2 :
B a s s M a n a g e m e n t
Bass Management in Domestic Systems
This section aims to clarify some of the issues surrounding the
use of Bass Management (or bass redirection as it is sometimes
known) in ATC multichannel systems. Topics discussed apply to
the whole range of ATC systems and can be used for guidance
when making installation decisions. Differences in professional
and domestic requirements dictate slightly different approaches
to Bass Management. In the recording studio, the primary aim is
to achieve a result which will transport well to a range of
domestic equipment and listening environments, whilst retaining
the artistic intentions. These notes however focus on the needs
of the domestic user which are rather more particular. The
primary function of Bass Management in domestic applications
(home theatre or multichannel audio only reproduction) is to
increase the dynamic range, or the total sound pressure that can
be delivered by the speaker system. However, depending on the
performance of the loudspeakers in use, this priority may not be
appropriate in some situations – this is commonly the case when
using ATC loudspeakers. Switching off Bass Management in the
majority of AV processors is simply a case of ensuring that the
Subwoofer output is turned “ON” and that all satellite speaker
size options are set to “LARGE”.
The advent of multichannel reproduction technology in the
home has led to the desire for inexpensive and robust speaker
systems which can reproduce high sound pressure levels.
Unfortunately the latter two requirements are in direct conflict
with the former. Obviously, the simplest way of reducing the
retail price of a product such as a loudspeaker is to cut back on
the quality of the components used.
However, when designed properly, there is a direct relationship
between the cost of a moving coil loudspeaker and its potential
dynamic range. This can be attributed to a number of factors.
For example, a drive-unit’s metal parts act as a sink for the heat
generated by its voice coil, so as the mass of steel used is
reduced for cost purposes, so the speaker’s ability to handle
power is degraded. Magnet size and diaphragm area also tend to
be reduced in an attempt to cut costs. Again, the trade-off is
efficiency and dynamic range, both of which suffer as the
compromises are made.
A convenient way of helping a low power system to deliver
more sound pressure is to divert the potentially more damaging
low frequencies away from the vulnerable speakers and into a
Subwoofer. Bass Management was devised to perform this task
in the digital domain. It is a system of software filters and gain
controls commonly fitted to AV processors/decoders that can
redirect low frequencies away from the satellite speakers
(left, centre, right, surround left and surround right in a 5.1
configuration) and route it to the dedicated low frequency
channel. Because the processing is done in software it is virtually
free of cost and thus attractive to those who wish to maximise
the dynamic range of a modest speaker system.
Compromises
As described earlier, Bass Management was devised for domestic
use as a means of extracting more performance from cost-
sensitive systems. However in high quality audio systems it
should be avoided. The improvement in dynamic range that may
be achieved with Bass Management is not without side effects
and in high quality systems these side effects are significant.
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