Zaph|Audio - SB Acoustics 2-Way : Final Crossovers - The Off-Axis

Crossovers: The Off-Axis

The off-axis response analyis is often neglected in practice, even though it's often discussed. The graphs on this page were generated by using the minimum-phase model in CALSOD, then selecting various points to display. Diffraction and driver directionality are not included. These relate specifically to the driver center-to-center spacing, the relative acoustic offset and the crossover type, order and any deviation allowed to control the phase. The phase can be controlled to some degree by allowing the slope to alter from the ideal response. This introduces changes in the phase response and can be useful for non-aligned acoustic centers as is the case in this design. The problem in so doing is that the breakup region suppression may suffer.

Quick Crossover Recap

The page on final crossovers shows only the on-axis responses. The optimization actually used a combination of On-Axis and 5 degrees up, down left and right, a 5-point windowed average relative to the tweeter axis and all at 1m. All of it was done in CALSOD (a long-standing DOS application) with its 5-axis option for optimization. Crossover points were chosen after reviewing the on-axis and off-axis response curves from the manufacturer along with the in-box measurements that includes the diffraction. This page shows the predicted response for various off-axis points. The 2180Hz crossover is left in to show how the power response can vary as the crossover is moved up. Those graphs were never updated with the new woofer model, just ignore that part.

Probably the most telling graph is for the vertical response. The 5/10 and 10/20 degree up/down results show just how much influence there is in low crossover points and different slopes. It also helps to show where the difference in power response comes from. You can see the dramatic difference between the LR8 and the LR4. Here's a quick re-cap of the crossovers and some key points related to them.

To identify the curve with the angle, top to bottom is as defined with the top curve always being on-axis for the tweeter, 0 degrees (green). For example, the 5/10 Up/Down is 5 degrees UP (yellow), 10 degrees UP (blue), 5 degrees DOWN (white) and 10 degrees DOWN (gray).

1500HZ LR8    1500HZ LR4    2000Hz LR4    2000Hz LR4 Alt    2180Hz LR4   

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David L. Ralph © 2009