BowersWilkins DM 23 Brochure

Page 1

Technical Release Information

B&W DM23

The Design Brief

The design brief for Model DM23 followed closely on
the lines of the DMt 0 in that a compact loudspeaker
was required having orthodox styling. low cost and
good performance In addition to these requirements.
the DM23 was to be a three-driver system so that the
important midfrequency range could be covered by a
single loudspeaker driver.

Within these guidelines it was felt essential to have a
highrquality wood veneered enclosure which would
look equally at home positioned upright or on its side.

The requirementsofgood performanceand compact
size led to the natural choice ofa vented lowfrequency
system for the DM23, To keep the system cost elfectrve.
a higher than usual crossover lrequency lrom the low
frequency system to the mid-frequency system was
proposed, This yielded two benefits; firstly it enabled a
reduction .in the snze and material content ol the
crossover network to be obtained, and secondly. it
enabled the use of a smaller midfrequency system to
be used. To obtain maximum gain from the latter
benefit B&W desrgned a completely new mid-frequency
driver and enclosure for Model DM23.

Following B&Ws normal practice, Model DM23 was
designed with careful regard to its measured acoustic
performance. However, B&W view a systems subjecA
tive performance with equal importance In listening
tests on Model DM23 the system was compared With
the reference standard acknowledged by many malor
recording companies - B&Ws own Model 80l. The
overall tonal balance of the DM23 was tailored to mlmic
that ol Model 801 , resulting in a system which provides
exceptionally accurate performance for a very modest
cost.

Without Front Grill

95w DM and Series so are registered trade marks or Haw loudspeakers Lid

Wrth Optional Stand

Page 2

B&W DM23

Technical Release Information

The Drivers

The driver configuration chosen for the DM23 is the well-
known 3 invline arrangement. In view of the compact dimen-
sions and high sensitivtiy required of the DM23. a departure
from B&Ws recognised "sealed box" technique has been
made in favour of the vented-box system. This offers higher
serisrtiwty compared to a closedrbox system of the same
enclosure Size and lovHrequency cutoff for only a small
degradation in transient performance. The DM23 bass driver
is of 200mm nominal diameter and uses a rigid cast alloy
chassis and a motor system optimised for the vented system.

The midsfrequency system of DM23 was designed specifi
cally for this model to take advantage of the operating range
chosen. The 80mm diameter mid-frequency driver uses a
Bextrene cone coupled toa26mm diameterhigh»temperature
votce coil. The rigid cast alloy chassis of the driver is mounted
into a tough plastic moulding which forms the mid»lrequency
enclosure The shape of this moulding has been chosen so
that structural resonances are minimised. The airspace within
the enclosure is filled with wool to provide acoustic damping.
The complete midfrequency system thus forms a neat single
component which can be mounted directly into the low
frequency enclosure without the need for enclosure
partitioning,

The highfrequencytransducer used in the DM23 isthewell
proven TW26 design which is used in several of the current
B&W loudspeaker designs it employs a 26mm diameter
polyester weave dome coupled to a hightemperature voice
coil of the same diameter. The TW26 offers wide dispersion.
high power handling capaCIty and an excellent transient
response.

The Crossover Network

Crossover frequencies of 900Hz (low/mid) and 4 5kHz
(mid/high) were chosen forthe DM23. The chotce of 900 Hz for
the lower crossover point enabled the use of a simple 2nd
order network here to provide an attenuation rate of
tZdB/ocfave in the stopbands. The attenuation rates in the
mid/high crossover region were chosen to be1 8dB/octave to
satisfy the power handling requirement specified for the high-

frequency system. The values of the components in the DM23
crossover network were selected by a computer optimisation
program pioneered by B&W Engineers and first used for the
design of the crossover networks for the B&W Model801 . This
sophisticated design technique ensures that the best pos-
sible performance is obtained With the minimum number of
components.

All the capacitors used in the crossover are close tolerance
reversible electrolytic types. while the inductors are ferrite
cored where it is necessary to minimise series resistance.

The Enclosure Design

As mentioned in the destgn brief, two important requirements
of the DM23 were that it should have an orthodox styling so as
to appeal to a wide market and that it should be finished in a
genuine wood veneer. A skitlul application of modern mitre
folding techniques has allowed expenstve genuine wood
veneers to be combined with a very sturdy 1 8mm thick particle
board enclosure.

By using isolated tixtng screws for the lovtrfrequency driver
the excitation of structural resonances of the enclosure is
minimised The enclosure volume is partly filled with acoustic
damping material to effectively eliminate the build-up of
internal standing waves. The length and diameter of the vent
were optimised to give the best possrble extension of low»
frequency response wrth negligible extraneous noise.

The Accessories

The DM23 is a true bookshelf loudspeaker system which can
be mounted upright or on its stde. Where a freestanding
system is preferred, B&Ws STAV22 loudspeaker stand (illus
trated overleaf) is highly suited.

Conclusion

With the DM23 E!&W have created a compact three-driver
system of wtde bandwrdth. high sensitivtty and high power
output. but at a remarkably low cost. In many respects the
DM23 is modelled on B&Ws very successful DM4 system
and thus it should appeal to a very wide audience.

SPECIFICATION

Frequency Response
75 Hz to 20kHz iSdB tree-field on listening axis at 2m.

Low-Frequency System
Computeroptimised ventedbox system. cutoff (-adBJ
frequency is approximately 60 Hz for half-space loading.

Dispersion
Venical: iZdB over IO arc.
Horizontal: iZdB over 40 arc. 20 H2-20kHz.

Drive Units
Three. vertical invline.

Bass Driver BM200/23

160mm diameter laminated fibre/polymer composition cone,
26mm diameter hightemperature voice COIl phenolic restn
impregnated on a fott-lined former, Vibration-isolation mount»
ings reduce excitation of minor structural resonances.

Mlthrequency Driver MRBO/23

Newlydeveloped 80mm diameter movingcoildriveremploying
a damped Bextrene cone and a 26mm diameter high,
temperature voice coil. The enclosure for this driver is in the
form of a tough plastic "pod" which is attached directly to the
cast alloy driver chassrs thus torming a perfectly sealed system,
The enclosed volume is filled with wool to provide acoustic
damping.

High-Frequency Driver TWZSSL

26mm diamei" oolyester weave dome driven by a 26mm
diameter highrtemperature voice coil. A total moving mass of
less than 0.39 ensures excellent transient response and
extended frequency range above 20kHz.

Distortion
For a nominal s.p.|. of 95dB at lm.

Second Harmonic: Less than 3% 20Hz to SOOHz
Less than 1% 500Hz to 20kHz
Less than 2% 20Hz to SOOHZ
Less than 0.5% 500 Hz to 20kHz

Third Harmonic:

Impedance
8 ohms nominal. Magnitude does not fall below 6.4 ohms
throughout the frequency range 20Hz to ZOOKHZ.

Sensitivity
1 watt mtoB ohms fora s.p.l. ot88dB atl metre. sinewave input
at 1 kHz

Power handling
Suitable for amplifiers having powor outputs between 10 and
100 watts.

Dimensions
Height: 495mm
Width' 250mm
Depth: 240mm

Weight
9 8kg

Cabinet Finishes

Genuine wood veneer of teak or walnut.
Simulated wood veneer of rosewood or black ash.

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B&W

B&W Loudspeakers Ltd.

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Meadow Road Worthing West Sussex aNii sax England in.

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