The Properties of Felt in the Reduction of Noise and Vibration

In order to provide engineering information for the use of felt in vibration isolation, the dynamic stiffness and damping of three widely different grades of felt were measured by means of resonance curves. The dynamic stiffness, which was much greater than the static stiffness, decreased with amplitude so that the resonance curves were unsymmetrical. Except for pressures below 6 p.s.i., the stiffness modulus of felt increased with static pressure at a rate which made their ratio nearly constant. The natural frequency of a mass supported by a felt pad is, therefore, nearly independent of the static pressure load on the felt. Curves are given showing natural frequencies for 1 inch thicknesses of soft, medium, and hard felt for a range of static pressure between 1.5 and 100 p.s.i. It is shown that, except at low pressures, there is little difference in the natural frequency of hard or soft felt, and that there is a low limit of about 20 c.p.s. for 1‐inch felt.