Fabrication Process Overhead Electronics Console - Car Audio System Build Part 5

Let's assume the reference material in this case is MDF, nominally 3/4-inch thick (actual thickness is 19.12mm). The values for modulus of elasticity, E2, for the various materials were substituted into Equation 2, along with 2.4 for E1, and 19.12 for t1, and solved for t2. Table 2 summarizes the results of the calculations. It's interesting to note that a fiberglass composite comprised of chopped stand mat would need to be 15.35mm (0.604 inch) thick to have the equivalent rigidity of the MDF reference. A fiberglass composite comprised of woven roving would need to be 12.28mm (0.483 inch) thick. It's common practice for mobile audio installation professionals to fabricate fiberglass composite loudspeaker enclosures approximately 1/4-inch (6.35mm) thick using chopped strand mat. Of course, these enclosures are plenty strong, but are they adequately stiff? Possibly not. Although this analysis applies only to flat plates, and the complex curvature of most fiberglass composite structures enhances its rigidity, it establishes important guidelines for the fabrication of enclosures and emphasizes that enclosures may need to be thicker than previously believed, if a system designer's loudspeaker enclosure rigidity goals are to be met.

Table 2. Equivalent thicknesses of materials for constant deflection.

I applied these principles and properties of materials in the design and fabrication of my audio system's structures, including the overhead electronics console, loudspeaker enclosures, headliners, and door panels. In fact, I took extraordinary measures to ensure my enclosures were as rigid as possible. For example, the loudspeaker enclosures on the dash, each of which houses a midrange and tweeter, were fabricated from 1-inch MDF, 1/4-inch steel, 1/4-inch aluminum, and fiberglass composite. The thickness of the fiberglass composite enclosure varied from 15mm to 32mm (0.591 to 1.26 inch), and weighed in excess of 106 N (24 pounds) each. The front baffle of these enclosures consisted of 1/4-inch-thick steel, 1/8-inch-thick Sorbothane (functioning as a constrained-layer damping material), and 1-inch-thick MDF backed by another 1/4-inch of fiberglass reinforcement.

The loudspeaker enclosures in the doors, each of which houses a powerful woofer, were fabricated using MDF and fiberglass composite, comprised solely of woven roving. The high specific strength and stiffness of this material was used to minimize weight and maximize rigidity. The thickness of the fiberglass composite was about 13mm (0.512 inch) in places subject to the greatest amount of deflection, which created enclosures that weighed 156 N (35 pounds) each. The mounting rings for each of the loudspeaker transducers, around which the fiberglass was securely molded, were fabricated from 52mm (2.2 inches) thick MDF.