Thermoacoustic stack for tri-clamp spools: Ø34.8, Ø47.5 and Ø72.9, honeycomb and spiral — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/thermoacoustic-stack/  (CC BY 4.0)
Basis: Stack OD = 16 ga spool bore (34.8 / 47.5 / 72.9), exact; channel width 2–4 thermal penetration depths (δκ ≈ 0.26 mm in air at 1 bar, 100 Hz; 0.15 mm at 300 Hz), Swift
Catalog version: 2026-10-20

Sizes: see table below
- The stack is the core of a standing-wave thermoacoustic engine: many narrow parallel channels between a hot face and a cold face, sitting in the resonator tube. It is drawn at the spool bore, so it is held in the bore itself.
- Honeycomb stack (1.5 and 2 in, × 40): hexagonal cells 1.5 mm across flats with 0.4 mm walls, every cell whole inside a 0.4 mm outer ring. Spiral stack (all three sizes, × 30, 40 and 50): one 0.4 mm wall wound with a 1.0 mm gas gap from a Ø6 core to a 0.5 mm outer ring.
- Channel size: half-width 2–4 × δκ, δκ = √(κ / (π f ρ cp)), so about 1–1.5 mm channels at 100 Hz and about 1.0 mm at 300 Hz in air at 1 bar.
- Placement: centred about λ/8 from the closed (hot) end of a λ/4 resonator; a closed-open tube resonates at f = c / 4L (150 Hz → 572 mm, 300 Hz → 286 mm in air at 20 °C).

spool_in  stack_od_mm  forms  lengths_mm  quarter_wave_150hz_mm  half_wave_150hz_mm
1.5  34.8  honeycomb 1.5 mm cells / spiral 1.0 mm gap  40 / 30, 40, 50  572  1143
2  47.5  honeycomb 1.5 mm cells / spiral 1.0 mm gap  40 / 30, 40, 50  572  1143
3  72.9  spiral 1.0 mm gap  30, 40, 50  572  1143

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Wikipedia: Thermoacoustic heat engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Thermoacoustic_heat_engine
- G. W. Swift (LANL): Thermoacoustics: A Unifying Perspective for Some Engines and Refrigerators (textbook; DeltaEC software free) — web, software — LANL [verify license at link] — https://www.lanl.gov/org/ddste/aldps/materials-physics-applications/condensed-matter-magnet-science/thermoacoustics/
- NASA (NTRS, public domain): Thermoacoustic Stirling heat engine for space power — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=thermoacoustic%20Stirling
- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/

Free files (CC BY 4.0, Xem Studio; STEP + STL, 11 parts): https://xemstudio.com/files/hardware/thermoacoustic-stack/index.json
API: https://xemstudio.com/api/geometry?object=thermoacoustic-stack