Acoustic transducer
An acoustic transducer with an acoustic element that emits or receives front-side acoustic radiation from its front side, and emits or receives rear-side acoustic radiation from its rear side. A housing directs the front-side acoustic radiation and the rear-side acoustic radiation. A plurality of sound-conducting vents in the housing allow sound to enter the housing or allow sound to leave the housing. A distance between vents defines an effective length of an acoustic dipole. The housing and its vents are constructed and arranged such that the effective dipole length is frequency dependent.
1. A loudspeaker, comprising:
a housing with an interior;
an acoustic radiator in the housing interior, wherein the acoustic radiator is configured to emit front-side sound from its front side into a front volume of the housing, and rear-side sound from its rear side into a rear volume of the housing;
a plurality of sound-emitting vents in the housing, the vents comprising a first front vent that is configured to emit front-side sound, a first rear vent that is configured to emit rear-side sound, and a second rear vent that is configured to emit rear-side sound;
wherein a first loudspeaker dipole is defined by the first front vent and the first rear vent, and a second loudspeaker dipole is defined by the first front vent and the second rear vent;
wherein the first rear vent is closer to the first front vent than is the second rear vent, so that the first loudspeaker dipole has a shorter effective length than does the second loudspeaker dipole; and
a structure that carries the housing, wherein the structure is configured to be worn on a user's head such that the housing is near but not on or in the user's ear, and with the first front vent closer to the ear canal opening than the first and second rear vents, and the first rear vent closer to the ear canal opening than the second rear vent.
2. The loudspeaker of claim 1 , wherein the effective dipole length is larger at lower frequencies than it is at higher frequencies.
3. The loudspeaker of claim 1 , wherein at least one of the plurality of sound-emitting vents comprises an opening in the housing covered by a resistive screen.
4. The loudspeaker of claim 1 , wherein at least one of the plurality of sound-emitting vents comprises a port opening.
5. The loudspeaker of claim 1 , further comprising an acoustic transmission line between the acoustic radiator and one of the plurality of sound-emitting vents.
6. The loudspeaker of claim 1 , further comprising a vented acoustic transmission line that receives rear-side sound, wherein a third rear vent is in the acoustic transmission line proximate the acoustic radiator and the second rear vent is in the acoustic transmission line farther from the acoustic radiator than is the third rear vent.
7. The loudspeaker of claim 6 , wherein the second rear vent comprises an opening at an end of the acoustic transmission line, wherein the acoustic transmission line is defined by walls, and the loudspeaker further comprises an active element in the acoustic transmission line that is configured to reduce standing wave resonances in the acoustic transmission line.
8. The loudspeaker of claim 7 , wherein the active element comprises an opening in a wall of the acoustic transmission line that is covered by a resistive screen.
9. The loudspeaker of claim 6 , wherein the third rear vent comprises an opening in the acoustic transmission line covered by a resistive screen.
10. The loudspeaker of claim 1 , further comprising a second front sound-emitting vent in the housing.
11. The loudspeaker of claim 10 , wherein the second front vent is closer to the ear than the first and second rear vents.
12. The loudspeaker of claim 10 , wherein all four vents are generally co-planar.
13. The loudspeaker of claim 10 , wherein the first front vent comprises an opening in the housing covered by a resistive screen, the first rear vent comprises an opening in the housing covered by a resistive screen, and the second rear vent comprises an opening in the housing covered by a resistive screen.
14. The loudspeaker of claim 1 , wherein a vent comprises a passive radiator.
15. A loudspeaker, comprising:
a housing with an interior;
an acoustic radiator in the housing interior, wherein the acoustic radiator is configured to emit front-side sound from its front side into a front volume of the housing, and rear-side sound from its rear side into a rear volume of the housing;
a plurality of sound-emitting vents in the housing, the vents comprising a first front vent that is configured to emit front-side sound, a first rear vent that is configured to emit rear-side sound and comprises an opening in the housing that is covered by a resistive screen, and a second rear vent that is configured to emit rear-side sound and comprises an opening in an acoustic transmission line that comprises walls;
wherein a first loudspeaker dipole is defined by the first front vent and the first rear vent, and a second loudspeaker dipole is defined by the first front vent and the second rear vent;
wherein the first rear vent is closer to the first front vent than is the second rear vent, so that the first loudspeaker dipole has a shorter effective length than does the second loudspeaker dipole; and
an active element in the acoustic transmission line that is configured to damp standing waves in the acoustic transmission line.
16. A loudspeaker, comprising:
a housing with an interior;
an acoustic radiator in the housing interior, wherein the acoustic radiator is configured to emit front-side sound from its front side into a front volume of the housing, and rear-side sound from its rear side into a rear volume of the housing;
at least four sound-emitting vents in the housing, the vents comprising a first front vent that is configured to emit front-side sound, a second front vent that is configured to emit front-side sound, a first rear vent that is configured to emit rear-side sound, and a second rear vent that is configured to emit rear-side sound;
wherein the first front vent, the second front vent, the first rear vent, and the second rear vent are generally co-planar; and
a structure that carries the housing, wherein the structure is configured to be worn on a user's head such that the housing is near but not on or in the user's ear, and with the first and second front vents closer to the ear canal opening than the first and second rear vents.
17. A loudspeaker, comprising:
a housing with an interior;
first and second acoustic radiators in the housing interior, wherein the first and second acoustic radiators are each configured to emit front-side sound from their front side and rear-side sound from their rear side, wherein the rear sides of the first and second acoustic radiators are fluidly coupled to a common rear acoustic volume;
a plurality of sound-emitting vents in the housing, the vents comprising a first rear vent that is fluidly coupled to the common rear acoustic volume, a first front vent that is fluidly coupled to the front side of the first radiator but not the second radiator, and a second front vent that is fluidly coupled to the front side of the second radiator but not the first radiator; and
a system for controlling a phase of the acoustic radiation emitted by each of the first and second acoustic radiators.
18. The loudspeaker of claim 17 , further comprising a third front vent that is fluidly coupled to the front side of the second radiator, wherein the third front vent is farther from the first rear vent than are the first and second front vents.