US 3047089 A
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Description (OCR text may contain errors)
EAR PLUGS Filed Aug. 31, 1959 INVENTOR. JOZEF J. ZWISLOCKI.
United States Patent This invention relates to earplugs, and more particularly to earplugs capable of substantially uniform sound attenuation through a substantial range of audible frequencies.
The development of increasingly powerful engines has ledto noise levels that interfere with auditory communication, and, sometimes, are harmful to the human organism. Conventional earplugs producing an average.
sound attenuation of 20 to 30 decibels are insuflicient for a growing number of industrial and military situations. They have been gradually replaced by ear muffs that enclose the whole ear and, when suffioiently large, provide to 20 decibels more attenuation than earplugs at medium and high frequencies. For communication purposes, earphones are secured under the ear muffs.
The ear muffs for ear protection against ambient noises have two basic disadvantages. In the first instance, they are bulky and cumbersome, and may interfere with additional equipment worn on the head, as for example crash helmets. In the second instance, the large volume of air enclosed between the shell of an effective ear muff and the ear drum substantially decreases the efiiciency of the earphone mounted in the ear muff.
Due to the disadvantages of ear muffs, numerous attempts have been made to increase the sound attenuation provided by earplugs. It has been found that this attenuation is inversely proportional to the acoustic impedance produced at the tip of the earplug by the ear drum and the volume of air enclosed in the ear canal; the larger the volume, the lower the resultant impedance and the higher the attenuation. The volume enclosed between the earplug and the car drum is determined by the anatomy of the ear canal. Nevertheless, the effective volume can be increased by coupling an external'enclosure through a perforation in the earplug. Experirnental devices of this kind, that became known in the past, produced the desired effect at low frequencies. However, at frequencies around 1,000 cycles per second, or above, the sound attenuation was decreased as compared With solid earplugs.
It is, therefore, the principal object of the present invention to provide earplugs of novel construction, with an enclosed volume of air connected to the external ear canal in such a way that the sound attenuation at frequencies below 1,000 cycles per second is increased above the level obtained without the additional volume, and at frequencies between 1,000 and 6,000 cycles per second either increased or practically unchanged. Higher frequencies are of little importance to communication and ear protection. I
It has been determined theoretically and confirmed expermientally that an enclosure coupled to the ear'canal by means of a tube can increase the sound attenuation produced by an earplug at low frequencies Without decreasing it at higher frequencies, provided the tube is sufficiently wide and short. The enclosure with the connecting tube constitutes an acoustic resonator with a negative input reactance at low frequencies and a positive one above the resonance frequency. The input reactance at the entrance to the ear canal is negative up to about 2,500 cycles per second and becomes positive at higher frequencies. When the resonator reactance changes its sign at a frequency lower than 2,500 cycles per second, an anti-resonance may be produced, leading to a deice creased sound attenuation. In order to prevent this condition, the inertance of the resonator, which is determined by the dimensions of the coupling tube, must remain small. It has been found, for instance, that a coupling inertance of 4 l0 g./om. does not decrease attenuation with any resonator volume. When the inertance is increased to 10 g./cm. the maximum decremen-t of attenuation below the reference level amounts to about 5 decibels with a resonator volume of 6 cubic centimeters and 4 decibels with a resonator volume of 4 cubic centimeters. The attenuation drop of 5 decibels should be considered a tolerance limit.
More specifically, it is an object of the invention to provide earplugs containing an essentially rigid enclosure ending on one side in a tubular member, said tubular member designed to connect the air volume of the enclosure to the ear canal and having an acoustic inertance of less than 10' g./cm. Such a small inertance which requires a short and wide tube can only be obtained when the enclosure is of a shape filling approximately the inner portion of the outer ear. An example of such a shape is .given in the accompanying drawing.
It is another object of the invention to provide ear plugs containing an enclosure ending in a tubular member, as specified above, so designed that they can be comfortably secured in the car without external support ing means.
It is another object of the invention to provide earplugs containing an enclosure, open toward the ear canal, and shaped and constructed in such a way that they can be comfortably secured in the car without external supporting means.
It is a further object of'the invention to provide earplugs containing an enclosure, as specified above, shaped and constructed in such a way that they can be held against the entrance to the ear canal by means of a headband, thereby providing a hermetic coupling between the enclosure and the ear canal.
It is a further object of the invention to provide at the outer wall of the enclosure means for hermetic attachment of an ear phone for communication purposes.
The above and other objects of the invention will appear more fully hereinafter from the following detailed description when taken with the accompanying drawings. It is expressly understood that the drawings are employed for purposes of illustration only and are not designed as a definition of the limits of the invention, reference being bad for this purpose to the appended claims.
In the drawings, wherein like reference characters indicate like parts:
FIGURE 1 is a view in side elevation of a preferred form of earplug embodying the invention;
FIGURE 2 is a view of said plug from the top of FIGURE 1;
FIGURE 3 is a view of said plug from the bottom of FIGURE 1;
FIGURE 4 is a sectional elevation taken on line 44 of FIGURE, 2; 7
FIGURE 5 is a side elevation of a modified form of earplug embodying the invention with a portion in section; and i FIGURE 6 is a view inside elevation of an earplug having a small car phone attached thereto.
