Xact Sound

The steering column support structure was then redesigned to minimize its size, getting it out of the way of the sound. The gauges (see sidebar) and controls were relocated to the center console area and the factory air conditioner system was totally removed. The modifications didn't stop there (see caption on the steering wheel).

Originally the Alpine DVI-9990 was mounted below the sound quality subwoofer in the center stack but ultimately the faceplate was relocated to a central location above the sub for better visibility. Behind the gauges and remote in the center console are a bank of switches to control important system functions: trunk open/close, system neon lighting, parking brake actuator, system and interior fans, audio system configuration (SQ only, SQ + SPL sub or SPL sub only) and hazard lights.

"The first step in the interior design was to locate the seats as far rearward and towards the center as possible. This allows the listeners to be further from the speakers and more centered between them. This minimizes the path length difference between the left and right speakers, allowing for a more coherent wave front with minimal time arrival and intensity differences, resulting in a much more controlled and stable soundstage and spatial qualities," says Biggs.

The rest of the interior is totally custom, but the modifications certainly can be characterized as low key. While it certainly isn't an OEM style, it isn't over the top as is often the case in show cars at this level. The primary goal, while using a variety of materials (paint, Ultraleather vinyl, suede, alligator skin, carpet, grille cloth and some tasteful aluminum details) and construction techniques, was strictly to optimize the listening experience. The cumbersome Mercedes OEM seats were discarded, replaced by Sparco sport seats reupholstered by Southeast Auto Trim in Tulsa, OK.

Behind the seats, the rear panel showcases the 15" JBL subwoofer, which seems to almost float above its enclosure. Petracca noted that throughout the installation, there are no visible fasteners. All fasteners are hidden behind trim pieces, OEM-style, to help with the overall clean appearance of the installation.

While discussing the system, Eldridge, Biggs, Buller and Petracca explained that the placement of the speakers eliminates the early reflections from hard surfaces near each speaker. "There is no way that any electrical signal processor can correct for acoustical problems in the listening environment," says Eldridge. "Once the signal is converted to mechanical energy and leaves the speaker as a sound wave, it is at the mercy of the acoustical environment within the listening space." The design of the system and the placement of each speaker either eliminates reflected sound or directs the energy to surfaces specifically designed to absorb these signals."

Import TuningAbove the subwoofer, flush-mounted into the rear deck, the pair of Alpine PXA-H990 processors are mounted between the rear speakers. Each speaker in the system is on a dedicated signal processing and amplification channel. No passive networks are used in the system.

The crossover points for the system are set at 2.8kHz between the mids and tweeters, 260Hz between the midbass and mids, and 80Hz from the sub to the midbass drivers. The crossover slopes vary from 12dB/octave to 36dB/octave, depending on what yielded the best sound quality for each set of speakers.

Signal delay is used only to align the speakers in each channel (i.e., the left tweeter, mid and midbass are all aligned, as are the center mid and tweeter, etc.). There is no differential delay between left and right channels. Because of the attention to detail in the design and installation of the speaker system, a differential left-right delay would not improve the sound quality from either seat.

The system required very minimal equalization, again due to the attention paid to the speaker system installation.

The all-important full-range speaker requirements were also filled by Zapco with an all new line of separates. Zapco, a subsidiary of ARPA of America, turned to Italy and corporate cousin ESB, for the line of hand-built separates that will form the basis of Zapco's new Competition Series. The speakers feature ESB's latest technology and will arrive at Zapco dealers in the first quarter of 2006.

Employing Alpine's PXA-H990, the install team spent 60+ hours tuning over a six-week period and found the DTS Neo algorithm provided the best overall sound quality. Compared to the traditional 2-channel setting, it added additional space to the left and right sides of the soundstage, additional depth and a better sense of ambience. This is not to say that DTS Neo will work best in all systems. Every system design is different, and it is likely that one of the other settings may work better in a different vehicle.The past 15 years of competition has rewarded Petracca with lifelong experiences and friendships. For him the best part has been seeing new people entering the hobby and bringing new outlooks and techniques that keep the old timers on their toes. He says, "The best advice I could give to a newcomer would be, get involved in our hobby for the love of music, cars and meeting people. If you do this for awards and accolades alone, the end result of your experience will not be nearly as rewarding."