 For any frequency (over the operating range of the midwoofers), the off-axis response exhibits different lobing patterns because of the vertical distance between the midwoofers, and as a function of the frequency and horizontal distance from the speaker.At any off-axis listening position, although both midwoofers operate in phase (are time-aligned), the waves from each reach the listening position at different times (and therefore have a relative phase difference) - at frequencies where the time displacement between the two midwoofers corresponds to one-half of one wavelength, the outputs of the two midwoofers will null.However, the time displacement itself is a function of the distance from the speaker and frequency, which means that the lobing for a given listening distance and off-axis position will be different at different frequencies.