Dynaudio AIR 15, Reference Manual

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Appendix: Acoustics
Dynaudio Professional AIR reference manual – 2014-09-28 117
Bass management
Bass management is a very important and useful tool
– and it is in general an absolute necessity if you want
to work with a five channel setup in a small room. The
bass management system is designed to subtract the
bass contents from all main channels and reproduce it
using a subwoofer. The AIR series provides a number
of possible crossover frequencies that can be selected
by the user.
Fig. 79: Basic bass management setup
Checking summing phase cancellation
In a basic two channel setup or a five channel setup
(such as ITU-775), a subwoofer is not specified and is
not required. But when creating audio that should be
played back using consumer equipment, one has to en-
sure that the mix will sound right in this situation. Many
consumer setups today contain a subwoofer. Accord-
ingly, it is very important to check what bass summing
will sound like. If the program material basically is out
of phase, the bass will be canceled when summed elec-
trically. But this is not the case if the bass signals are
reproduced by the main monitors and summed acousti-
cally. The difference can be dramatic!
Controlling standing waves
It can already be difficult to position two monitors cor-
rectly in order to prevent the excitation of the standing
waves. But placing five monitors is even more difficult.
In theory, each monitor should play under the same
conditions – but this is rarely the case.
Three front monitors can normally be placed away from
disturbing boundaries to prohibit the excitation of the
standing waves. But in small rooms, the rear monitors
are very often placed in corners or on a wall. Having
the full frequency range reproduced from such monitors
may lead to serious problems, resulting in poor low fre-
quency distribution in the room. This is another reason
for using bass management.
Simply put: When working with bass management, only
one monitor – the subwoofer – has to be placed in a
“safe” position. The crossover frequency can be set to a
value just above the problematic frequency range.