Acoustic transducer

1. A loudspeaker, comprising:

first and second acoustic drivers that each emit front-side acoustic radiation from a front side of the driver and rear-side acoustic radiation from a rear side of the driver;

a housing that comprises a rear acoustic volume that receives the rear-side acoustic radiation of both drivers and a front acoustic volume that receives the front-side acoustic radiation of a driver;

a plurality of sound-emitting openings in the housing, wherein a distance between sound-emitting openings defines an effective length of a loudspeaker dipole, and wherein the housing and its sound-emitting openings are constructed and arranged such that the effective dipole length is frequency dependent wherein the effective dipole length is larger at lower frequencies than it is at higher frequencies;

wherein first and second rear sound-emitting openings are acoustically coupled to the rear acoustic volume and wherein first and second front sound-emitting openings are acoustically coupled to the front acoustic volume, wherein the first rear sound-emitting opening is closer to the first front sound-emitting opening than is the second rear sound-emitting opening;

a resistive screen covering the first rear sound-emitting opening; and

an acoustic transmission line that is acoustically coupled to the rear acoustic volume and comprises the second rear sound-emitting opening.

2. The loudspeaker of claim 1 , further comprising a structure for wearing the loudspeaker on a user's head, wherein the drivers are held near but not covering an ear of the user when the loudspeaker is worn on the user's head.

3. A loudspeaker, comprising:

a housing with an interior;

first and second acoustic drivers in the housing interior, wherein the first and second acoustic drivers each emit front-side acoustic radiation from a front side of the driver into a front volume of the housing, and rear-side acoustic radiation from a rear side of the driver into a rear volume of the housing;

a plurality of sound-emitting openings in the housing, the openings comprising a first front opening that is configured to emit front-side sound, a first rear opening that is configured to emit rear-side sound, and a second rear opening that is configured to emit rear-side sound;

wherein a first loudspeaker dipole is defined by the first front opening and the first rear opening, and a second loudspeaker dipole is defined by the first front opening and the second rear opening;

wherein the first rear opening is closer to the first front opening than is the second rear opening, 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 by a user such that the housing is not on or in the user's ear, and with the first front opening closer to the ear canal opening than the first and second rear openings, and the first rear opening closer to the ear canal opening than the second rear opening.

4. The loudspeaker of claim 3 , wherein the effective dipole length is larger at lower frequencies than it is at higher frequencies.

5. The loudspeaker of claim 3 , further comprising a resistive screen covering a sound-emitting opening.

6. The loudspeaker of claim 3 , wherein a sound-emitting opening comprises a port opening.

7. The loudspeaker of claim 3 , wherein the housing comprises a rear acoustic volume that receives the rear-side acoustic radiation of both drivers.

8. The loudspeaker of claim 7 , wherein first and second rear sound-emitting openings are acoustically coupled to the rear acoustic volume.

9. The loudspeaker of claim 8 , further comprising a resistive screen covering the first rear sound-emitting opening.

10. The loudspeaker of claim 8 , further comprising an acoustic transmission line that is acoustically coupled to the rear acoustic volume and comprises the second rear sound-emitting opening.

11. The loudspeaker of claim 10 , wherein a front sound-emitting opening receives front-side acoustic radiation, and wherein the first rear sound-emitting opening is closer to the front sound-emitting opening than is the second rear sound-emitting opening.

12. The loudspeaker of claim 7 , further comprising an acoustic transmission line that is acoustically coupled to the rear acoustic volume and comprises the second rear sound-emitting opening.

13. The loudspeaker of claim 3 , wherein the housing comprises a front acoustic volume that receives the front-side acoustic radiation of a driver.

14. The loudspeaker of claim 13 , wherein first and second front sound-emitting openings are acoustically coupled to the front acoustic volume.

15. The loudspeaker of claim 14 , further comprising a resistive screen covering one of the first and second front sound-emitting openings.

16. The loudspeaker of claim 3 , further comprising wherein the structure that carries the housing is configured to be worn on a user's head, wherein the drivers are held near but not covering an ear of the user when the loudspeaker is worn on the user's head.