Thermoacoustic stacks (slicer-infill blanks, spiral), resonator lengths and a speaker driver cap for tri-clamp spools — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/thermoacoustic-stacks-and-resonators/  (CC BY 4.0)
Basis: Standing-wave thermoacoustic engine design (Swift): stack plate spacing ≈ 2–4 thermal penetration depths (δκ ≈ 0.1–0.3 mm in air at 1 bar, 100–300 Hz → gaps 0.5–1.5 mm), stack centred ~λ/8 from the closed end of a λ/4 resonator; stacks printed as a solid blank whose slicer infill IS the honeycomb
Catalog version: 2026-10-20

Sizes: see table below
- A thermoacoustic engine has no pistons: a stack (many narrow parallel channels) with a hot end and a cold end sits inside a resonator tube; above a critical temperature gradient the gas self-oscillates at the tube's resonance. Load it with a speaker-as-microphone (the driver cap) or a piston on a linear alternator. Driven backwards it pumps heat: a thermoacoustic refrigerator.
- Print the stack from the blank: 1 perimeter, 0 top and 0 bottom layers, infill pattern honeycomb (or grid / triangles), and set the infill density to the cell size you want. Cell pitch ≈ 2 × line width / density for grid; ≈ 1.7 × line width / density for honeycomb. With a 0.4 mm line: 60% → ~1.3 mm grid cells, 45% → 1.8 mm, 30% → 2.7 mm, 80% → 1.0 mm. The density slider is the stack's channel size; no new file needed. Print 0.1–0.15 mm layers so the walls are smooth.
- Stack physics: channel half-width 2–4 × δκ, δκ = √(κ/(π f ρ cp)) = 0.26 mm for air at 1 bar and 100 Hz (0.15 mm at 300 Hz), so cells of 1–1.5 mm at 100 Hz, ~1.0 at 300 Hz. Length 20–50 mm. Centre the stack about λ/8 from the closed (hot) end. Low-conductivity walls: PETG/resin for demonstrators (hot end on a metal plate, stack behind it), ceramic honeycomb (catalytic substrate, 400 cpsi ≈ 1.1 mm cells) for real heat.
- Resonator: closed-open tube f = c / 4L (λ/4): 100 Hz → 858 mm, 150 Hz → 572, 200 Hz → 429, 300 Hz → 286, 500 Hz → 172 (air, 20 °C, c = 343 m/s). Closed-closed (two caps) is λ/2, twice as long. Tri-clamp spools stack to any length: two or three 2 in × 12 in spools make a 200–300 Hz λ/4 engine with the hot end capped. Heat: nichrome coil or flame on the capped end; cold end a water jacket or the copper-pipe cooler.
- The spiral stack is the template for the classic rolled-Mylar-and-fishing-line stack; the explicit 1.5 mm hex file is a reference for the geometry the infill approximates.
- LES: the stacks, driver cap and tube-length table from the LES thermoacoustic builds; the infill trick is how LES prints them.

spool  bore_mm  stack  lengths_mm  quarter_wave_150hz_mm  half_wave_150hz_mm
1.5  34.8  blank + infill (table)  30 / 40 / 50  572.0  1143.0
2  47.5  blank + infill (table)  30 / 40 / 50  572.0  1143.0
3  72.9  blank + infill (table)  30 / 40 / 50  572.0  1143.0

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, 16 parts): https://xemstudio.com/files/hardware/thermoacoustic-stacks-and-resonators/index.json
API: https://xemstudio.com/api/geometry?object=thermoacoustic-stacks-and-resonators