Compensating the Acoustical Loading of Small
Loudspeakers Mounted Near Desktops
Andrew Goldberg, Aki Mäkivirta and Ari Varla
Genelec Oy, Olvitie 5, 74100 Iisalmi, Finland

ABSTRACTIn professional audio applications, small loudspeakers are often mounted on or near (within the loudspeaker’s nearfield region) large solid surfaces, such as mixing consoles, desktops and work surfaces. In approximately two-thirdsof loudspeakers mounted in such a fashion, the magnitude response is compromised in a predictable and systematicway. An upward deviation of peak value 5.0 dB ± 1.5 dB centred on 141 Hz ± 31 Hz was observable inapproximately 80% of the cases studied. An additional Room Response Control in active loudspeakers is proposed
to compensate for this aberration. A statistical analysis of 89 near-field loudspeakers helps define the correction
filter, and quantifies the effectiveness of the fixed filter design. Use of the proposed filter in an automated response
optimisation algorithm for in-situ response equalisation is demonstrated.

1. INTRODUCTION
Studies into the effects of acoustical loading on the insitu response of loudspeakers generally consider theeffects of room boundaries [1–5] and room modes [6–7].
Small two-way loudspeakers in control rooms and studios are positioned close to the listener in order to reduce room effects. These so-called “near-field monitors” are frequently positioned on the meter bridge oflarge format consoles, on some construction aroundmedium format consoles, or simply on the desktop ofa workstation control surface. Sometimes loudspeakers are mounted onto a stand in order to avoid mechanical coupling and reduce the level of the reflection off a surface. In all of these cases, acousticalloading of the surface reflection affects the in-situ
magnitude response. Assuming that the surface isacoustically solid, the desktop acoustical loading canbe predicted and is a function of the surface area. A
typical 1–3 m2 surface causes an upward deviation inDESKTOP ACOUSTIC LOADING COMPENSATIONGOLDBERG, MÄKIVIRTA AND VARLA

the in-situ magnitude response between 100–250 Hz
as well as comb filter in the mid-to-high frequencies.
The effects of a desktop (2.1 m x 1.2 m = 2.52 m2) on
the impulse response of a loudspeaker in anechoic
conditions are shown in Figures 1 and 2. A reflection
is visible about 1 ms after the direct impulse. In thefrequency domain, the reflection causes strong comb
filtering starting at 1 kHz as well as an acousticalloading related increase in level over the range 100 –500 Hz.
Impulse Response1
0.8

Other features often seen in the low frequencies areassociated with cancellations due to reflections off
nearby large acoustically solid surfaces such as thewalls, floor or ceiling. An example of 50 and 100 Hz
cancellations caused by these reflections can be seenin Figure 4.
Other cancellations can also be seen at higher frequencies. In the range 300–700 Hz there is often abroad dip in the magnitude response due to coincidence of higher frequency notches caused by comb
filtering due to reflections. An example of this can beseen in Figure 5. Also visible in this figure is comb
filtering in the range 0.5–5 kHz due to a reflection off
the desktop surface.

0.6
0.4

Magnitude Frequency Response

Pressure [Pa]

10
0.2
0

5

-0.2
0
Level [dB]

-0.4
-0.6
-0.8
-1
25

26

27

28

29

-5

-10

30

Time [ms]-15

Figure 1. Impulse response of a loudspeaker mounted
near a desktop in anechoic conditions. A reflection isclearly visible.

-20
10

Measured Response
Filter Response
Filtered Response100

1kFrequency [Hz]10k

Figure 3. A typical example of the effect of acousticalloading on the magnitude response of a loudspeaker
and the compensation filter required to correct for it.

