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Measurement
Use an MLS, TDS or two channel FFT type measurement system to directly obtain the phase fre-
quency response of the subwoofer and the center loudspeaker. In a correctly aligned system, the
subwoofer should be 180° out of phase from the center loudspeaker at 120 Hz. This is because the
bass management in the surround sound processor introduces 180° phase change at the selected
crossover frequency.
Listening
Use a CD with a deep and repetitive bass content. One person should sit in the center of the listen-
ing area and the other near the phase controls of the subwoofer. Make a very rough attempt to get
the subwoofer sounding right using the input sensitivity control then systematically set each of the
phase controls combinations so that the worst-case setting is found, i.e. the setting with the least
amount of bass (180° out of phase). This setting should be quite easy to find and then reverse the
180° phase control setting so that the system is in phase and the bass sounds full. Adjust the input
sensitivity to suit the new phase setting.
Calculation
If the listening distance from the subwoofer to the center of the listening area is the same as that
from the center loudspeaker to the center of the listening area, then the phase should be set to 0°.
A +90° phase change is required for every additional 72 cm (2'4") that the subwoofer is away
from center of the listening area compared to the center loudspeaker. The phase change control
on Genelec subwoofers is actually a phase delay (0°, -90°, -180° and -270°) at 120 Hz so some
simple maths is required to find the correct setting. For example, if the subwoofer is an extra 2.1
m (7') away from center of the listening area compared to the center loudspeaker then the phase
should be set to +270°, which is the same as -90°.
4.2.2
Using the Room Response Controls
All Genelec loudspeakers have room response controls and the larger models have more than the
smaller models to give a greater degree of control. These controls allow the installer to adjust the output
level to each driver and to change the Bass Tilt, Bass Roll-off and Treble Tilt depending on the model.
Using these controls will greatly enhance the sound of the Home Theater; unfortunately, in most cases
they are never touched. This means that the end user does not get the best possible sound out of the
system. This is a terrible shame as the controls are very easy to use, so with a little time and some lis-
tening, an installation can be transformed from a decent sounding system into an awesome sounding
Home Theater.
The main issue here is that the fear of taking away bass must be overcome. In Home Theater, it is often
thought that "the more bass, the better." This is not true, as a very bassy system will just result in listener
fatigue and a loss of intelligibility in the midrange.
Bass Tilt and Bass Roll-off
This is the most critical area of tuning a Home Theater System. Too much bass masks the
midrange thereby making speech less intelligible and guitars & vocals in music less open sound-
ing. Most loudspeakers are designed to perform best when placed on a stand away from the wall
but as soon as ANY loudspeaker is placed next to (or in) a wall or inside cabinetry, the loudspeaker
response becomes loaded, the bass response rises and midrange masking takes place. There-
fore, Genelec provides a means to reduce the bass output using the room response control DIP-
switches. Bass Tilt provides a gentle slope to compensate for boundary loading and corner loading
can be additionally compensated by using the Bass Roll-off control.
Treble Tilt (Treble Level)
The easiest control to adjust is the Treble Tilt on two-way systems (Treble Level on three-way sys-
tems). In most installations, it should be set to -2 dB. The reason for this is that most people do not
really want to hear a flat response up to 20 kHz (as done in recording studios). So, the loudspeakers
can be made a little less revealing, warmed up or rolled-off (choose the description that feels best!)
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