The crossover does NOT have any low frequency protection for the mid-frequency portion of the driver. So you need to provide a high pass solution in conjunction with this crossover. The crossover uses a third order low pass on the midrange portion, and a second order high pass on the high frequency section. There are no contour filters to shape the response. It is expected that you would do this by other means, such as the PEQ function within your chosen DSP for example.
Below is my measured frequency response result for the FB464-16 crossover. I've overlaid both the MF and HF to show the individual responses. (Red and Purple) The third order low pass is very effective at eliminating the resonant peak at 4kHz. You can barely see the peak in the response.
Just to make sure I was getting the best results I decided to move my test setup outside and re-measure the response. (see below)
B&C publishes their own frequency response mounted to the ME464 constant directivity horn. My own ES-290 biradial uses an exponential horn flare and so the resulting frequency response will not have the falling response associated with constant directivity designs. This can clearly be seen in the B&C published response graph below.
The B&C ME464 + DCX464 + FB464 published graph shows a response variation of 13dB (2.6kHz vs 9kHz). In contrast the ES-290 + DCX464 + FB464 shows a 9dB variation (2.6kHz vs 6kHz).
To highlight the differences in the responses I've overlaid the published frequency response from B&C for the ME464 horn against my results with the ES-290 Biradial (Black). I can tell you that I strongly suspect the bug screen has been removed in the B&C published result judging by the improved upper treble extension shown in their result (red). I was able to get similar extension by removing the bug screen (not shown).
Below is the burst decay result.
I decided to measure harmonic distortion from 90, 95, 100, and 105dB SPL levels at one meter.
Harmonic Distortion at 90dB SPL 1 meter shown below. D2 at 1kHz is 0.24% at 2kHz.
Harmonic Distortion at 95dB SPL 1 meter shown below. D2 at 1kHz is 0.60% at 2kHz.
Harmonic Distortion at 100dB SPL 1 meter shown below. D2 at 1kHz is 1.08% at 2kHz.
Harmonic Distortion at 105dB SPL 1 meter shown below. D2 at 1kHz is 2% at 2kHz.
I decided to test the driver at 90, 95, 100, and 105dB SPL levels using a multitone test to generate the IMD noise products. I had to measure both low decade and high decade tones to fully capture the frequency spectrum covered by the driver.
Low Decade (Male vocal region) IMD at various SPL levels
IMD is at 0.079% (-62dB) at 90dB as shown below.
Increasing SPL to 95dB raises IMD to -60dB (0.10%) as shown below
Increasing SPL to 100dB raises IMD to -53dB (0.22%) as shown below
Increasing SPL to 105dB raises IMD to -50dB (0.32%) as shown below
High Decade (Female vocal region) IMD at various SPL levels
IMD is at 0.32% (-50dB) at 90dB as shown below.
IMD is at 0.22% (-53dB) at 95dB as shown below.
IMD is at 0.35% (-49dB) at 100dB as shown below.
IMD is at 0.63% (-44dB) at 105dB as shown below.
The FB464-16 passive crossover is a good solution. The crossover should be used in conjunction with other filter elements either using DSP or passive solutions to optimize the frequency response further. The choice of horn largely dictates the resulting frequency response. There needs to be some EQ applied to extend the high frequency response. Some level adjustment may be required between the MF and HF depending on the horn used. If using the ME464 horn, you will certainly need to level adjust the HF upwards to account for the falling response of the horn. If this is the case then IMD will be higher on the ME646 versus the ES-290.