Magnitude Frequency Response
10

5

10

-5

5

-10

0

-15
Free-field Response
Desktop Loaded Response
-20
10

100

1k
Frequency [Hz]10k

Figure 2. Unsmoothed anechoic magnitude responseof a loudspeaker mounted near a desktop. Loading
and comb filtering are visible.
In non-anechoic conditions the in-situ response is often affected by reflections off other nearby boundaries. A typical example of a notch filter being required
to compensate for the acoustical loading of a mixing
console is shown in Figure 3.

Level [dB]

Level [dB]

Magnitude Frequency Response
0

-5

-10

-15

-20
10

Measured Response
Filter Response
Filtered Response100

1kFrequency [Hz]10k

Figure 4. A notch at 100Hz caused by a reflection reduces the effect of acoustical loading. Other cancellations are also apparent.

AES 117TH CONVENTION, SAN FRANCISCO, USA, 2004 OCTOBER 28-31

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DESKTOP ACOUSTIC LOADING COMPENSATIONGOLDBERG, MÄKIVIRTA AND VARLA⎛
sin (2π f 0 /f S ) ⎞⎟⎟⎜⎜1 + A
2Q
⎠
⎝
b0 =
a0

Magnitude Frequency Response
10

Level [dB]5

− 2 cos(2π f 0 /f S )
a0

0

b1 =

-5

⎛
sin (2π f 0 /f S ) ⎞⎜⎜1 − A
⎟⎟
2Q
⎝
⎠
b2 =
a0

-10

-15

Measured Response
Filter Response
Filtered Response

-20
10

100

1k
Frequency [Hz]

a1 =

10k

Figure 5. In addition to the effects shown in Figure 2,
constructive interference at 150 Hz increases the effect of acoustical loading. Desktop comb filtering is
also visible in the range 500–5000 Hz.
The purpose of this paper is to investigate the effect of
this acoustical loading within the frequency band of
100–250 Hz on 89 in-situ magnitude responses after
having already equalised the loudspeakers using theexisting set of Room Response Controls [8–13]. Secondly, the parameters are determined for a single compensating notch filter design to equalise this upward
deviation. Finally, a statistical evaluation is conducted
to determine the benefit of applying such a “one-sizefits-all” filter individually to each of the responses. An
optimisation algorithm is used to define notch filter
parameters.
2. IN-SITU EQUALISATION
A notch filter [14] was constructed using a biquadratic transfer function of the form,H ( z) =b0 + b1 z −1 + b2 z −2
1 + a1 z −1 + a2 z − 2(1)where the scaling of the transfer function is given by
the coefficients,sin (2π f 0 /f S )a0 = 1 +
2QA

(2)

G

A = 10 20
with the centre frequency f0, sampling frequency fS,
gain of the resonance A, calculated from the dB-gain
value G, and the Q-value Q. The transfer function coefficients are then defined as,(3)− 2 cos(2π f 0 /f S )a0⎛ sin (2π f 0 /f S ) ⎞
⎟⎟
⎜⎜1 −
2QA
⎠
⎝
a2 =
a0
3. OPTIMISATION OF THE EQUALISATION
Boundaries are defined for the gain G (0 to –20 dB),centre frequency f0 (100–250 Hz) and Q-value Q (0.5
to 20). Initial values were set to G = 0 dB, f0 = 150 Hz
and Q = 4.33 (third-octave). A least squares method,
Matlab’s “lsqnonlin” function [15], minimises theobjective function,
f2

min E =m∫f = f1am ( f ) x ( f )x0 ( f )

2

df

(4)

where x(f) is the third-octave smoothed [16] magnitude of the loudspeaker’s in-situ frequency response,am(f) is the notch filter magnitude response, x0(f) is thetarget response (a flat response at 0dB) and the frequencies f1 and f2 define the optimisation band frequency range (100–250 Hz).
Visual inspection of the loudspeaker magnitude responses after equalisation shows that the algorithm isrobust in finding the global minimum.
4. LOUDSPEAKER MEASUREMENTS
The 89 active loudspeakers analysed in this study
were Genelec 1030A (15 units), 1031A (52 units) and
1032A (22 units). The loudspeaker measurements
were supplied by one of the authors (62 measurements) and by a calibration engineer (27 measurements). The measurements were selected on the basisthat the loudspeaker cabinets were known to be positioned near a large reflecting surface such as a desktop
or mixing console. Two acoustic measurement systems were used to acquire the impulse responses(Table 1).

