossover can design each ele-
ment of the crossover – including inde-
pendent adjustment of phase and
amplitude, and filter curves as complex
as are required by the acoustic system –
without having to be concerned with
issues such as matching driver efficien-
cies or the impedance of the configura-
tion.
In addition, there is another major bene-
fit in that the amplifiers are connected
directly to the drivers: there is one
power amplifier per crossover band. The
directness of the connection means that
the amplifier can control the driver over
its entire range. DC coupling between
amplifier and driver results in a high
damping factor.
In simple terms, this means that if the
speaker cone makes a movement other
than because of an input signal – as a
result of a resonance, for example, the
electrical energy generated by this
movement is fed back to the amplifier
and restrains the motion of the cone –
allowing the amplifier to control the
driver.
This electromagnetic damping reduces
resonance, cone effects and spurious
responses. Not only that: the direct con-
nection between amplifier and driver
means that the amp can control cone
movement beyond the range of the
crossover band assigned to it – impor-
tant, because a tweeter’s resonant fre-
quency, for example, can often be out-
side the frequency band supplied to it
by the crossover. In an active system, the
amplifier can deal with this; in a passive
system, it can’t.
This tight control also allows a Meridian
to sound excellent at any level, from a
whisper to a surprisingly loud shout.
It’s also important to consider the loud-
speaker as a complete system. For the
designer, this gives a great deal more
possibilities than simply multi-amping an
existing passive design.
Less power, more sound
On the face of it, there is a downside to
this approach: the system requires a
power amplifier per crossover band,
rather than just one.
The truth is, however, that the active
loudspeaker is much more efficient.
When a single amplifier is used in a pas-
sive system, apart from the power wast-
ed producing heat in the crossover,
there also have to be allowances in the
power amplifier for all manner of
extraordinary unknowns: strange imped-
ances at certain frequencies, a wide
page 3 Meridian Loudspeakers: The DSP Path The Meridian Papers - 1
Digital Audio:
Music to the Ears
Digital audio technology is now widely
regarded by industry experts as the best
means to hear music in the home.
Because music recorded digitally can be
transmitted, even over long distances,
and played back with no change from the
original, like Morse code over a telegraph
line.
Why is this important? Traditional ana-
logue systems behave much like the child-
hood game in which each player repeats a
whispered message into the next player’s
ear, and so on down a chain. Each ana-
logue link – turntable, amplifier, cable,
speaker – whispers an analogy of what it
hears to the next, but something is
always lost or added. What emerges at
the end, while charming, may not resem-
ble the original message.
By contrast, digital audio first encodes
music as digits – ones and zeros – in pat-
terns describing specific sound waves.
This is the binary language of computers,
and it’s very difficult to mistake a one for
a zero. No matter how long the chain, at
its end digital equipment listens only for
patterns of those two digits, which it
reassembles into music, ignoring all other
whispered information as noise.… ➤