The present invention generally relates to associating an audio transducer with a substrate to create a soundboard and, more specifically, to an interface device which inserts into a substrate and which acts as an acoustic fidelity augmentation bridge between an inertial type audio transducer and the chosen substrate.
Inertial type audio transducers have been applied to various substrates permitting them to transfer acoustic energy to the substrate. Various substrates have been used successfully such as wood fiberboard, fiber reinforced composites, and gypsum paneling. In so doing the substrate is set into bending wave motion by the inertial type transducer. These bending waves radiate acoustic energy through a non-linear process in which acoustically radiating wave numbers are present at nearly all frequencies. This type of acoustic radiator is classically called Distributed Mode Loudspeakers.
Historically, the present art of improving the frequency response of a Distributed Mode Loudspeaker is to reduce the contact area, preferably to a point, which increases the high frequency content of the energy input into the desired acoustic substrate. As the drive point contact area is decreased, the shear stress at the contact point is increased, which on frangible materials such as gypsum, causes substrate failure.
A common characteristic of the common building materials that are used for acoustic radiators are relatively stiff for the given areal mass density of the substrate. These materials typically are porous in nature leading to lower areal density. The stiffness is gained by a thickness of the substrate system or outer skins that effectively act as structural members. In Distributed Mode Loudspeakers, it is desirable to have a high stiffness to areal density. This property leads to improved radiation efficiency. However, the generally porous nature of the substrate leads to low shear modulus of the substrate.
A means to improve frequency response and augment acoustic sensitivity was needed in an arrangement that avoids decreasing the contact area to the point of substrate failure, and provides appropriate stiffness and shear modulus of the substrate.
The focus of this invention is to improve frequency response and augment acoustic sensitivity by way of the interface between the transducer and the substrate. The non-restrictive illustrative embodiment will use the example of gypsum or mineral paneling.
It is an object of the present invention to provide a means to augment the acoustic fidelity and transmission of audio content generated by the inertial type acoustic transducer to the substrate.
It is therefore an object of the present invention to provide a system to affix an inertial type acoustic transducer to a substrate.
Another objective of the present invention is to provide an audio transmission fidelity augmentation interface between an inertial type acoustic transducer and a substrate to which it is affixed.
Yet another objective of the present invention is to provide for a means of easily assembling the audio transmission fidelity augmentation interface and inertial type acoustic transducer to the substrate.
It is yet another objective of the present invention to provide a means to affix an inertial type acoustic transducer to the inside of a gypsum type panel forming a wall, ceiling or other surface, such that the installation thereof hides the inertial type acoustic transducer such that it is not seen and is rendered not visible in standard applications.
Another objective of the present invention is to provide a means to have the transmission fidelity augmentation interface mate with more than one thickness of substrate material.
The application of inertial type transducers to a substrate is to introduce primarily bending waves into the substrate. Bending waves induced in the substrate propagate at frequency dependent speed. Nearly all real audio content contains a fairly broadband of frequency content, thus a typical audio waveform input will be altered not only in time but also in space as it propagates. The change in waveform is also a change in wavenumber. The wavenumber conversion generates modes, which consist of both radiating and non-radiating modes even though the input frequency is above the critical bending wave frequency.
The acoustic radiation efficiency is controlled by the dispersion (wavenumber/frequency) characteristics of the overall panel. In a composite panel, where two face plates are separated by a central core, the low frequency is influenced by the overall panel section stiffness, the mid frequencies by the central layer shear stiffness, and the high frequency by the bending stiffness of the face plates.
The elastic properties of the core and face plates can set up plate-core-plate dilatational resonances significantly increasing the radiation efficiency at the resonance frequency. The lower the core stiffness, the more likely this plate-core-plate resonance will occur within the desired frequency response range of the substrate. The resonance frequency may be increased, out of the frequency band of interest by locally increasing the core stiffness at the acoustic drive point.
However, locally increasing the core stiffness of the panel will adversely affect other critical properties of the panel, namely affecting the propagation of the bending wave through the acoustic drive point region and the mechanical bending wave input impedance.
Ideally, at the inertial type acoustic transducer drive point, a stiffer core material is introduced which locally increases the shear modulus, but ideally does not change the mechanical point input bending impedance, ZF:
Z
F=8[Eh3/12(1−v2)]1/2(m)1/2
c
B
=c
a
2√3/(πh)(ρ/E)
Critical listening of drywall panels has shown that the radiation efficiency of the panel is significantly increased around 2.5 kHz. In addition, the high frequency content of drywall lacks detail, regardless of the accuracy of the frequency response. It has been observed that when the critical shear wave frequency at the inertial type acoustic transducer drive point is raised several octaves above the human hearing range, the high frequency detail is greatly improved.
During the manufacture of gypsum paneling, the wet gypsum is foamed preferentially in the center to reduce the weight of the panel while also making the panel suitable for application of mechanical fasteners to attach it to structural support framing. The portion of the gypsum panel adjacent to the surface scrim contains less air content, increasing the panel sectional stiffness. An approach to locally increase the shear velocity is to eliminate the air voids in the gypsum material. Although this will increase the shear stiffness at the drive point, it will also increase the drive point impedance, mass and flexural bending stiffness causing other undesirable affects.
