Bose Direct / Reflecting 901 Series 4 - Manual (Page 14)

V. Living with your BOSE 901 Loudspeakers
The effect of listening room acoustics Is to radically modify
the tonal balance of any loudspeaker. This effect can be
greater than the difference between two loudspeakers of
substantially different cost.
As part of its ongoing research in sound reproduction, BOSE
Corporation has carried out an extensive program examining
the acoustic properties of a wide range of listening rooms.
The development of the 901 Series IV loudspeaker is an
important result of this research and development. The 901
Series IV loudspeaker system solves the problem of the effect
of the room on speaker performance with a new equalizer
design that provides controls specifically designed to compen­
sate for the effects of room characteristics, musical sources,
and speaker placement.
A contribution in achieving this new performance is the new
driver used with the 901 Series IV. This new driver assembly
has an improved efficiency in the range of 10-15 kHz.
Improvements in components, adhesives, and manufacturing
techniques have also made possible further improvements in
the high-power handling capability of the driver. The power
handling capability of the speaker system has been improved
to the point that there are no restrictions on the size of the
amplifier used with the 901 Series IV in non-commercial ap­
plications. providing the fusing recommendations in this
owner’s manual are followed.
The combination of new equalizer controls. Improvements in
high-frequency efficiency, and high-power handling capabili­
ties make the 901 Series IV speaker system unusually flexible
with respect to location In the listening room, room acoustics,
and choice of power amplifier.
A. SOURCE AND ROOM COMPENSATION CONTROLS
The 901 Series IV Active Equalizer Controls have been design­
ed from a radically different vantage point. Currently available
tone controls found on amplifiers and receivers feature bass
and treble controls that are primarily designed around estab­
lished circuits. These circuits were designed without any
specific compensation requirement and therefore cannot
compensate for the specific effects of room acoustics.
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For example, most current bass controls not only adjust the
mid-bass normally affected by room acoustics, but also the
deep bass and lower midrange. Also, adjusting the treble con­
trol, will adjust the extreme highs out of proportion to the
upper treble and midrange. The new 901 Series IV equalizer
addresses this dilemma with two new controls called Source
and Room Compensation Controls.
Certain portions of the midbass of any speaker system will
tend to vary dramatically as a function of listening room
acoustics. BOSE has addressed this problem with the LOW
FREQUENCY CONTROL that provides up to 16 dB Of change
in the 100 to 400 Hz range. This frequency contouring circuit
is designed to provide the compensation required to match
the acoustics of your listening room.
The HIGH FREQUENCY CONTROL is a shelving function that
begins affecting the sound at 1 kHz and can significantly ad­
just
the speaker's presence and sonic detail over the
midrange and high-frequency range without sacrificing perfor­
mance at the extreme high frequencies. Regardless of the
acoustics of your listening room, this control allows the
speaker system to achieve the correct spectral balance.