Pressure equalization in earphones
A headphone includes an electro-acoustic transducer dividing an enclosed volume into a front volume and a rear volume, a first port in the housing coupling the front volume to an ear canal of a user, a second port in the housing coupling the front volume to space outside the ear, a third port in the housing coupling the rear volume to space outside the ear, and an ear tip configured to surround the first port and including a flap to seal the ear canal from space outside the ear. The second port has a diameter and a length that provide an acoustic mass with an acoustic impedance with a high reactive component and a low resistive component, reducing the occlusion effect that otherwise results from sealing the ear.
1. A headphone comprising:
a housing defining an enclosed volume;
an electro-acoustic transducer dividing the enclosed volume into a front volume and a rear volume;
a first port in the housing arranged to couple the front volume to an ear canal of a user when the headphone is worn;
a second port in the housing arranged to couple the front volume to space outside the ear of the user when the headphone is worn;
a third port in the housing arranged to couple the rear volume to space outside the ear of the user when the headphone is worn; and
an ear tip configured to surround the first port and including a flap to seal the ear canal from space outside the ear when the headphone is worn, the housing comprising an extended tab for retaining the ear tip;
wherein
the second port has a diameter and a length that provide an acoustic mass with an acoustic impedance with a high reactive component and a low resistive component, and
an entrance to the first port is positioned next to a first side of the extended tab and an entrance to the second port is positioned next to a second side of the extended tab, such that the electro-acoustic transducer is approximately symmetrically loaded.
2. The headphone of claim 1 , wherein the second port has a diameter and a length that provide the second port with a low acoustic impedance at low frequencies and a high acoustic impedance at high frequencies.
3. The headphone of claim 1 , wherein the ear tip includes a void positioned to surround the second port exit, the ear tip protecting the second port exit from blockage.
4. The headphone of claim 3 , wherein the void does not impart additional acoustic impedance to the second port.
5. The headphone of claim 3 , wherein the ear tip is formed from materials having at least two different hardnesses, the portion of the ear tip defining the void being of a greater hardness than the portion of the ear tip forming the seal.
6. The headphone of claim 1 , wherein:
the transducer includes a diaphragm that is generally characterized by a first plane, is radially symmetric along a first axis perpendicular to the plane, and is bounded by an outer edge;
the first port extends from an entrance into the front volume near the outer edge of the transducer; and
the second port extends from an entrance into the front volume, the second port entrance being located along a line connecting the first axis to the first port entrance.
7. The headphone of claim 6 , wherein the second port entrance is located facing the diaphragm, between the first port and the first axis.
8. The headphone of claim 1 , wherein the first port has a lower characteristic acoustic impedance than the second port.
9. The headphone of claim 8 , wherein the second port has a characteristic acoustic impedance of at least 6.8×10 6 kg/m 4 at 20 Hz and at least 3.1×10 7 kg/m 4 at 3 kHz.
10. The headphone of claim 9 , wherein the third port has a characteristic acoustic impedance of at least 8.0×10 6 kg/m 4 at 20 Hz and at least 3.1×10 8 kg/m 4 at 3 kHz.
11. The headphone of claim 1 , wherein the second port has a characteristic acoustic impedance of at least 6.8×10 6 kg/m 4 at 20 Hz and at least 3.1×10 7 kg/m 4 at 3 kHz.
12. The headphone of claim 1 , further comprising a fourth port in the housing arranged to couple the front volume to space outside the ear of a user when the headphone is worn, the fourth port has a diameter and a length that provide the fourth port with a high acoustic impedance with a large resistive component and a low reactive component.
13. The headphone of claim 12 , wherein the fourth port has a characteristic acoustic impedance of at least 2.0×10 7 kg/m 4 at 3 kHz.
