© Hybrid Audio Technologies, 2010
Page 16 of 22
In scenario “a”, we show the installation of the I5 in the dashboard, high in a door panel, or a-
pillars. As you can see from the diagram, the PLD’s between the left and right speakers are
large, due to the proximity of the listener to the near-side speaker. While the mounting of
primary drivers in the dashboard or a-pillars has become increasingly popular, this
configuration will undoubtedly require both time and intensity domain equalization in most
vehicles to ensure a good, focused center image, properly located in the center of the vehicle
for
one seated position
. There are, however, some rare exceptions, and you may actually
find that the dashboard locations provide the best equalized PLD of the available mounting
locations; this is very rare though – in our experience, less than one percent of vehicles on the
market today have optimized dashboard speaker locations for the midbass drivers.
In scenario “b”, a typical door installation location is shown, and in many vehicles represents a
good improvement in PLD’s from the dashboard, high in the door panel, and a-pillar location
identified in scenario “a.” The door speaker installation scenario is the one detailed in the
basic installation section at the beginning of this manual, and in most vehicles represents a
satisfactory location to mount speakers; not ideal but satisfactory. The door speaker
installation scenario will likely also require some amount of time and intensity equalization to
ensure a centered image in most vehicles; this can be as simple as adjusting the balance
control on your source unit, to more advanced ways of digital time and intensity manipulation.
The third and final potential mounting location as shown in this diagram (scenario “c”)
represents a kick panel installation, where the midbass are placed far forward in the A-frame
cavity of the kick panels, present in most vehicles. The kick panels are the small panel next to
the throttle and brake pedals, down by your feet. While it is not immediately obvious looking
at a two-dimensional drawing, in many cases the kick panel location affords the best
equalization of pathlength differences for most vehicles. And the reason why this is a good
choice for most vehicles is defined in the second full paragraph of Lesson Three, below.
The lesson to be learned here is that by taking a few moments to evaluate the potential
mounting locations in your vehicle, in a very short period of time, you will be able to find the
best location for your I5 midbass by determining the location with the smallest PLD.
Lesson Three: The Effect of HRTF, ITD, and IID
Head-related transfer function (HRTF), interaural intensity differences (IID), and interaural
time delay (ITD) all play a key role in the optimum placement location for the Imagine
component speakers. A sound wave approaching the eardrum from your chosen speaker
location is shaped by interactions with the size and shape of your head, torso, and outer ear,
resulting in the HRTF. More specifically, the HRTF is the ratio between the sound pressures of
the wave at the eardrum, as compared to the sound pressure that would exist at the center of
the head if the head were removed. In general, the sound arriving at the ear further from the
source is attenuated and delayed relative to the sound arriving at the ear closer to the source.
This generates an interaural intensity difference (IID) and an interaural time delay (ITD). As a
sound approaches the head, the ratio of distances from the speaker location to the near and
far ears increases, and the effects of head-shadowing are amplified, causing the IID to
increase. The spectral shaping caused by the head and the shape of the outer ear may also
