The ARF-42 - Small but mighty Ambient Room Filter
Post Audio's Swiss Army filter. A couple of ARF-42's in your tool kit can cover almost any situation. Use on vocals, drums, guitars, woodwinds or any acoustic instrument.
There are other reflection filters on the market. Some are inexpensive and not so good and some others are good but crazy expensive. Post Audio hits the sweet spot with filters that do their job very well, are professional quality and are still reasonably priced. That's probably why Post Audio is the largest distributor of reflection filters in the USA.