14. A headphone comprising:
a housing defining an enclosed volume;
an electro-acoustic transducer dividing the enclosed volume into a front volume and a rear volume;
a first port in the housing arranged to couple the front volume to an ear canal of a user when the headphone is worn;
a second port in the housing arranged to couple the front volume to space outside the ear of the user with a characteristic acoustic impedance of at least 6.8×10 6 kg/m 4 at 20 Hz and at least 3.1×10 7 kg/m 4 at 3 kHz when the headphone is worn;
a third port in the housing arranged to couple the rear volume to space outside the ear of the user with a characteristic acoustic impedance of at least 8.0×10 6 kg/m 4 at 20 Hz and at least 3.1×10 8 kg/m 4 at 3 kHz when the headphone is worn; and
an ear tip configured to surround the first port and form a seal between the housing and the ear canal when the headphone is worn, wherein:
the housing comprises an extended tab for retaining the ear tip, and
an entrance to the first port is positioned next to a first side of the extended tab and an entrance to the second port is positioned next to a second side of the extended tab, such that the electro-acoustic transducer is approximately symmetrically loaded.
15. The headphone of claim 14 , wherein the ear tip includes a void positioned to surround the second port exit, the ear tip protecting the second port exit from blockage.
16. The headphone of claim 15 , wherein the void does not impart additional acoustic impedance to the second port.
17. The headphone of claim 15 , wherein the ear tip is formed from materials having at least two different hardnesses, the portion of the ear tip defining the void being of a greater hardness than the portion of the ear tip forming the seal.
18. The headphone of claim 14 , wherein:
the transducer includes a diaphragm that is generally characterized by a first plane, is radially symmetric along a first axis perpendicular to the plane, and is bounded by an outer edge;
the first port extends from an entrance into the front volume near the outer edge of the transducer; and
the second port extends from an entrance into the front volume, the second port entrance being located along a line connecting the first axis to the first port entrance.
19. The headphone of claim 18 , wherein the second port entrance is located facing the diaphragm, between the first port and the first axis.
20. A headphone comprising:
an ear tip configured to seal the headphone to an ear canal of a user to form an enclosed volume including the ear canal and a front cavity of the headphone,
a housing comprising an extended tab for retaining the ear tip,
a front reactive port coupling the otherwise-sealed front cavity to space outside the headphone, to provide a consistent response across the audible spectrum, wherein the extended tab and ear tip cooperate to form a channel that surrounds the front reactive port, the channel protecting the front reactive port from blockage when the headphone is worn in the user's ear, and
a rear reactive port and a rear resistive port coupling a back cavity to space outside the headphone in parallel, to provide a high level of output for a given input signal level in combination with the seal.
21. The headphone of claim 20 , wherein the headphone is coupled to the ear canal through a characteristic acoustic impedance of less than 6.8×10 6 kg/m 4 at 20 Hz and less than 3.1×10 7 kg/m 4 at 3 kHz.
22. The headphone of claim 20 , wherein the front reactive port has a characteristic acoustic impedance of at least 6.8×10 6 kg/m 4 at 20 Hz and at least 3.1×10 7 kg/m 4 at 3 kHz.
23. The headphone of claim 20 , wherein the rear reactive port has a characteristic acoustic impedance of at least 8.0×10 6 kg/m 4 at 20 Hz and at least 3.1×10 8 kg/m 4 at 3 kHz.
24. The headphone of claim 20 , further comprising a front resistive port coupling the front cavity to space outside the headphone in parallel to the front reactive port, the front resistive port having a characteristic acoustic impedance of at least 2.0×10 7 kg/m 4 at 3 kHz.
25. A headphone comprising:
an ear tip configured to seal the headphone to an ear canal of a user to form an enclosed volume including the ear canal and a front cavity of the headphone,
a housing comprising an extended tab for retaining the ear tip, and
a front reactive port and a front resistive port coupling the otherwise-sealed front cavity to space outside the headphone in parallel, to provide a consistent response across the audible spectrum, wherein
the extended tab and ear tip cooperate to form a channel that surrounds the front reactive port, the channel protecting the front reactive port from blockage when the headphone is worn in the user's ear.