Earphone with noise reduction having a modified port

Abstract

An earphone is provided, the earphone being configured to provide an acoustic output signal to an ear of a wearer in dependence on an earphone audio signal and further configured to be arranged on the wearer's head in an operating position such that a front cavity between the head and the earphone is separated from ambient space. The earphone comprises a housing having a housing wall separating a rear cavity from the front cavity and from ambient space, an ear cushion, a first diaphragm suspended across an opening in the housing wall between the front cavity and the rear cavity and configured to be actively driven. The earphone further has a port structure fluidly connecting the rear cavity and ambient space through the housing wall. The port structure having a first open end fluidly coupled to the rear cavity and a second open end fluidly coupled to ambient space, and having a port cavity defined by the first open end, the second open end and a port wall, the port wall extending from the housing wall into the rear cavity and/or into the ambient space. The port wall has one or more acoustically permeable sections fluidly connecting the port cavity with the rear cavity and/or the ambient space through the port wall.

Claims

1. An earphone configured to provide an acoustic output signal to an ear of a wearer in dependence on an earphone audio signal and further configured to be arranged on the wearer's head in an operating position such that a front cavity between the head and the earphone is separated from ambient space, the earphone comprising: a housing having a housing wall separating a rear cavity from the front cavity and from ambient space; an ear cushion arranged and configured to attenuate acoustic signals entering the front cavity from ambient space when the earphone is in the operating position; a first diaphragm suspended across an opening in the housing wall between the front cavity and the rear cavity and configured to be actively driven to provide at least a portion of the acoustic output signal; a port structure fluidly connecting the rear cavity and ambient space through the housing wall, the port structure having a first open end fluidly coupled to the rear cavity and a second open end fluidly coupled to ambient space, and the port structure having a port cavity defined by the first open end, the second open end and a port wall, the port wall extending from the housing wall into the rear cavity and/or into the ambient space, wherein the port wall has one or more acoustically permeable sections fluidly connecting the port cavity with the rear cavity and/or the ambient space through the port wall.

2. An earphone according to claim 1, wherein the port structure fluidly connecting the rear cavity and ambient space has a port structure resonance frequency, and wherein the port structure resonance frequency is between 100 Hz and 1 kHz, such as between 100 Hz and 500 Hz.

3. An earphone according to claim 1, wherein the port structure and the rear cavity are configured to act as a second order low pass filter.

4. An earphone according to claim 1, wherein the port structure is configured to act as an acoustically open hole between the rear cavity and ambient space at low frequencies.

5. An earphone according to claim 1, wherein the one or more acoustically permeable sections are distributed along a length of the port wall, or wherein the one or more acoustically permeable sections are distributed at different distances from the housing wall.

6. An earphone according to claim 1, wherein the port wall has a port wall area, and wherein the one or more acoustically permeable sections are distributed over between 5% and 50% of the port wall area.

7. An earphone according to claim 1, wherein the one or more acoustically permeable sections comprises through holes, acoustically resistive openings, through holes covered with an acoustical lossy material, through holes covered with an acoustical mesh.

8. An earphone according to claim 1, wherein the acoustic impedance of the one or more acoustically permeable sections is between 500 and 8000 L/m.sup.2s.

9. An earphone according to claim 1, wherein the one or more acoustically permeable sections are distributed discretely along the length of the port wall

10. An earphone according to claim 1 any of the procoding claims, wherein the port structure has a longitudinal extension in a longitudinal direction non-parallel with the housing wall which is larger than a transversal extension in a direction parallel to the housing wall.

11. An earphone according to claim 1, wherein the port structure comprises a tubular member having a first open end fluidly coupled to the rear cavity and a second open end fluidly coupled to ambient space, the tubular member having a tubular member wall defining the port cavity, and wherein the tubular member has a base and a height, the base having a circumscribed circle or the base being circular, wherein the height relative to a diameter of the circumscribed circle or of the circular base is larger than one.

12. An earphone according to claim 1, wherein the one or more acoustically permeable sections are dimensioned to dampen the resonance of the port structure by at least 6 dB.

13. An earphone according to claim 1, wherein at least one acoustically permeable section is a longitudinal section having a length corresponding to at least 80% of a length of the port wall, or wherein at least one acoustically permeable section is a circumferential section extending along at least 80% of a circumference of the port wall, and/or wherein a width of the longitudinal section and/or a width of the circumferential section corresponds to less than 25% of the length of the port wall.