AES 117TH CONVENTION, SAN FRANCISCO, USA, 2004 OCTOBER 28-31

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GOLDBERG, MÄKIVIRTA AND VARLA

Table 1. Settings in the measurement systems.
Measurement
WinMLS
MLSSA [17]System2000 [18]Neutrik 3382
OM2099RG2455Microphone [19]Sample rate, fs
75.5 kHz48 kHz
MLS sequence
14
14
order
Averages
1
1
Impulse response
0.217 s0.341 slengthTime window
Half-cosine
Half-cosine
FFT size
16384
16384
Frequency
4.61 Hz2.93 Hz
resolution
All loudspeakers were equalised using the existing setof Room Response Controls (Bass Roll-off, Bass Tilt
and Treble Tilt).
The RMS deviation within the optimisation range
100–250 Hz was recorded for each magnitude response before and after applying a notch filter designed individually to compensate any upwards deviation in the magnitude response. This statistic was used
to study how the objective response quality hadchanged due to individualised notch filtering.
5. RESULTS
Summary statistics of the upward deviations found in
the frequency range 100–250 Hz for the 89 loudspeaker magnitude responses are shown in Table 2.

DESKTOP ACOUSTIC LOADING COMPENSATION

upward deviations in the magnitude response in therange 100–250 Hz individually for each loudspeakermeasurement.
Despite the positioning of the loudspeakers near adesktop, 20 (22%) of the 89 loudspeaker measurements did not require notch filter equalisation tominimise the RMS deviation in the range 100–250 Hz.
These loudspeakers were therefore excluded from therest of the analysis.
The maximum height of the deviation and attenuationof the notch filter for each loudspeaker measurement
are shown in Figure 6. Figure 7 shows the same data
as a scatter plot that indicates good correlation between the peak gain in the loudspeaker measurement
and the notch filter gain. The frequency of the highest
deviation and the centre frequency of the notch filter
for each loudspeaker measurement are shown in
Figure 8. Figure 9 shows the same data as a scatterplot and again there is good correlation between the
loudspeaker measurement and the notch filter. The
notch filter Q-value for each loudspeaker measurement is shown in Figure 10. The RMS deviation in therange 100–250 Hz before and after applying a notch
filter and the change in the RMS are shown in Figure
11. Figure 20 in Appendix A shows box plots and histograms of the RMS deviation in the range 100–250
Hz before and after applying a notch filter. Also
shown is the change due to equalisation. Summary
statistics for the individually optimised notch filters
are shown in Table 3. In all cases the RMS deviation
has been reduced (improved) after the individually
optimised notch filter has been applied to each magnitude response.
Table 3. Individual notch filter summary statistics.

Table 2. Summary statistics for the upward deviations
in loudspeaker measurements within the frequency
range 100–250 Hz.
MedianPeak Frequency
Peak Deviation fromBaseline
RMS Deviation

141 HzStandard
Deviation
31.1 Hz5.00 dB

1.52 dB

3.38 dB

0.98 dB

5.1. Individually Designed Notch Filters
Third-octave smoothed magnitude responses were calculated for each loudspeaker measurement and a microphone correction applied. The pressure response ofeach loudspeaker measurement was normalised to themedian value of the range 400 Hz to 15 kHz. The leastsquares optimiser (Equation 4) was used to find theparameters for a notch filter (Equations 1–3) to correct

MedianNotch Centre Freq, f0
Notch Gain, G
Notch Q-value, Q
RMS Deviation AfterRMS Deviation
Change147 Hz–5.69 dB
5.36
2.31 dB

