{
 "version": "2026-10-20",
 "license": "Dimension sheets are written by Xem Studio from the cited sources and are free to use (CC BY 4.0, attribute 'Xem Studio'). Linked files belong to their publishers under the license shown; Xem Studio does not host them. 'license_verified: false' means the license shown is from memory or the publisher's page as last read and should be confirmed at the link before commercial use.",
 "slug": "thermoacoustic-stacks-and-resonators",
 "name": "Thermoacoustic stacks (slicer-infill blanks, spiral), resonator lengths and a speaker driver cap for tri-clamp spools",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Thermoacoustic & fluidyne",
 "year": null,
 "question": "What stack and tube length does a thermoacoustic engine need, and how do I print a honeycomb stack?",
 "tags": [
  "thermoacoustic",
  "stack",
  "resonator",
  "honeycomb",
  "infill",
  "speaker",
  "tri-clamp",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "thermoacoustic engine stack",
  "thermoacoustic stack 3d print",
  "honeycomb stack infill",
  "thermoacoustic resonator length",
  "thermoacoustic refrigerator stack",
  "tashe",
  "thermoacoustic stirling engine tri clamp"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 16,
 "url": "https://xemstudio.com/objects/thermoacoustic-stacks-and-resonators/",
 "sheet_txt": "https://xemstudio.com/objects/thermoacoustic-stacks-and-resonators/sheet.txt",
 "sheet": {
  "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",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "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."
  ],
  "table": {
   "columns": [
    "spool",
    "bore_mm",
    "stack",
    "lengths_mm",
    "quarter_wave_150hz_mm",
    "half_wave_150hz_mm"
   ],
   "rows": [
    [
     "1.5",
     34.8,
     "blank + infill (table)",
     "30 / 40 / 50",
     572,
     1143
    ],
    [
     "2",
     47.5,
     "blank + infill (table)",
     "30 / 40 / 50",
     572,
     1143
    ],
    [
     "3",
     72.9,
     "blank + infill (table)",
     "30 / 40 / 50",
     572,
     1143
    ]
   ]
  }
 },
 "sheet_text": "Thermoacoustic stacks (slicer-infill blanks, spiral), resonator lengths and a speaker driver cap for tri-clamp spools — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/thermoacoustic-stacks-and-resonators/  (CC BY 4.0)\nBasis: 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\nCatalog version: 2026-10-20\n\nSizes: see table below\n- 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.\n- 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.\n- 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.\n- 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.\n- 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.\n- LES: the stacks, driver cap and tube-length table from the LES thermoacoustic builds; the infill trick is how LES prints them.\n\nspool  bore_mm  stack  lengths_mm  quarter_wave_150hz_mm  half_wave_150hz_mm\n1.5  34.8  blank + infill (table)  30 / 40 / 50  572.0  1143.0\n2  47.5  blank + infill (table)  30 / 40 / 50  572.0  1143.0\n3  72.9  blank + infill (table)  30 / 40 / 50  572.0  1143.0\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Thermoacoustic heat engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Thermoacoustic_heat_engine\n- 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/\n- 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\n- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 16 parts): https://xemstudio.com/files/hardware/thermoacoustic-stacks-and-resonators/index.json\nAPI: https://xemstudio.com/api/geometry?object=thermoacoustic-stacks-and-resonators\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Thermoacoustic heat engine",
   "url": "https://en.wikipedia.org/wiki/Thermoacoustic_heat_engine",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "G. W. Swift (LANL)",
   "title": "Thermoacoustics: A Unifying Perspective for Some Engines and Refrigerators (textbook; DeltaEC software free)",
   "url": "https://www.lanl.gov/org/ddste/aldps/materials-physics-applications/condensed-matter-magnet-science/thermoacoustics/",
   "formats": [
    "web",
    "software"
   ],
   "license": "LANL",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "Thermoacoustic Stirling heat engine for space power",
   "url": "https://ntrs.nasa.gov/search?q=thermoacoustic%20Stirling",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine builds",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
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 },
 "related": [
  "tri-clamp-spool",
  "tri-clamp-end-cap",
  "tri-clamp-displacers-and-heads",
  "regenerator-and-heat-materials",
  "linear-alternator-kit",
  "copper-pipe-type-l-m",
  "adafruit-audio-speakers-mics",
  "stirling-configurations-guide"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "tri-clamp-spool",
     "why": "stack in the bore, spools as resonator"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "tri-clamp-end-cap",
     "why": "capped hot end"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "tri-clamp-clamps",
     "why": "clamp per joint"
    },
    {
     "slug": "regenerator-and-heat-materials",
     "why": "mesh heat exchangers"
    }
   ]
  }
 ],
 "faq": [
  {
   "q": "How do I 3D print a thermoacoustic stack?",
   "a": "Print the stack blank with 1 perimeter, 0 top/bottom layers and honeycomb or grid infill; the infill density sets the cell size (0.4 mm line: 60% ≈ 1.3 mm grid cells, 45% ≈ 1.8 mm, 80% ≈ 1.0 mm). No custom geometry needed."
  },
  {
   "q": "How long should a thermoacoustic engine tube be?",
   "a": "Closed-open (λ/4): L = 343 / (4f): 286 mm for 300 Hz, 429 mm for 200 Hz, 858 mm for 100 Hz in air; closed-closed tubes are twice that."
  },
  {
   "q": "What channel size should the stack have?",
   "a": "2–4 thermal penetration depths: about 1–1.5 mm in air at 1 bar and 100–300 Hz; finer at higher frequency or pressure."
  },
  {
   "q": "Where does the stack go in the resonator?",
   "a": "Centred about one-eighth of a wavelength from the closed (hot) end: 107 mm for a 400 mm λ/4 tube."
  },
  {
   "q": "Can a thermoacoustic engine make electricity?",
   "a": "A speaker in the driver cap becomes a generator (milliwatts), or a piston on the linear alternator kit for real power; NASA's TASHE used a travelling-wave loop with a linear alternator."
  }
 ],
 "files_license": null,
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   "note": "stack blank Ø34.2 × 30 for the 1.5 in bore: slice with 0 top/bottom layers, 1 perimeter, honeycomb or grid infill; density sets the cell size (see table)"
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   "stl": "https://xemstudio.com/files/hardware/thermoacoustic-stacks-and-resonators/stack-spiral-3in-40-g1.0.stl",
   "note": "spiral (rolled-sheet) stack 3 in, 40 long, 1.0 mm gap (also a template for rolling film + fishing-line spacers)"
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   "note": "3 in ISO 2852 cap with a socket for a 40 mm speaker (thermoacoustic refrigerator driver / engine load)"
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 "markdown": "https://xemstudio.com/objects/thermoacoustic-stacks-and-resonators/index.md"
}