{
 "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": "loudspeaker-envelope-40mm",
 "name": "40 mm loudspeaker envelope (the speaker in the thermoacoustic driver cap)",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Thermoacoustic & fluidyne",
 "year": null,
 "question": "How big is a 40 mm speaker, and how does it sit in a thermoacoustic driver cap?",
 "tags": [
  "speaker",
  "loudspeaker",
  "envelope",
  "alternator",
  "thermoacoustic",
  "tri-clamp",
  "long earth society"
 ],
 "aliases": [
  "40mm speaker dimensions",
  "speaker as generator thermoacoustic",
  "loudspeaker alternator",
  "40 mm speaker step file envelope"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/loudspeaker-envelope-40mm/",
 "sheet_txt": "https://xemstudio.com/objects/loudspeaker-envelope-40mm/sheet.txt",
 "sheet": {
  "basis": "Overall Ø40 × 25 and the step diameters measured from the manufacturer's published model of a 40 mm speaker (Adafruit #3968); drawn as a stepped envelope, nothing copied",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A stepped envelope of a common 40 mm speaker: the space it takes, not its parts. Front rim Ø40 × 3 with the cone behind it, a Ø34 × 4 step, the Ø28 basket and the Ø20 magnet; 25 mm overall.",
   "In the 2 in driver cap it sits rim down in the Ø40 × 6 socket, cone toward the gas through the cap's Ø28 port; the basket and magnet stand above the cap.",
   "As an alternator: the gas pressure moves the cone, the voice coil moves in the magnet's field and gives a voltage at the terminals. A small speaker gives milliwatts to a fraction of a watt; see the build lists for the model's acoustic power at the cap."
  ],
  "table": {
   "columns": [
    "feature",
    "value"
   ],
   "rows": [
    [
     "step 1",
     "Ø40 from 0 to 3"
    ],
    [
     "step 2",
     "Ø34 from 3 to 7"
    ],
    [
     "step 3",
     "Ø28 from 7 to 17"
    ],
    [
     "step 4",
     "Ø20 from 17 to 25"
    ]
   ]
  }
 },
 "sheet_text": "40 mm loudspeaker envelope (the speaker in the thermoacoustic driver cap) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/loudspeaker-envelope-40mm/  (CC BY 4.0)\nBasis: Overall Ø40 × 25 and the step diameters measured from the manufacturer's published model of a 40 mm speaker (Adafruit #3968); drawn as a stepped envelope, nothing copied\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A stepped envelope of a common 40 mm speaker: the space it takes, not its parts. Front rim Ø40 × 3 with the cone behind it, a Ø34 × 4 step, the Ø28 basket and the Ø20 magnet; 25 mm overall.\n- In the 2 in driver cap it sits rim down in the Ø40 × 6 socket, cone toward the gas through the cap's Ø28 port; the basket and magnet stand above the cap.\n- As an alternator: the gas pressure moves the cone, the voice coil moves in the magnet's field and gives a voltage at the terminals. A small speaker gives milliwatts to a fraction of a watt; see the build lists for the model's acoustic power at the cap.\n\nfeature  value\nstep 1  Ø40 from 0 to 3\nstep 2  Ø34 from 3 to 7\nstep 3  Ø28 from 7 to 17\nstep 4  Ø20 from 17 to 25\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Adafruit (CAD parts repository, MIT): #3968 Speaker 40mm: overall Ø40 × 25 and the step diameters measured from the published model; nothing copied — STEP — MIT; dimensions only — https://github.com/adafruit/Adafruit_CAD_Parts/tree/main/3968%20Speaker%2040mm\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, 1 parts): https://xemstudio.com/files/hardware/loudspeaker-envelope-40mm/index.json\nAPI: https://xemstudio.com/api/geometry?object=loudspeaker-envelope-40mm\n",
 "sources": [
  {
   "publisher": "Adafruit (CAD parts repository, MIT)",
   "title": "#3968 Speaker 40mm: overall Ø40 × 25 and the step diameters measured from the published model; nothing copied",
   "url": "https://github.com/adafruit/Adafruit_CAD_Parts/tree/main/3968%20Speaker%2040mm",
   "formats": [
    "STEP"
   ],
   "license": "MIT; dimensions only",
   "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,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "thermoacoustic-driver-cap",
  "adafruit-audio-speakers-mics",
  "list-ta-loop-2in",
  "list-ta-standing-half-wave-2in"
 ],
 "fits": [],
 "dimensions": "exact (nominal, no printing tolerance)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no printing tolerance. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn.",
 "mating": [
  {
   "feature": "front rim",
   "exact": "Ø40 × 3",
   "mates": "Ø40 × 6 socket of the 2 in driver cap",
   "fit": "socket",
   "files": "all"
  },
  {
   "feature": "basket and magnet",
   "exact": "Ø34 / Ø28 / Ø20",
   "mates": "space above the driver cap (no contact)",
   "fit": "designed",
   "files": "all"
  }
 ],
 "fit_classes": {
  "press": "stays put: pin, tube, bearing or magnet held by interference. Typical FDM: hole +0.0 to +0.1 mm on diameter.",
  "slide": "assembles by hand and is held by a grub, pinch or clamp: shaft in a hub, rod in a socket, spigot in a bore. Typical FDM: +0.2 mm.",
  "run": "turns or slides in use: pin in a link, rod through a guide. Typical FDM: +0.3 mm.",
  "socket": "large sliding fit: syringe barrel, sleeve, bobbin in a bore. Typical FDM: +0.3 mm.",
  "clamp": "split part that closes on the mating part with screws: make it at size.",
  "designed": "a gap that is part of the design (piston fit option, displacer gap, air gap): do not change."
 },
 "faq": [
  {
   "q": "Is this the speaker's real shape?",
   "a": "It is its envelope: every step is the largest diameter of the speaker over that height, so anything that clears the envelope clears the speaker."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "speaker-envelope-40mm",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/loudspeaker-envelope-40mm/speaker-envelope-40mm.step",
   "stl": "https://xemstudio.com/files/hardware/loudspeaker-envelope-40mm/speaker-envelope-40mm.stl",
   "note": "40 mm loudspeaker envelope: front rim Ø40 × 3 (cone side at z = 0), Ø34 × 4, basket Ø28 × 10, magnet Ø20 × 8; 25 overall"
  }
 ],
 "markdown": "https://xemstudio.com/objects/loudspeaker-envelope-40mm/index.md"
}