Standard
Deviation
27.5 Hz2.12 dB
4.91
1.13 dB–0.79 dB

0.73 dB

Scatter plots (Figures 12–14) of the optimised filter
parameters show that there is no correlation between
each of the parameter combinations, for example, alow Q factor does not correspond to a low gain or a
low centre frequency. The centre frequencies of individually designed notch filters do not in all cases coincide with the upward deviation peak values, creating
the outliers seen in Figure 9. These outliers result

AES 117TH CONVENTION, SAN FRANCISCO, USA, 2004 OCTOBER 28-31

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DESKTOP ACOUSTIC LOADING COMPENSATION

from the fact that the notch filter design considers therange 100-250 Hz, whereas the upward deviation frequency is taken to be the highest value in the upward
deviation. The highest value does not measure central
tendency of the upward deviation, whereas the notch
filter centre frequency will tend towards this value because of the design method, creating a possibility fordiscrepancy between the two.

Centre Frequency of 100-250 Hz Deviation and Notch Filter
250

200

Frequency [Hz]GOLDBERG, MÄKIVIRTA AND VARLA

160

125

Peak Value of 100-250 Hz Deviation and Notch Filter Attenuation
10

Loudspeaker Response
Notch Filter Response

8
100

6

10

20

Level [dB]

4

60

70

Figure 8. Frequency of the upward deviation and individually optimised notch filter centre frequency foreach loudspeaker measurement.

2
Loudspeaker Response
Notch Filter Response

0

30
40
50
Loudspeaker Measurement-2-4

Scatter Plot of L/S Meas. Peak Freq. vs. Notch Filter Centre Freq.

-6

250

-10

10

20

30
40
50
Loudspeaker Measurement

60

70

Figure 6. Peak value of the upward deviation and individually optimised notch filter attenuation for each
loudspeaker measurement.
Scatter Plot of Loudspeaker Measurement Peak Gain vs. Notch Filter Gain0

Notch Filter Centre Frequency [Hz]

-8

160

125

-2

Notch Filter Gain [dB]

200

100
100

125

160
200
Loudspeaker Measurement Frequency [Hz]

250

-4

Figure 9. Frequency of upward deviation and individually optimised notch filter centre frequency foreach loudspeaker measurement.

-6-8
Q-Value of Notch Filter
20

-10

18
0

2

4
6
8
Loudspeaker Measurement Gain [dB]

10

16

12

Figure 7. Peak value of the upward deviation and individually optimised notch filter attenuation for each
loudspeaker measurement.

14
12
Q-Value

-12

10
8
6
4
2
0

10

20

30
40
50
Loudspeaker Measurement

60

70

Figure 10. Individually optimised notch filter Q-value
for each loudspeaker measurement.

AES 117TH CONVENTION, SAN FRANCISCO, USA, 2004 OCTOBER 28-31

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DESKTOP ACOUSTIC LOADING COMPENSATIONGOLDBERG, MÄKIVIRTA AND VARLA

Effect of Individual Notch Filter Equalisation

Scatter Plot of Gain vs. Q-value

8

20
18

6

16
4

12
Q-Value

RMS Deviation [dB]

14
2
0

10
8

-2

6
-4
4
RMS Before Equalisation
RMS After Equalisation
RMS Change due to Equalisation

-6
-8

10

20

30
40
50
Loudspeaker Measurement

260

Figure 11. RMS deviation in the range 100–250 Hz
before and after equalisation, and the RMS deviationdifference after applying individually optimised notch
filters.
Scatter Plot of Centre Frequency vs. Gain
0
-1
-2
-3

Gain [dB]

-4
-5
-6
-7
-8
-9
-10
100

125

160
Frequency [Hz]

200

250

Figure 12. Scatter plot of centre frequency vs. gain.
Scatter Plot of Centre Frequency vs. Q-value
20
18
16
14

Q-Value

12
10
8
6
4
2
0
100

125

160
Frequency [Hz]

200

0
-10

70

250

Figure 13. Scatter plot of centre frequency vs. Qvalue.

