Patent Publication Number: US-8989427-B2

Title: Earphones

Description:
BACKGROUND 
     This description relates to earphones. 
     U.S. Pat. No. 5,208,868 discloses an apparatus for reducing pressure inside a headphone that includes a port between front and back cavities. Preferably there is a resistive element and a high compliance diaphragm. 
     SUMMARY 
     All examples and features mentioned below can be combined in any technically possible way. 
     In one aspect, an earphone includes a first acoustic chamber with one or more of a reactive element and a resistive element for acoustically coupling the first acoustic chamber with an environment external to the earphone. The earphone includes an acoustic transducer and a second acoustic chamber separated from the first acoustic chamber by the acoustic transducer. A housing supports the earphone from the concha of a wearer&#39;s ear and extends the second acoustic chamber at least to an entrance of an ear canal of the wearer&#39;s ear. A port acoustically couples the first and second acoustic chambers. 
     Embodiments may include one of the following features, or any combination thereof. There is only a single opening in the second chamber, besides an entrance to the port, which acoustically couples the second chamber to the ear canal of the wearer&#39;s ear. The second chamber does not have a pressure equalization port to connect the second chamber to the environment external to the earphone. The first acoustic chamber has a volume between about 0.1 cm 3  to about 3 cm 3 . The second acoustic chamber has a volume between about 0.05 cm 3  to about 3 cm 3 . The reactive element has an acoustic absolute value impedance in the range of from about 
             3   ×     10   7     ⁢     kg       m   4     ×   sec             
to about
 
             6   ×     10   8     ⁢     kg       m   4     ×   sec             
at 1 kHz. The resistive element has a specific acoustic impedance in the range of from about
 
             3   ×     10   7     ⁢     kg       m   4     ×   sec             
to about
 
             6   ×     10   8     ⁢       kg       m   4     ×   sec       .           
The port has a diameter in the range of from about 0.25 mm to about 3 mm. The port has a diameter of about 0.5 mm. The port has a length in the range of from about 0.25 mm to about 10 mm. The port has a length of about 1 mm. The port has an acoustic absolute value impedance in the range of from about
 
             1   ×     10   7     ⁢     kg       m   4     ×   sec             
to about
 
             3   ×     10   8     ⁢     kg       m   4     ×   sec             
at 1 kHz. A pair of earphones as described herein.
 
     In another aspect, an earphone includes a first acoustic chamber with one or more of a reactive element and a resistive element for acoustically coupling the first acoustic chamber with an environment external to the earphone. The earphone also includes an acoustic transducer and a second acoustic chamber separated from the first acoustic chamber by the acoustic transducer. A port acoustically couples the first and second acoustic chambers. There is only a single opening in the second chamber, besides an entrance to the port, which acoustically couples the second chamber to an ear canal of a wearer&#39;s ear. 
     Embodiments may include one of the above and/or below features, or any combination thereof. The earphone further including a housing to support the earphone from the concha of a wearer&#39;s ear and to extend the second acoustic chamber at least to an entrance of an ear canal of the wearer&#39;s ear. 
     In a still further aspect, an earphone includes a first acoustic chamber with one or more of a reactive element and a resistive element for acoustically coupling the first acoustic chamber with an environment external to the earphone. The earphone further includes an acoustic transducer and a second acoustic chamber separated from the first acoustic chamber by the acoustic transducer. A housing supports the earphone from the concha of a wearer&#39;s ear and extends the second acoustic chamber at least to an entrance of an ear canal of the wearer&#39;s ear. A port acoustically couples the first and second acoustic chambers. There is only a single opening in the second chamber, besides an entrance to the port, which acoustically couples the second chamber to the ear canal of the wearer&#39;s ear. 
     Embodiments may include one of the above features, or any combination thereof. Other features and advantages will be apparent from the description and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a human ear; 
         FIG. 2A  is a perspective view of an earphone located in the ear; 
         FIG. 2B  is an isometric view of an earphone; 
         FIG. 3  is a schematic cross section of a first example of an earphone; and 
         FIG. 4  is a schematic cross section of a portion of a second example of an earphone. 
     
