# Build list: Thermoacoustic traveling-wave loop, 2 in tri-clamp

> What parts do I need to build a Thermoacoustic traveling-wave loop, 2 in tri-clamp?

- Category: Stirling engines › Assembled engines
- Kind: List / guide
- Basis: Every part is a free STEP/STL on this site or a standard part with its own page; quantities are the full count, every screw, nut, pin, gasket and clamp; acoustic numbers from the low-amplitude network model in tools/gen_ta_family.py (Rott's equations, Swift).
- Page: https://xemstudio.com/objects/list-ta-loop-2in/ · JSON: https://xemstudio.com/api/geometry?object=list-ta-loop-2in · Plain text: https://xemstudio.com/objects/list-ta-loop-2in/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); linked files under their publishers' licenses
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- A looped traveling-wave thermoacoustic engine in 2 in tri-clamp, torch-heated, with a choice of output on the resonator (a 40 mm loudspeaker or the free-piston linear alternator) and an optional membrane in the loop.
- Numbers: Legs 359 mm apart, core 6 in, regenerator Ø44 × 40 of 50-mesh × 0.22 mm screen (r_h 107 µm, porosity 0.66) · 286 Hz · onset ≈ 184 °C at the hot exchanger · ≈ 24 W of sound into a matched end load at 3 kPa (3 % of 1 bar) at the tee · output: loudspeaker cap (A) or linear alternator (B)

