The dynamic properties of isotropic magneto-rheological rubber are examined through experiments within an audible frequency range covering 100 to 1250 Hz while applying an external magnetic field of 0 to 0.8 T. The shear modulus for this manufacturer convenient material, consisting of dispersed irregular, micrometer sized iron particles in a nitrile rubber matrix, is found to depend strongly on both frequency and magnetic field, while the loss factor is almost independent of those factors. Magneto-rheological rubbers applied to vibration isolators promise to have more functionality than conventional isolators while rapidly and reversibly change rigid body and stiffness peak frequencies.