Hybrid Audio Technologies Legatia-Series, Руководство пользователя

Страница: 56 / 65

Legatia User’s Manual ©Hybrid Audio Technologies Page 56 of 65
In scenario “a”, we show the installation of the Legatia midbass in the dashboard, high in a door
panel, or in the dashboard. 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 Legatia 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 Legatia 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
change. The ITD, which results from the absolute difference in path length from the source to the
ears, remains approximately constant as distance decreases. From this we learn:
•
ITD is the dominant factor for frequencies below about 500 Hz;