## Sizes

| subsystem | object | parts | qty | note |
|---|---|---|---|---|
| None | sanitary-clamp-elbows | elbow-90-2in | 4 | the four corners of the loop |
| None | sanitary-clamp-tees | tee-2in | 2 | top: resonator branch up; bottom: capped branch toward the front (the feedback compliance) |
| None | tri-clamp-spool | tc-spool-2in-6in | 2 | left leg = the core (exchangers, regenerator, thermal buffer tube); right leg = feedback |
| None | tri-clamp-spool | tc-spool-2in-12in | 1 | resonator, up from the top tee |
| None | tri-clamp-end-cap | tc-cap-2in-flat | 1 | closes the bottom tee's branch |
| None | tri-clamp-gasket | tc-gasket-2in | 9 | Type B at the loop, branch-cap and resonator joints (the right leg's lower joint is chosen below) |
| None | tri-clamp-clamps | clamp-half-2in | 20 | 10 joints, two halves each |
| None | socket-head-cap-screws-metric | shcs-m5x30 | 20 | two per clamp |
| None | hex-nuts-metric | nut-m5 | 20 | in the clamps' hex traps |
| None | thermoacoustic-bore-spacer | ta-spacer-2in-8.4 | 2 | core ends: gasket lip to each ambient exchanger |
| None | thermoacoustic-heat-exchanger | heat-exchanger-cold-2in | 2 | main ambient exchanger (top of the regenerator) and secondary ambient exchanger (bottom of the buffer tube) |
| None | regenerator-cage | regenerator-cage-47-5x40 | 1 | under the main ambient exchanger |
| None | regenerator-mesh-disc | mesh-disc-44mm | 80 | fill the cage, 40 mm: 50-mesh screen, 0.22 mm wire |
| None | dowel-pins-metric | dowel-3x30 | 1 | with the 3 × 10, fills the discs' Ø3 centre holes end to end (no bypass) |
| None | dowel-pins-metric | dowel-3x10 | 1 |  |
| None | thermoacoustic-heat-exchanger | heat-exchanger-hot-2in | 1 | under the regenerator, inside the flame shroud |
| None | thermoacoustic-bore-spacer | ta-spacer-2in-61.7 | 1 | thermal buffer tube liner: hot exchanger down to the secondary exchanger |
| None | thermoacoustic-water-jacket | ta-jacket-half-2in-14 | 4 | optional heat exchanger: two water jackets on the core, over the two ambient exchangers (9.35 from each face); without them the engine needs more heat to start, or cool those two bands any way you like |
| None | socket-head-cap-screws-metric | shcs-m4x25 | 4 | optional: jacket ears (only with the jackets) |
| None | hex-nuts-metric | nut-m4 | 4 | optional: jacket ears (only with the jackets) |
| None | thermoacoustic-hot-shroud | ta-shroud-2in-front | 1 | flame shroud round the hot exchanger, with the flue down to the torch |
| None | thermoacoustic-hot-shroud | ta-shroud-2in-back | 1 |  |
| None | socket-head-cap-screws-metric | shcs-m4x25 | 2 | shroud ears |
| None | hex-nuts-metric | nut-m4 | 6 | shroud (2), hangers (4) |
| None | tri-clamp-torch-stand | torch-stand-40 | 1 | on the bench under the flue, 25 below it; the heat source is a propane / butane torch head in the ring |
| None | set-screws-metric | set-m4x10 | 3 | centre the torch head in the ring |
| None | tri-clamp-gasket | tc-gasket-2in | 1 | choose one right-leg joint, G (gasket): under the right leg |
| None | tri-clamp-diaphragm-membrane | membrane-2in | 1 | choose one right-leg joint, M (membrane): in place of the gasket under the right leg: blocks the steady flow round the loop |
| None | tri-clamp-diaphragm-disc | diaphragm-disc-2in | 1 | choose one right-leg joint, M (membrane): centre disc, boss up into the right leg |
| None | tri-clamp-diaphragm-disc | diaphragm-backing-2in | 1 | choose one right-leg joint, M (membrane): under the membrane |
| None | socket-head-cap-screws-metric | shcs-m2x8 | 3 | choose one right-leg joint, M (membrane): heads under the backing disc |
| None | hex-nuts-metric | nut-m2 | 3 | choose one right-leg joint, M (membrane): on the centre disc |
| None | tri-clamp-gasket | tc-gasket-2in | 1 | choose one output, A (loudspeaker): resonator top |
| None | tri-clamp-clamps | clamp-half-2in | 2 | choose one output, A (loudspeaker): 1 joint, two halves each |
| None | socket-head-cap-screws-metric | shcs-m5x30 | 2 | choose one output, A (loudspeaker): two per clamp |
| None | hex-nuts-metric | nut-m5 | 2 | choose one output, A (loudspeaker): in the clamps' hex traps |
| None | thermoacoustic-driver-cap | driver-cap-2in-40mm-speaker | 1 | choose one output, A (loudspeaker): closes the resonator; Ø28 port to the speaker cone |
| None | loudspeaker-envelope-40mm | speaker-envelope-40mm | 1 | choose one output, A (loudspeaker): 40 mm loudspeaker in the cap's socket, cone toward the gas |
| None | tri-clamp-gasket | tc-gasket-2in | 1 | choose one output, B (linear alternator): resonator top to the 3 in spool |
| None | tri-clamp-clamps | clamp-half-2in | 4 | choose one output, B (linear alternator): 2 joints, two halves each |
