AX Series - Apparent Apex Error

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Apparent Apex Error is the Problem.
CSA Technology is the Solution.

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This typical front baffle layout of a 3-way loudspeaker creates significant off-axis asymmetries due to the spatial offsets of the three drivers.

This is a top-down "plan" view of the same loudspeaker. The various circles represent the acoustic centers of the three drivers at their actual and delayed apparent locations from the perspective of two measurement positions (MIC1 and MIC2). These position are actually 20 m from the loudspeaker, this distance being considerably foreshortened for drawing clarity.

The frequency and impulse responses, measured at the MIC1 position, show the distinct arrivals of the three different drivers and the resulting comb-filtered frequency response.

Signal delay can be used to synchronize the sounds of the HF and LF drivers to the MF driver. At the MIC1 position, the multiple arrivals disappear and the frequency response smoothes out. The apparent locations of the delayed HF and LF sources are indicated as HF1 and LF1. Problem solved - or is it? What happens if we move the measurement microphone about 20 degrees off axis to the MIC2 position or to a MIC3 position (not shown) elevated 30 degrees MIC1?

At the MIC2 position (red curves), the apparent source positions move to HF2 and LF2. The multiple arrivals reappear and so do the comb filters. The MIC3 position (green curves) in the vertical plane also shows multiple arrivals and a frequency response with substantial comb filtering. The further off axis one goes, the more severe the problems.

These two graphs of AX show its frequency responses and impulse responses at all three microphone positions: on axis (MIC1 black), 20 degrees horizontally off axis (MIC2 red), and 30 degrees vertically off axis (MIC3 green). It is easy to see that there is one impulse arrival from all drivers at all three microphone positions. The frequency response graph shows the expected, increasing, HF roll-off at the off axis positions. NOTE: The general HF rolloff seen in all the frequency response graphs is because of air absorption at the 20 m microphone distance.