An improved resonance apparatus for materials characterization is described. The apparatus accurately determines the propagation constants of an extensional acoustic wave by exciting a bar of material at one end with a noise source, while the other end is allowed to move freely. Miniature accelerometers measure the acceleration at two locations and their output signals are analyzed by a dual channel FFT spectrum analyzer. At certain frequencies, the acceleration ratio goes through resonant peaks whose amplitudes and frequencies are related to the Young’s moduli and loss factors of the material. The apparatus is capable of measuring the acceleration ratio over a frequency range of 25 Hz to 20 kHz. As illustrations of the technique, Young’s modulus and loss factor were determined on a viscoelastic material; polyurethane (over a temperature range −13.4° to 81 °C) and on two metal matrix composite materials: a silicon carbide–aluminum and a graphite–aluminum. The apparatus was found to be a fast and reliable method to determine dynamic constants.