A loudspeaker enclosure comprising: a housing having an inside volume and an exterior region; and a duct port assembly (200; 300; 400; 500; 600; 700; 1100) at least partially within the inside volume, the duct port assembly acoustically coupling the inside volume with the exterior region, the duct port assembly including: an input slot (220; 355; 520; 720; 1120) positioned within and configured to receive acoustic energy from the inside volume; a duct bend section (215; 300; 400) having a first and second end, the input slot being positioned at the first end, the duct bend section being configured to acoustically filter the acoustic energy received from the input slot to yield selectively attenuated acoustic energy, wherein the duct bend section has an inner radius and a center point, and wherein the duct bend section subtends at an angle between 160° -180° to the center point; a duct body section connected at the second end of the duct bend section, the duct body section being configured to channel the selectively attenuated acoustic energy towards the exterior region, the duct body section including a pair of planar, confronting walls (235A-B) connected to a pair of arcuate, confronting sidewalls (250A-B), which define a duct-body waist section (210; 1125); and an output slot (245; 545; 1145) connecting the duct body section to the exterior region, the output slot being configured to radiate the selectively attenuated acoustic energy to the exterior region, wherein the cross-section exit ratio of the output slot's longer dimension to its shorter dimension (225; 515) is at least 4:1. a housing having an inside volume and an exterior region; and a duct port assembly (200; 300; 400; 500; 600; 700; 1100) at least partially within the inside volume, the duct port assembly acoustically coupling the inside volume with the exterior region, the duct port assembly including: an input slot (220; 355; 520; 720; 1120) positioned within and configured to receive acoustic energy from the inside volume; a duct bend section (215; 300; 400) having a first and second end, the input slot being positioned at the first end, the duct bend section being configured to acoustically filter the acoustic energy received from the input slot to yield selectively attenuated acoustic energy, wherein the duct bend section has an inner radius and a center point, and wherein the duct bend section subtends at an angle between 160° -180° to the center point; a duct body section connected at the second end of the duct bend section, the duct body section being configured to channel the selectively attenuated acoustic energy towards the exterior region, the duct body section including a pair of planar, confronting walls (235A-B) connected to a pair of arcuate, confronting sidewalls (250A-B), which define a duct-body waist section (210; 1125); and an output slot (245; 545; 1145) connecting the duct body section to the exterior region, the output slot being configured to radiate the selectively attenuated acoustic energy to the exterior region, wherein the cross-section exit ratio of the output slot's longer dimension to its shorter dimension (225; 515) is at least 4:1. an input slot (220; 355; 520; 720; 1120) positioned within and configured to receive acoustic energy from the inside volume; a duct bend section (215; 300; 400) having a first and second end, the input slot being positioned at the first end, the duct bend section being configured to acoustically filter the acoustic energy received from the input slot to yield selectively attenuated acoustic energy, wherein the duct bend section has an inner radius and a center point, and wherein the duct bend section subtends at an angle between 160° -180° to the center point; a duct body section connected at the second end of the duct bend section, the duct body section being configured to channel the selectively attenuated acoustic energy towards the exterior region, the duct body section including a pair of planar, confronting walls (235A-B) connected to a pair of arcuate, confronting sidewalls (250A-B), which define a duct-body waist section (210; 1125); and an output slot (245; 545; 1145) connecting the duct body section to the exterior region, the output slot being configured to radiate the selectively attenuated acoustic energy to the exterior region, wherein the cross-section exit ratio of the output slot's longer dimension to its shorter dimension (225; 515) is at least 4:1.