-9

-8

-7

-6

-5
-4
Gain [Hz]

-3

-2

-1

0

Figure 14. Scatter plot of gain vs. Q-value.
5.2.

Fixed Notch Filter Based on the Medianof the Magnitude Responses
A notch filter was designed to compensate the upward
deviation in the median of the responses, and then applied to each individual magnitude response to evaluate the benefit of a fixed filter design.
Third-octave smoothed magnitude responses were calculated for each loudspeaker measurement and a microphone correction applied. The pressure response ofeach loudspeaker measurement was normalised to themedian value of the range 400 Hz to 15 kHz. The median of the 69 magnitude responses that remain in the
study was calculated. A least squares optimiser wasused to find the parameters for a single notch filter tocorrect the upward deviation within 100–250 Hz
range.
This median of the responses is shown in Figure 17.
Also shown are the upper and lower quartiles and the
10% and 90% percentiles. A systematic low frequency
upward deviation can be seen in all the percentile
curves. Figure 18 shows the median of the magnitude
responses, the notch filter to correct the upward deviation, and the equalised median of the magnitude responses.
The RMS deviations for all of the responses in therange 100–250 Hz before and after applying this notch
filter, and the change in the RMS deviation due toequalisation, are shown in Figure 19. Summary statistics for the single optimised notch filter are shown in
Table 4. Figure 21 in Appendix A shows box plots
and histograms of RMS deviation in the range 100–250 Hz before and after equalisation. Also shown isthe change due to equalisation. In the majority ofcases the RMS deviation has been improved, but 19 of
the measurements show no change or are made worse
by filtering.

AES 117TH CONVENTION, SAN FRANCISCO, USA, 2004 OCTOBER 28-31

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Table 4. Fixed notch filter design based on the medianof the magnitude responses, and the resulting statistics.
MedianStandard
Deviation
Notch Centre Freq, f0
146 Hz–Notch Gain, G–3.48 dB–
Notch Q-value, Q
3.23–
RMS Deviation After
2.99 dB
1.09 dBRMS Deviation–0.46 dB
0.51 dB
ChangeDESKTOP ACOUSTIC LOADING COMPENSATION

Magnitude Frequency Response1050Level [dB]

GOLDBERG, MÄKIVIRTA AND VARLA

-5

-10

-15

10/90% Percentiles
25/75% Percentiles
Median Response-20
10

Room Response Control Optimisation
Algorithm
The fixed notch filter based on the median of the magnitude responses has been incorporated into the automated in-situ optimiser (DIPtimiser), previously described in [9–12], as a Desktop LF Control. An example loudspeaker measurement, taken from Figure 3, isshown in Figures 15 and 16. As a result of applying
the new Room Response Control, the reported broadband RMS deviation has been improved from 2.41 dB
to 2.01 dB.

1k
Frequency [Hz]10k

Figure 17. Median and percentiles of the magnitude
responses for 69 loudspeakers.
Magnitude Frequency Response1050Level [dB]

5.3.

100

-5

-10

-15

Measured
Response

Median Response
Filter Response
Filtered Response-20
10

Equalised
Response

100

1kFrequency [Hz]10k

Figure 18. Median of the magnitude responses before
and after equalisation.
Effect of Overall Notch Filter Equalisation
8

Figure 15. Magnitude responses before and after
equalisation for the loudspeaker measurement shownin Figure 3.

6

RMS Deviation [dB]

4
2
0
-2
-4
RMS Before Equalisation
RMS After Equalisation
RMS Change due to Equalisation-6-8

Figure 16. Output section shows that only the Desktop
Control is required on the previously equalised loudspeaker.

10

20

30
40
50
Loudspeaker Measurement

60

70

Figure 19. RMS deviation in the range 100–250 Hz
before and after equalisation, and difference in the
RMS deviation, for each loudspeaker measurement
equalised with a fixed notch filter.

