“I cannot state with certainty what might be the factor for this. However, I do wonder if the narrow vertical directivity is one such factor (or even the factor). The majority of speakers I have heard thus far generally exhibit a vertical radiation pattern in the neighborhood of ±40 to ±50°. The Perlisten S4b, however, has a radiation pattern from ±20° ±30° thanks to the tweeter/midrange waveguide assembly. The center-to-center spacing of the midrange drivers is approximately 103 mm which yields a beaming point of approximately 850 Hz (using 1/4-wave; or ~1700Hz using 1/2-wave). The use of this vertical array with smaller drivers could, in some ways, be considered like a ribbon tweeter where the narrow width allows wider horizontal directivity, but the taller height limits the vertical radiation”