One embodiment of the present invention consists of a plate type plate, which has features of reduced substrate thickness at the inertial type acoustic transducer drive point, a transition region between the transducer drive point location and the base substrate, features for enhancing the bond between the plate type plate and the gypsum panel. The plate type plate is used as a localized replacement in the base gypsum panel, where a hole of like dimensions of the plate is cut into the base gypsum panel substrate and replaced with the plate type plate. Preferably, the plate type plate is made of gypsum (calcium sulfate hemihydrate) material, where when bonded with the base gypsum panel material with setting type gypsum joint compound, form primary crystalline bonds between the two elements. Introduction of fiberglass filaments at a rate of 5-6% to gypsum of the plate type plate will create a material which has a Young's modulus nearly 20 times greater than the base gypsum panel substrate, while increasing the density only 1.54 times. A commercial example of this material is USG HydroCal FRG-95 available from the Industrial Products Division of the United States Gypsum Company.
The thinned portion of the plate is nominally 40% the thickness of the base substrate. This thinning can range from 10-90% of the base thickness of the substrate. However, the nearly optimum thickness of the thinned region is 40% of the base substrate.
A second embodiment makes use of the outer skin of a composite panel as the plate type plate and removes the core and inner skin providing a hollow into which the transducer is placed. Sectional fingers or a cylinder element are placed in the hollow and bonded to the inside of the outer skin and the core and inner skin providing adequate bending stiffness matching that of the composite panel.
It has been observed that the best acoustic performance results are obtained when the interface maximizes the Young's Modulus, minimizes the areal density, and minimally affects the bending wave input impedance and bending wave critical frequency. Additionally, the ideal material will form primary crystalline bond with the overall gypsum (calcium sulfate hemihydrate) panel.
The above mentioned principal, of locally increasing the core stiffness while maintaining the bending wave input impedance and bending wave critical speed is suitable to all types of composite panels that consist of external layers and a central core.
In the appended drawings:
The present invention relates to an audio transmission fidelity augmentation interface bridging an inertial type audio transducer and a substrate into which it is transmitting acoustical energy. The interface will be described in two non-restrictive illustrative embodiments as a plate or as sectional fingers having several features that act as a bridging interface between an inertial type acoustic transducer and a substrate to which the transducer is driving. The interface permits an increased level of acoustic fidelity to be transmitted to the substrate as compared to placing the transducer directly onto the substrate as well as offering means to facilitate the transducer's installation and permit installation to various substrate thicknesses. The interface also provides for installing the transducer in a manner whereby it is not visually apparent to the user of the transducer.
A plate for use as an acoustical transmission interface, according to non-restrictive illustrative embodiments of the present invention, will now be described. In a first embodiment, the plate comprises of a disk having several features to facilitate its assembly to a substrate and an inertial type acoustical transducer. It is to be noted that the illustrative embodiment features a plate generally round in shape; however, it is understood that the plate may be triangular, square or have multiple sides or forms.
Referring now to
Still referring to
Describing in more detail the function of the stops 17 and 18 as well as tabs 16 and 15 when the plate assembly 5 is inserted in opening 31, we refer to
During the installation process of the audio transmission fidelity augmentation device, the person installing the plate assembly 5 comprising the transducer 25 can easily remove by way of breaking off either of the two tabs 15 or 16, leaving the tab of the desired dimension X, or Y to mate with the thickness of the substrate 26. This would position the surface 22 of the plate 10 to be at the same level as the outside surface 30 of the substrate 26.
If the device 1 is for use with gypsum type panels as described in this non-restrictive illustrative embodiment, it should noted that the plate 10 can be molded or otherwise formed from a stiff, possibly reinforced plaster type material. The reinforcement is typically, but not limited to chopped glass fiber, E type. Those skilled in the art will recognize that other structural fibers can be utilized as well. A commercial example of this material is USG HydroCal FRG-95 available from the Industrial Products Division of the United States Gypsum Company.
Describing the positioning and securing of the plate 10 further, the moment rotational force is balanced by the stops 17 and 18. Each stop comprises a contacting surface, 17a and 18a respectively. The contacting surface 17a or 18a abuts the outer surface 30 of substrate 26. The plate 10 with the transducer 25 affixed to it is now assembled in equilibrium in the substrate 26. Means to further secure 30 the plate 10 to the substrate 26 may be employed. In this case, a joint setting type plaster putty can be troweled into gap 27 forming a consistent space between the perimeter surface 11 of the plate 10, and circumference surface 28. In a more preferred embodiment and shown in
Once filled and set, means to further secure 30 which may comprise the setting joint plaster can be sanded so as to ensure the entire perimeter 11 has bonded contact with circumference surface 28. Further, the outer surface of the plate 22 may be made to be substantially coplaner with the outside surface 30 of the substrate 26 by sanding, breaking or otherwise removing now unwanted features such as tabs 17 and 18 as well as handle 23.
This assembly method provides acoustic coupling between the gypsum plate and the gypsum wall panel. The setting type joint plaster is preferably fundamentally the same chemical basis as the plate and wall board, calcium sulfate hemihydrate. The setting type plaster forms crystalline bonds between all components.
Referring now to a second embodiment of the interface,
Although the present invention has been described hereinabove by way of non-restrictive, illustrative embodiments thereof, these embodiments can be modified at will, within the scope of the appended claims, without departing from the spirit and nature of the subject invention.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB09/07360 | 10/9/2009 | WO | 00 | 4/8/2011 |