Meridian DSP420, M420 Operation Manual

Background

In-wall loudspeakers are not a new invention.
Indeed they have been employed for many years
by installers who wish to provide an unobtrusive
audio solution to customers who have been
unwilling or unable to install conventional free­standing loudspeakers.

However, the design restraints generally imposed
on an in-wall design – limited space and thus
limited enclosure volume, physical limitations on
materials and other restrictions – have meant
that in-walls have traditionally offered a level of
quality and performance that has lagged some
distance behind their free-standing counterparts.

Meridian’s DSP420 breaks that mould with
an in-wall loudspeaker that is a cut above the
rest. Inside each unit, Meridian’s unique high
technology digital signal processing is used to
free the sound from the walls: the result is clear
and open with a wide response, very much in
line with the performance of Meridian’s smaller
free-standing DSP-based loudspeaker models,

and with a similar character, enabling in-wall and
free-standing speakers to be combined in a single
system as required.

As a result, the DSP420 has become one of
Meridian’s most popular loudspeakers. Following
its success, and in response to customer
demand, an active analogue variant, the M420,
is now available, with the same bass drivers
and power amplifiers as the DSP version. In
addition, the back-box available for both units
has been redesigned to permit easier and quicker
installation, including BNC connectors on the
digital version and XLRs on the analogue.

Truly Active In-Walls

The DSP420 and M420 are truly active in-wall
speakers with separate internal amplification
for high and low frequency bands. Rated
at 65 and 85 Watts respectively and using
carefully selected bipolar output devices, the
idealised low feedback designs are based on
those used in other Meridian loudspeakers to
deliver exceptionally fast bass response and

DSP420

Digital Signal Processing
In-Wall Loudspeaker System

M420

Analogue Active In-Wall
Loudspeaker System

INSTALLATION & OPERATION

The world’s first DSP In-wall
based on technology used
in Meridian’s famous DSP
speakers

New analogue active version
also available

Easy-install sealed pre­construction enclosure with
redesigned, simplified back­box

Double sealed and damped
acoustic enclosure

Separate, on-board,
85W bass and 65W treble
power amplifiers

2 way active speaker with
DSP (DSP420) or analogue
line-level (M420) crossover

Custom paintable grille/
frame

The DSP420 accepts up to 96kHz/
24-bit inputs including Meridian
MHR Smart Link. The M420
accepts line-level balanced
analogue inputs. Unit is
designed to comply fully
with international building
regulations

high resolution. These amplifiers are coupled
directly to the drive units for the most efficient
delivery of power and the best possible control
over driver excursion. Both analogue and digital
variants exhibit extremely low levels of noise and
distortion, aided by careful star earthing, while
the power supply includes a substantial toroidal
transformer and audiophile-grade capacitors.

Meridian DSP

The DSP420 accepts digital input signals up to
96kHz/24bit, including Meridian High Resolution
(MHR) streams from Meridian Surround
Controllers, Processors and DVD Players.
Enclosed in a fully shielded housing, Meridian’s
unique DSP processing is performed on a
specially-designed six-layer PCB using a powerful
100 MIPS Motorola DSP engine. Thanks to
this sophisticated audio computer, the DSP420
embodies identical high-technology features
to those found throughout the Meridian DSP
Loudspeaker family. These include:

• Position control to compensate for speaker
location

• FIFO memory buffer at the input for the lowest
possible jitter

• Linear-phase crossover for precision drive unit
integration

• Tweeter delay for perfect driver alignment

• 48-bit resolution volume control

• Minimal frequency equalisation, delivering a
frequency response free from drive unit or
electronic colouration

• Transparent tone controls

• Absolute phase control

• Phase-corrected balance control

Active Bass Extension

A further DSP-enabled enhancement to the audio
performance of the DSP420 is Meridian’s active
bass extension. This deepens the response of the
system without excessive woofer excursion and
in turn produces a convincingly ‘big box’ sound
from an in-wall unit. At moderate volumes, a
psychoacoustically-correct filter significantly
extends the bass response, while at high volumes
dynamic DSP bass protection is used to prevent
the woofers from bottoming.

Analogue or Digital – Your Choice

Following the success of the original DSP420, the
loudspeaker is now also available in an analogue
active version, the M420. The M420 features a
balanced line-level audio input (which may be
unbalanced), with an XLR link from back-box
to speaker unit (the digital unit is connected
to the back-box via a 15-pin DSUB cable) and
analogue crossover. The amplifiers, bass drivers
and enclosure are identical in both variants. In
addition, a redesigned back-box is available,
common to both units, that features several
design improvements based on installer feedback
from the original design. Audio and power
interfacing are built into fire-retardant boxes.

