1 – Exploring Sound Qualities in architectural Design

Space A — Wydestrasse, side lane parallel to Hohlstrasse (Zürich)

Purpose and description

A small private lane runs parallel to Hohlstrasse with no through traffic. It sits between two quieter side streets where cars pass on and off. Facades face each other across about 5 meters of asphalt, creating a shallow urban canyon. Window reveals, balconies, and small setbacks break up and scatter sound. A kindergarten is opposite. The nearby trains are covered by some sound barriers, so only a light low rumble is audible. Short, close sounds stand out over the calm background: footsteps, keys, doors, clusters of children’s voices. 

I chose this lane because it looks peaceful, but it is constantly disturbed by the parallel main road. The space is not loud, yet a steady background hiss from that road is always present if you listen. A light echo persists as short reflections bounce across the lane, adding a thin reverberant layer.

Acoustic event

• Passing cars at cross-streets
• Footsteps, key jingle, door clack from resident
• Children at the kindergarten
• Wind in trees
• Leaves rustling 

Recordings 

At 20 cm my voice is very clear and close, but a faint background hiss from the parallel main road is still audible

At 1 m my voice blends more with the road noise, a nearby car makes a brief whistle while braking, and the wind is audible

At 2 m my voice sounds slightly quieter but not much different from 1 m. The distance is probably too short to make the volume decrease . The main road noise remains clearly audible.

Adjectives

open: outdoor volume with no roof lets sound expand.

a bit echoey: close facades create short, ping-pong reflections.

live: hard surfaces add a small reverberant tail.

muddy (after 10 m): distance and reflections smear consonants and boost low mids.

warm: leaf canopy and soft masking reduce harsh highs, so voices and low mids feel fuller.

Space B — Oerlikon school: open-air antechamber and stair to underground garage

The second space is a staircase in the parking lot that descends into a hole: the entrance to the underground garage of a school in Oerlikon. After the stairs, before the entrance, there is a small open-air space that connects the school and the garage. Here, since everything is made of concrete, the sound echoes more. The space is open-air but has recesses that act as an acoustic basin: the sound bounces around a lot, partly because the area is small. The materials are concrete and glass, so there is no absorption.

I find the space interesting because it is a “non place”: no one stops or talks there, and the acoustic qualities were not considered at all during the design phase because they were not necessary for its function.

Acoustic event

• stroller on paving: soft wheel roll 
• car starting in garage
• engine rumble
• brief rev
• cars on adjacent street: tire hiss
• occasional brake squeal
• electrical noise

Recordings

At 20 cm my voice is clear and crisp, with a slight room-like reverb already present. A low background noise from the road is audible because the space is still open to the outside.

At 1 m my voice has a stronger reverb and starts to blend with the space. The surrounding noise comes up in level. Wind, road hiss, and nearby activity are more audible.

At 2 m my voice is softer and less clear. Reverb from the space is stronger. The surrounding noise is closer in level to my voice, so the recording is less clear to understand.

Adjectives

live: hard concrete surfaces create strong reflections and a short reverb tail.

boomy: concrete and semi enclosed geometry amplify low frequencies.

boxy: small cavity with parallel walls emphasizes midrange.

loud: peak moments when traffic passes or cars start in the garage.

2 – Exploring the Emotional Impact of Everyday Sounds

Space 1_ HIL courtyard

I step through the large archway into the HIL courtyard, open to the sky and bathed in sunlight. The space is small, enclosed by tall walls and broad porticoes, so it feels like a secluded garden.

I begin to listen carefully. The soundscape is dominated by quiet, gentle noises. A light breeze rustles the leaves overhead. Occasionally a few leaves drift to the ground with a quiet flutter. These natural sounds are subtle and calming.

I also become aware of distant noises outside the courtyard. Beyond the arch, voices of students echo faintly under the covered walkway, a low murmur. I hear the soft click of footsteps against the stone pavement. Every few minutes, a heavy door opens or closes with a brief creak. These intermittent sounds reach me weakly, as if the courtyard buffers them.

For a few moments, I sit in near complete silence. The soft rustling of leavesfill the space. 

Suddenly, a harsh, piercing screech shatters the quiet. A bus pulls into the stop just outside. As its brakes engage, the noise is sharp and brash, echoing off the space. 

Immediately after, the bus engine’s rumble grows louder as it settles into the stop. A brief hiss marks the doors opening, followed by the murmur of passengers. The experience feels intrusive, I am more alert, a bit on edge.

After about fortyfive seconds, the door closes with a clunk, the engine revs, and the bus drives away. Within thirty seconds the bus is gone, and the courtyard is almost silent again. 

