The quality of amplified sound in a room depends not only on the microphone and loud speakers, but also to a large degree on the acoustical characteristics of the room. Sound is reflected by walls . Various frequencies are reflected in different amounts. Peaks in the frequency response cause a coloration of the original sound. This condition is marked by ringing and feedback.

Ringing is a prolongation of the reverberation time for those frequencies which are approaching unity gain.
Feedback is an oscillation at the frequency where loop gain exceeds unity.

The main ideology of acoustic resonances is improvement of the sound quality, better intelligibility of speech, more sound level through higher gain.
NOTCH FILTER: Effect unit includes four notch bandpass filter sections, which are identical. The filter type is SVF (State-variable filter).

The FDBKSPR650 effect unit is inspired by the original UREI™ Feeback Suppressor * effect device and includes additional functions, like additional BELL EQ mode.

Feedback Suppressor Notch Filter / Bell EQ can be added to the signal chain to reduce the microphone “proximity” effect and suppress any remaining high Q resonances. Also, one of the main functions is to improve gain before feedback.

Four Notch bandpass filters or four Bell EQ bands help finally to tweak incoming signal to minimize sound coloration, fight with feedback situations, and can fix resonance peaks.

Try FDBKSPR650 feedback suppressor effect for Reason rack right now.