The invention relates generally to sound absorbent material. In a particular embodiment, it relates to a thin, porous metal sheet which, when used with an air space, functions as a sound absorbent material for industrial applications.
Recently, increased attention has been focused on noise pollution, including that generated by the use of machinery, such as drills, lathes and the like. Noise is a problem to the operator of the machine, as well as to those in the area where the machine is being operated. As a result, efforts have and are being made to prevent or to reduce the noise level of machinery in order to provide a safer, quieter work area.
Attempts have been made to silence or to reduce machine noise by lining the inside of the machine, or housing surrounding the machine, with a material which will soak up or reduce the noise. It is important that the sound absorbent material be relatively inexpensive in addition to being an efficient and effective sound absorber. If the material is too expensive, the expense will make its use prohibitive even though it is efficient and effective, especially considering the number of machines which would use the material. Thus, an inexpensive material would find greater use, even where it was inefficient or would eventually become ineffective and have to be replaced, because of its low cost.
A typical lining material for machinery is open-cell polyurethane foam, which is a resistive sound absorber. It is a relatively inexpensive material, and it will reduce the noise level by providing a resistance to the passage of sound emanating from the machine. But, open-cell polyurethane foam has a tendency to soak up oil and the like used to lubricate the machine. Once the cells of the sound-absorbent foam material fill with oil, the material becomes noise reflective, and so is inefficient and ineffective. Further, the accumulated oil represents a fire hazard. Another sound absorbent material is the non-woven fiberglass pad which is similar to open-cell foam in its operation, and likewise becomes ineffective and/or hazardous due to oil absorption.
Other sound absorbing materials and structures are known in the art, but these materials are too sophisticated, too complicated and/or too expensive. Often the construction materials are expensive, ineffective, inefficient or hazardous, such as with paper, wood or asphalt materials. Such structures are not necessarily inoperative, as they are useful for general acoustical applications, but they are not useful in association with noise generating machinery.