Design and Fabrication of Front Monitors

It's important to note that not all lateral reflections are deleterious to stereo imaging. Research shows that certain controlled lateral reflections can actually improve the imaging and sense of spaciousness in the soundstage.10 For example, the LR reflection shown in Table 3 is expected to be diminished by at least 10dB, perhaps more if one considers the effects of narrowing horizontal polar dispersion with increasing frequency, before reaching the listener. This reflection was thought to be negligible. The RL reflection, luckily, strikes the B-pillar trim piece and will eventually be treated with a sound-absorbing system. The RR reflection emerges from the monitor at an angle 108.9 off-axis, so its magnitude will be substantially reduced at higher frequencies. Table 3 also provides predictions for the periodicity of "comb filter" effects.

Table 3. Characterization of lateral reflections

Fabrication of the Dash-Mounted Monitors
The front monitors took almost a year to design, fabricate, optimize, and finish. The following figures illustrate the fabrication process of the monitors.

Two posts, containing internally...        read full caption Two posts, containing internally threaded M5 holes on each end, were machined from aluminum. Each of these posts was anchored to a steel cross-member below the dash and supported the base monitor above the dash.	View of the driver-side binding...        read full caption View of the driver-side binding post plate anchored to its supporting post. The plate doesn't touch any of the surrounding surfaces. A Sorbothane gasket goes between this plate and the fiberglass enclosure to help isolate enclosure vibrations from the automobile's supporting structure.	The initial shape of the monitor's...        read full caption The initial shape of the monitor's enclosure was formed using Klean Klay (Art Chemical Products, visit www.kleanklay.com). Notice the constant thickness of modeling clay would result in an enclosure with a gap between the dash, windshield, and all other surrounding surfaces of about 13mm (0.5 inch). Also noteworthy is the knife-edge molded into the clay at the front of the A-pillar and the clearance around the centerline of the A-pillar to allow for the routing of loudspeaker cables. The enclosure was designed to be clamped against the rubber door gasket on the back edge of the A-pillar for improved vibration isolation.
Once the basic shape of the...        read full caption Once the basic shape of the enclosure was formed, the steel loudspeaker transducer mounting plate, the Sorbothane gasket, and the MDF baffle plate were mounted and carefully aimed. A magnetically attached MDF jig held a laser gun site exactly between, and on-axis with, the two loudspeaker transducers to assist in precisely aiming the loudspeaker transducers. The acoustic foam stuffed behind the baffle plate represented an attempt to reduce dipolar radiation. Literally hundreds of hours were dedicated to critical listening sessions and frequency response measurements to optimize the aim of the loudspeakers for optimal balance between soundstage width, center focus, minimization of early reflections, and tonal balance.	Once the optimum aim of the...        read full caption Once the optimum aim of the front baffle was determined, Klean Klay was used to create molds for portions of the enclosure walls. After about four campaigns of mold creation and fiberglass composite lay-up, the enclosure was complete. Notice the incorporation of Cascade Audio's VB-FD into the walls of the enclosure to provide them with internal damping. Care must be taken to remove the residue left by the Klean Klay mold. Multiple wipe downs with rags soaked with acetone, followed by sanding with 36-grit sandpaper, followed by additional wipe downs, provided an ideal substrate for additional layers of fiberglass composite.	After the internal walls and...        read full caption After the internal walls and the MDF baffle were reinforced with substantial amounts of fiberglass composite composed of both chopped mat and woven roving, the internal walls of the enclosures were each painted with six coats of Cascade Audio's VB-1X vibration damper.