14. An earphone according to claim 1, the earphone further comprising a noise cancelling circuit being configured to receive the earphone audio signal, to implement an active noise cancelling function and to provide a noise cancelling audio signal to the ear of a wearer.

15. A hearing device comprising one or two earphones according to claim 1 and configured to provide an earphone audio signal to each of the one or two earphones in dependence on one or more audio input signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The invention will be explained in more detail below in connection with preferred embodiments and with reference to the drawings in which:

[0069] FIGS. 1A-1B schematically show an earphone according to the present disclosure,

[0070] FIGS. 2A-2D schematically show different acoustically permeable sections distributed along a port wall,

[0071] FIGS. 3A-3F schematically show a plurality of possible base shapes for a port structure according to the present disclosure,

[0072] FIG. 4 shows a port structure as disclosed herein,

[0073] FIGS. 5A-5B are curves showing the attenuation and the sound pressure at the ear of a wearer,

[0074] FIG. 6 shows the attenuation of a port structure with and without acoustically permeable sections,

[0075] FIG. 7 shows an earphone according to an embodiment of the disclosure further comprising a resistive port,

[0076] FIG. 8 shows an earphone according to an embodiment of the disclosure further comprising an active noise cancelling circuit.

DETAILED DESCRIPTION OF THE DRAWING

[0077] FIG. 1A shows an earphone 1 arranged in an operating position on the head 2 of a user or wearer of the earphone 1. The earphone 1 comprises a housing 3 with an annular ear cushion 4. The housing 3 and the ear cushion 4 together separate a front cavity 5 between the head 2 and the earphone 1 from ambient space 6 when the earphone 1 is in the operating position. The earphone 1 is adapted to provide an acoustic output signal to an ear 7 of the wearer in dependence on an earphone audio signal, and the operating position is preferably chosen such that the front cavity 5 comprises the ear canal 8 of the ear 7. The ear cushion 4 is arranged and adapted to attenuate acoustic signals entering the front cavity 5 from ambient space 6 when the earphone 1 is in the operating position. The attenuation provided by the ear cushion 4 at frequencies above 1 kHz may preferably be e.g. greater than 20 dB, greater than 10 dB or greater than 6 dB. The ear cushion 4 may be permanently or detachably attached to the housing 3 in any known way, e.g. by means of adhesives, screws, snap couplings and/or bayonet couplings.

[0078] The housing 3 has a wall 9 that separates a rear cavity 10 from the front cavity 5 and from ambient space 6. In some embodiments, the front cavity 5 may be substantially larger than the rear cavity 10, in other embodiments, the front cavity 5 and the rear cavity 10 may be comparable in size, and in further embodiments, the rear cavity 10 may be substantially larger than the front cavity 5. A first diaphragm 11 of a first electrodynamic driver 12 is reciprocatably suspended across an opening or a through hole in the housing wall 9 between the front cavity 5 and the rear cavity 10 and is adapted to be actively driven to provide at least a portion of the acoustic output signal. The first driver 12 thus functions as an output transducer of the earphone 1. Within this document, a through hole in a wall refers to a passage through the wall that fluidly connects the two opposite sides of the wall or in the case that a diaphragm is suspended across the through hole and thus obstructs the fluid passage, a passage that would fluidly connect the two opposite sides of the wall if the diaphragm were absent. In the earphone 1, the first diaphragm 11 obstructs the fluid passage through the through hole that would otherwise fluidly connect the front cavity 5 and the rear cavity 10.

[0079] The earphone 1 is configured to provide an acoustic output signal to an ear of a wearer in dependence on an earphone audio signal. The acoustic output signal is provided to the wearer via diaphragm 11 and front cavity 5. The earphone is furthermore configured to be arranged on the wearer's head 2 in an operating position such that a front cavity 5 between the head 2 and the earphone 1 is separated from ambient space 6. The earphone 1 comprises a housing 3 having a housing wall 9 separating a rear cavity 10 from the front cavity 5 and from ambient space 6. The earphone 1 further comprises an ear cushion 4 arranged and configured to attenuate acoustic signals entering the front cavity 5 from ambient space 6 when the earphone 1 is in the operating position. A first diaphragm 11 is suspended across an opening in the housing wall 9 between the front cavity 5 and the rear cavity 10 and configured to be actively driven to provide at least a portion of the acoustic output signal.

