What do you think about this?

[JuliánFernández]

Take a look...

http://www.gearslutz.com/board/so-much-gear-so-little-time/189933-oh-reflections-will-work.html

I wonder if it would work...

 

[mshilarious]

Take a look...

http://www.gearslutz.com/board/so-much-gear-so-little-time/189933-oh-reflections-will-work.html

I wonder if it would work...

It depends on the size of the piece of foam, which determines the cutoff frequency for the sound simply going around the barrier. So it would work with high frequencies to some extent. But a cardioid mic will already have good rejection of rear sounds at high frequencies, so I'm not sure this would improve matters. It might simply change the polar response of the mic in a strange way.