Acoustic absorber with barrier facing

1. Field of the Invention

The invention relates generally to an acoustic absorber, particularly for use in building interiors, that is highly resistant to the penetration of water and fine particles including microorganisms and is essentially sound transparent in the voice frequency range.

2. Description of the Related Art

Acoustically absorbing materials are known in the art for use reducing the amount of noise and/or reverberation within a given space, such as a building interior. Acoustically absorbing materials, i.e., materials having a high absorption coefficient, reduce noise by absorbing acoustic energy. There are various types of acoustically absorbing materials. One of the most common types utilizes fibrous materials to dissipate sound energy by friction within the interfibrous voids. In general, the greater the thickness and the higher the density of the absorber, the greater is the acoustic absorption of the absorber, particularly at low frequencies, e.g. below about 500 Hz. Therefore, known solutions to achieve appreciable absorption at low frequencies tend to be expensive. Many known acoustically absorbing materials are formed of unconsolidated or partially consolidated, lofty fibrous materials including compressed fibers, recycled fiber or shoddy materials, fiberglass or mineral fiber batts and felts require a facing to contain the core of fibrous materials. While the fiber-based sound absorbers are generally inexpensive and are an effective solution for sound absorption over a wide frequency range, they have inherent disadvantages, such as possible release of particulates into the air, collection of dust and harboring bacteria and mold on their surface and inside the voids, as the area is not cleanable. Other known acoustically absorbing core materials can include foam, materials having a honeycomb structure, perforated and microperforated materials utilizing additional air spaces for sound absorption. Most of the known sound absorbers also require a protective and/or decorative facing for use in a building interior.

Facings for covering acoustic absorber core materials serve as durable coverings that protect the delicate structure of the core during handling, use and maintenance. It is desirable for facings for covering acoustically absorbing materials to be acoustically transparent or acoustically absorbent in order to enhance the absorption of sound provided by the absorber. Facings which are acoustically reflective undesirably contribute to the ambient noise. There two types of known facings for covering acoustically absorbing materials: thin impervious films and porous membranes (see, for example, D. A. Bies and C. H. Hansen Engineering Noise Control. Theory and Practice. Second edition, E&FN Spoon. London, New York, p. 249). Thin, commonly 6-35 micrometers, impervious film facings are acoustically transparent in the low and mid frequencies, but they are acoustically reflective at high frequencies, as such they do not allow sound waves to pass. Thin film facings also have a serious drawback of not being durable enough to sustain everyday use and should be additionally protected by sound transparent solid surfaces. Unfortunately, this complicates the structure and raises the expense of the solution. Examples of common facings include fabric, nonwoven sheet, paper, film and perforated solid surfaces (panels).

Waterproof acoustic absorbers are known in the art in which the absorber is covered with waterproof or impervious film, such as one disclosed in U.S. Pat. No. 6,197,403. However, film facings have the disadvantage of being insufficiently durable to be used as a finished surface of an absorptive article. Also, film facings do not provide adequate acoustic absorption at higher frequencies of the most desirable voice frequency range.

Impregnated woven fabrics have also been used as waterproof facings for acoustic absorbers. A vinyl coated fiberglass, style 3478-VS-2, from Alpha Associates is one example of an impregnated waterproof facing. Xorel® available from Carnegie Fabrics is an example of an acoustic facing material, which is a woven, heavily calendered polyolefin fabric. Impregnated fabrics are generally expensive to make, thick, heavy, acoustically reflective at mid and high frequencies, and have the tendency to off-gas volatile organic compounds and support the growth of mold and bacteria unless additional additives are used.

U.S. Pat. Appl. Pub. No. 2006/0065482 discloses a nonwoven acoustic insulating material including a nonwoven layer having a low surface tension fluid repellency treatment. Specific nonwoven materials disclosed for use in the nonwoven layer are fabrics or webs resulting from melt blowing processes, spunbonding processes, air laying processes and carded web processes. U.S. Pat. No. 5,824,973 discloses a sound absorption laminate comprising a porous insulation substrate and a paper, fabric or perforated film facing sheet having an airflow resistance between 200 and 1210 rayls. These known facing materials have the disadvantage that they are open to the penetration of water, dust, mold and microorganisms, thus limiting their application for indoor use where air quality is of concern. It would be desirable to have acoustically absorbing materials that are suitable for use in a variety of critical environments having facings that are durable, waterproof, hypoallergenic, cleanable, non-linting, non-off-gassing and resistant to the penetration of moisture, dust, mold and microorganisms without impeding the acoustic absorption capabilities in the human voice frequency range. It is also desirable to have highly acoustically absorptive materials that are effective at low frequencies without incurring significant thickness, density and expense. It would additionally be desirable for such acoustically absorbing materials to be capable of being printed thereon with a graphic image and/or text.

According to one embodiment, the present invention is directed to an acoustically absorbing article comprising:

a core of acoustically absorbing material having two major surfaces; and

a facing for covering the core on at least one major surface, the facing comprising a porous flash spun plexifilamentary film-fibril sheet having a coherent surface, having a basis weight of no greater than about 140 g/m² and comprising a plurality of pores having a pore diameter between about 100 nm and about 20,000 nm and a mean pore diameter of less than about 20,000 nm.

According to additional embodiments, the present invention is directed to an assembly comprising the acoustically absorbing article encased in a sound permeable rigid casing, an acoustically absorbing partition and an acoustically absorbing architectural surface covering.

According to yet another embodiment, the invention is directed to a method of improving acoustic absorption in an environment comprising:

• • (a) providing an acoustically absorptive article comprising a core of acoustically absorptive material covered by a facing of porous flash spun plexifilamentary film-fibril sheet having a coherent surface, having a basis weight of no greater than about 140 g/m² and comprising a plurality of pores having a pore diameter between about 100 nm and about 20,000 nm and a mean pore diameter of less than about 20,000 nm; and
  • (b) positioning the article within the environment to cause ambient sound to be absorbed by the article.