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GOLDBERG, MÄKIVIRTA AND VARLA

6. DISCUSSION
The existing Room Response Controls in the active
loudspeakers (Bass Roll-off, Bass Tilt and Treble Tilt)
achieve a good broadband balance but fine detail is
not corrected. Also uncorrected is a systematic effectdue to the loading from a desktop positioned near the
loudspeaker cabinet. An upward deviation of peakvalue 5.00 dB ± 1.52 dB centred on 141 Hz ± 31.0 Hz
is observable in approximately 80% of the 69 analysed cases in this study requiring additional equalisation. This effect would be expected in any conventional direct radiating two-way design mounted insuch a way, as it occurs below 250 Hz where loudspeakers of this size are relatively omni-directional.
Correcting fine detail at high frequencies may not be
as significant as correcting for the broadband frequency response balance, because the human hearing
system is more sensitive at detecting wideband imbalances than small narrow band deviations in the magnitude response [20,21]. The desktop loading at low frequencies (100–250 Hz) becomes subjectively important, creating a “boomy” sound quality, because thecritical bandwidth decreases towards low frequencies.
The acoustical loading due to a large surface or a tabletop positioned in front of a loudspeaker is independent of the listening position and the upward deviation was seen in varying amounts across all percentiles of the magnitude responses. This can be corrected using a single notch filter.
When a notch filter is optimised for each loudspeakermeasurement individually, the median improvement in
the RMS deviation in the range 100–250 Hz is 0.81
dB. The magnitude response is improved in all cases
but a spread is found in the individual notch filter parameters.
When a single notch filter (fixed filter design) is designed based on the median of the magnitude response
all the loudspeakers pooled together, and this single
filter is applied to all the magnitude responses, themedian improvement in the RMS deviation in therange 100–250 Hz is 0.46 dB. The fixed notch filter
achieves 57% of the improvement achieved by notch
filters optimised individually for each loudspeaker. 19
measurements show no change or degradation interms of the RMS deviation, so the magnitude response is improved in 72% of cases. Accounting forthe other 20 cases where no equalisation was required,establishes that 56% of loudspeakers placed near adesktop benefit from applying a fixed notch filter.
Median parameter values for notch filters optimised
individually for each loudspeaker are f0 = 147 Hz, G =–5.43 dB and Q = 5.29. The parameters of the fixednotch filter design are f0 = 146 Hz, G = –3.48 dB and
Q = 3.23. The centre frequency shows good agree-

DESKTOP ACOUSTIC LOADING COMPENSATION

ment but the gain is shallower and Q-value lower for
the fixed design. This reflects the effect of filtering
individual loudspeaker measurements before poolingrather than pooling the loudspeaker measurements before optimising the filter.
In the case of the fixed filter design, it is interesting tonote that a graphic equaliser cannot be used to simulate this notch filter, although the Q-value is similar tothat of a graphical analyser and the gain of a graphicalequaliser band can be freely adjusted, as the optimum
notch filter centre frequency lies between two standard centre frequencies 125 Hz and 160 Hz [22,23].
The proposed desktop loading compensation filter is
now available in active loudspeakers [13] and has
been successfully added to the automated optimisation
algorithm for use in automated in-situ calibrations(DIPtimiser) [9–12].
7. CONCLUSIONSThe objective of this paper was to find a notch filter
that can compensate for the effects of acoustical loading when two-way loudspeakers are mounted neardesktops.
To define the shape of the most useful fixed compensating filter, a study was performed of 89 in-situ
equalised responses of loudspeakers positioned nearlarge reflecting surfaces. The magnitude responses
were normalised and pooled to visualise any systematic effects. After equalisation using the current set ofRoom Response Controls, the remaining major featurein the magnitude response was attributable to thedesktop acoustical loading. The typical loading can be
described as an approximately third-octave wide 5 dBhigh upward deviation centred at 141 Hz.
The median of the magnitude responses was used todesign the correcting notch filter. The optimal parameters were found to be f0 = 146 Hz, G = –3.48 dB and
Q = 3.23. A graphic equaliser cannot be used to simulate this notch as the centre frequencies do not match.
Applying the correcting filter improved the RMS deviation in the range 100–250 Hz from 3.38 dB to 2.99
dB. An improvement was seen in over 50% of themagnitude responses. When a loudspeaker is mounted
near a desktop, the proposed filter can improve themagnitude response in more that one in two cases.
Given that the acoustical loading effect caused by a
nearby reflecting surface is relatively common in twoway near-field installations, an additional control has
been added to the standard Room Response Control
set built in loudspeakers. This “Desktop Low Frequency Control” is an active notch filter added in thebass channel of an active loudspeaker. The new con-