    
    
     DETAILED DESCRIPTION 
     “Earphone” as used herein refers to a device that fits around, on, or in an ear and which radiates acoustic energy into the ear canal. An earphone may include an acoustic driver to transduce audio signals to acoustic energy. An around the ear earphone uses an acoustic driver that is much larger relatively speaking than a driver used in an in-ear earphone. The substantially smaller driver of the in-ear earphone typically has much lower acoustic output capability due to a reduction in air volume displacement. As such, acoustic cancellation caused by out of phase acoustic energy radiating from both sides of a diaphragm of the driver is much more of a concern for an in-ear earphone than an around (or on) the ear earphone. While the figures and descriptions following use a single earphone, an earphone may be a single stand-alone unit or one of a pair of earphones, one for each ear. An earphone may be connected mechanically to another earphone, for example by a headband or by leads which conduct audio signals to an acoustic driver in the earphone. An earphone may include components for wirelessly receiving audio signals. Unless otherwise specified, an earphone may include components of an active noise reduction (ANR) system. 
     As shown in  FIG. 1 , a human ear  10  includes an ear canal  12  which leads to the sensory organs (not shown). The pinna  11 , the part of the ear outside the head, includes the concha  14 , the hollow next to the ear canal  12 , defined in part by the tragus  16  and anti-tragus  18 . An earphone is generally designed to be worn over the pinna, in the concha, or in the ear canal. 
     As shown in  FIGS. 2A and 2B , an earphone  100  has a housing including a first region  106  designed to support the earphone from the concha  14  of the wearer&#39;s ear  10 , and a second region  104  to be located at the entrance to, or in, the ear canal  12 . A region  102  “floats” outside the wearer&#39;s ear between the tragus  16  and antitragus  18  ( FIG. 1 ). ( FIGS. 2A and 2B  show a wearer&#39;s left ear and corresponding earphone  100 . A complementary earphone may fit the right ear, not shown. In some examples, only one earphone is provided. In some examples, a left earphone and a right earphone may be provided together as a pair.) A cushion  106  (i.e. ear tip) couples the acoustic components of the earphone to the physical structure of a wearer&#39;s ear. A plug  202  connects the earphone to a source of audio signals, such as a CD player, cell phone, MP3 player, or PDA (not shown), or may have multiple plugs (not shown) allowing connection to more than one type of device at a time. A circuit housing  204  may include circuitry for modifying the audio signal, for example, by controlling its volume or providing equalization. The circuitry may also provide noise cancellation signals to the earphones. The housing  204  may also include switching circuitry, either manual or automatic, for connecting the signals output by one or another of the above mentioned sources to the earphone. A cord  206  conveys audio signals from the source to the earphones. In some examples, the signals may be communicated wirelessly, for example, using the Bluetooth™ wireless protocol, and the cord  206  would not be included. Alternatively or additionally, a wireless link may connect the circuitry with one or more of the sources. 
     As shown in  FIG. 3 , the first region  102  of the earphone  100  includes a rear acoustic chamber  112  and a front acoustic chamber  114  defined by shells  113  and  115  of the housing, respectively, on either side of a driver (acoustic transducer)  116 . In some examples, a 14.8 mm diameter driver is used. Other sizes and types of acoustic transducers could be used depending, for example, on the desired frequency response of the earphone. The driver  116  separates the front and rear acoustic chambers  114  and  112 . The shell  115  of the housing extends ( 126 ) the front chamber  114  to at least the entrance to the ear canal  12 , and in some embodiments into the ear canal  12 , through the cushion  106  and ends at an opening  127  that may include an acoustic resistance element  118 . In some examples, the resistance element  118  is located within the extended portion  126  (i.e. a nozzle), rather than at the end, as illustrated. An acoustic resistance element dissipates a proportion of acoustic energy that impinges on or passes through it. In other examples, no resistance element is included, but a screen may be used in its place to prevent debris from entering the front chamber  114 . The front chamber  114  does not have a pressure equalization (PEQ) port to connect the chamber  114  to an environment external to the earphone. A PEQ port can be a source for a leak and thus a path for acoustic noise to enter the headphone. 
     A port  119  acoustically couples the front acoustic chamber  114  and the rear acoustic chamber  112 . The port  119  serves to relieve air pressure that could be built up within the ear canal  12  and front chamber  114  when (a) the earphone  100  is inserted into or removed from the ear  10 , (b) a person wearing the earphone  100  experiences shock or vibration, or (c) the earphone  100  is struck or repositioned while being worn. The port  119  preferably has a diameter of between about 0.25 mm to about 3 mm, and more preferably has a diameter of about 0.5 mm. The port  119  preferably has a length of between about 0.25 mm to about 10 mm, and more preferably has a length of about 1 mm. 
     The amount of passive attenuation that can be provided by a ported earphone is often limited by the acoustic impedance through the ports. Generally, more impedance is preferable. However, certain port geometry is often needed in order to have proper system performance. Ports are used to improve acoustic output, equalize audio response and provide a venting path during overpressure events. Impedance may be changed in a number of ways, some of which are related. Impedance is frequency dependent, and it may be preferable to increase impedance over a range of frequencies and/or reduce the impedance at another range of frequencies. The impedance has two components: a resistive component (DC flow resistance R) and a reactive or mass component jωM, where ω is the frequency, 
             M   =         ρ   ⁢           ⁢   l     A     .           
M is the acoustic mass, l is the length of the port, A is the cross-sectional area of the port, and ρ is the density of air (which if actual measurement is difficult or impossible, may be assumed to be 1.2). The total impedance can be calculated at a specific frequency of interest by determining the magnitude or absolute value of the acoustic impedance |z|.
 
