Adding lowpass filter

I have 2 mmats 601.8 midrange speakers running in parallel and bridged off the amp.

i want to add a low pass filter or filters inline. My question is because the speakers are in parallel and amp seeing a 4 ohm load do I just need one 4 ohm filter wired inline after the amp before the first speaker. Or do I need 2 -8 ohm filters inline at each speaker.

thanks for the help

ken ,Canada