This project provides a parametric 3D CAD model (using CadQuery) for a "clip-on" practice mute for Bb trumpet. Unlike traditional mutes that fully plug the bell and often stifle the "blow feel," this design uses a metamaterial-inspired side-branch shunt approach to reduce radiated sound while maintaining a more natural airflow.
The mute is designed as a clip-on rim cap that sits over the trumpet bell rim with minimal insertion. It achieves noise reduction through several mechanisms:
- Central Vent Bore: A straight-through hole on the center axis preserves the primary airflow path, keeping the blow resistance closer to playing without a mute.
- Junction Manifold: A internal cavity (manifold) under the top face acts as a compliance volume where sound energy is diverted.
- Labyrinth Side Channels: Multiple detuned helical ducts (labyrinth paths) act as lossy transmission lines. They introduce thermo-viscous losses in narrow tubes and present frequency-dependent shunt impedance at the junction.
- Radial Vents: These side channels vent to the outside air through the side wall of the cap.
This combination of a central bore and resonant side-branches is based on the concept of consecutive Fano resonances for broadband ventilated sound insulation.
- Clip-on Attachment: 3 flexible clip fingers with inward hooks designed to retain the cap on the bell's outer rim.
- Gasket Groove: A ring pocket on the underside for a soft seal (e.g., foam or TPU cord) against the bell rim.
- Solid Body Construction: The body is mostly solid to avoid uncontrolled large cavity resonances and improve structural integrity/printability.
- Self-Supporting Cavities: Internal manifold transitions use lofted cones (approx. 54°) to enable support-free FDM printing.
The script includes a lightweight acoustic proxy function that:
- Models side channels as lossy transmission lines (simplified thermo-viscous propagation).
- Approximates radiation impedance at the vents.
- Estimates a mean shunt-admittance score over 100–2200 Hz to guide relative tuning.
Ensure you have Python 3.9+ installed. You will need cadquery, numpy, and casadi (optional, but recommended for some CQ builds).
pip install cadquery==2.4.0 cadquery-ocp numpyRun the script to generate the 3D models:
python clip_on.pyclipon_metamaterial_cap_v6.step: High-fidelity STEP file for CAM/CAD.clipon_metamaterial_cap_v6.stl: STL file for 3D printing.- Terminal output showing the Acoustic proxy mean score and Central bore ratio.
The design can be customized by editing the CapParams dataclass in clip_on.py:
| Parameter | Default | Description |
|---|---|---|
instrument_bore_mm |
11.73 | Inner bore of the trumpet (for scaling). |
bell_inner_diameter_mm |
123.0 | Inner diameter of the trumpet bell. |
central_bore_ratio |
0.88 | Ratio of central bore to instrument bore (controls resistance). |
channel_count |
2 | Number of helical labyrinth channels. |
channel_inner_diameter_mm |
5.5 | Diameter of the internal tubes. |
channel_lengths_mm |
[580, 730] | Lengths of the helical paths (for tuning resonances). |
clip_count |
3 | Number of attachment clips. |
- Material: PLA, PETG, or ABS.
- Supports: Ideally none required for internal geometry. The radial vents and clips are optimized for minimal support or bridging.
- Wall Thickness: Ensure at least 3-4 perimeters for a "solid" acoustic response.
- Post-processing: Install a soft gasket (3mm foam cord or TPU) into the underside groove for an airtight seal against the bell.
This work is based on verified acoustic research including:
- Xu, Z. et al. (2024). "Broadband ventilated sound insulation based on acoustic consecutive multiple Fano resonances," Physical Review Applied.
- Du, S. et al. (2024). "Model analysis and experiment study for effects of thermal viscous and fluid flow on ventilated acoustic metamaterials labyrinth," Scientific Reports.
Full references are listed in references.md.