Metadiffuser similar to a 7-period quadratic diffuser

Quadratic diffusers (QRD) are well-known technology for scattering sound. Their operating principle is that some number of wells are created, usually 7, with specific depths, and thus a planar wavefront splits into each well, becomes delayed by the flight time of sound of that specific well, and then sums together again outside the diffuser. The phase shift of all the wells combine in sound waves being reflected in diffuse way towards far field within the operating frequency range of the diffuser. Downside of quadratic diffusers is their depth: for effective low-frequency behavior, the wells must have a substantial depth because low frequency waves are long.

Metamaterials, such as shown here, provide an alternative to using deep wells. In these cases, there are wells within wells, of various widths and depths, optimized by an algorithm, to create a phase shift. The required depth of the diffuser can be shrunk by an order of magnitude by placing these wells sideways and carefully choosing their dimensions. This diffuser has been built and measured to operate between 700 - 2800 Hz with well depth of just 3.8 cm.

The design is not my own. It is simply the 3D printable version from the parameters presented by Jaroslaw Rubacha's in "Sound Diffuser Made of Acoustic Metamaterial: Numerical and Experimental Investigation", published in 2021 by VPS. I took the numbers from Table 1, and created the geometry in OpenSCAD.

The print requires use of a backing material and a frame. A thin few mm plywood surface of approximately 70 cm x 43 cm in size could be used as the backing plane, and 3.8 cm sides -- the height of the wells -- should frame the plane to provide rigidity and the edge for the first well. Into this frame, you need lines drawn every 10 cm apart, 6 in total, separating the longer side to 7 equal sections. The printed parts -- with the number of the part facing down -- would be glued down in numeric order, so that the notch on the one side faces left and the smooth surface faces right, and that right side surface should be aligned with the 10 cm divisor lines (or the frame edge, in case of the part 7).

I only provide a single STL file with the 7 parts -- use e.g. OrcaSlicer's function "split to objects" and auto arrange to create the separate 7 printable parts so that they can fit on your plate. I also provide an illustrative picture of the final design, which is not intended to be printed, but shows the complete object. I also recommend reading the referenced paper for more context.