Once more, I’m with the quiet sounds of the courtyard. The wind picks up; leaves rustle overhead. Minutes later, the cycle repeats: calm quietude, then sharp bus noise, then calm quietude again. 

This cycle also influences my emotions. While the courtyard is quiet, I feel peaceful and relaxed. When the bus noise explodes, I feel a spike of stress.

The piercing screech of the bus brakes is especially irritating because it intrudes suddenly. Loud, sudden noises of human origin make me tense and disrupt my thoughts. Continuous soft sounds like the wind in the trees or distant, muffled chatter feel pleasant or neutral. The courtyard’s design filters much of the noise, letting through mostly natural sounds, except for occasional loud intrusions that really catch my attention.

Space 2_My apartment_(The kitchen extractor fan)

For the second listening session, I chose to stay in my flat in Zurich. At first glance, it seemed obvious and predictable: the environment appeared completely silent. However, as soon as I concentrated on listening carefully, sounds emerged that I hadn’t noticed at first and that proved increasingly annoying. The most obvious was that of a fan: I had left the kitchen extractor fan on for almost three hours without realising it. Now that I have noticed it, I find it difficult not to hear its continuous humming. The sound of the extractor hood is louder than I would have thought, even though it is set to the lowest power setting.

The large space is organised into a single open space room that includes a kitchen, living room and dining room. The extractor hood is about four metres away from where I am sitting at the table, where I was initially sitting with my back to it. When, intrigued, I turn to look at the hood, the sound experience changes: in this new position, I perceive the humming with higher and more resonant tones, as if the sound were bouncing around the kitchen before reaching my ears clearly. When I was sitting with my back to the hood, however, the humming seemed to be lower in frequency and less penetrating.

This constant sound begins to make me a little uncomfortable. It bothers me because it is always present, almost unchanged over time: it does not seem to have any noticeable drops or variations in frequency, probably because the hood is new and working well. However, when I concentrate more closely, I notice that even this hum is not perfectly uniform: every now and then I perceive an imperceptible change in tone, as if the sound were oscillating slightly with a light, rhythmic beat. At the moment, the change is so minimal that it resembles the sound of a small acoustic signal (like a very faint alarm), but it is so slight that it requires great concentration to be aware of it. My flat overlooks a quiet side street. Every now and then a car passes by and I hear a distant noise, more like a sense of vibration or continuous flow than a distinct sound. The window panes are very thick and do an excellent job of muffling outside noise. In this situation, the outside soundscape is muffled and indistinct, and I cannot clearly distinguish one car from another. The only perceptible difference is between a motorbike and a car, because motorbikes have a higher engine speed and produce a noise that is on average higher-pitched and more intrusive. Of course, if I opened a window, the soundscape would change radically: external noises would penetrate my flat and mix with the internal ones, creating a new sound balance.

What remains unchanged, however, is the sound of the extractor fan, which has become increasingly annoying. It largely covers the external noises, preventing me from distinguishing them clearly. Until recently, when I was busy doing other things, I hadn’t noticed this background hum at all. Now that I listen to it, however, the constancy and intensity of this sound affect my acoustic comfort at home, making me realise how often the small everyday sources of sound go unnoticed.

3 Empirical and numerical estimation of room acoustic properties

task 1

The room I have chosen to analyse for this exercise is the living room in my house. It is the only room where I am at the moment that is free from significant external noise and therefore suitable for a clean recording. It is an open space that also includes the kitchen, with a central corridor leading to the bedrooms. The house and the fixtures are new, which helps reduce noise from outside.

The predominant materials are parquet flooring and smooth plastered walls. These surfaces, together with the probable reinforced concrete structure, reflect much of the sound and do not offer much absorption, creating a generally reverberant environment. However, the presence of a sofa, armchairs and some plants introduces sound-absorbing elements, helping to slightly reduce the sound decay time.

For the measurement, the computer was placed on the table, at the position corresponding to the blue pyramid in the diagram, while I stood where the red cone is shown. I produced sounds by clapping my hands at various points in the room.

Subsequent analysis using Audacity confirmed the hypothesis: the reverberation time (RT60) detected is approximately 0.51 s.

I also tried recording from other locations in the house, but the reverberation time (RT60) consistently remained around 0.53 s. In terms of auditory perception, the reverberation seemed to me to be less than a second, although still noticeable.

