Bose 901 - Manual (Page 12)

position, it reduces turntable rumble and other low frequency distur­
bances in a manner that has much less effect upon music than that
caused by conventional rumble filters. This is achieved, as shown in
Figure 4, by a unique filter design which provides a uniform attenuation
below 40 Hz while causing no audible amplitude or phase deviations
above 50 Hz.
TREBLE LJSVEL AND'TREBLE CONTOUR - The combination
of these two switches provides a wide range of control over the reproduc­
tion of notes in the higher octaves of the musical scale. It has long been
recognized that the better speaker is more sensitive to the quality of
program material and the more selective the listener must be in choosing
his recordings. The purpose of these switches is to extend the excellent
performance attainable with good recordings to an extremely wide range
of commericial recordings and to enable you to exercise personal taste
with respect to music reproduction in your particular listening room.
When the TREBLE LEVEL control is in the dot position, the
high frequency response of the system may be varied by moving the
TREBLE CONTOUR syitch. The highs maybe either increased or de­
creased as shown in Figure 4.
When the TREBLE LEVEL switch is in the DECREASE position,
the system reduces the response in the midrange and highs. The degree
of reduction obtained may be selected by the TREBLE CONTOUR switch.
Unlike ordinary tone controls, the response of the system remains at
a fixed level for high frequencies and does not continue to fall, as shown
in Figure 5. This enables a reduction of response in the midrange (such
as the sound of violins) without destroying the timbre of the instruments
and without eliminating the very high frequencies (affecting percussion,
for example).
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