Earphone

BACKGROUND

0001This specification describes an earphone as well as a positioning and retaining structure for an earpiece.

0002<patcit id="pcit0001" dnum="WO2010040351A"><text>WO2010040351</text></patcit>, <patcit id="pcit0002" dnum="WO2010040350A"><text>WO2010040350</text></patcit>, <patcit id="pcit0003" dnum="EP1874080A"><text>EP1874080</text></patcit> and <patcit id="pcit0004" dnum="WO2009153221A"><text>WO2009153221</text></patcit> are prior art references disclosing earphones.

SUMMARY

0003The invention proposes an earphone as recited in claim 1. Other embodiments are described in the dependent claims.

0004Other features, objects, and advantages will become apparent from the following detailed description, when read in connection with the following drawing, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

0005<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a side view of a human ear;</li><li><figref idref="f0002">Fig. 2</figref> shows several views of an earpiece;</li><li><figref idref="f0003">Fig. 3</figref> shows several view of a portion of the earpiece;</li><li><figref idref="f0004">Fig. 4</figref> is a view of a human ear with the earpiece in position;</li><li><figref idref="f0005">Fig. 5</figref> is an isometric view and a cross-sectional view of a portion of the earpiece;</li><li><figref idref="f0006">Fig. 6</figref> is a diagrammatic cross-section of a portion of the earpiece;</li><li><figref idref="f0007">Figs. 7A - 7D</figref> show views of a portion of the earpiece;</li><li><figref idref="f0008">Fig. 8</figref> is a blowup view of the earpiece;</li><li><figref idref="f0009">Fig. 9</figref> is an isometric view and a cross-sectional view of a portion of the earpiece; and</li><li><figref idref="f0010">Fig. 10</figref> is an isometric view of the body of the earpiece, with a portion of the body removed.</li><li><figref idref="f0011">Fig. 11</figref> is an isometric view of the body of the earpiece.</li></ul>

DETAILED DESCRIPTION

0006<figref idref="f0001">Fig. 1</figref> shows the human ear and a Cartesian coordinate system, for the purpose of identifying terminology used in this application. In the description that follows, "forward" or "front" will refer to the + direction along the X-axis, "backward" or "rear" will refer to the - direction along the X-axis; "above" or "up" will refer to the + direction along the Y-axis, "below" or "down" will refer to the - direction along the Y-axis; "on top of" and "outward" will refer to the + direction along the Z-axis (out of the page), and "behind" or "under" or "inward" will refer to the - direction along the Z-axis (into the page).

0007<b>The</b> description that follows will be for an earpiece that fits in the right ear. For an earpiece that fits in the left ear, some of the definitions, or the "+" and "-" directions may be reversed, and "clockwise" and "counterclockwise" may mean rotation in different directions relative to the ear or other elements than is meant in the description below. There are many different ear sizes and geometries. Some ears have additional features that are not shown in <figref idref="f0001">Fig. 1</figref>. Some ears lack some of the features that are shown in <figref idref="f0001">Fig. 1</figref>. Some features may be more or less prominent than are shown in <figref idref="f0001">Fig. 1</figref>.

0008<figref idref="f0002">Fig. 2</figref> shows several views of an in-ear earpiece 10. The earpiece 10 includes a body 12, an acoustic driver module 14, which may be mechanically coupled to an optional electronics module 16. The body 12 may have an outlet section 15 that fits into the ear canal. Other reference numbers will be identified below. The earpiece may be wireless, that is, there may be no wire or cable that mechanically or electronically couples the earpiece to any other device. Some elements of earpiece 10 may not be visible in some views.

0009<b>The</b> optional electronics module 16 may include a microphone at one end 11 of the electronics module 16. The optional electronics module 16 may also include electronic circuitry to wirelessly receive radiated electronic signals; electronic circuitry to transmit audio signals to, and to control the operation of, the acoustic driver; a battery; and other circuitry. The electronics module may be enclosed in a substantially box-shaped housing with planar walls.

