Passive input filters

Hi all
In the process of building an active horn speaker setup. I have the 3 amps needed and was thinking about using simple passive filters on the input of each amp, are there any reasons not to try this?
I want the bass to roll off at say 400 hz with a first order slope so a simple resistor and capacitor filter on the amp input could do this, correct?

What do you think......

Thanks

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