A headphone comprising: a support structure that is adapted to sit on a head or upper torso of a user; an acoustic driver (32; 52) carried by the support structure such that the acoustic driver is configured, in use, to be located off of an ear of the user, wherein the acoustic driver has front and rear sides and sound is radiated from both sides of the acoustic driver; and a structure that defines a first acoustic chamber (34; 65) on the front side of the acoustic driver and a second acoustic chamber (36; 55) on the rear side of the acoustic driver, wherein the first acoustic chamber has at least one opening (40; 68; 70) therein and the second acoustic chamber has at least one opening (42; 50; 60; 81-86) therein, and wherein: acoustic impedances of the front and rear sides of the acoustic driver are approximately equal, such that, at low frequencies, a polar pattern of the acoustic driver behaves approximately like a dipole, and at high frequencies, a polar pattern of the acoustic driver exhibits a higher order directional pattern, wherein the front side of the driver, the first acoustic chamber and the at least one opening in the first acoustic chamber together have a first effective impedance, and the rear side of the driver, the second acoustic chamber and the at least one opening in the second acoustic chamber together have a second effective impedance, where the ratio of the first effective impedance to the second effective impedance ranges from approximately 0.95 to approximately 1.05 at frequencies ranging from about 20 Hz to about 2 kHz, and where the ratio of the first effective impedance to the second effective impedance is less than approximately 0.95 at frequencies above about 2 kHz. a support structure that is adapted to sit on a head or upper torso of a user; an acoustic driver (32; 52) carried by the support structure such that the acoustic driver is configured, in use, to be located off of an ear of the user, wherein the acoustic driver has front and rear sides and sound is radiated from both sides of the acoustic driver; and a structure that defines a first acoustic chamber (34; 65) on the front side of the acoustic driver and a second acoustic chamber (36; 55) on the rear side of the acoustic driver, wherein the first acoustic chamber has at least one opening (40; 68; 70) therein and the second acoustic chamber has at least one opening (42; 50; 60; 81-86) therein, and wherein: acoustic impedances of the front and rear sides of the acoustic driver are approximately equal, such that, at low frequencies, a polar pattern of the acoustic driver behaves approximately like a dipole, and at high frequencies, a polar pattern of the acoustic driver exhibits a higher order directional pattern, wherein the front side of the driver, the first acoustic chamber and the at least one opening in the first acoustic chamber together have a first effective impedance, and the rear side of the driver, the second acoustic chamber and the at least one opening in the second acoustic chamber together have a second effective impedance, where the ratio of the first effective impedance to the second effective impedance ranges from approximately 0.95 to approximately 1.05 at frequencies ranging from about 20 Hz to about 2 kHz, and where the ratio of the first effective impedance to the second effective impedance is less than approximately 0.95 at frequencies above about 2 kHz. acoustic impedances of the front and rear sides of the acoustic driver are approximately equal, such that, at low frequencies, a polar pattern of the acoustic driver behaves approximately like a dipole, and at high frequencies, a polar pattern of the acoustic driver exhibits a higher order directional pattern, wherein the front side of the driver, the first acoustic chamber and the at least one opening in the first acoustic chamber together have a first effective impedance, and the rear side of the driver, the second acoustic chamber and the at least one opening in the second acoustic chamber together have a second effective impedance, where the ratio of the first effective impedance to the second effective impedance ranges from approximately 0.95 to approximately 1.05 at frequencies ranging from about 20 Hz to about 2 kHz, and where the ratio of the first effective impedance to the second effective impedance is less than approximately 0.95 at frequencies above about 2 kHz.