0010It is desirable to place the in-ear earpiece 10 in the ear so that it is oriented properly, so that it is stable (that is, it remains in the ear), and so that it is comfortable. Proper orientation may include positioning the body so that the electronics module, if present, is oriented so that the microphone is pointed toward the mouth of the user and so that a planar surface of the electronics module 16 is positioned near or against the side of the head of the user to prevent excessive motion of the earpiece. An electronics module 16, if present, and the possible wireless characteristic of the earpiece makes the orientation and stability of the earpiece more complicated than in earpieces that have wires or cables and that do not have the electronics module. The wires tend to orient the earpiece so that the wire or cable hangs down, so the absence of the wire or cable makes proper orientation more difficult to achieve. If the electronics module is not present, proper orientation could include orienting the body so that the outlet section 15 is oriented properly relative to the ear canal. The electronics module 16 tends to be heavy relative to other components of the earpiece so that it tends to shift the center of mass outward, where there is no contact between the earpiece and the head of the user, so that the earpiece tends to move downward along the Y-axis and to rotate about the Z-axis and the X-axis.

0011<figref idref="f0003">Fig. 3</figref> shows a cutout view of the body 12. The body 12 includes a passageway 18 to conduct sound waves radiated by the acoustic driver in the acoustic driver module to the ear canal. The body 12 has a substantially planar surface13 that substantially rests against, the concha at one end. Extending from the body 12 is a positioning and retaining structure 20 that, together with the body 12 holds the earpiece in position without the use of ear hooks, or so-called "click lock" tips, which may be unstable (tending to fall out of the ear), uncomfortable (because they press against the ear), or ill fitting (because they do not conform to the ear). The positioning and retaining structure 20 includes at least an outer leg 22 and an inner leg 24 that extend from the body. Other implementations may have additional legs such as leg 23, shown in dotted lines. Each of the two legs is connected to the body at one end 26 and 28 respectively. The outer leg is curved to generally follow the curve of the anti-helix at the rear of the concha. The second ends of each of the legs are joined at point 30. The joined inner and outer legs may extend past point 30 to a positioning and retaining structure extremity 35. In one implementation, the positioning and retaining structure 20 is made of silicone, with a 16 Shore A durometer. The outer leg 22 lies in a plane.

0012The positioning and retaining structure is substantially stiffer (less compliant) when force is applied to the extremity 35 in the counterclockwise direction as indicated by arrow 37 (about the Z-axis) than when force is applied to the extremity 35 in the clockwise direction as indicated by arrow 39 about the Z-axis. The difference in compliance can be attained by the geometry of the two legs 22 and 24, the material of two legs 22 and 24, and by prestressing one or both of the legs 22 and 24, or a combination of geometry, material, and prestressing. The compliance may further be controlled by adding more legs to the legs 22 and 24. The positioning and retaining structure is substantially more compliant when force is applied to the extremity along the Z-axis, indicated by arrow 33 than when force is applied about the Z-axis, indicated by arrows 37 and 39.

0013In one measurement, the stiffness when force is applied the counterclockwise direction (indicated by arrow 37) was approximated by holding the body 12 stationary, applying a force to the extremity 35 along the X-axis in the -X direction, and measuring the displacement in the -X direction; the stiffness when force is applied in the clockwise direction (indicated by arrow 39) was approximated by holding the body 12 stationary and pulling the extremity 35 along the Y-axis in the -Y direction. The stiffness in the counterclockwise direction ranged from 0.03 N/mm (Newtons per millimeter) to 0.06 N/mm, depending on the size of the body 12 and of the positioning and retaining structure 20. The stiffness in the clockwise direction ranged from 0.010 N/mm to 0.016 N/mm, also dependent on the size of the body 12 and of the positioning and retaining structure 20. For equivalent sized bodies and positioning and retaining structures, the stiffness in the counterclockwise direction ranged from 3.0x to 4.3x the stiffness in the clockwise direction. In one measurement, force was applied along the Z-axis. The stiffness ranged from 0.005 N/mm to 0.008 N/mm, dependent on the size of the body 12 and of the positioning and retaining structure 20; a typical range of stiffnesses might be .001 N/mm to .01 N/mm. For equivalent sized bodies and positioning and retaining structures, the stiffness when force was applied along the Z-axis ranged from 0.43 to 0.80 of the stiffness when force was applied in the counterclockwise direction.