| None | socket-head-cap-screws-metric | shcs-m5x30 | 4 | choose one output, B (linear alternator): two per clamp |
| None | hex-nuts-metric | nut-m5 | 4 | choose one output, B (linear alternator): in the clamps' hex traps |
| None | tri-clamp-spool | tc-spool-2in-3in | 1 | choose one output, B (linear alternator): piston cylinder at the resonator end |
| None | tri-clamp-hot-gasket | hot-gasket-2in | 1 | choose one output, B (linear alternator): flat, bore ID, under the flexure head: the piston skirt passes it |
| None | tri-clamp-flexure-head | fp-flexure-head-2in | 1 | choose one output, B (linear alternator): clamps on the 3 in spool, carries flexure stack A |
| None | tri-clamp-power-piston | piston-2in | 1 | choose one output, B (linear alternator): full-bore, closed crown (no rod hole: the resonator stays sealed) |
| None | tri-clamp-piston-plug | fp-piston-plug-2in | 1 | choose one output, B (linear alternator): in the skirt, carries the tube rod |
| None | dowel-pins-metric | dowel-3x16 | 2 | choose one output, B (linear alternator): wrist dowels through bosses and plug legs |
| None | tube-piston-rods-5mm | tube-rod-5x3.4x120 | 1 | choose one output, B (linear alternator): plug to stack B, through stack A and the mover |
| None | linear-alternator-mover | alt-mover-35-2x8-10x3 | 1 | choose one output, B (linear alternator): on the tube rod, centred in the coils |
| None | set-screws-metric | set-m3x3 | 1 | choose one output, B (linear alternator): mover hub grub |
| None | neodymium-disc-magnets | magnet-10x3 | 16 | choose one output, B (linear alternator): row 1 all N out, row 2 all S out |
| None | linear-alternator-bobbin | alt-bobbin-37-2x10 | 1 | choose one output, B (linear alternator): |
| None | linear-alternator-coil | alt-coil-bay | 2 | choose one output, B (linear alternator): one per bay, the second wound the other way |
| None | linear-alternator-back-iron-sleeve | alt-back-iron-sleeve | 1 | choose one output, B (linear alternator): |
| None | linear-alternator-housing | alt-housing-2in-flex80 | 1 | choose one output, B (linear alternator): |
| None | linear-alternator-cap-ring | alt-cap-2in-flex80 | 1 | choose one output, B (linear alternator): |
| None | tri-clamp-flexure-ring | fp-flexure-ring-80 | 1 | choose one output, B (linear alternator): carries stack B |
| None | spiral-flexure-bearing | flexure-80-3arm-w2.5-t2 | 4 | choose one output, B (linear alternator): two per stack, opposite spiral hand |
| None | flexure-stack-spacer | spacer-80-t2 | 2 | choose one output, B (linear alternator): between the leaf rims |
| None | flexure-rim-clamp-plate | clamp-plate-80 | 2 | choose one output, B (linear alternator): on each stack's rims |
| None | flexure-hub-clamp-washer | hub-clamp-80-b5 | 2 | choose one output, B (linear alternator): 2 mm hub washer between the leaf hubs |
| None | flexure-hub-collar | hub-collar-80-b5 | 4 | choose one output, B (linear alternator): two per stack on the tube rod |
| None | threaded-standoffs-metric | standoff-m3x15 | 3 | choose one output, B (linear alternator): head to alternator housing |
| None | threaded-standoffs-metric | standoff-m3x10 | 3 | choose one output, B (linear alternator): alternator cap to the flexure ring |
| None | socket-head-cap-screws-metric | shcs-m3x20 | 3 | choose one output, B (linear alternator): up through head and stack A into the 15 mm standoffs |
| None | socket-head-cap-screws-metric | shcs-m3x10 | 7 | choose one output, B (linear alternator): 3 housing base flange, 4 hub-collar pinch screws |
| None | socket-head-cap-screws-metric | shcs-m3x12 | 3 | choose one output, B (linear alternator): up through the housing's top flange and cap into the 10 mm standoffs |
| None | socket-head-cap-screws-metric | shcs-m3x16 | 3 | choose one output, B (linear alternator): down through stack B and the ring into the 10 mm standoffs |
| None | 2020-aluminum-extrusion | 2020-200 | 8 | per stand: two rails on the bench, two uprights |
| None | t-slot-corner-brackets | corner-bracket-20 | 8 | two per upright, front and back, onto its rail |
| None | button-head-screws-metric | button-m5x10 | 16 | bracket screws, a washer each |
| None | flat-washers-metric | washer-m5 | 16 |  |
| None | drop-in-t-nuts | tnut-dropin-20-m5 | 20 | 8 per stand for the brackets, 2 per hanger |
| None | spool-hanger-collars | hanger-2in-tab | 2 | clamps a spool tube; its bar bolts to both uprights |
| None | spool-hanger-collars | hanger-2in-plain | 2 | the other half of each hanger |
| None | socket-head-cap-screws-metric | shcs-m5x16 | 4 | hanger bar into the uprights' T-nuts |
| None | socket-head-cap-screws-metric | shcs-m4x20 | 4 | close each hanger on its tube |

