1 dimensional acoustic quadratic residue diffuser is highest sequence wall treatment available in industry. It is designed to reduce or eliminate flutter echos from reflections on walls, FlutterX comes in two sequence choices, FlutterX11 and FlutterX19. It shall be based on one dimensional phase grating diffuser design, using an array of slotted, routed cells along the vertical axis. The depth of wells shall be based on minimum prime 11 quadratic residue number sequence.