Quote Hugh Robjohns:
If you think about the way a (cardioid) mic works, it becomes very obvious that a broadband absorber (eg. duvet) placed in front of the mic but behind the performer (and ideally, extending around the sides too) will have a significantly greater effect in reducing unwanted room reflections than a 'filter' placed behind the mic.
Both are useful, but I'd rig the duvet before worrying about a filter.
I agree with Hugh on this.
I use an absorber behind the singer, in front of the mic.. This minimises room reflections bouncing back off a hard surface into the mic.. It works very well.
Personally, I can't really see the point of these reflection filters as they are behind the mic. where the mic. is least sensitive anyway.
John - Sound-Link ProAudio
President - Federation Internationale des Chasseurs de Sons