## Where the files are

- Nature (S. Backhaus, G. W. Swift): [A thermoacoustic Stirling heat engine, Nature 399, 335–338 (1999)](https://doi.org/10.1038/20624) — web — journal article; cited (verify at link)
- J. Acoust. Soc. Am. (S. Backhaus, G. W. Swift): [A thermoacoustic-Stirling heat engine: Detailed study, JASA 107(6), 3148 (2000): regenerator |Z| 15–30 ρc/A with p and U nearly in phase, thermal buffer tube, inertance and compliance, jet pump against Gedeon streaming](https://sites.science.oregonstate.edu/~hetheriw/energy/topics/doc/thermo/heat_eng/Stirling_engine/thermoacoustic-Stirling.heat.engine.detailed.study.j.acous.soc.2000.pdf) — PDF — journal article; numbers cited (verify at link)
- G. W. Swift (LANL / Acoustical Society of America): [Thermoacoustics: A Unifying Perspective for Some Engines and Refrigerators (Rott's equations, screen relations, DeltaEC)](https://www.lanl.gov/org/ddste/aldps/materials-physics-applications/condensed-matter-magnet-science/thermoacoustics/) — web, software — LANL (verify at link)
- Phys. Rev. Lett. (T. Yazaki, A. Iwata, T. Maekawa, A. Tominaga): [Traveling wave thermoacoustic engine in a looped tube, PRL 81, 3128 (1998)](https://doi.org/10.1103/PhysRevLett.81.3128) — web — journal article; cited (verify at link)
- Phys. Rev. (H. Levine, J. Schwinger): [On the radiation of sound from an unflanged circular pipe, Phys. Rev. 73, 383 (1948): end correction 0.6133 a](https://doi.org/10.1103/PhysRev.73.383) — web — journal article; cited (verify at link)
- Applied Energy (Z. Yu, A. J. Jaworski, S. Backhaus): [Travelling-wave thermoacoustic electricity generator using an ultra-compliant alternator, Applied Energy 99, 135–145 (2012): atmospheric air, a commercial loudspeaker as the alternator, 11.6 W electric](https://doi.org/10.1016/j.apenergy.2012.04.046) — web — journal article; cited (verify at link)
- Xem Studio: [Free-piston Stirling build list and its checked assembly (tools/asm_free-piston-2in.py): the alternator section reused here](https://xemstudio.com/objects/list-free-piston-2in/) — web — CC BY 4.0
- Long Earth Society: [Engine builds](https://longearthsociety.com/engineering/) — web, video — LES site

## Build order

1. Stands: rails, uprights and brackets for two stands, one under the left leg and one under the right leg.
2. Core (6 in spool, lower face down): 8.4 spacer on the lower lip, secondary exchanger, 61.7 liner, hot exchanger, cage with 80 mesh discs and the 3 × 30 + 3 × 10 dowels through their centre holes, main ambient exchanger, 8.4 spacer to the upper lip.
3. Optional water jackets on the core 9.35 mm in from each face, one M4 × 25 and nut each side; shroud halves round the hot exchanger, flue to the front, M4 × 25 each side.
4. Loop: bottom-left elbow, core, top-left elbow, top tee (branch up), top-right elbow, right 6 in spool, bottom-right elbow, bottom tee (branch to the front) back to the bottom-left elbow; Type B gaskets and clamps at all eight loop joints. Gasket, cap and clamp on the bottom tee's branch.
5. Hangers on the core and on the right leg between the lower jacket and the shroud, bars to the uprights.
6. Torch stand on the bench under the flue, torch head in the ring with its three M4 set screws.
7. Right leg's lower joint: Type B gasket (G), or the membrane, discs and M2 screws assembled flat and clamped in place of the gasket (M).
8. Output A: 12 in resonator spool on the top tee's branch; driver cap with the speaker in its socket, cone down, on top.
9. Output B: 12 in resonator spool on the top tee's branch; Type B gasket, 3 in spool; piston with plug, dowels and the 120 tube rod into the 3 in spool; flat gasket, flexure head; stack A, standoffs, alternator, stack B and ring as on the free-piston build.

