| Material | Modulus of elasticity
E GPa (mpsi) | Strength”
σ MPa (kpsi) | Density kN/m³ (lb/in³ ) | Specific Stiffness
E/ρm x 106
(in x 106)
| Specific Strength
σ/ρm x 10³ (in x 10³ ) |
| MDF | 2.40 (0.348)1 | 24 (3.48)1 | 7.3062 (0.027) | 0.328 (12.89) | 3.28 (129) |
| Fiberglass composite, |
| chopped strand mat | 4.643 (0.673) | 693 (10) | 14.5724 (0.054) | 0.318 (12.5) | 4.74 (185) |
| Fiberglass composite, |
| woven roving | 9.055 (1.31) | 1415 (20.5) | 15.7106 (0.058) | 0.576 (22.6) | 8.98 (353) |
| Plywood, Baltic Birch | 7.58 (1.10)7 | 30 (4.35)7 | 7.058 (0.026)8 | 1.07 (42.3) | 4.25 (167) |
| Aluminum, 6061-T69 | 71.0 (10.3) | 276 (40) | 26.6 (0.098) | 2.67 (105) | 10.4 (408) |
| Steel, 1010 cold-drawn9 | 207 (30) | 303 (44) | 76.5 (0.282) | 2.71 (106) | 3.96 (156) |
| Table 1. Physical properties of materials common to mobile audio applications. |
There are other practical ways to use the information in Table 1. For instance, let's assume a sealed box loudspeaker enclosure is to be designed using an alternative material to MDF. For the sake of simplicity, let's assume the loudspeaker enclosure consists of six flat panels bonded together. The loudspeaker transducer produces an internal pressure, q, which acts uniformly on the walls of the enclosure, thereby producing deflections in the walls of the enclosure. The maximum deflection, ymax, in any given wall of the enclosure can be estimated using the equation for the deflection of a plate, simply supported at its edges, and subjected to uniform pressure over its entire area10:
C1 is a constant based on the ratio of plate width-to-length, q is the uniform load per unit area, b is the plate width, E is the modulus of elasticity, and t is the thickness of the plate. Equation 1 indicates that the deflection of a plate is inversely proportional to the product of the modulus of elasticity and the thickness cubed. For a given deflection, the required thickness of an alternative material, t2, may be calculated:
Where E1 and t1 are the modulus of elasticity and thickness of the reference material, respectively, and E2 is the modulus of elasticity of the alternative material.