The earplug according to the preferred embodiment shown in FIGURES l-4 comprises an enclosure 10 open toward the ear canal through a tube portion 12, and a sealing tube 14.
The walls 16, 18 of the enclosure, including the top cover 20, and the tube portion 12, are made of a rigid material of sufficient thickness to produce the necessary sound attenuation. The Wall thickness depends on the rigidity of the material.
When metal alloys, fiberglass,
The sealing tube 14 is made of a soft resilient material,
as for example, polyvinyl chloride or silicone rubber. It is removably secured on the tube portion 12 by means of a groove 22 and flange 24 in the ear plug tube por tion, and sealing tube respectively.
The sealing tube is divided into four sections: the opening area 26, the convex portion 28, the neck portion 30 and the flange 24. At the level of the flange, there is a finger tab 34 which serves to remove the sealing tube from the ear canal, should it .become'detached and remain there by accident, after the rest of the earplug has been removed. The cross section of the sealing tube is essentially round or slightly elliptical, and the convex portion 28 is made in several sizes in order to better conform to variations in the size and shape of the individuals ear canals to which it is to be adapted. The pear-like shape of tube 12 helps to retain the earplug in the ear canal, and provides a tight seal against the outside air. At the same time the sealing tube allows the acoustic inertance, coupling the earplug'enclosure to the ear canal, to remain at its practical minimum. By
. acoustic inertance is meant the product of the efiective length of the tube and the density of the medium, divided by the effective cross sectional area of the tube.
The rigid enclosure is shaped to conform approximately to the concha portion of the outer ear of the majority of people. It is widest in the vicinity of the cover and narrowest in the tube portion 12 which is inserted into the ear canal. The cross-section in the vicinity of the cover 20 is circular and becomes gradually elliptical in the midportion of the enclosure, with the long axis in the plane of FIGURE 4. In the vicinity of the groove 22 the crossection is circular again and becomes elliptical in the tube portion 12, with the long axis perpendicular to the section plane of the FIGURE 4. The wall portion 18 has a slight reverse curve and fits approximately the contour of the anti-tragus of the outer car. This shape helps effectively in retaining the earplug in the ear.
The volume of the' earplug enclosure amounts to approximately 2 cubic centimeters. The tube portion is approximately 0.8 centimeter long and its crossection area is an average .24 square centimeter.
When well fitted, the earplugs produce a sound attenuation of somewhat more than 40 decibels in the frequency range between 100 and 6000 c.p.s.
It is possible to modify the cover .20 so that a small earphone 21 can be attached to it. The alternative design is shown in FIGURE 6. In this design, cover 20 replaces cover 20 of FIGURE 4. Cover 20' comprises a central opening which provides a passage for the sound from the earphone and at the same times serves as a means. for attaching said earphone.
An alternative construction embodying the general principle of the invention is illustrated in FIGURE 5. In this embodiment the enclosure portion 50 which is essentially the same as the enclosure 10 in FIGURES 1-4 is extended by an additional enclosure 52. The two parts of the enclosure communicate with each other through a Wide opening. The enclosure portion 52 is closed by a cover 54, carrying a headband holder 56 for the attachment of a headband not shown.
The tube portion 58 is short. It has an internal groove 60 for the attachment of a sealing ring 62. The sealing ring is adapted to lit the entrance to the ear canal of the majority of people. It carries a flange 64 for attachment to the tube 58 and a safety tab 66 which performs the same function as the tab 34. The cross section of both. the tube 58 and the sealing ring 62 are oval or elliptical with the long axis perpendicular to the plane of FIGURE 5.
The walls of the enclosure 50 and 52 and of the tubular portion 58 are made of a rigid material; the sealing ring 62, of a soft resilient material.
While the invention has been described and illustrated as embodied in certain specific examples of earplugs carrying the internal enclosure, it is to be understood that the invention is not so limited and comprehends other forms and configurations within the terms of the claims.
What is claimed is:
1. An ear plug comprising an essentially rigid thin wall enclosure having a volume in the order of 2 cubic centimeters, said enclosure ending at one side in a short thin wall rigid tubular portion adapted for communication with the ear canal and of a length in the order of 0.8 centimeter, said tubular portion having an acoustic inertance of less than 10* g./cm.*.
2. An ear plug according to claim 1, wherein the enclosure is pearshape-d so as to nest in the concha region of the ear without protruding substantially beyond the auricle.
3. An ear plug according to claim 1, wherein the tubular portion is provided with means tforhermetically sealing the end thereof to the wall of the ear canal.
4. An ear plug according to claim 8, wherein the tubular portion is provided with a soft resilient coupling member adapted to seal the end of the tubular portion to the ear canal, and secure the plug in position.
5. An ear plug according to claim 1, wherein the enclosure is provided with an outer wall, and the wall is provided with a connection for a head band for sealing under slight pressure.
6. An ear plug according to claim 1 wherein the enclosure is provided with a cover plate and an earphone mounted thereon.
References Cited in the file of this patent Norway o Oct. 14,