Acoustical Filter Device

Abstract

An acoustical filter device characterized by a filter element serving to screen out substantially all noise about a predetermined level while permitting sound below such level to pass therethrough without deleterious loss. The filter is preferably carried in a support body adapted to be inserted in the outer ear canal of the human ear and to form-fit the respective left-hand and right-hand ear canals. An acoustical filter passage is defined through the support body in open communication with the outside surroundings through which sound is screened out in the above manner.

Description

One way to reduce the level of transmitted sound is to merely provide a complete blockage of the sound path. Thus, to reduce objectionable sound levels to protect the ear, the use of ear plugs has previously been common. Ear plugs have the disadvantage of reducing all sound levels thereby interfering with desired transmissions of sound such as normal speech. Another disadvantage in the use of ear plugs is that they block the inner ear producing imbalance and danger of ear infection caused by the ears being sealed from the atmosphere for extended periods of time.

In general, there is provided an acoustical filter device characterized by a filter element which serves to screen out substantially all noise above a predetermined level while permitting sound below such level to pass therethrough without deleterious loss.

Accordingly, and in a particularly preferred construction, the filter device is carried in a support body adapted to be inserted into the outer ear canal of the human ear. An acoustical filter passage is defined through the support body in open communication with the outside surroundings. The formation of the filter passage serves to restrict the passage of sound above a predetermined level while permitting lower levels of sound to pass therethrough.

In a particularly preferred embodiment, the support body is form-fitted to each of the respective left-hand and right-hand ear canals in a manner whereby all sound entering the inner ear must pass through the filter passage. Thus, the exterior surface of the support body forms an acoustically sealed interface with the ear canal surfaces.

This invention relates to an acoustical filter device which is particularly useful as a filter device adapted to be worn within the outer ear canal.

In general it is an object of this invention to provide an improved acoustical filter device.

It is a further object of this invention to provide an acoustical filter device adapted to be worn within the outer ear canal of the human ear whereby the inner ear is in open communication with the outside surroundings.

It is a further object of the invention to provide an acoustical filter element serving to screen out substantially all noise above a predetermined level while permitting sound below such level to pass therethrough without deleterious loss.

Further objects of the invention will be readily apparent from the following detailed description of preferred embodiments, when considered in conjunction with the drawings.

FIG. 1 is an elevation schematic view in section of an acoustical filter device according to the invention.

FIG. 2 is an elevation schematic view of another embodiment according to the invention,

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In providing an acoustical filter to be carried in the outer ear canal 13 of the human ear, such as the ear 10, schematically shown in FIG. 1, an acoustical assembly 11 includes a generally annular elongated support body 12 of suitable resilient, deformable material, such as rubber or polypropylene shaped to conform to the interior surfaces of the outer ear canal.

While being formed in the general nature of an "ear plug" in the sense that it is a body of material which can be carried within the ear, the form of body 12 provides exterior surfaces which conform in a closely fitting relation to the canal surfaces to provide an acoustically sealed interface around body 12. Thus, no sound will be permitted to pass around the exterior surface of body 12 to enter canal 13. Body 12 includes a filter passage 15 defined therethrough.

Thus, an acoustical filter element 14, lodged centrally of body 12, serves to restrict the passage therethrough of substantially all sound levels above a predetermined level, preferably established at the upper level of human speech. Accordingly, the transmission of noise levels via the filter element 14 is limited to those noise levels falling below a noise level on the order of 80 decibels.

Element 14 engages support body 12 and is held affixed thereto by insertion into an annular bore 16 formed through body 12 to open into canal 13. Element 14 thus includes a conical leading surface portion 18 formed about the inner end thereof and provided with a retaining shoulder 17 at the rear edge of portion 18. The deformable nature of body 12 serves to expand around and behind shoulder 17 whereby withdrawal of element 14 is resisted while insertion of element 14 is aided by the conical surface portion 18.

The exterior portions at the outer end of element 14 are generally concentrically arranged, right cylindrical, portions disposed in steps whereby if it is desired to remove element 14 from body 12, it is possible to manually grip and disengage element 14 from body 12 merely by pulling one from the other against the resistance provided by shoulder 17.

Means for screening out the higher sound levels above a predetermined cutoff level, such as the 80 decibel speech level, is effected by the central passageway defined through element 14 as now to be described.

Thus, the outer end of passageway 19 includes an outer funnel-shaped sound collecting dishlike surface portion 21 which first receives the incoming sound waves.

Immediately inside the region of surface 21, a relatively large cylindrical recess 22 further serves to collect the incoming sounds for travel along passageway 19.

From inspection of the drawing, it will be readily evident that passageway 19 is in open communication between ear canal 13 and the outside surroundings. The incoming sound waves next encounter a somewhat reduced cylindrical resonant chamber 23 which cooperates with a much smaller vent passage 24. At the junction formed at the transition between chamber 23 and vent 24, the end wall surface 26 is abruptly diminished to the restricting diameter of vent 24 whereby incoming sound waves serve to develop an increasing pressure caused by the constriction of the relatively small diameter vent 24 with respect to the relatively large diameter of chamber 23.

The length of chamber 23 is tuned to pass a frequency band on the order of 250 to 4,000 cycles per second as well as the first three harmonics thereof. For example, chamber 23 can be on the order of 3 millimeters in length.

It has been observed that, in order to dissipate and cut off substantially all sound levels above the usual upper level for speech, such as 80 decibels or the like, the ratio of the diameter of chamber 23 with respect to the diameter of vent 24 should run on the order of three to one.

Thus, the foregoing ratio of diameters between chamber 23 and vent 24 serves to screen out noise levels above a predetermined level of noise such as on the order of eighty decibels. This type of device, therefore, is suitable for most industrial usages, such as machine shops and the like, whereby high noise levels can be expected to be experienced.

