To give an
example from
Meridian’s
product line, the
DSP6000 includes
four channels of 70W
amplification.This is equiva-
lent to about 1kW driving a
conventional passive system.
It is evident from these comparisons
that an active system can produce sur-
prisingly high levels from a significantly
smaller amplification system. There are
significant improvements in efficiency
that can be realised with an active sys-
tem, even if it is more difficult to design
– or rather, we could say that it is possi-
ble to implement a more sophisticated
design, with many additional features,
to deliver these and other benefits.
Bass Extension
There is more to an active loudspeaker
than simply improving the efficiency and
overall performance of the system. An
active approach can deliver benefits that
are simply impossible for a passive sys-
tem to realise. We can’t change the
laws of physics, but we can use them to
our advantage.
There is a known relationship between
the low –3dB cutoff frequency (f), the
physical volume of the enclosure (V) and
the efficiency (e). It is:
e = V/f
3
x K
where K is a constant relating to the
system’s design. In a nutshell, this
means that the cost of a smaller cabinet
is either less bass or lower efficiency.
The ability to consider an active loud-
speaker as a total system – an active
crossover with filtering, amplifier, power
supply, driver and enclosure – allows the
overall response and performance of the
system to be modified, essentially alter-
ing that constant, K, in the equation
above.
For example, the original Meridian
“Interactive Bass” system used auxiliary
filtering, and the particular alignment
provides a sixth-order rolloff plus an
additional octave of bass compared to a
passive speaker of the same volume and
efficiency (see Fig. 4). Putting this more
impressively, a passive speaker with
equivalent bass response would need to
have eight times the volume, or twice
the linear dimensions.
In addition, this alignment minimises
cone movement of the bass driver for a
given output – indeed, cone deflection
for a ported system such as the
DSP7000, 5000 or 5500 is one third as
much as using the same drivers in a pas-
sive sealed box with equal broad-band
excitation.
page 5Meridian Loudspeakers: The DSP Path The Meridian Papers - 1
DSP8000 – the inside story
The rigid enclosure, laminated from Russian
Birch plywood and aluminium alloy, has six
coats of hand-finished piano lacquer. The six
horizontally-opposed bass drive units neutralise
cabinet resonance. The rear-mounted sealed
DSP crossover and eight power amplifiers are
mounted on a precision machined heat sink.