0014Referring now to <figref idref="f0004">Fig. 4</figref>, to place the earpiece in the ear, the body is placed in the ear and pushed gently inward and preferably rotated counter-clockwise as indicated by arrow 43. Pushing the body into the ear causes the body 12 and the outer leg 22 to seat in position underneath the anti-tragus, and causes the outlet section 15 of the body 12 to enter the ear canal. Rotating the body counter-clockwise properly orients in the Z-direction the outer leg 22 for the steps that follow.

0015The body is then rotated clockwise as indicated by arrow 41 until a condition occurs so that the body cannot be further rotated. The conditions could include: the extremity 35 may contact the base of the helix; leg 24 may contact the base of the helix; or the extremity 25 may become wedged behind the anti-helix in the cymba concha region. Though the positioning and retaining structure provides all three conditions (hereinafter referred to as "modes", not all three conditions will happen for all users, but at least one of the modes will occur for most users. Which condition(s) occur(s) is dependent on the size and geometry of the user's ears.

0016Providing more than one mode for positioning the earpiece is advantageous because no one positioning mode works well for all ears. Providing more than one mode of positioning makes it more likely that the positioning system will work well over a wide variety of ear sizes and geometries

0017Rotating the body 12 clockwise also causes the extremity and outer leg to engage the cymba concha region and seat beneath the anti-helix. When the body and positioning and retaining structure 20 are in place, positioning and retaining structure and/or body contact the ear of most people in at least two, and in many people more, of several ways: a length 40 of the outer leg 22 contacts the anti-helix at the rear of the concha; the extremity 35 of the positioning and retaining structure 20 is underneath the anti-helix 42; portions of the outer leg 22 or body 12 or both are underneath the anti-tragus 44; and the body 12 contacts at the entrance to the ear canal under the tragus. The two or more points of contact hold the earpiece in position, providing greater stability. The distributing of the force, and the compliance of the portions of the body and the outer leg that contact the ear lessens pressure on the ear, providing comfort.

0018Referring again to View E of <figref idref="f0002">Fig. 2</figref> and Views B, C, and D of <figref idref="f0003">Fig. 3</figref>, the body 12 may have a slightly curved surface 13 that rests against the concha. The periphery of the slightly curved surface may line is a plane, hereinafter referred to as the body plane. In one implementation, the projection of the outer leg 22 of the positioning and retaining structure 20 on the Y-Z plane may be angled relative to the intersection of the body plane 13 and the Y-Z plane, as indicated by line 97 (a centerline of leg 22) and line 99 (parallel to the body plane). When in position, the body plane 13 is substantially parallel to the X-Y plane. Stated differently, the outer leg 22 is angled slightly outward.

0019<b>The</b> angling of the positioning and retaining structure 20 has several characteristics. The structure results in a greater likelihood that the extremity will seat underneath the anti-helix despite variations in ear size and geometry. The outward slant conforms better to the ear. The positioning and retaining structure is biased inward, which causes more force to resist movement in an outward direction more than resists movement in an inward direction. These characteristics provide a marked improvement in comfort, fit, and stability over earpieces which have a positioning and retaining structure that is not angled relative to the plane of a surface contacting the concha.

0020If the angling of the position and retention structure does not cause the extremity to seat behind the anti-helix, the compliance of the extremity in the Z-direction permits the user to press the extremity inward so that it does seat behind the anti-helix.

