Shure DFR11EQ (2 units) - $50 (floyd)

Shure DFR11EQ Digital Feedback Reducer and Graphic Equalizer.
There are two units racked together.
Units have been tested.
The Shure Model DFR11EQ is a single channel signal processor that combines a feedback reducer and graphic equalizer in a single, half-rack enclosure.
The DFR11EQ is designed to be placed in a sound reinforcement signal path to automatically detect and control acoustical feedback and equalize overall sound system response.
The DFR11EQ is designed for installed sound reinforcement applications: theater, conference rooms, meeting halls, etc.
The DFR11EQ is also an effective setup tool for controlling major feedback modes in live music applications.
The feedback reducer of the DFR11EQ automatically inserts narrow notch filters at detected feedback frequencies.
These notch filters stop a sound system from feeding back, but are narrow enough so their effect on audio quality is minimized.
The feedback detection algorithm constantly searches for feedback, with or without the presence of program audio.