Thermal Compression Compensation; Production "Cloning - Bang & Olufsen BeoLab 90 Technical Sound Manual

loudspeaker are reached (for example,
a woofer is approaching its maximum
excursion, or a power amplifier is close
to clipping) the loudspeaker either
prevents that limit from being reached,
or the transition to that limit is
"softened" (depending on the
component in question).
In addition, BeoLab 90's processing
continually monitors the individual
temperatures of many internal
components including:
Individual loudspeaker driver
magnets
Power Amplifier modules
DSP circuit boards
Power Supply circuit boards
Using this information, combined with
the power that the amplifiers deliver to
the loudspeaker drivers, the
temperatures of many more
components within BeoLab 90 are
calculated using customised thermal
models of the loudspeaker.
If the temperature of a component
inside the loudspeaker approaches its
"thermal limit" (the temperature at
which it stops working due to
overheating) the signal processing of
the BeoLab 90 adjusts the signals to
1
Note that these values have not yet been finalised.
protect the component. The exact type
of adjustment depends on the
particular component that is
approaching its limits. As a simple
example, if a tweeter voice coil is
calculated to be approaching its limit,
then its gain is reduced to attempt to
protect it from destruction.
It is important to state that this does
not mean that the BeoLab 90 is
indestructible – but it does make it
very di cult to destroy.
More information can be found in
Appendix 6: ABL - Adaptive Bass
Linearisation.
9.4 Thermal Compression
Compensation
BeoLab 90's processing includes
automatic compensation for changes in
loudspeaker driver response as a result
of internal changes in temperature.
For more an in-depth discussion of this
feature, please read Appendix 7:
Thermal Compression Compensation.
36

9.5 Production "Cloning"

Every BeoLab 90 that leaves the
production line is measured in a
custom-built anechoic chamber to
ensure that its performance matches
the master reference loudspeaker. This
automated measurement is performed
using 18 microphones (one for each
loudspeaker driver) where small
di erences in the responses are found
and custom correction filters are
created and loaded into the Digital
Signal Processing. This ensures that
each loudspeaker's third-octave
smoothed response matches that of
the master reference loudspeaker
within 0.2 dB between 20 Hz and 20
1
kHz.
Figure 9.2: An early prototype in the
anechoic chamber at the end of the
BeoLab 90 production line where ev-
ery loudspeaker is measured and cali-
brated.