Wayne Parham Messages: 18748 Registered: January 2001
Illuminati (33rd Degree)
A horn acts like a band-pass filter, having both low-pass and high-pass features. That's why phase shifts with respect to frequency, because it is passing through each of these types of filters. At low-frequencies, the system appears electrically capacitive, like a high-pass filter. At high-frequencies it appears electrically inductive, like a low pass filter. There are several other resonance modes in the passband due to reflections of standing waves, and those appear as blips in the impedance curve, also reflected as blips in both amplitude and phase response.