0021Providing features that prevent over-rotation of the body results in an orientation that is relatively uniform from user to user, despite differences in ear size and geometry. This is advantageous because proper and uniform orientation of the earpiece results in a proper and uniform orientation of the microphone to the user's mouth.

0022<figref idref="f0005">Fig. 5</figref> shows a cross-section of the body 12 and positioning and retaining structure 20 taken along line A - A. The cross-section is oval or "racetrack" shaped, with the dimension in a direction Z' substantially parallel to the Z-axis 2.0 to 1.0 times the dimension in direction X', substantially parallel to the X-axis, preferably closer to 1.0 than to 2.0, and in one example, 1.15 times the dimension in the X' direction. In some examples, the dimension in the Z' direction may be as low as 0.8 times the dimension in the X' direction. The cross-section permits more surface of the outer leg to contact the anti-helix at the rear of the concha, providing better stability and comfort. Additionally, there are no corners or sharp edges in the part of the leg that contacts the ear, which eliminates a cause of discomfort.

0023As best shown in Views B and E of <figref idref="f0002">Fig. 2</figref>, the acoustic driver module is slanted inwardly and forwardly relative to the plane of the body 12. The inward slant shifts the center of gravity relative to an acoustic driver module that is substantially parallel to the positioning and retaining structure 20 or the electronics module 12, or both. The forward slant combined with the inward slant permits more of the acoustic driver module to fit inside the concha of the ear, increasing the stability of the earpiece.

0024<figref idref="f0006">Fig. 6</figref> shows a diagrammatic cross-section of the acoustic driver module 14 and the body 12. A first region 102 of the earpiece 10 includes a rear chamber 112 and a front chamber 114 defined by shells 113 and 115, respectively, on either side of an acoustic driver 116. In some examples, a 15 mm nominal diameter driver is used. A nozzle 126 extends from the front chamber 114 into the entrance to the ear canal, and in some embodiments into the ear canal, through the body 12 and may end at an optional acoustic resistance element 118. In some examples, the optional resistance element 118 is located within nozzle 126, rather than at the end, as illustrated. An acoustic resistance element, if present, dissipates a proportion of acoustic energy that impinges on or passes through it. In some examples, the front chamber 114 includes a pressure equalization (PEQ) hole 120. The PEQ hole 120 serves to relieve air pressure that could be built up within the ear canal 12 and front chamber 114 when the earphone 10 is inserted into the ear. The rear chamber 112 is sealed around the back side of the acoustic driver 116 by the shell 113. In some examples. the rear chamber 112 includes a reactive element, such as a port (also referred to as a mass port) 122, and a resistive element, which may also be formed as a port 124. <patcit id="pcit0005" dnum="US6831984B"><text>U.S. patent 6,831,984</text></patcit> describes the use of parallel reactive and resistive ports in a headphone device. and is incorporated here by reference in its entirety. Although ports are often referred to as reactive or resistive, in practice any port will have both reactive and resistive effects. The term used to describe a given port indicates which effect is dominant. In the example of <figref idref="f0006">Fig. 6</figref>, the reactive port is defined by spaces in the shell 113. A reactive port like the port 122 is, for example, a tube-shaped opening in what may otherwise be a sealed acoustic chamber, in this case rear chamber 112. A resistive port like the port 124 is, for example, a small opening in the wall of an acoustic chamber covered by a material providing an acoustical resistance, for example, a wire or fabric screen, that allows some air and acoustic energy to pass through the wall of the chamber. The mass port 122 and the reactive port 124 acoustically couple the back cavity 112 with the ambient environment. The mass port 122 and the resistive port 124 are shown schematically. The actual location of the mass port 122 and the resistive port 124 will be shown in figures below and the size will be specified in the specification. Similarly, the actual location and size of the pressure equalization hole 120 will be shown below, and the size specified in the specification.

