Acoustic Energy L3 - Manual (Page 7)

Lessons Learned
Initial In-Car Set-Up; Lessons Learned
Lesson One: Off-Axis Response
When a speaker like the Legatia L3 is placed in an automotive environment we hear the direct
(shortest path) and reflected (longer path) sounds, such as resonances and reverberations.
The two sounds are processed by the brain as one sound, and this influences our perception
of height, width, and depth of soundstage, as well as rearward ambience. For this reason, the
off-axis radiation pattern of any speaker in a car environment has a significant influence on
how natural the music sounds. In general, the closer the vehicle approaches semi-anechoic
conditions (see “Acoustic Treatments” below), the less off-axis response plays a roll in the
visceral experience. The lesson to learn here is that most car audio sound systems benefit
greatly from having the front stage speakers at least partially off-axis.
Lesson Two: Equalization of Pathlength Differences
Quite possibly the most important functional consideration that an installer or do-it-yourself
(DIY) enthusiast should give to the Legatia L3 speaker placement is to optimize, as best as
possible, pathlength differences (PLD’s) in the vehicle. PLD’s are defined mathematically as
follows (this example assumes a right-hand driven vehicle---PLD’s are always a positive
number):
X – Y = Z
Where:
X = distance of the center of the left speaker from your left ear.
Y = distance of the center of the right speaker from your right ear.
Z = pathlength difference.
Applying this formula, assume that the distance of the left speaker from your left ear is
140cm, and the distance of the right speaker from your right ear is 100cm, then the
pathlength difference is 40cm.
Good stereo imaging is completely dependent on arrival times of the fundamental vocal
frequencies. Differences as little as 10 microseconds can be detected by the brain. A PLD of
30 centimeters equates to the sound from the nearest channel arriving about 9 milliseconds
earlier than the furthest channel. It is Hybrid Audio’s opinion that the installer should try to
keep PLD’s to less than 30 centimeters in a vehicle which is intended to have good imaging
and staging character from both seated positions.
The best way to go about evaluating certain locations in your vehicle is, in general, to look for
the potential locations as far forward and away from you as possible, but with still a “line of
sight” to the speakers (if you can’t see the speakers, this might not be an ideal location). An
easy way to test various potential locations is to have a friend help you hold a tape measure or
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