[0080] The first diaphragm 11 may be reciprocally suspended across the opening or the through-hole in the housing wall 9 between the front cavity 5 and the rear cavity 10, and thus be suspended to reciprocate. The first diaphragm 11 is configured to be actively driven to provide at least a portion of the acoustic output signal. The earphone 1 may comprise a first driver 12, such as a first electrodynamic driver, for driving the diaphragm 11.

[0081] The earphone 1 further comprises a port structure 15 fluidly connecting the rear cavity 10 and ambient space 6 through the housing wall 9. The port structure 15 has a first open end 13 fluidly coupled to the rear cavity 10 and a second open end 14 fluidly coupled to ambient space 6, and the port structure 15 has a port cavity defined by the first open end 13, the second open end 14 and a port wall 16, the port wall 16 extending from the housing wall 9 into the rear cavity 10 and/or into the ambient space 6. The port wall 16 has one or more acoustically permeable sections 18 fluidly connecting the port cavity 17 with the rear cavity 10 and/or the ambient space 6.

[0082] The first diaphragm 11, the rear cavity 10 (more precisely: the air or the gas within the rear cavity 10) and the port structure 15, i.e. the acoustic mass of the port structure, may together constitute or define a first acoustic system 10, 11, 15 having a first system frequency response. Typically, the first acoustic system has one or more resonance frequencies. For example, the diaphragm and the rear cavity, i.e. the air or the gas within the rear cavity, may form a primary first system resonance frequency. The port structure and the rear cavity, i.e. the air or the gas within the rear cavity may form a secondary first system resonance frequency.

[0083] The primary first system resonance frequency is controlled mainly by the acoustic mass of the first diaphragm 11 and the combined acoustic compliance of the air or gas in the rear cavity 10, of the air in the front cavity 5 and of the suspension of the first diaphragm 11. The secondary system resonance frequency is mainly controlled by the acoustic compliance of the air or gas in the rear cavity 10, and of the acoustic mass of the port structure 15.

[0084] In FIG. 1B, the port structure 15 is shown in more detail. The port structure 15 fluidly connects the rear cavity 10 and ambient space 6 through the housing wall 9. The port structure 15 has a first open end 13 fluidly coupled to the rear cavity 10 and a second open end 14 fluidly coupled to ambient space 6. The port structure 15 thus has a port cavity 17 defined by the first open end 13, the second open end 14 and a port wall 16. The port wall extends from the housing wall 9 into the rear cavity 10 and/or into the ambient space 6. The port wall 16 has one or more acoustically permeable sections 18 fluidly connecting the port cavity 17 with the rear cavity and/or the ambient space through the port wall 16.

[0085] FIGS. 2A-2D show schematically different acoustically permeable sections distributed along a port structure 20. The schematised illustrations can be a view of the port structure 20 from any viewing angle, such as a side view, a top view, etc.

[0086] In FIG. 2A the acoustically permeable sections 21 are shown as longitudinal slits 21 in the port wall 16, the length l1 of the longitudinal slits 21 is comparable to an overall length of the port wall, lp. In some examples the longitudinal slits 21 may have a length l1 corresponding to at least 90% of the overall length lp of the port wall 16, such as corresponding to at least 80%, such as corresponding to at least 75%, such as corresponding to at least 66%, such as corresponding to at least 50% of the overall length lp of the port wall 16.

[0087] The slits 21 may have a width w1 being much smaller than the length l1, and the width may be less than 50% of a perimeter of the port structure 15, such as less than 33%, such as less than 15% of a perimeter of the port wall 16.

[0088] The distance dl between neighbouring slits may be comparable to the width w1 of the slits 21, and thus the distance d1 may be within +/10%, such as within +/20% of the width w1, such as within +/50% of the width.

[0089] In FIG. 2B, the acoustically permeable sections 22 are shown as slits 22. Slits 22 are shown in a port wall 16 of a port structure 20. The slits 22 having a length l2 being smaller than the overall length 1p of the port wall 16. The length l2 may be less than 50%, such as 50%, such as less than 33%, such as less than 25%, such as less than 10% of the overall length lp of the length of the port wall 16. The width w2 and the distance d2 between neighbouring slits may be comparable to the width w1 and the distance d1 as discussed in connection with FIG. 2A. The slits 22 may be distributed along the port wall 16 in any regular or irregular way.

[0090] It is furthermore envisaged that also a combination of slits 21 and slits 22 may be provided on the port wall 16, so that different slits 21, 22 provided on a same port wall 16 may have different widths and different lengths.

