This test was performed by using a RD-75 driver and measuring the frequency response off axis. Measurements were taken on axis and 10, 20, 30 and 40 degrees off-axis. High frequency fall off is clearly visible. As part of the learning curve we changed the number of averages to 64. All other parameters remained the same.
Important to note here is the expected fall-off in the high range in function of off-axis angle.