     The port  119  preferably has an absolute value |z| acoustic impedance of between about of 
             1   ×     10   7     ⁢           ⁢     kg       m   4     ×   sec             
to about
 
             3   ×     10   8     ⁢           ⁢     kg       m   4     ×   sec             
at 1 kHz and more preferably has an absolute value |z| acoustic impedance of about
 
             4   ×     10   7     ⁢           ⁢     kg       m   4     ×   sec             
at 1 KHz. The port  119  preferably has an absolute value |z| acoustic impedance of between about of
 
             6   ×     10   5     ⁢           ⁢     kg       m   4     ×   sec             
to about
 
             2   ×     10   8     ⁢           ⁢     kg       m   4     ×   sec             
at 10 Hz and more preferably has an absolute value |z| acoustic impedance of about
 
             1.2   ×     10   7     ⁢           ⁢     kg       m   4     ×   sec             
at 10 Hz.
 
     The primary purpose of the port  119  is to avoid an over-pressure condition when, e.g., the earphone  100  is inserted into or removed from the user&#39;s ear  10 , or during use of the earphone. Pressure built up in the front acoustic chamber  114  escapes to the rear acoustic chamber  112  via the port  119 , and from there to the environment via back cavity ports  122  and  124 , mainly the mass port  122  (discussed in more detail below). Additionally, the port  119  can be 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. Adding the port  119  makes a tradeoff between some loss in low frequency output and more repeatable overall performance. The port  119  provides substantially the same passive attenuation as completely blocking a typical front chamber PEQ port with similar architecture. It was expected that adding the port  119  would cause a loss in low frequency output (e.g. in the frequency band of about 20-100 Hz) due to front-to-back self-cancellation of signals from the driver  116 , but surprisingly this did not happen. The port  119  in series with the rear cavity ports  122  and  124  provides a higher impedance venting leak path compared with using a traditional front chamber PEQ instead of the port  119 . Surprisingly, however, it was found that this higher impedance results in a more linear behavior during pressure equalization events which reduces the negative impact of the higher impedance. 
     The rear chamber  112  is sealed around the back side of the driver  116  by the shell  113  except that the rear chamber  112  includes one or both of 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 . The reactive element  122  and the resistive element acoustically couple the rear acoustic chamber  112  with an environment external to the earphone, thereby relieving the air pressure mentioned above. U.S. Pat. No. 6,831,984 describes the use of parallel reactive and resistive ports in a headphone device, and is incorporated here by reference. Although we refer to ports 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. 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 element 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 reactive element  122  preferably has an absolute value acoustic impedance |z| in the range of from about 
             3   ×     10   7     ⁢     kg       m   4     ×   sec             
to about
 
             6   ×     10   8     ⁢           ⁢     kg       m   4     ×   sec             
at 1 kHz, and more preferably about
 
             1.5   ×     10   8     ⁢       kg       m   4     ×   sec       .           
The reactive element  122  preferably has an absolute value acoustic impedance |z| in the range of from about
 
             1   ×     10   6     ⁢           ⁢     kg       m   4     ×   sec             
to about
 
             2   ×     10   8     ⁢           ⁢     kg       m   4     ×   sec             
at 10 Hz, and more preferably about
 
             1.1   ×     10   7     ⁢       kg       m   4     ×   sec       .           
The resistive element  124  preferably has a specific acoustic impedance in the range of from about
 
             3   ×     10   7     ⁢     kg       m   4     ×   sec             
to about
 
               6   ×     10   8     ⁢           ⁢     kg       m   4     ×   sec         ,         
and more preferably about
 
