Patent Application
20100119076
Various embodiments of the invention relate to hearing protection devices, and more specifically to an improved ear seal for use in headsets and the like that incorporates an acoustic barrier that attenuates the level of external noise that reaches the interior of the ear cup.
Hearing protection devices such as headsets, headphones and hearing protectors are useful in a variety of endeavors ranging from aviation to military and industrial uses, to home audio use and others. In the industry, the term “headset” generally refers to device that includes a microphone and speakers in each ear cup. The term “headphone” refers to a device that has speakers only, and is therefore a receive-only communications device. A “hearing protector” is an earmuff-only device that is used only for protection of the user's hearing.
Most hearing protectors have two ear cups that are connected to a headband. Each ear cup includes an ear seal that encircles the user's ear—the ear seal has a ring of cushioning material that fits against the user's head around the ear, and helps attenuate the level of noise that reaches the ear. The ear seal is an important component of a hearing protector, as it provides comfort, and more importantly, contributes to the attenuation of external noise so that the interior of the ear seal is relatively quieter than the exterior.
It is of course desirable to minimize the amount of environmental noise that reaches the interior of the ear cup, and hence the user's ear. There are several approaches to noise attenuation, and these may be generally categorized into active and passive noise reduction strategies. Active noise reduction, or noise cancellation, relies upon reversing of waveform polarity to cancel undesirable noise. This type of noise reduction is very effective at low frequencies and can be selective, for example to cancel airplane engine noise.
Passive noise reduction on the other hand is a form of soundproofing that relies upon physical barriers to block, absorb or dampen the energy of sound waves. Ear seals are one form of passive noise reduction. Generally speaking, from a noise attenuation perspective it is best to have a thin ear seal because the noise attenuation properties are better. However, a thin ear seal is likely to be less comfortable, so there is inherently a tradeoff between the comfort of the device and the level of noise reduction that the designer must balance. For example, a variety of foam products, gels and liquid may be used for cushioning/noise attenuation materials in ear seals. The physical properties of the cushioning material directly affect the level of noise attenuation, and comfort. Thick, soft foam tends to conform well to the wearer's head and is quite comfortable, but soft foam does not attenuate noise very effectively. Dense foam is generally better at cross sectional noise attenuation, but tends to be heavier and conforms to the wearer's head less effectively, and is less comfortable.
There is a need for ear seals for use in hearing protective devices that provide more effective noise attenuation, yet are comfortable and highly conformable.
To address this and/or other needs, the present invention devised, among other things, exemplary hearing protection devices, such as headsets, headphones, or protective earmuffs, which include a novel ear seal. In one exemplary embodiment, the ear seal includes a ring-like ear cushion and an acoustic barrier ring arranged coaxially with the circumaural ear cushion. The acoustic barrier ring comprises a physical barrier located within the ear seal that is more acoustically dense than the cushioning material so that the barrier acts as a physical barrier to prevent sound from reaching the interior of the ear seal. In some embodiments, the acoustic barrier ring is at least partially buried in the ear cushion. However, in other embodiments the barrier ring lies outside and adjacent the ear cushion. Moreover, in some embodiments the barrier ring takes the form of a circumferential flange extending axially from a base portion of the ear seal. In operation, the barrier ring generally increases the passive acoustic attenuation of the ear seal, and thus mitigates the conventional tradeoff between comfort and noise attenuation. This ultimately enhances the ability of headsets, headphones, and earmuffs to block undesirable noise.
The invention will be better understood and its numerous objects and advantages will be apparent by reference to the following detailed description of the invention when taken in conjunction with the following drawings.
The following detailed description, which references and incorporates the above-identified figures, describes and illustrates one or more specific embodiments of the invention. These embodiments, offered not to limit but to exemplify and teach, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention. Where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art.
A headset 10 of the type that incorporates an acoustic barrier according to the present invention is illustrated in
Each ear cup 12 and 14 includes a housing 24 to which U-shaped connector 18 is attached. Housing 24 is typically a plastic or metal material and houses the headphone speaker 22, other electronics and components that may be used in the device, and serves as a base for the ear seals 26. For example, the headset 10 illustrated in
Each ear seal 26 comprises a generally circular ring of cushioning material 28 that attaches directly to the housing 24 such that the ear seal encloses the headphone speaker 22. The cushioning material 28 conforms to irregularities in the user's head. When the headset 10 is worn, the wearer's ears are completely encircled by the ear seals 26 with the ear seals conforming to the wearer's head around the pinna under the side pressure applied by headband 16. The side pressure provides 100% contact between the ear seal and the user's head, even when the wearer is speaking. The ear seals 26 thus provide an effective and isolated chamber or interior cell 25 where the ears rest when the headset is worn. The environment external of the ear seals is referred to herein as the exterior cell.
