In this installment of “Similar, Yet Different,” we take a good look at two very different looking diffusers in the 2’x2′ size… the classic ArtDiffusor® Model C and the organic, rippled ArtDiffusor® Model D – while there are some similarities, there are some key differences in how they look (obviously) and how they perform. 

Quick Similarities.

The ArtDiffusor® Model C and Model D are both 2’x2′ diffusers which are made to be either wall mounted or installed in a standard drop-tile ceiling grid. They are both formed from a Class A fire-rated polymer in a single piece. Both are mathematical diffusers, which create their different physical features in a “form follows function” methodology. They also cover roughly the same frequency bands, with some minor variation in how they execute their control.

Difference in Math

The Model C is an interesting configuration. Often you will see quadratic residue diffusers with flat blocks or wells in a relatively standard quadratic cell formula configuration. The Model C runs in a much different alternating binary configuration. The basic idea is that cells are placed in a 45° array with each cell adjacency calculated as an alternating array of higher and lower cells starting in the middle and working in a pattern of alternating low/high cell clusters decreasing toward the edges of the diffuser. These diffusers also do not have flat tops on the blocks – they are angled at 10°. The orientation is then rotated in 90° steps in a pattern that maximizes the spatial redistribution of reflected sound. This was a vast design departure over the original quadratic design, and created a diffusion profile that was distinctly different.

The Model D was an even greater departure. It began with a Maximum Length Sequence (MLS) concept that first changed the varied straight channels into rings of different dimensions. These rings then broke from the MLS mold by getting varied height profiles based on the QRD sequence. As if having different size rings at different heights wasn’t enough… the randomness was further perpetuated through a Boolean process of assigning certain rings a random property that would either add or subtract height from any other ring that they crossed. Finally, the entire surface geometry was smoothed using a bicubic interpolation, creating the organic undulating surface which gracefully spans the entire profile.

What this difference in math does to the acoustic performance.

The Model C has a nice even diffusion profile through it’s primary working range. This is a product of the QRD design and binary distribution. The set size for the blocks guarantees a solid primary frequency range from about 1KHz to over 4Khz. This tunes the Model C squarely in the most sensitive bands of the human hearing range. Below this range the device becomes a bit of an absorber. Above this range and the performance becomes more effective at intervals, which can be seen in the areas of wide diffusion at 6KHz – 18 KHz. These repeating zones are common in “stepped” quadratic designs. Due to the heights of the well being at specific intervals, the intervals repeat at octaves of their effective bands. 

The Model D doesn’t have the same stepping. The spline interpolation and the random Boolean shifts smooth the transition from one quadratic height to the next, and the MLS sequence causes a bit of a high-pass filter pushing the start of the primary range to around 2KHz – which is a little higher than the Model C. The main difference is that once the Model D starts it’s range it diffuses everything up to and over 20KHz without the banding that can happen in other quadratic designs. 

Another difference in symmetry.

The ArtDiffusor® Model C is a fairly symmetric design, but it’s 45° angle pushes that symmetry along the diagonal (corner to corner) across the unit. The asymmetry is subtle but allows for enough variation to account for any “lobing” issues that can occur in more simple geometric devices The 10° block faces being at varied orientations is key to increasing the spatial directivity over the older “flat-faced” Quadratics. This was a very novel design when it was first introduced, and those benefits are crucial to the longevity of the Model C’s reign – It just works. It’s predictable and musical… and that’s why it’s here to stay!

The ArtDiffusor® Model D is a completely different animal from the Model C when it comes to symmetry… as a matter of fact… there isn’t really much on it that is symmetric! The Model D was designed as a departure from symmetry. Focusing on the mid to high frequencies, which are very specular, the organic geometry creates an asymmetric reflection pattern. This pattern can be used to steer the sound into a wider field.. and that profile changes with the wavelength of the sound that hits it. This steering ability and the wide frequency range has made the Model D a favorite in mixing and mastering environments, where they can get smooth performance through the entire frequency spectrum.

How these differences benefit everyone.

We have stated before that there isn’t really a one-size-fits-all solution in acoustics. Many environments will use various treatments to achieve their desired goals. You will often have different devices to address different problems, in different frequencies, in different locations, in the same space. Bass traps for controlling the lows. Absorption to reduce gross energy across the board. Large geometric surfaces to break up parallel reflections and steer the projection of sources. Mid range diffusers to create clarity to the sources and reduce artifacts. High frequency diffusers to reduce flutter and add a feeling of envelopment and airiness in the space. These devices all have their place – from the smaller listening rooms, to critical listening environments, and large multifunction spaces and venues.

It is also worth noting that these two devices have a very different aesthetic visually. The classic blocks of the Model C have become a signature look for quality sound environments, and people recognize them as they would classic geometric pyramids and barrels. The Model D aesthetic provides a visual accent that people take advantage of to set their space apart from others. The undulating, asymmetric pattern changes drastically when you rotate the individual units in the array. This allows for not only varied acoustic performance, but also a unique visual possibilities – with numerous variations.

The ArtDiffusor® Model C and Model D are two tools that are used to craft ideal listening environments around the world… and in those roles they are indeed Similar, Yet Different.