User manual

System Installation
Bass Management
• High quality systems have enough dynamic
range and bass extension without the use of
Bass Management.Less software processing of
the source material implies less potential for
undesirable artefacts.
• High quality active speakers often have built-in
protection against the extreme low
frequencies responsible for the majority of
undesirable bass-related effects so
underminining the value of Bass Management.
This is the case for ATC active speakers.
• Without accurate knowledge of the acoustic
character of satellite and sub-woofer it is
impossible for Bass management to achieve a
flat overall frequency response. Similarly the
phase response will be unpredictable.
• Bass Management encourages the crossover
frequency between sub-woofer and satellites
to be above the onset of directionality in the
sub-woofer output. The resulting ability to
hear the location of the sub-woofer is clearly
to be avoided.
• When a significant proportion of the
frequency range is separated from the
satellites and passed to the sub-woofer, any
difference in the dynamic behaviour between
the two types of loudspeaker will cause the
system frequency response to change with
output level.
• The addition of filter slopes to the existing
roll-off shapes of the loudspeakers may incur
time-domain ringing and audible colouration.
5.4 Conclusion
There is good argument for the use of Bass
Management in modest, cost sensitive systems
with restricted dynamic range. However, when
applied to high quality systems the side effects are
likely to be intrusive.We strongly recommend that
Bass Management should not be used with ATC
loudspeakers in domestic applications.
5.2 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 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 Sub-woofer 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 sub-woofer. 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.
5.3 Bass Management Compromises
As described above,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. The reasons for avoiding its use in high
quality systems,such as ATC systems,are these:
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