Sonic Facade – Comprehensive Study Notes

Thesis Metadata

  • Author: Alina Granville
  • Degree: Bachelor of Science in Architecture, MIT, June 2012
    • Thesis submitted: May 25, 2012
    • Supervisor: John Fernandez (Associate Professor of Architecture and Building Technology and Engineering Systems)
    • Committee: Terry Knight, Rizal Muslimin (Shape-Grammar critics)
  • Title: “Sonic Facade, Creating a Sounding Architecture”
  • Copyright © 2012. MIT may reproduce and distribute the thesis in any medium.
  • Accompanying media: Embedded/​CD audio tracks 1–14 corresponding to precedents, tube tests, and example buildings.

Motivation

  • Architecture is dominated by the visual; acoustic potential is often ignored.
  • Everyday built elements already generate sound (e.g., footsteps on floors, wind at windows).
    • Materials either amplify/reflect or dampen/absorb sound.
    • Form can channel sound, creating spatial auditory experience.
  • Author’s background as a woodwind player → curiosity about wind-driven sound in pipes.
  • Inspiration from sound artists who scale traditional instruments for nature:
    • Wind replaces a musician’s breath, water can replace bellows, rain acts as mallets, etc.
  • Historic tension: Murray Schafer notes concert halls evolved to separate sonic experience from everyday life; author aims to reintegrate them.
  • Critique by Bernhard Leitner: modern architecture lacks relationship among “sound, space, body.”
  • Thesis challenge: Can a façade itself become a wind-powered musical instrument that also informs occupants about exterior conditions (wind, rain, passer-by interaction)?

Objectives & Scope

  • Design a wind-powered sonic façade that integrates into existing walls.
  • Develop a seven-rule shape grammar enabling users to decide placement/implementation on varied buildings.
  • Conduct extensive studies:
    1. Wind behavior around buildings & tubes.
    2. Tube acoustics, scaling, and typology.
    3. Spatial grammars for aggregation.
  • Limit thesis to three demonstrative building applications; grammar intended to be universal.
  • Produce hypothetical composite audio for each example based on recorded tube samples.

Precedents

  • Instrument classification (Hornbostel–Sachs): focus on aerophones (vibrating columns of air).
    • Simple pan flute → complex brass & woodwinds show variety of tube geometries.
  • Large wind-driven sound projects:
    • Singing, Ringing Tree (Tonkin Liu) – mixed tube types; Track 1.
    • Aeolus (Luke Jerram) – Aeolian harp strings + resonating tubes; Track 2.
    • Songlines (Joe Snell) – 10 m cylinder with Aeolian harps + LEDs; Track 3.
    • Chimecco (Mark Nikkon) – bridge-hung pipes act as chimes; Track 4.
    • Sonambient (Harry Bertoia) – rod clusters producing metallic drones; Track 5.
    • Organ of Corti (Liminal) – sonic crystal tube array filtering/amplifying ambient sounds; Track 6.

Instrument & Tube Typologies Examined

  • Straight circular tubes: open–open, open–closed (+ block), transverse-slot variants.
  • Bent tubes: mild bend, 180^{\circ} U-bend, U-bend with closed end, split-length U-bend.
  • Split & partition tubes: dual branches, interior cross walls (little acoustic change).
  • Transverse-opening tubes (slots, flaps) – most variants showed negligible change except long narrow slot.
  • Aeolian-harp hybrids (strings across square/circular sections) – ineffective in wind tests.
  • Bottle/organ-pipe and tapered sections – required direct wind; unsuitable for façade context.
  • Harry Bertoia style rods – sound, but hard to excite naturally.

Wind Studies

Relationship of Wind to Building Form

  • Wind seeks shortest path around obstacles → acceleration at edges.
    • High-velocity zones near corners & openings ideal for tube placement.
  • Visualization via Wind Tunnel Pro HD (iPad app): pressure, speed, vectors over drawn building profiles.