0025Each of the body 12, cavities 112 and 114. driver 116, damper 118, hole 120, and ports 122 and 124 have acoustic properties that may affect the performance of the earpiece 10. These properties may be adjusted to achieve a desired frequency response for the earphone. Additional elements. such as active or passive equalization circuitry, may also be used to adjust the frequency response.

0026<b>To</b> increase low frequency response and sensitivity, a nozzle 126, may extend the front cavity 112 into the ear canal, facilitating the formation of a seal between the body 12 and the ear canal. Sealing the front cavity 114 to the ear canal decreases the low frequency cutoff, as does enclosing the rear of transducer 116 with small cavity 112 including the ports 122 and 124. Together with a lower portion 110 of the cushion, the nozzle 126 provides better seal to the ear canal than earphones that merely rest in the concha, as well as a more consistent coupling to an individual user's ears. The tapered shape and pliability of the cushion allow it to form a seal in ears of a variety of shapes and sizes. In some examples, the rear chamber 112 has a volume of 0.26 cm³, which includes the volume of the driver 116. Excluding the driver, the rear chamber 112 has a volume of 0.05 cm³.

0027The reactive port 122 resonates with the back chamber volume. In some examples, it has a diameter in the range of about 0.5 mm to 2.0 mm, for example 1.2 mm and a length in the range of about 0.8 mm to 10.0mm, for example 2.5 mm. In some embodiments. the reactive port is tuned to resonate with the cavity volume around the low frequency cutoff of the earphone. In some embodiments, he low frequency cutoff is around 100 Hz, which can vary by individual, depending on ear geometry. In some examples, the reactive port 122 and the resistive port 124 provide acoustical reactance and acoustical resistance in parallel meaning that they each independently couple the rear chamber 112 to free space. In contrast, reactance and resistance can be provided in series in a single pathway, for example, by placing a resistive element such as a wire mesh screen inside the tube of a reactive port. In some examples, a parallel resistive port is covered by 70x800 Dutch twill wire cloth, for example, that is available from Cleveland Wire of Cleveland, OH. Parallel reactive and resistive elements, embodied as a parallel reactive port and resistive port, provides increased low frequency response compared to an embodiment using a series reactive and resistive elements. The parallel resistance does not substantially attenuate the low frequency output while the series resistance does. Using a small rear cavity with parallel ports allows the earphone to have improved low frequency output and a desired balance between low frequency and high frequency output.

0028The PEQ hole 120 is located so that it will not be blocked when in use. For example. the PEQ hole 120 is not located in the portion of the body 12 that is in direct contact with the ear, but away from the ear in the front chamber 114. The primary purpose of the hole is to avoid an over-pressure condition when the earpiece 10 is inserted into the user's ear. Additionally, the hole can used to provide a fixed amount of leakage that acts in parallel with other leakage that may be present. This helps to standardize response across individuals. In some examples, the PEQ hole 120 has a diameter of about 0.50 mm. Other sizes may be used, depending on such factors as the volume of the front chamber 114 and the desired frequency response of the earphones. Adding the PEQ hole makes a trade off between some loss in low frequency output and more repeatable overall performance.

0029The body 12 is designed to comfortably couple the acoustic elements of the earphone to the physical structure of the wearer's ear. As shown in <figref idref="f0007">figures 7A-7D</figref>, the body 12 has an upper portion 802 shaped to make contact with the tragus and anti-tragus of the ear, and a lower portion 110 shaped to enter the ear canal 12, as mentioned above. In some examples, the lower portion 110 is shaped to fit within but not apply significant pressure on the flesh of the ear canal 12. The lower portion 110 is not relied upon to provide retention of the earphone in the ear, which allows it to seal to the ear canal with minimal pressure. A void 806 in the upper portion 802 receives the acoustic elements of the earphone (not shown), with the nozzle 126 (of <figref idref="f0006">Fig. 6</figref>) extending into a void 808 in the lower portion 110. In some examples, the body 12 is removable from the earpiece 10, examples, the body 12 is formed of materials having different hardnesses, as indicated by regions 810 and 812. The outer region 810 is formed of a soft material. for example, one having a durometer of 16 shore A, which provides good comfort because of its softness. Typical durometer ranges for this section are from 2 shore A to 30 shore A. The inner region 812 is formed from a harder material, for example, one having a durometer of 70 shore A. This section provides the stiffness needed to hold the cushion in place. Typical durometer ranges for this section are from 30 shore A to 90 shore A. In some examples, the inner section 812 includes an O-ring type retaining collar 809 to retain the cushion on the acoustic components. The stiffer inner portion 812 may also extend into the outer section to increase the stiffness of that section. In some examples. variable hardness could be arranged in a single material.

