Acoustics – Sound-modifying means – Mechanical vibration attenuator
Reexamination Certificate
1999-12-29
2001-08-28
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Mechanical vibration attenuator
C181S199000
Reexamination Certificate
active
06279679
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates generally to vibration attenuation devices, and more particularly to a vibration absorber tuned to resonate at a selected low frequency upon installation onto the low frequency drive unit of an in-wall loudspeaker.
SUMMARY OF THE INVENTION
In this invention, a stack of viscoelastic polymer damping plates, secured together with spacers at both ends and having metal tuning weights attached onto the topmost plate in the stack, is secured to the low frequency drive unit of an in-wall loudspeaker with a metal mounting plate between the vibration absorber and the low frequency drive unit. Upon installation onto the low frequency drive unit of an in-wall loudspeaker, both ends of the vibration absorber, where the damping plates are secured together, are cantilevered over a tuning mounting plate that is centered between both ends of the unit. The degree of cantilever between the tuning mounting plate and both ends of the unit, in addition to the mass contained in the metal weights added to the topmost damping plate in the stack, are varied such that the vibration absorber may be tuned to resonate at the fundamental resonance frequency of the low frequency drive unit to which the vibration absorber is attached. The vibration absorber, because it is selectively tuned, absorbs vibrations at the fundamental resonance frequency of the low frequency drive unit, thus reducing baffle vibrations and the distorted sound that results from these vibrations. In virtually all in-wall loudspeakers, the low frequency drive unit, as well as other drive units they employ, are mounted onto a thin flexible plastic baffle. Whenever an in-wall loudspeaker is in operation, mechanical energy originating in the low frequency drive unit is transmitted from the mounting frame of the low frequency drive unit into the in-wall loudspeaker's plastic baffle. During the energy transmission process, the baffle is subjected to periodic, or oscillating stress, causing mechanical energy to be released as baffle vibrations. Therefore, the low frequency drive unit, as well as other drive units that may be attached to the baffle, instead of remaining stationary in space, vibrate along with the baffle, causing severe response errors in the in-wall loudspeaker's sound radiation pattern. These response errors are responsible for causing the sound quality of in-wall loudspeakers to be severely distorted and therefor irritating to listeners. With the vibration absorber of this invention connected directly to the steel backplate of an in-wall loudspeaker's low frequency drive unit, mechanical energy originating in the drive unit at it's fundamental resonance frequency, instead of being transmitted solely into the thin plastic baffle causing it to vibrate, transfers more efficiently into the vibration absorber. As the unwanted mechanical energy transfers into the vibration absorber, the damping plates comprised in the absorber, being selectively tuned, are exited into sympathetic resonance at the fundamental resonance frequency of the low frequency drive unit. The transfer of mechanical energy from the low frequency drive unit into the vibration absorber causes this unwanted energy to be dissipated in the resonating modes of the vibration absorber's damping plates as heat. Converting mechanical energy to it's thermal state makes this energy unavailable in the in-wall loudspeaker to produce baffle vibrations and distorted sound.
Heretofore, a wide variety of vibration absorbing devices have been employed in the attempt to reduce vibrations that occur in loudspeakers that employ enclosures comprising rigid panels and a rigid baffle on which to support the loudspeaker's drive units. In these enclosures, there is usually ample space inside to install vibration absorbers onto the panels in order to reduce panel vibrations. However, in-wall loudspeakers differ mainly because they do not employ enclosures. In-wall loudspeakers, which are comprised only of a plastic baffle onto which their drive units are mounted, are normally installed into standard residential walls which, in most cases, have an inside depth of 3½ inches. A standard in-wall loudspeaker, with an 8 inch low frequency drive unit, once installed into a residential wall, will leave approximately ½ inch remaining between the back of its low frequency drive unit and the wallboard behind it. Mechanical energy originating in the low frequency drive unit of an in-wall loudspeaker is the source of severe baffle vibrations that occur at, and in near proximity to, the low frequency drive units fundamental resonance frequency. To be effective in substantially reducing such severe baffle vibrations, it is necessary to attach a vibration absorbing device directly onto the back of an in-wall loudspeaker's low frequency drive unit which is known to be the very source of unwanted baffle vibration.
It is therefore among the objects of this invention to provide a vibration absorbing device that is attached directly onto the low frequency drive unit of in-wall loudspeakers to reduce objectionable baffle vibrations and the distorted sound resulting from these vibrations. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.
REFERENCES:
patent: 5528005 (1996-06-01), Bschorr et al.
patent: 5550335 (1996-08-01), Ermert et al.
patent: 5583324 (1996-12-01), Thomasen
patent: 5691516 (1997-11-01), Thomasen
patent: B1 6173805 (2001-01-01), Thomasen
Dang Khanh
Johnson Larry D.
Johnson & Stainbrook LLP
Stainbrook Craig M.
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