An engine is a rhythm at a pitch. Cylinder count sets the pattern, load sets the pitch and strain, and fuel type sets the texture: petrol is smooth, diesel clatters, electric hums with no rhythm at all. Everything in this collection is a combination of those three, which is why one page covers motorbikes, boats and generators.
Every clip shows the exact prompt that produced it. The render script reads its prompts from the same file as this page. Copy one, change a word and generate your own.
heavy diesel truck engine idling, rhythmic clattering combustion with a low rumble, exterior close, seamless loop
motorcycle engine revved hard twice then dropping back to idle, sharp exhaust bark, exterior close
electric vehicle motor accelerating, smooth rising harmonic whine with no combustion, close exterior
small outboard boat motor running at speed, buzzing two-stroke with water slapping the hull, open water
petrol lawnmower engine running and bogging down as it cuts thick grass, exterior, garden
large V8 muscle car engine idling with a lumpy uneven cam, deep burbling exhaust, exterior close, seamless loop
large engine cranking on a weak battery, slow laboured turns before catching roughly, exterior close
jet turbine spooling up from rest to full power, rising harmonic whine into a roaring blast, tarmac, distant
portable petrol generator running steadily then dipping as load is applied, exterior, seamless loop
two-stroke engine idling unevenly, high buzzing exhaust note with irregular misfires, close mic, outdoor
These models respond to physical description. Name the material, the action and the space.
heavy diesel truck engine idling, rhythmic clattering combustion with a low rumble, exterior close, seamless loop
"Clattering combustion" is the diesel tell: mechanical noise on top of the exhaust note. Naming it separates diesel from petrol.
electric vehicle motor accelerating, smooth rising harmonic whine with no combustion, close exterior
"No combustion" is a negative instruction that works. It removes the rhythmic pulsing the model otherwise adds.
petrol lawnmower engine running and bogging down as it cuts thick grass, exterior, garden
"Bogging down" gives you the drop in pitch and rise in effort of an engine doing work.
large V8 muscle car engine idling with a lumpy uneven cam, deep burbling exhaust, exterior close, seamless loop
An uneven cam is why muscle cars burble. Asking for the cause produces a more characterful idle than describing the effect.
An engine's identity is its firing pattern. A single-cylinder thumper is slow and uneven, a four is a smooth buzz, a V8 is a deep uneven burble, and a turbine has no pattern at all, only tone. You can prompt this directly, and it is more reliable than describing the vehicle: "single-cylinder", "four cylinder", "V8" and "turbine" each give a distinct result from otherwise identical prompts.
A free-revving engine has little drama. Under load, the pitch drops, mechanical noise rises and the engine sounds strained, and a single phrase such as "bogging down", "labouring", "under load" or "straining uphill" produces all three. If a vehicle scene feels flat, the engine is probably running free when it should be working.
An engine bed under a scene has to stay even end to end, or the loop point shows up as a level jump. "Seamless loop" plus "idling steadily" gets you that. A rev inside a loop breaks it, because a rev is a change. Keep loops steady and generate the events (starts, revs, shifts, stops) as separate one-shots to place on top.
The models run on your machine, which changes the cost, the privacy and what you can automate.
Weights are fetched once. After that, generation, the library and the API all work with the network off. Everything lives in one SQLite file and one folder of WAVs under ~/.soundbox, and nothing is uploaded.
Soundbox runs an MCP server in the same process, with tools for generating and listing sounds. Generated files come back as absolute paths, so an agent can copy them into a project.
Every model's terms are shown before you download it, and non-commercial weights need an explicit confirmation. Soundbox is MIT. The licence of the model that made a sound governs what you may do with it.
claude mcp add --transport http soundbox http://127.0.0.1:17494/mcpcurl -X POST http://127.0.0.1:17494/api/generate \
-H 'Content-Type: application/json' \
-d '{"model":"audiocpp-stable-audio-3-sfx","prompt":"8-bit coin pickup blip","duration_s":1}'