Acoustics – Anatomic or prosthetic relation – Ear and mouth
Reexamination Certificate
2000-11-03
2002-08-06
Dang, Khanh (Department: 2837)
Acoustics
Anatomic or prosthetic relation
Ear and mouth
C128S864000, C128S865000
Reexamination Certificate
active
06427800
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the technical field of sound-attenuating ear plugs and in particular to the kind which comprises an elongate body of elastic material, which is adapted to be inserted into the auditory meatus or canal of a user's ear. The invention also relates to a method of manufacturing an ear plug. The invention is particularly directed to indicating an ear plug having an improved attenuation characteristic.
Here the term “plug” refers to an ear protector which, when used, is at least partially inserted into an auditory meatus of a user's ear, in contrast to earmuffs which are to be applied to the outside of the user's ear.
BACKGROUND OF THE INVENTION
In the technical field of ear plugs, it is known that it is desirable but difficult to obtain an attenuation curve which is substantially frequency-independent or which at least does not vary excessively with varying frequency.
FIG. 1
of the accompanying drawings shows, by means of a curve marked “Ideal”, an example of such an ideal attenuation characteristic which in this example is at a constant attenuation value of 17 dB up to 8 kHz. However, prior-art ear plugs exhibit attenuation characteristics which are rather far from such an ideal-straight characteristic. A particular problem is that the attenuation is often undesirably high within the frequency range that is most important to the perception of speech, i.e. substantially in the range of 1 kHz to 4 kHz (marked with vertical lines in FIG.
1
). This problem is discussed, for instance, in SE 8102931-6 (Racal), in which the aim is a substantially straight attenuation characteristic up to 2 kHz. A generally known problem is that it is difficult to provide suitable low-frequency attenuation while not excessively attenuating high-frequency sound.
The Applicant of the present application currently manufactures and sells glass “down” ear plugs of the kind which is described in EP 0 050 601 and which is schematically shown in
FIG. 2
of the accompanying drawings. The ear plug consists of an elongate body
3
which is made of elastic material and which is surrounded by a sheath
1
of flexible plastic material. Referring to its direction of insertion into the auditory meatus, the plug has a front end A and a rear end B.
The sheath
1
serves to facilitate the handling of the plug and to provide improved hygiene. The sheath
1
also helps to maintain the desired shape of the elastic body
3
. At the rear end B of the plug, the sheath
1
has a circumferential more rigid portion
7
, such as an outwardly directed collar or flange portion. The sheath
1
is made of a deep-drawn, thin and flexible film made of, for instance, polyvinyl chloride (PVC), polyurethane (PUR) or polyethylene (PE). Since the sheath is thin and flexible, a satisfactory adjustment is obtained between the elastic body and the inner wall of the auditory meatus.
The elastic body of the ear plug which is currently manufactured is made of glass down and is considerably blocking as regards air-flow, i.e. very airtight and thus provides a relatively high sound-attenuating effect. The curve which is marked “Prior-art glass down plug” in the diagram in
FIG. 1
shows the result of a measurement of the attenuation (according to ISO 4869-1) of this prior-art glass down plug at the frequencies which are specifically indicated on the x-axis in the diagram. It is to be noted that the attenuation characteristic of the plug deviates considerably from the ideal, straight characteristic, in particular in the range of speech where the attenuation is considerably higher.
The Applicant of the present application presently manufactures and sells also elastic ear plugs made of foam material. The curve marked “Prior-art foam plug” in the diagram in
FIG. 1
shows the result of a measurement of the attenuation of this prior-art foam plug. Admittedly, the characteristic is somewhat straighter than in the case of the glass down plug of
FIG. 2
, but the attenuation of the foam plug is not lower in the range of speech but on the contrary higher, and therefore the perception of speech as such is not improved. For higher frequencies, the attenuation amounts to about 40 dB.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a sound-attenuating ear plug having improved attenuation characteristic. A particular object of the invention is to indicate an ear plug which reduces the above-identified problems concerning (i) nonlinear or frequency-dependent attenuation and (ii) excessive attenuation in the range of speech.
These objects are achieved by means of an ear plug having the features defined in the appended claims.
According to one aspect of the invention, a sound-attenuating ear plug is provided, comprising an elongate elastic body adapted to be inserted at least partially into an auditory meatus, said body being essentially non-attenuating as regards sound, and a foil held by said body, as seen along a longitudinal axis of said body, in a three-dimensionally rounded concave or convex shape which provides such acoustical properties that the foil is responsible for the major part of the sound-attenuating effect of the ear plug.
According to another aspect of the invention, a sound-attenuating ear plug is provided, comprising an elastic body adapted to be inserted into an auditory meatus, said elastic body being made of a material which is substantially non-attenuating as regards sound, and a sheath which at least partially surrounds the elastic body, at least a part of said sheath having acoustical properties being responsible for the major part of the sound-attenuating effect of the ear plug.
According to a further aspect of the invention, a method is stated of manufacturing an ear plug, which comprises an elongate body made of elastic material and surrounded by a sheath made of flexible plastic material, a thermoplastic plastic film or foil being deep-drawn into a sheath in a manner known per se and the sheath, subsequently or simultaneously, being filled with elastic material. According to this method, as said elastic material, use is mainly made of a material which is substantially non-blocking as regards air-flow.
According to yet another aspect of the invention, use, in an ear plug, of an airtight foil is provided, which foil is three-dimensionally rounded in the direction of the auditory meatus and is the component of the ear plug that is responsible for the major part of the sound-attenuating effect of the ear plug.
According to an additional aspect of the invention, a method is provided of controlling the sound-attenuating effect of a sound-attenuating ear plug, comprising the steps of providing the ear plug with a foil which is three-dimensionally rounded in the longitudinal direction of the auditory meatus, and choosing the thickness of the rounded foil so as to obtain a desired sound-attenuating effect of the ear plug.
The invention is based on the understanding that it is possible to obtain an improved attenuation characteristic by lowering the air-flow blocking properties of an elastic body included in the plug, and instead using a rounded foil to provide the major part of the attenuation effect of the ear plug. This is apparently a solution which goes against traditional practice within the field, where elastic materials having relatively good air-flow blocking properties are normally desired to provide the sound-attenuating effect of the plug. It has thus been found that if, for instance, the starting-point is the prior-art glass down plug which is described above with reference to FIG.
2
and which consists, on the one hand, of a thin plastic sheath and, on the other, of a glass down body having a high flow resistance, and this glass down body is replaced by an elastic body which is substantially non-blocking as regards air-flow, a sound-attenuating ear plug is provided having considerably improved frequency characteristic. The attenuation characteristic of an ear plug according to the invention can be made much flatter (more frequency-independent) comp
Hiselius Per
Nilsson Lars
Burns Doane , Swecker, Mathis LLP
Dalloz Safety AB
Dang Khanh
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