An audio loudspeaker comprising: a longitudinal, semi-enclosed structure having an internal baffle creating a first wave-column having a first closed end and a first exit , and a second wave-column (A) having a second closed end and a second exit ; a first driver (LS1) mounted to a first end of the baffle and configured to project resonant acoustic energy from a first polarity side of the first driver down the first wave-column at every effective odd one-quarter wavelength frequency and directly out of the second exit of the second wave-column from a second polarity side of the first driver; and a second driver (LS2) mounted to a second end of the baffle and configured to project resonant acoustic energy from a first polarity side of the second driver down the second wave-column at every effective odd one-quarter wavelength frequency and directly out of the first exit of the first wave-column from a second polarity side of the second driver, wherein: the first polarity sides of the first and second drivers are front sides of the first and second drivers, respectively, and both the drivers are provided with the same phase electrical connections; or the first polarity sides of the first and second drivers are back sides of the first and second drivers, respectively, and both the drivers are provided with the same phase electrical connections; or the first polarity side of one of the first and second drivers is a front side of that driver while the first polarity side of the other driver is a back side of that other driver, and the first and second drivers are wired out-of-phase relative to each other. a longitudinal, semi-enclosed structure having an internal baffle creating a first wave-column having a first closed end and a first exit , and a second wave-column (A) having a second closed end and a second exit ; a first driver (LS1) mounted to a first end of the baffle and configured to project resonant acoustic energy from a first polarity side of the first driver down the first wave-column at every effective odd one-quarter wavelength frequency and directly out of the second exit of the second wave-column from a second polarity side of the first driver; and a second driver (LS2) mounted to a second end of the baffle and configured to project resonant acoustic energy from a first polarity side of the second driver down the second wave-column at every effective odd one-quarter wavelength frequency and directly out of the first exit of the first wave-column from a second polarity side of the second driver, wherein: the first polarity sides of the first and second drivers are front sides of the first and second drivers, respectively, and both the drivers are provided with the same phase electrical connections; or the first polarity sides of the first and second drivers are back sides of the first and second drivers, respectively, and both the drivers are provided with the same phase electrical connections; or the first polarity side of one of the first and second drivers is a front side of that driver while the first polarity side of the other driver is a back side of that other driver, and the first and second drivers are wired out-of-phase relative to each other. the first polarity sides of the first and second drivers are front sides of the first and second drivers, respectively, and both the drivers are provided with the same phase electrical connections; or the first polarity sides of the first and second drivers are back sides of the first and second drivers, respectively, and both the drivers are provided with the same phase electrical connections; or the first polarity side of one of the first and second drivers is a front side of that driver while the first polarity side of the other driver is a back side of that other driver, and the first and second drivers are wired out-of-phase relative to each other. <EOS>