Specification
General Description
B. & W. D M 7 0 is a h y b r i d design employing
exclusive Model 701 11-element wide dis-
persion doublet electrostatic unit (patent
n o . 1239658), DW 13/70 high power low
distortion moving coil bass u n i t w i t h com-
plex crossover and filter u n i t and dividing
network. Relative sensitivities between the
dynamic and electrostatic units are accu-
rately equalised by a massive auto trans-
former.
The vitally important middle and upper fre-
quencies are handled w i t h o u t the attendant
phase distortion associated w i t h crossovers
in this region and the exceptionally wide
dispersion of these frequencies give a much
greater degree of stability of the stereo
image.
Alternative Cabinet stylings are available but
b o t h offer an extremely rigid critically
damped infinite enclosure w i t h l o w system
resonance. The bass driver is a no com-
promise unit capable of handling high power
w i t h extremely low distortion and employs
a specially braced cone assembly w i t h damp-
ing pads at critical damping points and the
exclusive B. & W. triple suspension.
Detailed Specification
Drive Units
DW13/70. This low frequency u n i t , of nom-
inal piston diameter twelve inches (305 mm)
is of size consistent w i t h the enclosure
volume and method of acoustic loading used.
The resulting system resonance is 40 Hz.,
the u n i t itself having a free air resonance of
approximately 28 Hz.
The cone is f o r m e d f r o m long fibre paper
material, w i t h mass adjustment and damping
(to discourage cone break-up) provided by
critically positioned rectangular section of
synthetic rubber attached to the cone face.
The massive ceramic magnet assembly, in
conjunction w i t h the low impedance of the
voice c o i l , ensures high damping leading to
excellent transient-handling capacity.
Electrostatic mid-and high-frequency u n i t .
The 701 electrostatic module (patent n u m -
ber 1239658) covers all audio frequencies
above 500 Hz. 3y virtue of the relatively
small vertical dimension of the u n i t , t h e
vertical distribution is excellent in the m i d -
frequency region and the curved geometry
of the eleven integrated modules in each
701 provides very wide and u n i f o r m f r o n t a l
radiation of sound, w i t h a strong rear
radiation pattern which can be controlled to
suit ambient conditions or personal judge-
ment.
In terms of d i s t o r t i o n , new standards are
set and reference to the figures, in the
f o l l o w i n g pages, showing harmonic content
w i l l demonstrate the extremely low levels
of the c o m m o n l y troublesome o d d harm-
onics at high sound power o u t p u t .
The power handling of this mid-high fre-
quency unit confirms research findings that
it is w i t h i n the mid-frequency band (say
5 0 0 Hz. to 5 kHz) that m a x i m u m power is
applied. The concept of the 701 electro-
static u n i t provides coverage of all audio
frequencies above 5 0 0 Hz. reducing inter-
modulation distortion and Doppler effect.
13
DW 13/70 Bass Unit