3. Minimize the vertical separation between the tweeter and midrange loudspeaker transducers.
The midrange transducer would be mounted as closely as possible to, and on-axis with, the tweeter in an attempt to achieve not only point-source coherency and uniform off-axis horizontal polar dispersion, but also to minimize the effects of lobing. As you'll see later in the discussion of the fabrication process, the center-to-center distance between the tweeter and the midrange transducer was reduced to only 107mm (4.21 inches), well below the expected wavelength (5.06 inches) of sound at the crossover frequency, by the use of a special mounting scheme.
4. Align transducers horizontally.
The horizontal driver separation between the tweeter and the midrange transducers would be physically minimized in an attempt to optimally align the acoustic centers of the transducers.
5. Minimize diffraction.
The loudspeaker enclosures would be fabricated with smooth contours and generous radii, greater than 50.8mm (2 inches) on all sides, to minimize the effects of diffraction. The internal shape of the enclosures would consist entirely of curved and non-parallel walls to minimize the effects of internal standing waves. In addition, the enclosures would be mounted to the automobile in ways that would minimize the transmission of enclosure vibrations to the structure of the automobile.
6. Isolate a rigid loudspeaker transducer mounting plate from the enclosure.
Each tweeter and midrange loudspeaker transducer would be mounted to a steel baffle plate. The steel baffle plate, chosen for its favorable mass and rigidity, would sandwich a constrained damping layer against the MDF and fiberglass composite enclosure.
7. Maximize enclosure rigidity and damping.
The fiberglass composite enclosures would be fabricated to achieve maximum rigidity and treated with a variety of damping materials to minimize extraneous noise from the enclosures.
8. Optimize imaging.
The placement and aim of the tweeter and midrange transducers would be determined by critical listening evaluations designed to arrive at the best balance between soundstage width, center focus, minimization of early reflections, and tonal balance. The ideally sloped windshield and headliner in the cockpit of the Dodge (Mercedes-built) Sprinter essentially precluded the existence of detrimental reflections from above the listening position. In addition, the high placement of the monitors above and at the front edge of the dash, along with other geometrical and physical parameters, essentially precluded the existence of detrimental reflections from below the listening position. The virtual elimination of these detrimental vertical reflections was expected to substantially improve the stereo imaging.
Figure 6 shows the geometry of the cockpit relative to the listening position. It's important to note that this geometry was measured and documented only after hundreds of hours of critical listening to establish optimal imaging. Lines of direct and reflected sound were mathematically determined and illustrated in Figure 6. The nomenclature for the reflections is as follows. The first letter indicates the source of the reflection, either the left or the right channel, indicted by an L or an R, respectively. The second letter indicates the side of reflection, L for the left side and R for the right side. The data in Table 3 characterizes the lateral reflections illustrated in Figure 6.