0030In some examples, both regions of the cushion are formed from silicone. Silicone can be fabricated in both soft and more rigid durometers in a single part. In a double-shot fabrication process, the two sections are created together with a strong bond between them. Silicone has the advantage of maintaining its properties over a wide temperature range, and is known for being successfully used in applications where it remains in contact with human skin. Silicone can also be fabricated in different colors, for example, for identification of different sized cushions, or to allow customization. In some examples, other materials may be used, such as thermoplastic elastomer (TPE). TPE is similar to silicone, and may be less expensive, but is less resistant to heat. A combination of materials may be used, with a soft silicone or TPE outer section 812 and a hard inner section 810 made from a material such as ABS, polycarbonate, or nylon. In some examples, the entire cushion may be fabricated from silicone or TPE having a single hardness, representing a compromise between the softness desired for the outer section 812 and the hardness needed for the inner section 810.

0031<figref idref="f0008">Fig. 8</figref> shows a blowup view of the electronics module 16, the acoustic driver module 14, and the body 12. The electronics module comprises plastic enclosure 402 (which may be multi-piece) that encloses electronic circuitry (not shown) for wirelessly receiving audio signals. Acoustic driver module 14 includes shell 113, acoustic driver 116, and shell 115. The position of the mass port 122 and the reactive port 124 in shell 113 are shown. The position of the PEQ hole 120 on shell 115 is also shown. When the earpiece 10 is assembled, nozzle 126 fits inside the outlet section 15 of the body 12. Referring again to <figref idref="f0006">Fig. 6</figref>, the outside diameter of the nozzle 126 may be approximately the same as the inside dimension of the outlet section 15, as indicated by arrows 702 and 704.

0032<figref idref="f0009">Fig. 9</figref> shows a variation of the assembly of <figref idref="f0006">Fig. 6</figref>. The implementation of <figref idref="f0009">Fig. 9</figref> is the mirror image of the implementation of <figref idref="f0006">Fig. 6</figref>, to indicate that the earpiece can be configured for either ear. In the implementation of <figref idref="f0009">Fig. 9</figref>, an outside dimension of the nozzle is smaller than the corresponding inside dimension of the outlet section 15, as indicated by arrows 702' and 704'. The difference in dimensions provides a space 706 between the nozzle and the outlet section 15 of the body 12. The space permits the lower portion of the body 15 to better conform to the ear canal, providing additional comfort and stability. The rigidity of the nozzle results in the ability of the outlet section to conform to the ear canal, without substantially changing the shape or volume of the passage to the ear canal, so the acoustic performance of the earpiece is not appreciably affected by changes in ear size or geometry. The smaller dimension of the nozzle may adversely affect high frequency (e.g. above 3 kHz. However, the circuitry for wirelessly receiving audio signals enclosed in electronics module 16 may be limited to receiving audio signals up to only about 3 kHz, so the adversely affected high frequency performance is not detrimental to the overall performance of the earpiece. One way of allowing an earpiece to play louder is to overdrive the acoustic driver. Overdriving an acoustic driver tends to introduce distortion and adversely affects the bandwidth.

