Acoustics – Sound-modifying means – Mechanical vibration attenuator
Reexamination Certificate
2000-12-08
2003-11-11
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Mechanical vibration attenuator
C181S208000, C181S290000, C428S174000
Reexamination Certificate
active
06644435
ABSTRACT:
BACKGROUND OF THE INVENTION
It is known from civil engineering physics that in buildings, sufficient footfall sound insulation of partition components and—at the same time—a realistic mass of these components can only be attained with multi-shell components (double-shell components, as a rule) or with a combination of heavy single-shell partition ceilings and softly resilient wear surfaces. Double-shell partition ceilings generally are realized as floating floor screeds, and thus as a rule give rise to relatively thick designs which especially in the renovation of old buildings having predetermined joining heights can hardly be installed in practice. When calculating the footfall sound improvement factor (FSI
req
) of multi-shell ceiling covers that is required for the minimum footfall sound insulation of the full structure, not all European countries allow softly resilient wear surfaces to be taken into account. Moreover, such surfaces sometimes are not acceptable or not suitable, particularly so in wet areas (bathrooms).
In recent times, to the contrary, floor and wall coverings which are relatively thin and rigid are increasingly applied, for instance coverings consisting of chipboards or presspan panels in boarding sizes which have extremely hard surfaces, such as laminated plastic. The properties of these floor and wall coverings, which act as single-shell structures, are subjectively unpleasant and critical particularly with respect to footfall sound projection.
In Germany and Austria, floating floor screeds are the technical standard in footfall sound insulation. However, floor coverings cannot be included when technically demonstrating that minimum footfall sound insulation is attained, since they are subject to aging and can be exchanged. The resonant frequency of softly resilient wear surfaces decreases with increasing contact time; this in turn depends on the depth of penetration of the sound-generating object into the surfacing, and this depth in turn will of course be a function of the dimensions and mass of the footfall sound generator. This correlation also constitutes the reason why the results obtained when measuring the sound level reduction by wear surfaces with the aid of a standardized hammer mill basically differ from those obtained when walking on the same partition ceiling structure.
In building practice, thin, rigid wear surfaces can be installed as floating structures when they can guarantee a sufficient load distribution, and thus could basically constitute a solution intermediate between a floating floor screed and a softly resilient wear surface. Today, however, most of these wear surfaces still have the disadvantage with respect to footfall sound insulation that
on one hand the mass of the load-distributing layer generally is relatively small, and hence the dynamic stiffness of the intermediate layer must be distinctly below 10 MN/m
3
in order to attain an acceptable footfall sound improvement factor for the double-shell structure, but traditional footfall sound-proofing materials can provide such an improvement only when used in rather large layer thicknesses resulting, in their turn, in large overall thicknesses of the structure.
on the other hand the footfall sound properties of the rigid, single-shell wear surface itself are extremely unsatisfactory because of its usually very hard top layer, the associated small depth of penetration of the footfall sound generator (short contact times), and the resulting unfavorable resonant frequency, which can even be felt in a subjective way. Often this becomes noticeable as well in the form of unpleasant walking noise (“rattle”) in the room.
The standard DIN 4109 that is applicable when technically demonstrating the sound reduction factor provides examples of ceiling covers that will attenuate footfall sound. For instance, a footfall sound improvement factor of as much as 25 dB can be expected for wooden sub-floors consisting of chipboard panels with a minimum thickness of 22 mm installed so as to be floating over their full surface area on fibrous insulating materials having a dynamic stiffness s′ of at most 10 MN/m
3
. It can already be seen from this example, however, that special precautions will be required in order to attain improvement factors of the same order of magnitude with distinctly thinner floor coverings, such as wood or laminate flooring.
SUMMARY OF THE INVENTION
It has been the task of the invention, therefore, to provide a composite sound insulation system that improves, both the footfall sound insulation and the room acoustics, and this particularly when using thin, hard wear surfaces or wall and ceiling covers. This task is accomplished by the combination of the actions indicated in claim 1. Further developments and improvements of the inventive idea are reflected in the characteristics of the dependent claims. If, in the present application, reference is made to footfall sound insulation, then by analogy, this is meant to include sound insulation as such when speaking of wall or ceiling covers.
When combining a thin sound-proofing layer that has positive effects with respect to the sound projection properties of rigid, acoustically stiff coverings, with a sound-attenuating layer that preferably is also relatively thin, and in particular consists of blister sheet filled with gas or air, one can take advantage of the sound-insulating benefits of double-shell designs while sticking to small design thicknesses which are particularly advantageous for renovations.
Air blister sheets are already known for footfall sound insulation beneath floating floor screeds, for instance from DE-A1-2841208 or CH-B-645968; however, with respect to room acoustics or aerial sound insulation, these proposals do not provide an adequate solution.
On the other hand, in contrast to technical sound-insulation precautions which are state of the art, such as an additional single layer like for instance the air blister sheet in the two documents cited above, or a sound-proofing layer according to DE-U1-29280016 consisting of cork and/or rubber chips bonded with polyurethane or of modified plaster of Paris, in the composite sound insulation system according to the invention, the two parameters chiefly influencing the sound projection properties of acoustically stiff wear surfaces, viz., inner sound attenuation and footfall sound improvement, which as such are known are now made optimizable for individual applications by the functional subdivision among several separate individual layers.
The materials of the first sound-proofing layer which is glued directly onto the bottom side of the wear surface should preferably have a density of more than 1600 kg/m
3
, which is a high value when considering materials for construction, and at the same time an inner loss factor &eegr;
int
of 0.2 to 6.0. The attenuating layers contemplated in the composite sound insulation system according to the invention should advantageously attain masses per unit area of 10 kg/m
2
or even less, depending on the layer thickness.
Apart from technical properties relating to thermal insulation and vapor diffusion, the composite sound insulation system according to the invention has three acoustic functions, viz.,
a) a precaution primarily concerning room acoustics, improving the sound projection properties of thin, rigid and acoustically stiff wear surfaces in the walking space, so as to avoid the rattling noise in the upper frequency range that is relevant to building acoustics, a noise which is typical for such floorings and extremely unpleasant subjectively.
b) a precaution to reduce footfall sound and achieve an acceptable footfall sound improvement factor even in the instance of acoustically stiff wear surfaces (as a variant of the softly resilient wear surfaces used most commonly to this effect in practical applications),
c) a precaution that in addition is effective as well with respect to aerial sound insulation.
The composite sound insulation system of the invention, by combining a thin, relatively light load distribution panel
Dang Khanh
Oliff & Berridg,e PLC
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