All printed STLs: https://xemstudio.com/objects/list-ta-loop-2in/stl-list.txt

## Questions

**What frequency does it run at?**

78 parts, every one a free STEP/STL on this site; see the table and the build order on this page.

**How hot does it need to get?**

The model starts it at about 184 °C at the hot exchanger with the loudspeaker (179 °C with the alternator); I expect the real engine to need more, perhaps 250–350 °C.

**Why is the core vertical with the hot end up?**

So the thermal buffer tube has hot gas over cold gas and does not convect; the flame shroud and flue bring the torch to it.

**Do I need the water jackets?**

No. They are optional heat exchangers clamped on the plain spool; without them the ambient exchangers warm up and the engine needs more heat to start. Any cooling of those bands works, even a wet rag.

**Which output should I build?**

The loudspeaker (A): milliwatts to a fraction of a watt from the 40 mm speaker by my estimate, and a bigger matched speaker is the upgrade. The linear alternator (B) fits exactly, but at this frequency its piston hardly moves.

**What does the membrane do?**

It blocks the steady flow round the loop (Gedeon streaming) that otherwise carries heat from the hot exchanger to the ambient one; Backhaus & Swift used a jet pump for the same job.

## Fits with

- [Thermoacoustic hot-head shroud: flame shroud and flue for a vertical 2 in tri-clamp core](https://xemstudio.com/objects/thermoacoustic-hot-shroud/)
- [Thermoacoustic water jacket: 14 mm clamp-on halves for a 2 in tri-clamp tube](https://xemstudio.com/objects/thermoacoustic-water-jacket/)
- [Thermoacoustic bore spacers and liners for 2 in tri-clamp spools: 8.4, 60 and 61.7 mm](https://xemstudio.com/objects/thermoacoustic-bore-spacer/)
- [Thermoacoustic heat exchangers, hot and cold, parallel plate, for 1.5, 2 and 3 in tri-clamp spools](https://xemstudio.com/objects/thermoacoustic-heat-exchanger/)
- [Regenerator cage for 2 in and 1.5 in tri-clamp spools (Ø47.5 and Ø34.8)](https://xemstudio.com/objects/regenerator-cage/)
- [Regenerator matrix disc Ø44 / Ø32 × 0.5 mm (mesh counts #40–#200)](https://xemstudio.com/objects/regenerator-mesh-disc/)
- [Sanitary clamp elbows, 90° and 45°, ½ to 4 in (tri-clamp style, BPE)](https://xemstudio.com/objects/sanitary-clamp-elbows/)
- [Sanitary clamp tees and short-outlet tees (7MP, 7MPS): ½ to 4 in](https://xemstudio.com/objects/sanitary-clamp-tees/)
- [Torch stand for a horizontal tri-clamp hot leg](https://xemstudio.com/objects/tri-clamp-torch-stand/)
- [Thermoacoustic driver cap: ISO 2852 cap with a Ø40 speaker socket, 1.5, 2 and 3 in](https://xemstudio.com/objects/thermoacoustic-driver-cap/)
- [40 mm loudspeaker envelope (the speaker in the thermoacoustic driver cap)](https://xemstudio.com/objects/loudspeaker-envelope-40mm/)
- [Linear alternator mover: Ø35 carrier for 16 Ø10 × 3 magnets](https://xemstudio.com/objects/linear-alternator-mover/)
- [Tri-clamp flexure head: ISO 2852 cap with Ø60, Ø80 and Ø100 flexure seats](https://xemstudio.com/objects/tri-clamp-flexure-head/)
- [Tri-clamp diaphragm membrane: flat, 1.5 and 2 in clamped size](https://xemstudio.com/objects/tri-clamp-diaphragm-membrane/)
- [Build list: Free-piston Stirling, 2 in tri-clamp (flexure-suspended)](https://xemstudio.com/objects/list-free-piston-2in/)