             1.15   ×     10   8     ⁢       kg       m   4     ×   sec       .           
The reactive element  122  preferably has a diameter of between about 0.5 mm to about 2 mm, and more preferably has a diameter of about 1 mm. The reactive element  122  preferably has a length of between about 5 mm to about 25 mm, and more preferably has a length of about 15 mm. The resistive element  124  preferably has a diameter of about 1.7 mm and a length of preferably about 1 mm covered with a 260 rayl resistive material (e.g. cloth). These dimensions provide both the acoustic properties desired of the reactive port  122 , and an escape path for the pressure built up in the front chamber  114  and transferred to the rear chamber  112  by the port  119 . The total absolute value impedance from the front chamber  114  through the port  119  and out the back chamber ports  122  and  124  is preferably less than about
 
             1   ×     10   8     ⁢     kg       m   4     ×   sec             
at 10 Hz. The ports  122  and  124  provide porting from the rear acoustic chamber  112  to an environment external to the earphone. Furthermore, in order to receive a meaningful benefit in terms of passive attenuation when using a front to back port  119  in a ported system, the ratio of the impedance of the ports  122  and  124  to the impedance of the port  119  is preferably greater than 0.25 and more preferably around 1.6 at 1 kHz.
 
     For an ANR earphone two functions (of many) of the ports  119 ,  122  and  124  are to increase the output of the system (improves active noise reduction) and provide pressure equalization. In addition, it is desirable to maximize the impedance of these ports at frequencies that can improve the total system noise reduction. At certain frequencies (e.g. at low frequency) it may be preferable for the impedance to be low for venting pressure or increasing low frequency output, and at certain other frequencies (e.g. at 1 kHz) it may be preferable for the impedance to be high in order to maximize passive attenuation. Ports allow this to occur as they can have both a resistive DC component and a reactive frequency dependent component depending upon their design. 
     Each of the cushion  106 , cavities  112  and  114 , driver  116 , damper  118 , port  119 , and elements  122  and  124  have acoustic properties that may affect the performance of the earphone  100 . 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. The rear chamber  112  preferably has a volume of between about 0.1 cm 3  to about 3.0 cm 3 , and more preferably has a volume of about 0.5 cm 3  (this volume includes a volume behind a diaphragm of the driver  116  (inside the transducer), but does not include a volume occupied by metal, pcb, plastic or solder). Excluding the driver, the front chamber  114  preferably has a volume of between about 0.05 cm 3  to about 3 cm 3 , and more preferably has a volume of about 0.25 cm 3 . 
     The reactive port  122  resonates with the back chamber volume. 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 made from an 80×700 Dutch twill wire cloth, for example, that available from Cleveland Wire of Cleveland, Ohio, and has a diameter of about 1.7 mm. 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. 
     Some or all of the elements described above can be used in combination to achieve a particular frequency response (non-electronically). In some examples, additional frequency response shaping may be used to further tune sound reproduction of the earphones. One way to accomplish this is with passive electrical equalization using circuitry. Such circuitry can be housed in-line with the earphones, for example, inside the circuit housing  204  ( FIG. 2A ). If active noise reduction circuitry or wireless audio circuitry is present, such powered circuits may be used to provide active equalization. 
     In  FIG. 4 , another example of an earphone  300  includes a rear acoustic chamber  312  and a front acoustic chamber  314  defined by shells  313  and  315  of the housing, respectively, on either side of a driver (acoustic transducer)  316 . In some examples, a 16 mm diameter driver is used. Other sizes and types of acoustic transducers could be used depending, for example, on the desired frequency response of the earphone. The driver  316  separates the front and rear acoustic chambers  314  and  312 . The front chamber  314  does not have a pressure equalization port to connect the chamber  314  directly to an environment external to the earphone. 
     A port  319  acoustically couples the front chamber  314  and the rear acoustic chamber  312 . The port  319  serves to relieve air pressure that could be built up within the ear canal and front chamber  314  during over pressure events (e.g. when the earphone  300  is inserted into the ear). As discussed above, that pressure is then released into the environment through a reactive port from the rear chamber  314 . The port  319  preferably has the same dimensions and characteristics that were mentioned above. The rear chamber  312  is sealed around the back side of the driver  316  by the shell  313  except that the rear chamber  312  includes one or both of a reactive element, such as a port (also referred to as a mass port), and a resistive element, which may also be formed as a port (not shown in this sectional view). The reactive element and the resistive element acoustically couple the rear acoustic chamber  312  with an environment external to the earphone. The reactive element and the resistive element preferably have the same dimensions and characteristics that were mentioned above. The front chamber  314  includes a nozzle and an ear tip (not shown in this sectional view) that couple the front chamber  314  to the user&#39;s ear (not shown). 
     A number of implementations have been described. Nevertheless, it will be understood that additional modifications may be made without departing from the scope of the inventive concepts described herein, and, accordingly, other embodiments are within the scope of the following claims.