Possible Tube Placements (Section & Plan)

  • Parallel, slanted, reverse-slanted, perpendicular; options:
    • Exterior surface mount.
    • Wall-penetrating (inside–outside sonic link).
    • Ground-supported positions rejected (airflow blocked).
  • Only placements ensuring unobstructed mouth exposure to wind are viable for sound.

Sound Studies

Basic Acoustics

  • Sound waves = longitudinal; speed depends on conditions.
    • Use constant c\;=\;340\,\text{m/s} (approx.).
    • More precise: c\;=\;331.3 + 0.6\,t (with t in °C).
  • Two primary tube categories:
    1. Open–open (both ends pressure nodes).
    2. Open–closed (pressure node + antinode).
    • Tube with two closed ends unusable – no radiation path.

Fundamental & Harmonics

  • For any tube: f = \dfrac{c}{\lambda}.
  • Open–open:
    • Fundamental wavelength \lambda = 2L.
    • Length correction: L = \dfrac{n\,\lambda}{2} - 0.8d (end correction; d = diameter).
  • Open–closed:
    • Fundamental \lambda = 4L.
    • Length correction: L = \dfrac{n\,\lambda}{4} - 0.4d.
  • Harmonic content:
    • Open–open supports all integer n.
    • Open–closed supports only odd n.

Human Hearing & Design Limits

  • Audible band: 20 Hz – 20 kHz; piano range 27.5 Hz – 4186 Hz chosen as practical subset.
  • Selected façade tube diameter: 6 in (≈150 mm) – compromise between ease of excitation and structural scale.
  • Extreme lengths derived:
    • Open–open at 27.5\,\text{Hz}\Rightarrow L \approx 19.88'.
    • Open–closed at same frequency \Rightarrow L \approx 9.94'.
    • High piano C (1318.5\,\text{Hz}) corresponds to impractically short lengths (<0.5').
    • Minimum usable length set to 2' to keep wind speed requirements reasonable.

Empirical Testing

  • Air sources & measured speeds:
    • Desk fan ≈ 9 mph.
    • A/C vent ≈ 7.5 mph.
    • Hair-dryer: low 5 mph, high 12.5 mph.
    • Human blowing: ~23 mph but unrealistic for façade.
  • Early piccolo-scale tubes (1/4"–1") failed → scaling up to 2"+ diameters succeeded.
  • Hundreds of variants tested; only 3 selected for final grammar (see below).

Selected Tube Set (Uniform external form, distinct acoustics)

  1. Type 1 (T = 1): Circular, open–open – medium-pitch hum.
  2. Type 2 (T = 2): Circular, open–closed – one octave lower.
  3. Type 3 (T = 3): Circular, open–closed + long transverse slot – higher pitch with whistle overtone (fundamental & 1st harmonic recorded).
  • Recordings cleaned in Audacity using noise-cancel & amplification.

Spatial Relation & Basic Grammars

Pillar Abstraction

  • Tube represented by square pillar in plan; two pillars placed 15° rotated form base relation.
  • Pillar has 16 symmetry operations → 16 label conditions.

Basic Grammar Outcomes

  • One-rule grammars (16 variants): tight/loose spirals, fans, lines, identity (no growth).
  • Two-rule grammars (256 possible): patterns A–B–A–B; identity rules (labels 2,5,10,13) halt growth (unsuitable for façades).
  • Three-rule grammars (4096 possible): patterns A–B–C; increased complexity, less predictable aggregations; all examined sets used non-turning labels (1,6,9,14).