The available redesigned back-box kit includes
both analogue and digital input boards, allowing
the correct board to be installed as appropriate.
While the original screw terminals are retained,
digital audio and Meridian Comms connections
also employ BNC connectors, while analogue
audio is on XLR. Power is hard-wired into the
back-box and supplied to the speaker assembly
via an IEC connector, thus helping to maximise
the speed and efficiency of installation.

Acoustics

The DSP420/M420 front baffle and acoustic
back box are made from aluminium. This offers
very low resonance at low frequencies and is
further damped by the incorporation of stiffening
into the back-box. Additional high frequency
damping means that the whole system suffers
exceptionally low cabinet colouration and delivers
excellent mid-range transparency. All damping
materials have been fully tested and in all cases
comfortably meet or exceed building regulations
for in-wall design.

The bass drive units are two parallel 5in woofers
with cast alloy chassis, carbon fibre cones and
very large shielded magnets that provide excellent
drive and control.

The tweeter (aluminium-domed in the DSP420,
silk-domed in the M420) has a Neodymium
magnet and a protective grille, while an
acoustically transparent grille protects the front
baffle and drive units from harm when installed.
Its powder finish means the grille can be easily
painted, helping the unit to blend in with its
surroundings.

Introduction

The DSP420 Digital In-Wall Loudspeaker System
uses high technology digital signal processing to
remove the compromises previously associated
with in-wall speakers, allowing them to achieve
the same clear open sound and wide frequency
response as traditional free-standing speakers.
The M420 Analogue In-Wall Loudspeaker System
employs a similar design to the DSP model, but
instead of digital inputs provides a line level
analogue audio input.

DSP420 or M420 loudspeakers are ideal as part
of a home theatre system, or as the basis for a
compact stereo system where the loudspeakers
need to be hidden or unobtrusive.

Available accessories

The DSP420 is shipped ready to be used as a
speaker in a small Meridian Digital Theatre with
a Meridian optical disc player such as the 800 or
G98, or a Meridian Digital Surround Controller
such as the 861 or G68. The M420 may be
attached to a controller or preamplifier with
analogue outputs at line level.

Other applications, and some advanced features,
may require one or more of the following
accessories, which can be purchased from your
Meridian dealer:

• Meridian System Remote Plus.

• G12 Remote Eye for infrared remote control
reception.

Indicator lights: (*DSP420 only)
The following table explains the function of the
indicator lights on the front panel:

Light State What it means

Red On Power supplied to speaker.
Flashing Speaker is being reset, or
speaker has overheated and
has shut down.
*Green On Speaker is locked to a digital
input.
Off Speaker is in standby.

Note: The indicator lights are blanked if the
Meridian system displays have been blanked.

Configuration: DSP420

The DSP420 can be configured either with a
PC, using the Meridian graphic configuration
program or via RS232 commands. The use of
the configuration application is described in
its manual, which can be downloaded, along
with the latest version of the program, from the
Meridian web site, www.meridian-audio.com.

RS232 control: DSP420

The primary RS232 command to which the
DSP420 responds is the Position command, which
adjusts the loudspeaker parameters according
to its position in the room. Send the command
PO followed by 0 (default), 1 or 2. 0 sets the
loudspeaker for the tweeter at ear level. Use 1 if
the speaker is near the ceiling and 2 if it is in a
corner. The complete list of RS232 commands is
available from the Meridian web site.

To reset the configuration of the DSP420

The following procedure can be used to reset the
configuration of the DSP420 loudspeaker to the
default settings, without needing a computer,
using the reset switch accessible below the front
panel.

• Turn off the power at the front panel.

• Press and hold in the reset switch, using a
suitable object such as a bent paperclip or the
grille removal tool.

• Turn on the power. The red power indicator on
the front panel will flash. When the indicator
stops flashing:

• Release the reset switch.

Troubleshooting

This section provides suggested solutions to
typical problems that may occur when setting
up the M420 and DSP420 loudspeaker(s). If you
are still not able to resolve a difficulty with the

DSP420

Digital Signal Processing
In-Wall Loudspeaker System

M420

Analogue Active In-Wall
Loudspeaker System

INSTALLATION & OPERATION