Supports – Including additional vibrating mass
Patent
1991-06-28
1993-08-31
Talbott, David L.
Supports
Including additional vibrating mass
181207, 188379, 2671411, 381158, F16M 1300
Patent
active
052402215
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a device and method for attenuating a selected wavelength band of vibrations produced by a vibrating member. More specifically, it is directed to a viscoelastic damping device which may be connected with a vibrating elastic member, such as a loudspeaker enclosure, so as to attenuate those vibrations. Additionally, the invention relates to a method of contacting an assembly including a viscoelastic material with a vibrating member, so as to attenuate a selected wavelength band of vibrations emanating therefrom.
DESCRIPTION OF RELATED ART
The secondary vibrations of an enclosure, for example the enclosure cabinet panels of a loudspeaker, are vibrations which may produce audible sound waves. With a loudspeaker, the acoustic output caused by these secondary vibrations may add or subtract from the output of the loudspeaker, thereby causing the listener to perceive the results as spectral changes or "coloration" of the sound being reproduced by the speaker. Thus, it is desirable to minimize or eliminate these secondary sound waves.
The sound waves that are produced by a loudspeaker's enclosure panels are the result of energy that is injected into these panels by a low-frequency loudspeaker whose functional role is to reproduce the lower frequency range of the sound spectrum. Once this low frequency energy is transferred into the enclosure panels, it is stored as periodic stress and recovered in the form of periodic deformations or, vibrations. The resulting sound waves that these panel vibrations produce in the adjacent air will be dispersed along with the loudspeaker's main-signal energy. The resulting two signals, one being slightly delayed behind the other, will "smear" or interfere with the sound quality of the loudspeaker.
Moreover, at various frequencies, these delayed energy signals will alternately change in their phase relationship with the loudspeaker's main-signal sound waves. This disparity in phase relationships between the two signals over a wide range of frequencies will produce peaks and dips in the loudspeaker's frequency response causing the listener to perceive poorer quality reproduction. These problems represent a major barrier to high-quality sound reproduction. Thus, eliminating their acoustical affect upon a listener would be a major step in improving the sound quality of loudspeakers.
Heretofore, a wide variety of vibration damping methods have been proposed or implemented to reduce the acoustical output and therefore the perceived acoustical affect of enclosure panel vibrations upon the listener. However, these attempts have failed because the physical properties of the materials which have been used are not suitable to retard the extremely small periodic deformations (in the range of 20 to 20,000 hertz) such as those exhibited by the loudspeaker's enclosure panels, but which can nevertheless produce a relatively large magnitude of acoustic output.
One of these prior attempts employs rigid braces which are secured against the inner walls of the enclosure to resist the periodic forces which cause the enclosure panels to vibrate. Being rigid in nature, the braces are made of materials which classify them as an elastic solid. Having elastic material properties makes these braces suitable for transmitting energy but not for attenuating or absorbing energy. By "elastic solid" it is meant a material composed of individual atoms or small molecules in crystalline lattices. In these materials, molecular motion is rapid and short-range. As a result, whenever periodic forces having high velocity are exerted into such materials, they can produce rapid, short-range bending and stretching of interatomic bonds and rapid elastic response, thereby enabling them to transmit mechanical energy effectively. However, this molecular behavior also enables rigid enclosure braces made of such elastic materials to produce sound waves in the adjacent air through their ability to transmit periodic forces between the panels being braced. Through the nature of the
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"Delta Tech Research," Speaker Builder, May 1989, p. 6, column 1.
Delta Tech Research, Inc.
Talbott David L.
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