Genelec response controls Manual

Performance Comparison of Graphic
Equalisation and Active Loudspeaker Room
We compare the room response controls available in active loudspeakers to a third-octave graphical equaliser. The
room response controls are set using an automated optimisation method presented in earlier AES publications. A
third-octave ISO frequency constant-Q graphic equaliser is set to minimise the least squares deviation from linear
within the passband in a smoothed acoustical response. The resulting equalisation performance of the two methods
is compared using objective metrics, to show how these standard room response equalising methods perform. For all
loudspeaker models pooled together, the room response controls improve the RMS deviation from a linear response
from 6.1 dB to 4.7 dB (improvement 22%), whereas graphic equalisation improves the RMS deviation to 1.8 dB
(improvement 70%). Both equalisation techniques achieve a similar improvement in the broadband balance, which
has been shown to affect a subjective lack of colouration in sound systems. The optimisation time for a graphic
equaliser is up to 48 times longer compared to that for active loudspeaker room response controls.
1. INTRODUCTION
The purpose of room equalisation is to improve the
perceived quality of sound reproduction in a listening
environment. Electronic equalisation to improve the
subjective sound quality has been widespread for at
least 40 years (an early example is [1]). Equalisation is
prevalent in professional sound reproduction such as
recording studios, mixing rooms and sound rein-
forcement. In-situ response equalisation is often im-
plemented using third-octave equalisers, which are
normally set with the help of real time analysers. This
measurement and equalisation combination is cheap,
readily available and a relatively simple concept to
grasp with a little training [2-4]. Room response cor-
recting equalisers are now also increasingly built into
active loudspeakers, but these equalisers have an en-
tirely different approach as to how the equaliser ad-
dresses any acoustic problems of the reproduction.
Response Controls
Andrew Goldberg and Aki Mäkivirta
Genelec Oy, Olvitie 5, 74100 Iisalmi, Finland
ABSTRACT
Since the loudspeaker-room transfer function is of
substantially higher order than the equalisation filters,
the effect of either type of equalisation is to gently
shape the acoustic response [5]. The room transfer
function is position dependent, which poses major
problems for all equalisation techniques. At high fre-
quencies the required high-resolution correction can
become very position sensitive [6,7]. Even with these
limitations, in-situ equalisers have the potential to sig-
nificantly improve perceived sound quality. The prac-
tical challenge is to find the best compromise for the
parameters in the in-situ equaliser. An acceptable
equalisation is typically a compromise to minimise the
subjective coloration in the audio due to room effects.
Despite advances in psychoacoustics, it is difficult to
quantify what the listener actually perceives the sound
quality to be [8-10], or to optimise equalisation based
on that evaluation. Because of this, in-situ equalisation
typically attempts to obtain the best fit to some objec-