loudpy 0.0.8

Python API for Fluid-solid interaction FEM simulations

LoudPy Beta

LoudPy is an open-source Python API dedicated to loudspeaker finite element simulation, released under the GPL-3.0 license.

⚠️ Beta version — The API is still under active development. Proper documentation will be provided soon.

Overview

Designing a loudspeaker with FEM means choosing between complex general-purpose tools that require deep expertise, or expensive commercial software. LoudPy is a free, Python-based alternative built specifically for loudspeaker/transducer engineers and researchers.

Starting from a CAD file of your loudspeaker, LoudPy lets you:

• run harmonic frequency-domain simulations (structural, acoustic, or fully coupled FSI)
• extract eigenfrequencies and mode shapes of the mechanical structure
• simulate nonlinear behaviour
• post-process results directly as NumPy arrays and plot them

The finite element formulations are entirely custom — this project does not depend on any external FEM library. Numerical computations rely exclusively on NumPy, SciPy, and Numba, while meshing is handled by Gmsh.

This project was developed by Romain Degraeve as part of the IMDEA Master's programme in Acoustics (International Master Degree in Acoustics).

Installation

The easiest way to install LoudPy is via pip:

pip install loudpy

For development installation, see the Developer Setup section below.

Examples

The LoudPy_exemples/ folder contains ready-to-run scripts:

Example	Description
Frequency_study/FSI	Coupled structural–acoustic frequency sweep
Frequency_study/Meca	Mechanical-only frequency sweep
Eigen_study	Complex eigenfrequency analysis
Time_study/Single_tone	Nonlinear time-domain simulation, single tone
Time_study/Multitone	Nonlinear time-domain simulation, multi-tone

Publication

LoudPy will be presented at Acousticum 2026 — (ref. 226).

Contributing

If you want to contribute to this open-source project, feel free to reach out:

• Email: [e-mail]
• LinkedIn: Romain Degraeve

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Technical Details

Workflow

LoudPy handles 2D axisymmetric geometries. The full pipeline is:

1. Import — a STEP file is loaded and converted to BREP format by LoudPy
2. Physical entity assignment — the Gmsh standalone app is used to assign named physical groups: closed curve loops define subdomains, individual curves define boundaries. This produces two paired files: a .brep (geometry) and a .geo (named entities)
3. Meshing — LoudPy loads both files, links named entities to materials and boundary conditions, and generates the mesh via the Gmsh Python API (bundled — no separate install needed)
4. Solve — the chosen study assembles and solves the FEM system
5. Export — results are saved to HDF5 (.h5) files; fields and coordinates are stored as NumPy arrays and reloaded with the built-in reader classes

Solvers

Study	Class	Description
Frequency-domain FSI	FreqStudy	Coupled structural–acoustic harmonic solver
Frequency-domain meca	FreqStudy	Mechanical-only harmonic solver
Complex eigenvalue	EigenStudy	Complex eigenfrequency analysis (mechanical domain)
Nonlinear time-domain	TimeStudy	Geometrically nonlinear transient solver

Physics

• Structural domain — 2D axisymmetric linear elasticity, T6 elements
• Acoustic domain — pressure-based formulation, T6 elements
• Fluid-structure coupling — InterfaceAcouMeca coupling assembled automatically
• Damping — Rayleigh (α, β) and hysteretic (η), both supporting non-proportional formulations
• Radiation — Perfectly Matched Layer (PML) for free-field acoustic radiation

Material Library

Built-in materials (materials.json): Polypropylene, Paper, Copper, Rubber, Kapton, PhenolicCloth, Air, SolidGlue. Custom materials can be added to the JSON file or defined directly in the study script.

Post-processing

• FreqReader / EigenReader / TimeReader — context-managed HDF5 readers
• extract_subdomain(snap, name, field) — field values restricted to a named subdomain
• extract_interface(snap, name, field) — field values along a coupling interface
• Built-in plotting: SPL sweeps, field maps, deformed interface, mechanical sweeps

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Developer Setup

LoudPy uses PDM for package management.

Install PDM via pipx (recommended — keeps PDM isolated):

pipx install pdm

Or via uv:

uv pip install pdm

Verify:

pdm --version

Install LoudPy in editable mode:

pdm install -e .

LoudPy is developed under Python 3.13. To install it with uv:

uv python install 3.13