Lesson Two: Equalization of Pathlength Differences
Quite possibly the most important functional consideration that a do-it-yourself enthusiast or professional
installer should give to the Imagine 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 drive 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, 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 0.9 milliseconds earlier than the furthest channel. It is
Hybrid Audio’s opinion that the end-user 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 still with a general “line of sight” to the speakers
(particularly the speaker on the far side of the vehicle). An easy way to test various potential locations is
to hold a tape measure or other measurement device from the potential speaker mounting locations, and
measure those locations with respect to your ears.
Reference the figure, below. In this scenario, three potential locations for the mounting of the Clarus
midbass driver are shown:
Section II • Moving Forward
Advanced System Installation
The previous section detailed a typical, basic installation of the Imagine product. In this section,
Hybrid Audio Technologies has prepared a more advanced topical discussion of Imagine
installation techniques, concepts, and principals, where a little bit of additional installation work
can net immense gains in overall sound quality.
There are certainly many things you can do to improve your mobile audio system, such as addition
of amplification, a dedicated subwoofer system, higher-gauge speaker wire, and higher-end
passive crossovers, and active crossovers. All of these things require an additional amount of
monetary investment into your audio system, and may not net the immediate gains that other,
more elementary installation items can net. The following discussion is pertinent to easy and
cost-effective enhancements you can do for your audio system, particularly as it relates to the
installation of Imagine component speakers.
In any mobile audio system, the weakest link will always be the speaker systems, followed closely
by installation techniques (sometimes its vice-versa). Since the Imagine component system you
have purchased has solved the first issue, the second issue, that being installation techniques,
can see a significant improvement as well by understanding and incorporating some or all of the
techniques in the following sections.
Lessons Learned
We like to call this our “Lessons Learned” section, where we expose some critical lessons that we
have learned through thousands upon thousands of hours of trial and error:
Lesson One: Off-Axis Response
When a speaker system like the Imagine 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 vehicular environment has a significant influence on how
natural the music sounds.
The lesson to learn here is that most mobile audio sound systems benefit greatly from having the
front stage speakers at least partially “off-axis.” Off-axis means that the speakers are not pointing at
you, but rather at some angle less than 90 degrees away from you.
Figure 1: Potential Locations for Mounting the Imagine Midbass Speakers
© Hybrid Audio Technologies • Cumming, GA • 770.888.8200
© Hybrid Audio Technologies • Cumming, GA • 770.888.8200
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