Long Range is a long expanse of dark green glass hexagons of varying depths and curvatures.

Composed of double and pocketed layers, its shaping was designed to exhibit gradients of acoustic reflection, diffusion, absorption, and transmission.

In acoustics, it would not be an exaggeration to call the most subtle convexity profound.

Planar surfaces have zero curvature, which means they reflect sound without altering its rate of dissipation. (This is a thought experiment that assumes ample dimensions and perfect rigidity. Dimensions and material cause significant variations in acoustic behavior, but the isolation of form as a driving acoustic factor was important in the design philosophy of Long Range.) Sound expands outwardly, and whatever sound energy is originally present dissipates as the wavefront grows and covers more and more surface area. When an expanding sound wave encounters a solid planar surface, it changes direction but its expansion and dissipation proceed in an uninterrupted manner. If it encounters a convex surface, however, its rate of dissipation will increase. This is where the shape of architecture begins to exert its influence.

Long Range comprises flat panes at one end, which yield to panes of gentle convexity, which themselves yield to panes of more and increasingly aggressive shaping.

In the fabrication process we discovered that our first attempt at gentle convexity appeared as too large a jump from the flat condition. That first attempt was already a minimum deviation given the fixed kiln stages of rising temperature, hold, and lowering temperature. Going deeper into that moment required the introduction of anticipation, a blurring of stages with a precisely-timed early cutoff of the heating elements that allowed the temperature to rise and fall off momentum alone. The new panel of even gentler convexity lies between flat and the first attempt. While the jump was softened considerably, it is clear that this halving could be repeated again and again and again. There is in fact an extreme and important difference between flat and the first instance of curvature.

Optically, this difference is readily apparent because it takes glass from essentially invisible to visible. 

The transparency of glass is ideal for this kind of study because even the smallest adjustment in curvature creates a strikingly different reflective quality than that of a flat plane. All sides can be viewed simultaneously, and a single vantage gives a glimpse at the complexity of the form of the whole. Acoustically, though, the transition point between inert and influential warrants further study, as it is complicated by the relatively large wavelengths of sound and by testing methods that measure repeated rather than initial interactions. In any case, convexity is a doorway to acoustic design possibility.

Every component of Long Range begins from the same flat hexagonal glass plate. 

Slumping pulls the form continuously from primarily reflective to diffusive to absorptive to transmissive. One mechanism for absorption is Helmholtz resonance, which means that sound energy is absorbed when an air cavity with carefully-determined openings responds intensely in a narrow band of frequencies. (See Helmolz, On the Sensations of Tone, for more.)

For Long Range the second layer of glass allowed for these cavities to be produced through the pairing of different slumped components. Auxetic cut patterns gave precise control over the number and size of openings that expose these cavities. 

There is also variation in the thickness of glass, which reduces as the slump depth increases. These tunable factors - volume of air cavity, area of openings, and glass thickness - combine to make Helmholtz resonators that were intentionally accessed via the surface shaping of Long Range.

Because all components start from the same glass blank and the slumping and auxetic unwindings preserve the amount of material in each panel, the weight does not change regardless of the resulting form. At the laboratory, the obligatory weighing of each component required by the testing standard became an exercise in redundancy. Conceptually, Long Range explores form as a dominant factor contributing to differences in acoustic behavior. 

Every panel is of identical material, perimeter condition, and mass to all other panels, and yet the resulting acoustic behavior changes along its length as the arrangement exhibits different proportions of the traditional categories of reflection, diffusion, absorption, and transmission.

Deviations from the plane in the other direction (...or simply turning a convex surface over - whether concave or convex depends entirely on which side of a surface the observer is on…) breaks to concavity rather than convexity, and this territory is just as rich. Concave surfaces have a generally poor reputation in acoustics because they form the domes and curved walls that can reverse the natural outward dissipation of sound, causing it to focus and yield strange amplification conditions. But whether and how an undesirable condition occurs depends on the curvatures involved and the location of the source and listener. Even severely concave surfaces manifest as diffusive if the sound has the space to pass through its point of  focus and dissipate beyond that. Long Range incorporates some of these concave surface geometries, where the focusing effects can be heard only if the sound source and listener are in a very close and precise location. Beyond that particular spot, the surfaces contribute to the overall diffusivity and average surface depth of Long Range. Additionally, concave components increase the range of cavity sizes for Helmholtz resonance, so extended frequency ranges for absorption are possible.

Together, convex and concave curvatures encompass surface shaping that historically resulted from imprecisions of fabrication and intentional ornamentation (e.g. a hand-formed plaster wall and coffered ceiling versus machine-made and laser-installed painted gypsum board).

Even today's advanced high-coefficient absorbers can be thought of as an aggressive mix of concavity and convexity if the shaping of pores and fibers are considered down to small scales. 

Placing typical acoustic reflectors, diffusers, and absorbers next to each other makes an increase in surface shaping complexity across these categories clear. In some ways, the modern acoustic panel can be considered a descendant of architectural ornamentation with maximized complexity and influence per unit area. 

Long Range, however, is not a collection of acoustic panels that were each designed for acoustic specificity.

It's not an arrangement of reflectors, diffusers, and absorbers, and it's not intended to fix rooms or to be applied in any fashion. It's a single surface that could itself be a room boundary, and from its shaping emerges a blurry, overlapping range of intrinsic acoustic properties. The surface amounts to more than the sum of its parts. By using a fabrication process that systematically draws these behaviors out of a traditional enclosure material, Long Range asks us to imagine not an empty rectangular glass box that warrants acoustic treatment, but a deformation of that box until it no longer needs such appliqué.

The increasingly aggressive shaping of Long Range from one end to the other was inspired by this kind of progression, though the range is intentionally limited to a smaller region of relatively mild shaping. Since so much of our built environment is flat planes and acoustic panels, the region near the breaking of the plane is largely unexplored in the context of contemporary design and fabrication possibilities.

Zackery Belanger, Catie Newell, and Wes McGee

Excerpted from:

Chapter 7: Embracing subtlety: Reflections on an acoustic surface of glass

in

The Routledge Companion to the Sound of Space

Edited By Emma-Kate Matthews, Jane Burry, and Mark Burry