How to Build a Sonic Ramjet

Overview

Engine: A 3D-printed resonance chamber that channels ~40 Hz sound into a compressed jet.
Propulsion Method: Stacking and resonating a 40 Hz tone roughly three times to form a uniform wave jet.
Inspiration: Sonic booms, deep-bass cars that rattle houses, and acoustic friction reduction (like water striders).

A single-engine STL is typically used, though multi-engine setups are possible. See the main site for the STL downloads.

STL Files

You’ll find multiple variants (1.5" vs. 3" speaker designs). Remember to confirm the speaker’s diameter matches the model or scale as needed in your slicer. Printing orientation is vertical (nozzle facing up or down).

Basic Requirements

1. Speaker: Typically 1.5" or 3". Scale up if you want 4"+.
2. Amplifier: ~10 W output (e.g., TPA3116).
3. 40 Hz Signal: Sine wave generator or Bluetooth module streaming test tones.
4. Scaling: Adjust STL if speaker size differs from 1.5" or 3".

Bill of Materials (BOM)

• Audio Amplifier – e.g. TPA3116 D2 XH-M543.
• Bluetooth Receiver – e.g. XY-BT-Mini.
• Speaker (1.5") – SOTAMIA 40 mm (4 Ω / 5 W).
• Speaker (3") – SOTAMIA 3" full-range speaker (2 Ω / 5 W).
• Battery – 8.4 V Li-ion 2S pack recommended.
• Bearings (Optional) – If building a “sound buggy.”

Updates

- 3" Version Added: Easily scales to 4"+. Contains a mount for potential plasma arcs (experimental). Not as optimized as the 1.5" design; single solid piece for trial runs. Larger speaker is more efficient. Up to 12 V can yield surprising thrust.

Assembly Instructions

1. Mounting the Speaker

- 1.5" Version: Tape the speaker to the rear opening with electrical tape.
- 3" Version: Use 4× M3 screws in the mounting holes. A foam gasket can help seal edges.

2. Bluetooth Module Wiring

- Identify L, R, G on the module’s underside.
- Solder these to the amplifier’s left/right audio input and ground.

3. Amplifier & Speaker Connections

1. Connect Bluetooth module L, R, G to amp input.
2. Connect speaker leads to amp’s speaker output (watch polarity).
3. Double-check +/– alignment.

4. Power Considerations

- Amp can handle higher voltages (8.4 V+). Bluetooth often needs 3.7–5 V. Use a buck converter or separate power line. If unsure, use two separate supplies (amp + BT).

5. Volume Control

- Many TPA3116 boards have volume knobs for each channel. Dial in the volume for a strong 40 Hz output without distortion.

6. Operation

1. Power the amp (e.g., 8.4 V).
2. Power the BT module (5 V).
3. Pair a phone or send a 40 Hz sine wave signal.
4. Adjust volume for a resonant tone.

Safety & Sound Levels

Low-frequency waves can be quite loud. Wear hearing protection. If you experiment with high-voltage arcs, use caution and proper safety gear.

Final Thoughts

This sonic ramjet concept showcases how low-frequency acoustic energy can generate measurable thrust using minimal mechanical complexity. Explore, modify, scale, and share your findings with the maker community. Enjoy your tabletop propulsion experiments!