AES 117TH CONVENTION, SAN FRANCISCO, USA, 2004 OCTOBER 28-31

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GOLDBERG, MÄKIVIRTA AND VARLA

trol has also been added to the automated optimisation
algorithm for use in in-situ calibrations.
8. ACKNOWLEDGEMENTS
The authors would like to thank Christophe Anet for
supplying 20 of the loudspeaker measurements usedin this analysis and Genelec Oy for facilities to produce this paper’s content.
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DESKTOP ACOUSTIC LOADING COMPENSATION[11] Goldberg A. P., “In-Situ Frequency Response
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[17] MLSSA, http://www.mlssa.com (2004 Aug).
[18] WinMLS2000, http://www.winmls.com (2004Aug).
[19] Neutrik
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[20] Toole F. E., Olive S. E., “The Modification of
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[22] ISO 266:1997 “Acoustics – Preferred Frequencies, 2nd Ed”, International Standards Organisation, Geneva (1997).
[23] IEC 1260: 1995-07: “Electroacoustics - Octave-band and fractional-octave-band filters, 1st Ed”,
International Electrotechnical Commission, Geneva(1995).

AES 117TH CONVENTION, SAN FRANCISCO, USA, 2004 OCTOBER 28-31

9

DESKTOP ACOUSTIC LOADING COMPENSATIONGOLDBERG, MÄKIVIRTA AND VARLA

7

7

1

6

6

0.5

5

5

4

4

3

Quantity

3

2

2

1

1

0

0
ValuesValuesRMS Deviation [dB]

APPENDIX A – BOX PLOTS AND HISTOGRAMS

-1
-1.5

0

1
Before Equalisation

-0.5

-2

1
After Equalisation

15

15

15

10

10

10

5

5

5

0

0

0

2
4
6
RMS Deviation [dB]01Change due to Equalisation

0
-2

2
4
6
RMS Deviation [dB]

-1
0
RMS Deviation [dB]

1

7

7

1

6

6

0.5

5

5

4

4

3

Quantity

3

2

2

1

1

0

1
Before Equalisation

0
ValuesValuesRMS Deviation [dB]

Figure 20. Responses equalised using individually designed notch filter designs. RMS deviation in the range 100–250 Hz before applying the filters (left plots) and after applying the individually optimised notch filters (centre
plots) equalisation. Change due to equalisation (right plots).

-0.5
-1
-1.5

0

1
After Equalisation

-2

15

15

15

10

10

10

5

5

5

0

0

2
4
6
RMS Deviation [dB]

0

0

2
4
6
RMS Deviation [dB]1
Change due to Equalisation

0
-2

-1
0
RMS Deviation [dB]1

Figure 21. Responses equalised using a fixed filter design. RMS deviation in the range 100–250 Hz before applying
the notch filter (left plots) and after applying the fixed notch filter design to all responses (centre plots). Change due
to applying the fixed notch filter design (right plots).

AES 117TH CONVENTION, SAN FRANCISCO, USA, 2004 OCTOBER 28-31

10