Seven-Rule Sonic Facade Grammar

  1. Rule 1 – Locate Façade
    • User marks start & end points on existing building; progression counter-clockwise in plan.
  2. Rule 2 – Tube Height
    • Bottom ≥ 3" off grade.
    • Length limits 2' \le L \le 19.88'.
    • Relative to building height: equal, above, or below roofline.
  3. Rule 3 – Calculate Quantities
    • For façade segment distance D: N = \dfrac{D}{6"} tubes.
    • Count corners C.
  4. Rule 4 – Place First Pillar
    • Offset ≥ 3" from wall.
    • Initial labels: tube number Z = 1, tube type T = 1.
  5. Rule 5 – Aggregate Pillars
    • Apply straight rule while Z \le N.
    • If Z=N & C>0 apply one turn rule (pillar width sized to maintain 3" clearance).
    • Tube-type labeling sequence:
      • If L > 9.94' → pattern 1-2-1-2-…
      • Else L \le 9.94' → 1-2-3-1-2-3-…
  6. Rule 6 – Color Coding
    • Apply one of four possible color orientations on each pillar; drives connection-detail parametrics.
  7. Rule 7 – Substitute Tubes & Details
    • Pillar replaced by physical tube according to T.
    • Connection bracket depth s = 2.5\"; offsets: 0.1L or 0.2L for aesthetic staggering.
  • Grammar supports non-determinism & user choice; accommodates openings; not yet written for curved surfaces.

Example Applications

Example 1 – “Complicated with Awning”

  • Two walls: pattern (1-9-14) on short side, (1-6-9) on long side; one corner turn.
  • All tubes 8' long (equal height), W = 3", G = 3".
  • Visual result: undulating spiral forming awning + niches.
  • Acoustic output: only 3 base sounds (equal lengths).

Example 2 – “Simple with Openings”

  • Patterns use only label rule 6; differentiation via starting label positions.
  • Tube lengths: 2', 3.25', 9'; varying ground clearances 3"–7.25".
  • No corner tubes; façade wraps around windows/doors.
  • Produces 9 distinct pitches; overall higher register.

Example 3 – MIT Green Building (Bldg 54)

  • Site wind rose (Project Full Breeze) → prevailing NW wind.
  • Façade located on NW wall, framing entry near Bldg 56.
  • Tube length maximized 19.88'; two tube types (open–open, slot).
  • Tubes 15' above grade; low, droning composite sound.

Creating Final Sounds (Composites)

  • Method in Audacity:
    • Layer multiple recordings of each tube type.
    • Use Change Speed, Change Pitch, Amplify, Reverse per layer.
    • Pitch shifts match relative tube lengths; number of layers matches count of each type.
  • Tracks 12–14 correspond to Example 1–3 composites.

Discussion & Future Work

  • Applicability: best for public, educational, or museum façades; domestic/office users may need optional tube caps to mute sound.
  • Strengths of Grammar: adaptable, user-driven aesthetics, limited tube palette keeps sonic range intelligible.
  • Limitations:
    • No curved-wall logic.
    • Fixed tube lengths within a run; finer musical control deferred.
    • Opening creation rule could be formalized.
    • Does not compute exact frequencies; author argues environment-dependent variability makes strict tuning less relevant.
  • Next Steps:
    • Physical mock-ups to validate acoustics.
    • Extend grammar to structural elements, interior-exterior sonic dialogue, furniture scale.

Numerical & Equation Highlights

  • Speed of sound (ideal): c = 340\,\text{m/s} ; temperature-corrected: c = 331.3 + 0.6t.
  • Fundamental wavelengths:
    • Open–open: \lambda = 2L.
    • Open–closed: \lambda = 4L.
  • Tube frequency: f = \dfrac{c}{\lambda}.
  • Practical length bounds for 6" tubes: 2' \le L \le 19.88' (≈ 0.61 m – 6.06 m).
  • Wind test air speeds: 5–12.5 mph (mechanical); 23 mph (human blow) – unrealistic.

References & Credits (Condensed)

  • Major sources: Araujo & Dykes (Project Full Breeze), Fletcher & Rossing (Physics of Musical Instruments), Schafer, Kahn, Hopkin, etc.
  • Image credits: Tonkin Liu, Luke Jerram, Joe Snell, Mark Nikkon, Harry Bertoia studio, Liminal.
  • Sound credits: YouTube clips of Singing Ringing Tree, Aeolus, Aeolian Harp, Chimecco, Sonambient, Organ of Corti.