[0091] It is furthermore envisaged that even though the slits 21, 22 are shown schematically as being rectangular, it is envisaged that the acoustically permeable sections may have any form, and be circular, elliptical, rectangular, be regular or irregular.

[0092] In FIG. 2C, an acoustically permeable section is provided as a through hole 23 of the port wall 16 covered with an acoustical mesh 25. The acoustical mesh 25 may have an acoustical mass or an acoustical impedance designed to provide a desired secondary resonance frequency.

[0093] The port wall 16 may have more than one through hole 23, and different through holes 23 may be covered with different acoustical mesh, or some through holes may be covered with acoustical mesh while others may remain through holes in the port wall 16.

[0094] In FIG. 2D, the housing wall 9 of the earphone housing 3 is shown, and it is seen that the port structure extends on both sides of the housing wall 9, and thus extends into the rear cavity 10, and into the ambient space 6. It is seen that the one or more acoustically permeable sections 24, 24, 24 may be distributed along a length of the port wall 16, the one or more acoustically permeable sections 24, 24, 24 may be distributed at different distances d3, d4, d5 from the housing wall.

[0095] It is envisaged that any of the acoustically permeable sections as discussed in connection with FIGS. 2A-2D may be used in any combination to obtain an acoustic impedance of the one or more acoustically permeable sections so as to be able to dampen the secondary first system resonance frequency. The one or more acoustically permeable sections may have a combined acoustic impedance of between 500 and 8000 L/m.sup.2s in order to dampen the secondary first system resonance frequency.

[0096] The port structure may have a port wall having any shape and being configured to define a port cavity, such as being configured to at least partly. enclose a cavity.

[0097] The port structure may be a longitudinal port structure, such as a port structure having a longitudinal extension being larger than a diameter, or a cross-section of a width, of the port structure, such as a port structure having a longitudinal extension in a longitudinal direction non-parallel with the housing wall which is larger than a transversal extension in a direction parallel to the housing wall.

[0098] In FIGS. 3A-3F different shapes of port structures are shown. The port structure 15 may for example have a base 31, 33, 35, 36, 37, 38, and a wall part 32, 34 extending from the base 31, 33, 35, 36, 37, 38. The wall part 32, 34 may have a center corresponding to a center of the base along the entire length of the wall part, or the wall part may be for example tapered or conical.

[0099] The port structure may have open ends, so that the base 31, 33, 35, 36, 37, 38 of the port structure is open, while the port wall 32, 34 defines a cavity 17, 17 within the port wall 32, 34 having two open ends.

[0100] The base 31, 33, 35, 36, 37, 38 may have any shape, such as a polygon shape, a circular shape 31, a square shape 33, a rectangular shape 35, a triangular shape 36, a parallellogramic shape 37, or any irregular shape 38, etc. The shape of the base may have a circumscribed circle, 33, 38, or the base may be circular, and the height relative to a diameter of the circumscribed circle or of the circular base may be larger than one. For example in FIG. 3F, a base 38 having an irregular shape is shown. It is seen that the irregular shape of the base 38 has a circumscribed circle 38, and the circumscribed circle has a diameter d.

[0101] The base 31, 33, 35, 36, 37, 38 may have a diameter or a cross-section, or a circumscribed circle of the base may have a circumscribed circle diameter. In some examples, the diameter of the base, the cross-sectional width of the base or the circumscribed circle diameter may be between 0.5 mm and 3 mm, such as between 0.8 mm and 2 mm, such as between 1.0 and 1.5 mm, such as about 1.2 mm

[0102] The port structure 15 may comprise a tubular member 32, 34 defining the port cavity 17, and the tubular member may be an open tubular member having a base 31, 33, 35, 36, 37, 38 and a height 39, 39. Typically, the base may be an open end of the tubular member. The tubular member may have a same size along the height as a cylinder, or the tubular member may tapered. The base may have any shape as set out above.

[0103] Regardless of the shape of the port structure, and regardless of the shape of the base, the height relative to a diameter of a circumscribed circle of the base is preferably larger than one.

[0104] FIG. 4 shows an exemplary port structure 40 extending inside the cavity 10, away from the inside 9 of the housing wall 9. The port structure 40 has a port wall 42 defining a port cavity 43. An acoustically permeable section 41 extends around a perimeter of the port wall 42. It is seen that at least some sound 44 entering the port structure 40 through opening 45 may escape the port cavity 43 through the acoustically permeable section 41. Also sound 44 may be guided through the port structure and escape through the opening (not shown) of the cavity opposite the opening 45.