It has been further observed, that in using the above ratio for the relative diameters, the lower levels of sound pass relatively undiminished through the entire length of passageway 19 whereby a person can hear another party talking clearly, notwithstanding the fact that the listener may be in the immediate presence of noisy operating equipment.

For example, in utilizing the above filter element disposed in support bodies carried in the ears, it has been observed that the sound of a jet engine is reduced to the point where only the low level sound produced by the rush of passing air being discharged from the engine is heard, since the remainder of the noise lies at levels higher than 80 db.

This can be explained by the observation that noise occurring from any given source can be expected to cover a relatively wide range of levels and that the lower levels are normally not heard or registered by virtue of the fact that they are drowned out by the greater levels of noise. Once the higher noise levels have been eliminated, however, by the filter device 14, the lower levels will pass through to the listener.

Accordingly, it has been observed that, when wearing the acoustical assembly 11, the report of a shotgun is minimized whereby only that portion of the sound generated by the firing of the shotgun is transmitted to the listener which lies below the predetermined cutoff level.

Thus, filter element 14 can be arranged to provide a cutoff of all sound above a predetermined level and, if desired, the sound levels below the cutoff level can be reduced by forming vent 24 with a relatively smaller diameter.

Thus, in certain circumstances, such as in the environment of extremely high noise levels as found in and about airports in close proximity to jet engine operation and the like, the above construction may permit the passage of enough higher noise levels, for example, up to a level on the order of 90 or 95 decibels that, if these are objectionable, a reduction in the noise level can be achieved by further increasing the ratio of the diameter of chamber 23 with respect to the diameter of vent 24. Thus, for use under such circumstances, a ratio on the order of seven to one has been observed to screen out substantially all noise levels above 80 decibels. Under these extreme circumstances some reduction in the transmission of those noise levels below 80 decibels may be experienced which could, for example, require people in conversation to speak somewhat more loudly to be fully heard.

More specifically, an operable filter element and ear assembly 11 have been constructed and operated in accordance with the above wherein chamber 23 has a length of 0.118 inch and a diameter of 0.225 inch, and vent 24 has a length of 0.0787 inch and a diameter of 0.0625 inch.

For high intensity noise levels, such as experienced in the proximity of jet engines and the like, an assembly 11 has been constructed and operated in accordance with the above teaching wherein chamber 23 has a length of 0.118 inch and a diameter of 0.0938 inch, and vent 24 has a length of 0.0787 inch and a diameter of .0135 inch.

Another embodiment, according to the invention, includes the addition of an L-shaped sound transmission tube 27 formed at its inner end with an enlarged exterior diameter for providing a press fit within recess 22 for holding the L-shaped tube 27 in any desired radial orientation.

By utilizing tube 27, it is possible to partially dissipate all incoming sound by a factor on the order of 10 percent. This can be further improved simply by directing the open outer ends 28 away from the source of the sound.

From the foregoing, it will be readily evident that there has been provided an acoustical filter device whereby a party wearing the filters in each ear can conduct a normal conversation even in the presence of highly objectionable sound.

Further, it will be readily evident that various sizes of support bodies can be made to fit different sizes and shapes of outer ear canals. Thus, a single relatively standard size filter element 14 can be utilized in conjunction with a great number of different support bodies so as to accommodate a wide range of users with a minimum of parts.

Claims

1. An acoustic device comprising a support body of resilient material shaped and adapted to be inserted into the outer ear canal of the human ear to be worn therein, an acoustic filter passage defined within the body for open communication between the outside surroundings and said ear canal, said acoustic passage being formed to include an open end for collecting and receiving substantially all ambient sound substantially undiminished in energy from the outside surroundings, said filter passage comprising a resonant chamber of predetermined length open to receive substantially all said sound, and a vent of a reduced diameter relative to the diameter of said chamber and forming a junction therewith, said vent leading from said chamber to transmit sound to said canal, the junction between said chamber and vent providing a sufficiently abrupt reduction in said passage and said predetermined length being sufficiently long to cause an increase in pressure in said chamber for sounds above a predetermined level to cause said sounds to become dissipated within said chamber while said vent passes sounds below said level into said canal substantially free of deleterious reduction in the level thereof.

2. An acoustic device according to claim 1 wherein the ratio of the respective diameters of said chamber and vent lies substantially within a range of between seven and three to one.

3. An acoustical filter device comprising a filter element having an open acoustical filter passage therein, said acoustical passage being formed to include an open end for collecting and receiving sound, an L-shaped tube having one end communicating with the source of sound entering said passage, said tube serving to partially dissipate the sound prior to receipt by said filter passage, a resonant chamber of predetermined length open to receive the sound collected, and a vent of reduced diameter relative to the diameter of said chamber, the junction between said chamber and vent providing an abrupt reduction in said passage to cause sounds of a predetermined level to resonate and become dissipated within said chamber while said vent passes sounds below said level.

4. An acoustical filter device to be worn in the ear comprising a form-fitted support body forming an acoustically sealed interface with the ear canal surfaces of the wearer, filter means carried by said body and forming an acoustic passageway in continuously open communication between the ear canal and the outside surrounding, the outer portion of the passageway being formed to define an elongated chamber open at its outer end for receiving all ambient sounds therein at a substantially undiminished energy level and formed at its outer end to include an abruptly diminished vent opening, said acoustic passageway at the junction between said chamber and vent opening being sufficiently abruptly diminished to cause the sound waves entering said chamber to develop an increase in pressure in said chamber and to dissipate energy therein for those sounds above a predetermined level while passing sounds below said level via said vent opening directly into the ear canal of the wearer substantially undiminished relative to those sounds above said level.