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Bass Management Theory
Bass management is a method for extending the bass response of small, near-field
speakers used in 5.1 surround sound systems (familiarly called home-theatre systems). This
is done by routing frequencies below a cutoff point to a separate subwoofer
(sometimes called “bass redirection” in home-theater receivers). This can usually be
enabled by selecting “Small Speakers” from a speaker set up menu. This process places a
group of two-way filters in the speaker output path, typically at 80Hz. These filters route all
sonic energy above this given frequency (e.g. 80Hz) to the Left, Center, Right, Left
Surround and Right Surround speakers. In turn, the process redirects the low-frequency
energy from the five full-range channels to a single subwoofer, which also reproduces the
separate LFE channel.
Bass management is used in practically every consumer home-theater system. Therefore,
audio engineers mixing for modern listeners should realize that their studio monitoring
systems must be able to reproduce sufficient low frequencies so they can avoid recording
undesirable subsonic information. Without such studio monitoring, it is possible to release
a mix with infrasonic problems, such as pops, air conditioner rumble, traffic noise,
footsteps, etc. These subsonic noises will be eliminated (masked) by the natural high-pass
filter effect of using near-field monitors with a response that goes down only as low as 40
or 50Hz. Thus, infrasonic problems may not be recognized (heard) in the studio. However,
since virtually all home-theatre systems use subwoofers with bass management,
consumers will hear these infrasonic problems at high volume levels in their home.
Bass management effectively extends the low-frequency response of near-field monitors
down well into the 25 to 40Hz range (depending on the subwoofer used). This allows the
engineer to take evasive action in the studio, such as engaging high-pass filters on input
channels and microphones, adding pop filters and suspension mounts to microphones and
correcting HVAC and other rumble problems.
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