5
TECHNICAL DESCRIPTION
The Bose
®
901 speakers represent a fundamental advance in realistic home music reproduc-
tion. The unique acoustic design of the speakers provide sound distribution in accurate simula-
tion of live sound. The Active Equalizer provides unprecedented accuracy and control of
frequency response characteristics.
Each speaker contains nine high compliance, full range speakers with high energy magnets to
allow large excursions without audible distortion on any program material. The speakers are
acoustically coupled to eliminate audible resonances.
The 901 speakers can be used with any high quality amplifier. Its efficiency enables operation
with moderately powered amplifiers, yet it can be used with the highest powered amplifiers to
reproduce undistorted orchestral peaks at high volume levels.
The Bose 901 Active Equalizer is a highly sophisticated electronic console containing ten
transistors and more than a hundred components to equalize accurately the stereo response
for the effects of radiation impedances, speaker characteristics, enclosure dimensions and
even for the presence of the fashion fabric grille cloth. This equalization to flat power radiation
is achieved with absolutely no audible distortion of any music or speech signals.
Active equalization of the signal before the power amplifier is far superior to passive equaliza-
tion after the amplifier because it avoids the need to handle high power and does not require
the iron-core inductors that introduce distortion in passive equalizers. In addition, it is feasible
to use many more elements in an active network to provide much greater accuracy in equaliza-
tion than is practical in the passive network.
The Active Equalizer does much more than just equalize. In addition to providing the flat
acoustic output of the Bose 901, the Active Equalizer offers the choice of nineteen additional
contours that can be selected from the front panel. This gives the listener the flexibility to
exercise his own taste in compensating for recording techniques, listening room characteristics
and the other variables described above. As an example of what is possible through active
equalization, the equalizer panel contains a switch marked "BELOW 40", which reduces
turntable rumble and other low frequency disturbances through a unique filter design that
provides a uniform attenuation below 40 Hz while causing no audible deviations above 50 Hz.
The rumble is removed without removing the life of the bass along with it.
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