0033<figref idref="f0010">Fig. 10</figref> shows a body 12 with a portion of the outlet section 15 and the nozzle 126 removed. The inside of the outlet section 15 and the outside of the nozzle 126 are both ovals. The minor axis of the outside of the nozzle, represented by line 702' is 4.05 mm. The minor axis of the inside of the outlet section 15, represented line 704' is 4.80 mm. The width of the space 706 at its widest point is 0.75 mm.

0034One way of achieving good acoustic performance is to use a larger driver. A larger acoustic driver, for example a 15 mm nominal diameter acoustic driver can play louder with less distortion and with better bandwidth and intelligibility than conventional smaller acoustic drivers. However the use of larger acoustic drivers has some disadvantages. Acoustic drivers that have a diameter (nominal diameter plus housing) of greater than 11 mm do not fit in the conchas of many people. If the acoustic driver is positioned outside the concha, the center of mass may be well outside the ear so that the earpiece is unstable and tends to fall out of the ear. This problem is made worse by the presence of the electronics module 12, which may be heavy relative to other components of the earpiece, and which moves the center of mass even further away from the side of the head.

0035As best shown in Views B and E of <figref idref="f0002">Fig. 2</figref>, the acoustic driver module is slanted inwardly and forwardly relative to the plane of the positioning and retention structure 20 and the plane of the electronics module 12. The inward slant shifts the center of gravity relative to an acoustic driver module that is substantially parallel to the positioning and retention structure 20 or the electronics module 12, or both. The forward slant combined with the inward slant permits more of the acoustic driver module to fit inside the concha of the ear, increasing the stability of the earpiece.

0036While human ears show a great variability in size and shape, we have found that a majority of the population can be accommodated by providing sets of ear pieces offering a small number of pre-defined sizes, as long as those sizes maintain particular relationships between the dimensions of the retaining structure 20. <figref idref="f0011">Fig. 11</figref> shows dimensions characterizing the shape and size of the positioning and retaining structure 20. Of particular interest are the radii and lengths of the outer edges 222 and 224, respectively, of the legs 22 and 24, i.e., the shape of the outer perimeter of the portion that contacts the ear.

0037To fit to the antihelix, the outer edge 222 of the outer leg 22 has a variable radius of curvature, more-sharply curved near the body 12 and flattening out at positions farther from the body 12. In some examples, as shown in <figref idref="f0011">figure 11</figref>, the leg is defined by two segments 22a and 22b, each having a different radius R_oa and R_ob, that is constant within that segment. In some examples, three different radii are used, with an intermediate radius smoothing the transition between the outer, flatter portion, and the inner, more-curved portion. In other examples, there may be many segments with different radii, or the entire leg may have a continuously variable radius of curvature. The center points from which the radii are measured are not necessarily the same for the different segments; the radius values are merely characterizations of the curvature at different points, not references to curves around a common center. The outer edge 222 has a total length L_o as measured from a point 226 where the leg joins the body 12 and an end point 228 where it meets the flat tip at extremity 36.

0038Similarly, the outer edge 224 of the inner leg 24 in <figref idref="f0011">Fig. 11</figref> also has two segments 24a and 24b, with different radii R_ia and R_ib, and a total length Li measured between points 230 and 232. In examples having more than two segments in the inner leg, unlike the outer leg, the radii may not have a monotonic progression. In particular, a middle segment may have the shortest radius, to make a relatively sharp bend between relatively straighter sections at either end. As with the outer leg, the inner leg may have two different radii, as shown, three radii, or it may have more, up to being continuously variable.

0039The radii and lengths of the inner and outer legs are interrelated. As the two legs are joined at one end, making the outer leg larger without a corresponding increase to the inner leg would cause the radii to decrease (making the curves more extreme), and vice-versa. Likewise, changing any of the radii would require one or the other of the legs to change length. As the retention feature is made smaller or larger, to fit different sized ears, the relationships between the different segments may be changed or kept the same. Using a particular set of relative lengths and curvatures allows a single retention feature design to fit a wide range of individuals with a small number of unique parts.

