Proceedings of the Institute of Acoustics
Table 12. Use of available room response controls.
Room Response Control
Usage vs. availability
% Usage
Midrange Level
27/33
82%
Treble Level
22/33
67%
Bass Tilt
37/67
55%
Treble Tilt
11/37
30%
Bass Level
8/33
24%
Bass Roll-off
10/67
15%
Appendix D shows quartile difference and RMS deviations for each loudspeaker in the study, for the
broadband and each subband. The quartile difference or RMS deviation after equalisation is sub-
tracted from the same before equalisation. An improvement will produce a negative value of differ-
ence. Quartile difference and RMS deviation values represent different ways to look at the deviation
from the distribution median value. Quartile limits are more robust to outlier values while the RMS
value is affected by them.
For small two-way systems (Figures 9-10
41
), the main improvement is seen at low frequencies in
four out of 12 cases. Only in one case is there is a significant improvement in the broadband flat-
ness.
The broadband flatness of the two-way systems is improved in four (quartile data, Figure 11) or
eight (RMS data, Figure 12
41
) cases out of 22. An equal number of reductions and increases of low
frequency quartile values can be seen. MF subband quartile values improve in one case and dete-
riorate in 5 cases while there are no changes in the HF subband. The flatness in the broadband and
LF subband as indicated by RMS deviation data has improved, indicating a reduction of outlier val-
ues. The MF and HF subbands show no changes or a slight increase of the RMS deviation.
Three-way systems show in most cases a clear reduction of both the quartile difference (Figure
13
41
) and RMS deviation (Figure 14
41
) for the broadband and LF subband. There is no significant
change in the MF and HF subbands.
A similar trend is seen for the three large systems included in this study (Figures 15-16
41
). Mainly
the LF subband flatness is improved and this is reflected in broadband flatness improvement.
Some responses appear to worsen in terms of quartile difference and RMS deviation in the sub-
band analysis. This was not evident in the broadband metrics, indicating that the arbitrary definition
of subband frequency division introduced some error. The cases where this happened originally suf-
fered from severe response anomalies due to extremely bad room acoustics. The equalisation was
not designed to compensate for such problems.
Subband median level differences (Figure 3) demonstrate the broadband frequency balance.
Acoustical loading of a loudspeaker by nearby boundaries is reflected in the LF subband median
level before equalisation, especially for three-way models that are typically flush mounted. The me-
dian level of the LF subband is reduced by equalisation, indicating that equalisation compensates
well for this loading. Smaller difference in median values across subbands shows that equalisation
has improved broadband flatness. The largest improvement is seen in three-way loudspeakers. For
two-way systems equalisation has improved broadband flatness only marginally. The broadband
flatness improvement is mainly a result of better alignment of the LF subband with the MF and HF
subbands. The equalisation has not only reduced the variation inside individual subbands but also
improved the broadband flatness of the acoustical response. This should translate to a reduced au-
dio colouration at the listening position.
All loudspeakers pooled together (Figure 3), equalisation reduces median value variance for the LF
subband for all loudspeaker types. Only in three-way systems an improvement is seen also in MF
and HF subband median value variances.
Figure 4 shows pooled results for all products and results for each product cathegory, excluding the
three main monitors. For all models, the broadband flatness has been improved (by 0.4 dB), and
the RMS deviation has been reduced. The largest reduction is seen in three-way systems. To some
extent, the result is similar for the quartile difference but the small two-way and two-way systems do
not experience such large improvement. This indicates that the improvement is mainly a reduction
of extreme magnitude values (peak height and notch depth) in the low frequency response.