[0105] FIG. 5A shows the frequency response for a prior art earphone having a diaphragm, a rear cavity and a port structure having a solid port wall, i.e. an earphone according to FIG. 1, however, having a solid port wall 16. The prior art earphone may have a secondary system resonance frequency determined primarily by the rear cavity and the port structure, see area 53. The frequency response may exhibit further resonance frequencies, these are however omitted from the frequency response for simplification. In FIG. 5A, the curve 51 shows the frequency dependent passive attenuation of the noise, while the curve 52 shows the sound pressure at the ear.

[0106] In FIG. 5A, it is seen that about the secondary resonance frequency fr for the prior art earphone, see the area 53 of the chart, the noise is amplified, while there is a significant drop in pressure at the ear.

[0107] In FIG. 5B, a first system frequency response for an earphone corresponding to an earphone according to the present disclosure is shown. It should be noted that the first system frequency response may exhibit further resonance frequencies, these are however omitted from the illustrated frequency response in FIG. 5B for simplification. In FIG. 5B, the curve 54 shows the frequency dependent passive attenuation of the noise, while the curve 55 shows the sound pressure at the ear.

[0108] It may be seen from FIG. 5B that at about the resonance frequency, see the area 56, i.e. about the secondary first system resonance frequency, fr, the amplification of the noise, ambient sound, etc., is reduced and the amplification is seen to be about 1-2 dB, and thus the amplification of the noise is less than 5 dB, such as less than 2 dB, such as less than 1 dB. Thus, the reduction of the amplification is more than 50%, such as more than 80% compared to a structure having a solid port wall. It is furthermore seen from FIG. 5B that also the reduction of a sound pressure at the ear of the user is significantly reduced, and the sound pressure may only drop to e.g. 5 dB, such as less than 5 dB, such as less than 10 dB, whereas in an earphone having a solid port wall, the pressure at the ear may drop by 20 dB as seen from FIG. 5B.

[0109] In FIG. 6, a comparison is made between the relative port pressure as a function of frequency. From FIG. 6, it is seen that if the relative port pressure at the resonance frequency for a solid port wall is equalled 1, see frequency response curve 61, then the relative sound pressure at a leaky port wall, i.e. a port wall having one or more acoustically permeable openings, see frequency response curve 62, the port pressure is significantly reduced, and at the resonance frequency, the relative port pressure may be reduced by at least 50%, such as by at least 45%.

[0110] FIG. 7 shows an earphone according to the present disclosure, and the earphone 70 is configured to provide an acoustic output signal to an ear of a wearer in dependence on an earphone audio signal and further configured to be arranged on the wearer's head 2 in an operating position such that a front cavity 5 between the head 2 and the earphone 70 is separated from ambient space 6. The earphone 70 comprises a housing 3 having a housing wall 9 separating a rear cavity 10 from the front cavity 5 and from ambient space 6. The earphone 70 further comprises an ear cushion 4 arranged and configured to attenuate acoustic signals entering the front cavity 5 from ambient space 6 when the earphone 70 is in the operating position. A first diaphragm 11 is suspended across an opening in the housing wall 9 between the front cavity 5 and the rear cavity 10 and configured to be actively driven to provide at least a portion of the acoustic output signal.

[0111] The first diaphragm 11 may be reciprocally suspended across the opening or the through-hole in the housing wall 9 between the front cavity 5 and the rear cavity 10, and thus be suspended to reciprocate. The first diaphragm 11 is configured to be actively driven to provide at least a portion of the acoustic output signal. The earphone 70 may comprise a first driver 12, such as a first electrodynamic driver, for driving the diaphragm 11.

[0112] The earphone 70 further comprises a port structure 15 fluidly connecting the rear cavity 10 and ambient space 6 through the housing wall 9. The port structure 15 has a port wall 16 defining a port cavity 17 and the port wall 16 extends from the housing wall 9 into the rear cavity 10 and/or into the ambient space 6. The port wall 16 has one or more acoustically permeable sections 18 fluidly connecting the port cavity 17 with the rear cavity 10 and/or the ambient space 6.

[0113] The earphone 70 furthermore comprises a resistive opening 71, the resistive opening 71 acting as a vent. Such a vent typically acts as a first order filter, and may provide an attenuation of about 6 dB/decade.