As indicated above, the design of the ear seals and the cushioning materials used to fabricate the ear seals has a direct and important, and often limiting effect on the level of noise attenuation, and the comfort of the headset. Design of hearing protectors to maximize passive noise reduction involves consideration and balancing of a variety of factors, including the weight of the device, and the amount of side pressure applied by the device on the wearer's head. Each of these factors directly impacts noise attenuation: the best possible goal would be a very light device that requires minimal side pressure and is very comfortable for long periods of time, yet provides a high level of attenuation. As noted, good passive noise reduction requires contact between the ear seal and the wearer's head 360° around the ear. This is referred to as 100% contact. Since no two user's heads are shaped identically, and because the contour of the user's head changes as the user speaks, it is important that the ear seals are designed with the ability to provide 100% contact at all times on all users.
Many different cushioning materials may be used in the ear seals. These include for example open and closed cell foam, silicone gel, liquid, and liquid foam. Choice of one of these over another depends upon other factors. For example, of the materials just listed, silicone gel has the best cross sectional attenuation properties (i.e., the best ability to block external noise) but has the least ability to conform to the wearer's head and thereby create the desired condition of 100% contact and conformance between the user's head and the ear seal. Table 1 provides a list of some basic properties of some common materials used in ear seals.
From the foregoing it will be appreciated that selection of one particular material over another requires balancing of the goal of comfort with the best noise attenuation. Liquid demonstrates the best conformance to uneven surfaces such as found on a typical head, but requires relatively higher side pressure because of the vertical orientation of the ear seal; the liquid flows to the lowermost portion of the seal unless the side pressure is sufficient to squeeze the fluid up around the ear. On the other hand, silicone gel tends to provide better attenuation since it stays in place in the ear seal. Foam/liquid and thermal-conforming foams do not have as much cross-sectional density as either liquid or silicone gel to provide the same levels of passive attenuation.
From a comfort standpoint, silicone gel ear seals may not be the best choice because, as noted above, the gel is a dense material and does not easily conform to the many variations posteriorly of human ears. Moreover, silicone gel only conforms under relatively high pressure, compared to the other materials listed. And silicone gel is quite heavy at twice the weight of the other ear seals. Liquid seals require medium side pressure for a good seal, and temperature-sensitive foam materials are excellent for conformability, minimum side pressure, and ear cavity volume. Furthermore, temperature sensitive foam is particularly effective when the user is wearing glasses. The conformability of the foam helps minimize the localized pressure of the arms of the glasses pushing on the wearer's temples.
It will be readily appreciated that the different criteria noted above must all be considered when designing a headset. The present invention as embodied herein and as defined by the claims may be used with any material used for ear seals, including those materials specifically listed above, and enhances the noise attenuation of the ear seal regardless of what type of cushioning is used. Nonetheless, for purposes of the present description of the invention, the ear seal it is illustrated herein and shown in the drawings being used with temperature sensitive foam. This is done by way of example only, and not by way of limitation.
Turning now to
As noted above, many different cushioning materials may be used in place of the foam used in foam core 28. Accordingly, the ear seal is at times referred to herein as a circumaural ear ring. This term contemplates an ear seal that uses any cushioning material. The internal foam core 28 described in the present embodiment is preferably soft, conformable foam that provides good noise attenuation qualities. Thermally conforming foam sold under the brand name CONFOR, available through E-A-R Specialty Composites (www.earsc.com), a division of Aearo Company (www.aearo.com) is one example of foam that works well for internal foam core 28. CONFOR is slow recovery urethane foam that softens when exposed to warm temperature, and therefore tends to conform very well to a wearer's head around the ear to provide pressure-free conformance and comfort. CONFOR also provides good noise attenuation performance. The foam core 28 used in accordance with the present invention has a height and width dimension, illustrated on
The flattened base 32 of the internal foam core is bonded to a backing layer 34, which typically is a flexible material such as cloth, but may also be materials such as KEVLAR, plastic and the like. Backing layer 34 is in turn bonded to a backing plate 36, which preferably is a semi-rigid plastic material. The backing plate is a sometimes referred to as the ear shell. As illustrated in
For reference purposes herein, flattened base 32 defines a first plane that is parallel to the plane defined by shelf 40, described below. Likewise, the surface of the ear seals 26 that contact the user's head, i.e., the outer surface of cover 30, is generally flattened and defines a second plane. The first and second planes are generally parallel, and the first plane is sometimes referred to as the back plane, and the second plane as the front plane.
