  We use a transfer-matrix method to study the localization properties of
vibrations in a `mass and spring' model with simple cubic lattice structure.
Disorder is applied as a box-distribution to the force-constants $k$ of the
springs. We obtain the reduced localization lengths $\Lambda_M$ from calculated
Lyapunov exponents for different system widths to roughly locate the squared
critical transition frequency $\omega_{\text{c}}^2$. The data is finite-size
scaled to acquire the squared critical transition frequency of
$\omega_{\text{c}}^2 = 12.54 \pm 0.03$ and a critical exponent of $\nu = 1.55
\pm 0.002$.