0040Table I shows a set of values for one embodiment of a retention feature design having three sizes with common relative dimensions (all given in mm). Table 2 shows the ratios of the various dimensions, including the mean and the percent variation from the mean of those ratios across the three sizes. One can see that the ratio of R_oa to R_ob, the two radii of the outer edge of the outer leg, and the ratio of L_o to L_i, the lengths of the outer edges of the two legs, are very similar across all three sizes, with the ratio farthest from the mean still within 10% of the mean ratio. Two of the ratios involving the inner leg's radii vary farther from their mean than that, though the ratio of the end radius of the outer leg to the end radius of the inner leg is very consistent across all three sizes, varying only 6% from the mean. As the curvature of the inner leg is largely dictated by the curvature of the outer leg and the relative lengths of the two legs, it is the R_oa/R_ob and L_o/L_i measures that will matter most. In general, three ear tips of the shape described, and having an outer edge 222 defined by two radii R_oa and R_ob having a ratio within 10% of 0.70 and a total length L_o of the outer edge that is within 10% of 2.6 times the length Li of the opposite edge 224, and covering an appropriate range of absolute sizes between about 30 mm for the smallest outer leg length and 45 mm for the largest outer leg length, will fit a significant portion of the population. <tables id="tabl0001" num="0001"><table frame="all"><title>Table I</title><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="21mm" align="center" /><colspec colnum="2" colname="col2" colwidth="14mm" align="center" /><colspec colnum="3" colname="col3" colwidth="17mm" align="center" /><colspec colnum="4" colname="col4" colwidth="14mm" align="center" /><thead valign="top"><row><entry>Dimension</entry><entry>Small</entry><entry>Medium</entry><entry>Large</entry></row></thead><tbody valign="middle"><row><entry>R_oa</entry><entry>9.28</entry><entry>12.0</entry><entry>12.63</entry></row><row><entry>R_ob</entry><entry>12.16</entry><entry>17.5</entry><entry>19.67</entry></row><row><entry>R_ia</entry><entry>3.75</entry><entry>5.25</entry><entry>5.00</entry></row><row><entry>R_ib</entry><entry>7.75</entry><entry>13.0</entry><entry>10.00</entry></row><row><entry>L_o</entry><entry>31</entry><entry>36</entry><entry>46</entry></row><row><entry>L_i</entry><entry>11</entry><entry>15</entry><entry>19</entry></row></tbody></tgroup></table></tables><tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="6"><colspec colnum="1" colname="col1" colwidth="17mm" align="center" /><colspec colnum="2" colname="col2" colwidth="14mm" align="center" /><colspec colnum="3" colname="col3" colwidth="17mm" align="center" /><colspec colnum="4" colname="col4" colwidth="14mm" align="center" /><colspec colnum="5" colname="col5" colwidth="14mm" align="center" /><colspec colnum="6" colname="col6" colwidth="14mm" align="center" /><thead valign="top"><row><entry>Ratio</entry><entry>Small</entry><entry>Medium</entry><entry>Large</entry><entry>Mean</entry><entry>% Var</entry></row></thead><tbody valign="middle"><row><entry>R_oa/R_ob</entry><entry>0.76</entry><entry>0.69</entry><entry>0.64</entry><entry>0.70</entry><entry>9%</entry></row><row><entry>R_ia/R_ib</entry><entry>0.48</entry><entry>0.40</entry><entry>0.50</entry><entry>0.46</entry><entry>13%</entry></row><row><entry>R_oa/R_ia</entry><entry>2.47</entry><entry>2.29</entry><entry>2.53</entry><entry>2.43</entry><entry>6%</entry></row><row><entry>R_ob/R_ib</entry><entry>1.57</entry><entry>1.35</entry><entry>1.97</entry><entry>1.63</entry><entry>21%</entry></row><row><entry>L_o/L_i</entry><entry>2.82</entry><entry>2.40</entry><entry>2.42</entry><entry>2.59</entry><entry>9%</entry></row></tbody></tgroup></table></tables>