[0114] FIG. 8 shows another earphone according to the present disclosure, and the earphone 80 is configured to provide an acoustic output signal to an ear of a wearer in dependence on an earphone audio signal and further configured to be arranged on the wearer's head 2 in an operating position such that a front cavity 5 between the head 2 and the earphone 80 is separated from ambient space 6. The earphone 80 comprises a housing 3 having a housing wall 9 separating a rear cavity 10 from the front cavity 5 and from ambient space 6. The earphone 80 further comprises an ear cushion 4 arranged and configured to attenuate acoustic signals entering the front cavity 5 from ambient space 6 when the earphone 80 is in the operating position. A first diaphragm 11 is suspended across an opening in the housing wall 9 between the front cavity 5 and the rear cavity 10 and configured to be actively driven to provide at least a portion of the acoustic output signal.

[0115] The first diaphragm 11 may be reciprocally suspended across the opening or the through-hole in the housing wall 9 between the front cavity 5 and the rear cavity 10, and thus be suspended to reciprocate. The first diaphragm 11 is configured to be actively driven to provide at least a portion of the acoustic output signal. The earphone 80 may comprise a first driver 12, such as a first electrodynamic driver, for driving the diaphragm 11.

[0116] The earphone 80 further comprises a port structure 15 fluidly connecting the rear cavity 10 and ambient space 6 through the housing wall 9. The port structure 15 has a port wall 16 defining a port cavity 17 and the port wall 16 extends from the housing wall 9 into the rear cavity 10 and/or into the ambient space 6. The port wall 16 has one or more acoustically permeable sections 18 fluidly connecting the port cavity 17 with the rear cavity 10 and/or the ambient space 6.

[0117] The earphone 80 furthermore comprises an active noise cancelling circuit 81, the active noise cancelling circuit being configured to actively counteract incoming noise. The earphone 80 thus further comprises a feedforward microphone 82 and/or a feed backward microphone 83, and the active noise cancelling circuit 81 receives microphone signals 85, 86 from the feedforward and/or feed backward microphones 82, 83 and generates an active noise cancelling output signal 87 which is fed to the driver 12 of the diaphragm 11 to provide a noise cancelling signal to the user or wearer of the earphone.

[0118] Any of the earphones 1, 70, 80 described above may further comprise any suitable combination of the features described above as generally possible features of an earphone. Any of the earphones 1, 70, 80 may be comprised in a hearing device (not shown), such as e.g. a headset, a headphone, a hearing protector or a hearing aid. The hearing device may further comprise any suitable combination of the features described above as generally possible features of a hearing device and may further comprise any suitable combination of further features that are part of known hearing devices. Where suitable, such features may be comprised by the earphone 1, 70, 80.

[0119] Although particular embodiments have been shown and described, it will be understood that it is not intended to limit the claimed inventions to the preferred embodiments, and it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the claimed inventions. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense. The claimed inventions are intended to cover alternatives, modifications, and equivalents.

LIST OF REFERENCES

[0120] 1 earphone

[0121] 2 head of a user

[0122] 3 housing

[0123] 4 ear cushion

[0124] 5 front cavity

[0125] 6 ambient space

[0126] 7 ear

[0127] 8 ear canal

[0128] 9 housing wall

[0129] 10 rear cavity

[0130] 11 diaphragm

[0131] 12 driver

[0132] 13 first open end

[0133] 14 second open end

[0134] 15 port structure

[0135] 16 port wall

[0136] 17, 17, 17 port cavity

[0137] 18 acoustically permeable section

[0138] 21,22 slit

[0139] 23 through hole

[0140] 24, 24, 24 acoustically permeable section

[0141] 25 acoustical mesh

[0142] 31, 33, 35, 36, 37, 38 base

[0143] 32, 34 wall part

[0144] 39, 39 height

[0145] 40 port structure

[0146] 41 acoustically permeable section

[0147] 42 port wall

[0148] 43 port cavity

[0149] 44 sound

[0150] 45 opening

[0151] 51 curve showing frequency dependent passive attenuation

[0152] 52 curve showing the sound pressure at the ear

[0153] 53 area of chart

[0154] 54 curve showing frequency dependent passive attenuation

[0155] 55 curve showing the sound pressure at the ear

[0156] 56 area of chart

[0157] 70 earphone

[0158] 80 earphone

[0159] 81 active noise cancelling circuit

[0160] 82 feedforward microphone

[0161] 83 feed backward microphone

[0162] 85, 86 microphone signals

[0163] 87 active noise cancelling output signal