Despite the reverberation, no distinct echoes or returns are perceived, due to the small size of the space. However, the sound is still quite present and “loud” even at a distance of more than two metres from the point of origin, indicating reflective surfaces and limited overall absorption.

task 2

I also analysed the reverberation time specifically at 500 Hz and 1000 Hz. At 500 Hz, the RT60 remained essentially constant, while at 1000 Hz it should theoretically decrease to around 0.48 seconds.

4 Final Assignment

Acoustic Description (Existing)

The measurements at the three receivers show very similar reverberation times in all frequency bands. T30 stays roughly between 1.4 and 1.7 seconds, with only small differences of a few hundredths of a second between positions. This means that, wherever you sit in the room, you experience the same long, “wet” reverberation.
C50 values are mostly negative and STI lies around 0.51–0.55, which confirms that the room is rather echoey and that speech is not very clear. These results match the space as it is now: a large volume with concrete and plaster surfaces and one full glazed wall, with only a partially absorbing ceiling.

Design proposal

For the new use I propose to transform the space into a meditation room, where people mostly sit in silence or with a soft layer of mantra music in the background. The aim is not perfect speech intelligibility, but a feeling of calm, softness and acoustic privacy. Shorter reverberation times and a strong reduction of high frequency reflections are important, while some low-level warmth can remain.

Following the SIA category for resting rooms, the target is a reverberation time below about 0.9–1.0 seconds in the mid frequencies. This would make the room clearly quieter than now, but not completely “dead”.

Design Strategy – Materials and Atmosphere

The main acoustic intervention is to replace hard, reflective surfaces with soft, textile elements. Thick cotton sheets are suspended from the ceiling and allowed to drape in loose, overlapping waves. They act as the primary absorbers, especially for mid and high frequencies, and visually create a kind of fabric canopy. The floor is finished in wood, but it is almost fully covered with cushions and soft seating, which add another layer of absorption close to the listeners.

With this transformation, the only large exposed hard surface that remains is the floor to ceiling glazing. This keeps a small amount of reflection and brightness in the room, so the space does not become completely muffled, and it preserves a visual and acoustic connection to the outside.

In the new condition, impulsive sounds such as footsteps, breathing, or the rustling of clothes are quickly damped by the textiles and cushions instead of bouncing around the room. Quiet mantra music would wrap gently around the listeners without strong echoes or sharp highs. Overall, the space becomes acoustically soft, intimate and protective, supporting stillness and focused breathing rather than loud conversation.

As a first step, the existing room condition is evaluated against the SIA recommendations. Because the space is intended as a quiet meditation, it is assigned to category 2c rather than to a speech or music use. For this group, the recommended mid frequency reverberation time depends on the room height h and is given by

With a height of h=4.8 m, the limit becomes

The measured RT30 values from all three receivers, however, lie between 1.4 s and 1.7 s across most octave bands, with an average of about 1.6 s. The following sections develop measures to bring the reverberation time down to approximately 0.8 s, comfortably within the target range for this use.

I used the measured situation: the room has a volume of about 527 m³ and an average mid frequency reverberation time of roughly 1.6 s. With Sabine’s relation this corresponds to about 50–55 m² of equivalent absorption in the current state.

Then I looked at the target: for an SIA 2c resting / meditation room the reverberation time should be around 0.8 s. For the same volume this means that the room would need roughly twice as much absorption, on the order of 100–105 m². In other words, I have to add about 50 m² of “effective” absorption to the existing situation.

https://delius.de/en/kollektionen/acoustics/

This missing absorption is almost entirely provided by the textile canopy. For heavy cotton curtains that are pleated and draped, literature gives a mid-frequency absorption coefficient of about 0.6. That means that every square metre of fabric behaves like 0.6 m² of perfect absorber. To get the 50 m² of absorption I therefore need a bit more than 80 m² of actual fabric. In the design the canopy covers about 60 m² of ceiling in plan, but it is installed with strong draping (factor 1.5), so the developed fabric surface is approximately 90 m². This is enough to supply the missing absorption and even a small safety margin.

If I plug this back into Sabine’s formula, the total equivalent absorption in the room increases to just over 100 m², and the resulting reverberation time drops from about 1.6 s to roughly 0.8 s in the mid bands.

the soft cushions on the floor then act as an additional safety margin and further soften the subjective impression.

Conclusion

In conclusion, the draped cotton canopy alone turn what was a hard, echoey volume into a much softer and more intimate acoustic environment, where small sounds decay quickly . At the same time, the intervention remains extremely flexible: because all absorption is introduced through removable textiles and loose cushions, the original hard shell of the room is preserved. If the use changes in the future, the space can easily be returned to a more neutral, reverberant condition simply by taking down the fabric, without any irreversible construction work.