Exploring Sounds in Different Built Forms
Space_01 Staircase Shaft HIL, ETH Hönggerberg
The 8×8 m staircase block operates as a vertical echo chamber. Defined by terrazzo flooring, plastered walls and ceilings, and metal railings, the space is composed entirely of hard, reflective surfaces with no acoustic treatment. The staircase detaches from the walls, forming three deep voids that act as vertical sound shafts, enabling multi-level reflection and vertical spilling of sound .
As a result, even the faintest sound from the lowest floor is amplified, reverberated, and sonically stacked as it rises. Footsteps, voices, and incidental noises collide mid-air, producing overlapping frequencies and prolonged decay. A sound of clap stayed in the space for almost 6 seconds. The space becomes acoustically turbulent, a reverberation-heavy, metallic, and brutally resonant environment where sound bleeds across levels, creating a dense, chaotic, and disorienting atmosphere.
Space_02 HPI Courtyard, ETH Hönggerberg
The courtyard is enclosed on all four sides by exposed concrete walls, with gravel underfoot and three dry trees rising toward the open sky. Punctures in the walls form corridors and selective openings to the exterior. Visually, the space suggests acoustic softness due to its open roof and granular ground surface; however, the auditory experience contradicts this expectation.
Despite being open to the sky, the hard concrete perimeter creates a reflective enclosure. A single clap lingers for nearly two seconds, producing a clear and prolonged decay. Louder impulses generate a distinct flutter echo as sound waves rebound between opposing walls. The reflections remain crisp and legible rather than chaotic, with minimal frequency overlap likely moderated by the wall openings that allow partial sound escape and diffusion.
The result is a sky-open yet acoustically contained courtyard: bright, articulate, and perimeter-amplified, where sound transfers clearly across the space without becoming sonically congested.
Empirical and numerical estimation of room acoustic properties
For assignment number three I chose the first room. I chose this room because of the staircase’s acoustics the space is highly reverberant, and I was curious to analyze how long it retains and reflects sound.
From the above reading, we can observe that the sound level drops from −10 dB at 1.15 seconds to −60 dB at 3.6 seconds. This indicates a 50 dB decay over a period of 2.45 seconds, representing the reverberation time.
The reverberation time(RT60) of the space is approximately 2.9 seconds.
This is quite high, which aligns with your observation of a very reverberant staircase space. Toward the end, the sound returns as a faint echo with significantly reduced intensity.
Final Assignment –
In the selected Room D24.1 on the D floor of the HIL Building, I reimagined it as a performance-oriented space, a place where people can gather to perform, rehearse, and jam together using different instruments. This shift in function requires the acoustics of the room to be carefully reconsidered and designed to support both musical clarity and collaborative interaction.
The room measures 13.5 m × 9.7 m × 4.8 m, resulting in a total volume of approximately 630 m³, with a total surface area of around 490 m². Currently, the floor and ceiling are constructed of concrete, the north-facing wall consists of glass panels, and the remaining three walls are made of plasterboard. The space is presently used as an office/computer room, furnished with tables, chairs, and some suspended ceiling panels.
The room falls in the A1 category in this graph
For an A1 (“Musik”) room according to the graph you attached, the target reverberation time depends on room volume.
Your room volume is approximately:
TA1≈1.28–1.35 s
| Frequency | Your Current T30 | Recommended A1 Range | Assessment |
|---|---|---|---|
| 63 Hz | 1.24 s | 1.55–1.70 s | low bass reverberation |
| 125 Hz | 1.46 s | 1.40–1.50 s | excellent |
| 250 Hz | 1.46 s | 1.30–1.40 s | slightly high |
| 500 Hz | 1.45 s | 1.25–1.35 s | high |
| 1000 Hz | 1.66 s | 1.20–1.30 s | too high |
| 2000 Hz | 1.74 s | 1.10–1.20 s | much too high |
| 4000 Hz | 1.48 s | 1.00–1.10 s | too high |
| 8000 Hz | 0.97 s | 0.90–1.00 s | excellent |
Iteration 01 — Over-Treated Acoustic Condition
In the first iteration, the space was heavily treated with multiple acoustic elements, including curtain systems, reflector fins (red), ceiling reflectors, and absorptive panels (blue), in an attempt to control reflections and distribute sound evenly across the performance space. While the treatments successfully reduced flutter echoes and harsh reflections, the overall amount of absorption became excessive, especially in the mid and high frequencies. This caused the reverberation time to drop significantly, making the room acoustically dry and lacking the warmth and liveliness required for a music-oriented performance space. The results showed that the room was over-treated, leading to a rapid decay of sound energy and reduced spatial richness. This iteration helped identify the need for a more balanced approach between absorption, reflection, and diffusion, leading to the gradual removal and adjustment of acoustic elements in later iterations.
Final Iteration:
Learning from the first iteration, the final design reduced the excessive use of absorbers and diffusive elements to achieve a more balanced acoustic environment suitable for music performances. Angled reflector fins (red) were strategically placed to redirect the early sound projections from the instrument evenly across the audience area, improving clarity and spatial distribution without creating harsh direct reflections. CurtainI and absorptive surfaces were introduced to absorb the later reflected sound waves and control excessive reverberation and flutter echoes. This combination of controlled reflection and selective absorption helped create a warmer and more balanced acoustic atmosphere, allowing the space to maintain both musical reverberance and speech clarity while providing a more uniform listening experience for the audience.
Isometric exploded view of the space
Material Selection:
Reflector Material:
Lacquered birch plywood acoustic reflector panels with low absorption and high reflective performance for controlled early sound distribution.
Pleated Velour Acoustic Curtain:
Heavy pleated velour acoustic curtain with approximately 60–80% fullness and an air gap behind the fabric, used to control flutter echoes and absorb late reflected sound waves while maintaining a soft and diffuse acoustic response suitable for intimate music performance spaces.
Perforated timber acoustic wall panels :
Perforated timber acoustic wall panels with mineral wool backing designed to absorb mid and high frequency reflections while maintaining a warm and reflective acoustic character suitable for music-oriented performance environments. The perforated wooden surface also provides moderate sound scattering, helping reduce flutter echoes and improve spatial diffusion within the room.
Acoustic Reading After Material Integration:
The final acoustic iteration achieved a balanced reverberation profile through the integration of angled reflector fins, acoustic curtains, and perforated wooden absorptive panels. The reflector fins distributed early sound reflections evenly across the audience area, improving spatial clarity and sound coverage, while the curtains and absorptive treatments controlled later reflections and reduced excessive reverberation. The resulting T-30 values created a warm yet controlled acoustic environment suitable for an intimate music performance space, while the C-50 clarity values indicated a good balance between musical reverberance and speech intelligibility.
Particle Animation:
Rendered View:
