GOLDBERG AND MÄKIVIRTA
AUTOMATED IN-SITU EQUALISATION
AES 23RD CONFERENCE, May 23-25, 2003
6
cies and a dB drop/lift value. A positive slope can
also be set but is generally not desirable. The tol-
erance lines are set to ±2.5 dB. Some relevant
slope settings include:
•
–2 dB slope from low frequency –3 dB cut-off
to 15 kHz for the large systems to reduce the
aggressiveness of sound at very high output
levels
•
–2 dB slope from 4 kHz to 15 kHz to reduce
long-term usage listening fatigue
•
–3 dB slope from 100 Hz to 200 Hz for Home
Theatre installations to increase low frequency
impact without affecting midrange intelligibil-
ity
3. ‘
Another Measurement
’ allows the user to opti-
mise a loudspeaker’s frequency response magni-
tude to that of another loudspeaker. For example,
measure the left loudspeaker and optimise it, then
measure the right loudspeaker and optimise this to
the optimised left loudspeaker response. The result
will be the closest match possible between the left
and right loudspeaker pair ensuring a good stereo
pair match and phantom imaging. Tolerance lines
are set at ±2.5 dB.
4. ‘
X Curve – Small Room
’ will give the closest ap-
proximation to the X Curve for a small room as
defined in ANSI/SMPTE 202M-1998 [7]. This is a
target response commonly used in the movie in-
dustry. A small room is defined as having a vol-
ume less than 5300 cubic feet or 150 cubic meters.
The curve is flat up to 2 kHz and rolls off 1.5 dB
per octave above 2 kHz. Tolerance lines are set to
±3 dB.
1
5. ‘
X Curve – Large Room
’ will give the closest ap-
proximation to the X Curve for a large room as de-
fined in ANSI/SMPTE 202M-1998 [7]. The curve
is flat from 63 Hz to 2 kHz and then rolls off at 3
dB per octave above 2 kHz. Below 63 Hz there is
also a 3 dB roll off, with 50 Hz being down by 1
dB and 40 Hz by 2 dB. Tolerance lines are set to
±3 dB with additional leeway at low and high fre-
quencies.
1
An example of the room equaliser settings output for
the large system optimised in Figure 1 is shown in
Figure 2. The optimised result is displayed in green
and dark grey boxes. The green boxes are room re-
sponse controls that should be set on the loudspeaker.
The light grey boxes are room response controls that
1
The room response controls do not directly support
the X Curves but it may be possible to achieve X
Curves in a room due to particular acoustic circum-
stances. This is also a good way to check how close
the response is to the selected X Curve.
are not present on the loudspeaker. Also displayed in
this area is the error function, which is an RMS of the
optimised frequency response pass band.
Figure 1. Typical graphical output of the optimiser
software. Original response
x
(
f
), target response
x
0
(
f
)
and final response
y
(
f
). Also, –3 dB cut-off frequen-
cies (triangles), optimisation range (crosses) and target
tolerance (dotted).
Figure 2. Output section displays all settings and val-
ues to be changed (green background) as well as the
value of the error function and processing time.
4. PERFORMANCE OF THE OPTIMISATION
ALGORITHM
To assess the performance of the combination of
optimisation algorithm and equalisation in the
loudspeakers, the analysis compares the unequalised
in-situ frequency response to the response after
equalisation.
The MLS measurement technique was used to meas-
ure the in-situ acoustical frequency responses. The
acquisition system parameters are shown in
Table 10.
The values in parentheses are the parameters used for
acquiring the impulse response for models that have a
bass extension below 30 Hz.
The room response control settings were calculated
for each loudspeaker response according to the algo-
x
(
f
)
y
(
f
)
x
0
(
f
)