The ear seal 26 is an independent unit that is detachable from ear cup 14. With reference once again to
Acoustic barrier 42 comprises a relatively thin strip of material that is relatively denser than the foam cushioning material used in the ear seal, in this case foam core 28. Because the acoustic barrier 42 is denser than the cushioning material, it provides significantly increased cross sectional noise attenuation compared to the foam. Acoustic barrier 42 is associated with the foam core 28 such that the strip extends in a direction that is generally transverse to the plane of the shelf 40—i.e., the first plane—onto which ear seal 26 fits when headset 10 is assembled, and also the plane defined by backing material 34 and backing plate 36. Stated another way, there is a central axis extending through the middle of each ear cup 12 that is transverse to the first and second planes; the wall of the acoustic barrier 42 extends parallel to the central axis. As shown in
A variety of materials may be used to fabricate acoustic barrier 42, but in all cases the material is denser than the cushioning material used in the ear seal such as foam core 28. Preferred materials for acoustic barrier 42 include copper, KEVLAR, rubber, plastics of various types, foams having relatively high density than the cushioning material used for foam core 28, and fiberboard-based materials. It will be appreciated that other materials work well, too. Testing has shown that of the specific materials listed above, copper provides the best noise attenuation properties. However, virtually any material that is more dense than the cushioning material will suffice for acoustic barrier 42. It is also envisioned that acoustic barrier 42 could be formed with a liquid polymer material injected into the foam core, wherein the polymer hardens to form the barrier. Because the acoustic barrier is very thin and light, it does not appreciably increase the weight of headset 10 and has no effect on the conformability of the ear seal to the user's head.
In some cases the material selected for acoustic barrier 42 will be dependent upon the type of foam used for foam core 28. For example, if a relatively dense and non-compressible foam is used for foam core 28, the material selected for acoustic barrier 42 may be relatively stiffer. On the other hand, if foam core 28 is formed of soft foam, a relatively more flexible material may be appropriate for the acoustic barrier.
As shown in
Acoustic barrier 42 is inserted into the foam core 28 during manufacture of the ear seal. With reference to
Once the acoustic barrier 42 is inserted into the slit 44, the cover 30 may be applied to the foam core 28 and the ear seal 26 may be fully assembled with the other components described above. Because the outermost edge 50 of the acoustic barrier 42 resides in foam core 28, there is a portion of foam shown generally at 52 that completely covers the barrier material. This helps insure the comfort of the headset.
A first illustrated alternative embodiment for the structure of acoustic barrier 42 is shown in
An alternative to the embodiment shown in
In
An ear seal 26 incorporating an acoustic barrier 42 as described herein and as illustrated in the drawing figures defines an ear seal having a cushioning material with a first density in an outer region—that is, externally of the acoustic barrier, a cushioning material having a second density in an inner region—internally of the acoustic barrier, and a third region having a density higher than the first and second regions, i.e., the acoustic barrier. In most instances the acoustic density of the cushioning material in the inner and outer regions is the same, while the density of the barrier is relatively greater.
The relative size dimensions of the headset components may vary widely, depending upon the type of cushioning material used in the ear seal, the material used to fabricate the acoustic barrier, etc. Assuming that the ear seal uses a form core 28 for the cushioning material, a preferred height dimension for the acoustic barrier 42 (dimension H in
An ear seal fitted with an acoustic barrier as described herein provides significant and substantial noise attenuation. One direct result is that by incorporating an acoustic barrier in the ear seal, a relatively thinner ear seal (i.e., lower height) may be used, and the side pressure may be reduced. Thus, by using an acoustic strip as described herein, the same levels of noise attenuation may be attained with thinner ear seals and less side pressure than conventional devices that require thick ear seals and significantly more side pressure. As a result, the same or better levels of noise attenuation are achieved with better comfort.
As noted above, acoustic barrier 42 may be used in the form of an endless strip (e.g.,
It will be appreciated that when a headset incorporating an acoustic barrier of the type illustrated herein is worn on the head of a user, the strip resides in foam core 28 such that the height dimension of the strip (dimension H,
It will be understood that the fixed flange 43 illustrated in
While the present invention has been described in terms of a preferred embodiment, it will be appreciated by one of ordinary skill that the spirit and scope of the invention is not limited to those embodiments, but extend to the various modifications and equivalents as defined in the appended claims.
