Don't lump borosilicate with snake oil. There's a reason why Totem uses this instead of the regular acoustic insulation found in other speakers.
Here's what borosilicate is.
http://en.wikipedia.org/wiki/Borosilicate_glass
This is the patent on its use;
http://en.wikipedia.org/wiki/Borosilicate_glass
From this page;
SUMMARY OF THE INVENTION
The present invention, according to one embodiment, is directed to a device or structure for acoustically controlling and attenuating various frequencies of sound, comprising a composite multiple layer acoustical absorbing coating formed of separate and distinct layers which are applied to the surface of a substrate or structure in proper sequence to each other. Usually, although not necessarily, the first layer to be applied can be a priming coat which is directly disposed on the surface of a substrate to provide a base to which the second acoustical coat can be better bonded to a particular substrate structure. The following coat is thereafter applied to the bonding primer coat as a second sound absorbing coat, which is designed to substantially absorb sound waves impinging thereon and which are transmitted through an adjacent sound transmitting medium. Such second coat can consist of an elastomer matrix, for example, of a mixture of a silicone or other elastomer, as described more fully below, and inorganic filler particles, e.g. a metal powder, such as, for example, tungsten, iron oxide, or similar metal powders. It is to be noted that various combinations of metals can also be incorporated within the elastomer depending on the acoustical problems to be solved. Hence, when the second coating is prepared for a particular application, the elastic modulus of the base elastomer and its frequency-temperature characteristics are selected from a mathematical model of the composite such that when loaded with the predetermined filler or loading material, as described more fully below, an effective sound absorbing coat is formed for the specified frequency range and temperature environment to which the structure is to be exposed. The third coating can be comprised of various materials such as a polymeric material in the form of an elastomer or resin, which may or may not include inorganic filler particles, such as powered metal or metals, or siliceous powders, to form an impedance matching coating to match approximately, or as closely as possible, the impedance of the absorber coat to that of the surrounding sound transmitting medium. Thus, the outer impedance matching layer provides a means to substantially eliminate sound reflection from the outermost surface of the composite coating by establishing an extremely low reflection coefficient.
As previously noted, where one of the layers or coatings, e.g. the sound absorber coating, of the combination of sound absorber coating and impedance matching coating, of which the composite coating essentially consists, can be suitably adhesively bonded to the substrate surface without requiring application of a primer coat to such surface, such latter coat can be omitted. On the other hand, such primer or bonding coat, if necessary, can be used to bond the adjacent sound absorber and impedance matching coatings where the elastomeric or polymeric matrix of such coatings do not have sufficient adherence to each other. Further, where the substrate and the sound transmitting medium are the same common material, as for example where the substrate and the sound transmitting medium is one and the same glass body, as in the delay line application hereinafter described, the impedance matching coat can be applied as the interior coating adjacent to the surface of the glass substrate and the absorber coat is applied as the outer coat over the impedance matching coat, the latter coating functioning to substantially eliminate any sound reflection from the absorber coat back into the glass sound transmitting medium.
Hence it will be understood that the invention basically contemplates and comprises a composite coating for substantially completely absorbing sound at various frequencies, on a substrate, such composite coating being formed of two coatings, an impedance matching coat over a sound absorbing coat, both as above described, or a sound absorbing coat over an impedance matching coat. The present invention is also directed to the method for applying the composite coating to a substrate.
More specifically, according to one embodiment of the invention, the first coat can be a base bonding primer coat, e.g. of a silicone primer paint; the second coat can be a mixture of metal of siliceous powder filler in a suitable elastomer, e.g. a silicone elastomer, which is turned to the proper frequency range to provide a means for near total absorption within a predetermined frequency and temperature range, thus hiding the surface of the substrate or structure from incident sound energy. This coat prevents direct transmission through and out the other side by its attenuation coefficient. The third coat can be a preselected material such as an elastomer or resin, e.g. an epoxy resin, and which may or may not contain a metal or
siliceous powder filler, and providing a means to prevent reflection from the absorbing coat by matching the impedance of said absorber to that of the surrounding acoustical transmission medium.
OBJECTS AND ADVANTAGES OF THE INVENTION
The present invention thus has for an important object the provision of an acoustical damping device which is applied to a substrate structure, in the form of a coating or paint which can have varying thicknesses, e.g. a thickness of much less than an inch, depending upon the specified frequency and temperature environment.
It is another object of the present invention to provide an acoustical composite coating or paint that is capable of being tuned to various frequencies to meet a variety of conditions for ultrasonic and sonic applications.
It is still another object of the present invention to provide a thin wall acoustical coating having a frequency range which covers both the nominal sonar frequencies (500 Hz to 5KHz) as well as the higher sonic and ultrasonic frequency noises.
It is a further object of the invention to provide a device of this character that contains as an essential element a heavily loaded elastomer using a metal or siliceous powder for the filler or loading material.
Another object is to provide a device of the character above described containing a composite coating comprising as essential components an acoustical absorbing coat and an impedance matching coat.
It is still a further object of the invention to provide a device of this character formed of a composite coating on a substrate, wherein three specific coatings are used to form the composition coating, first a bonding priming coat, second an acoustical absorbing coat, and a final coat to provide a low reflection coefficient.
Other characteristics, advantages and objects of this invention can be more readily appreciated from the following description and appended claims. When taken in conjunction with the accompanying drawings, this description forms a part of the specification wherein like references and characters designate corresponding parts in the several views.
