SMALL: Spherical Microphone Array Little Library

Introduction

In this tutorial, we’ll learn how to easily build an Ambisonic microphone using the Spherical Microphone Arrays Little Library (SMALL).

SMALL¹ is an open source project consists of:

1. A set of Computer Aided Designs (CAD) for open or rigid Spherical Microphone Arrays (SMA) mechanical structures, ready to 3D-print.
2. Signal processing algorithms, available through ambitools, to encode the SMA signals to Spherical Harmonics signals.
3. Python tools to use a robotic arm for the SMA acoustic calibration, in a research context.

More infos on this project can be found in the repository or by reading this paper¹.

Although SMALL allows a multitude of SMA configurations, we focus in this tutorial on the realization of a 2^nd order Ambisonic microphone, using MEMS PDM microphones, with an embedded USB sound card.

List of Material

To build and use the microphone you will need:

Software:

• openSCAD,
• PrusaSlicer >= 2.6 or equivalent 3D printer slicer,
• SMALL: retrieve the repository here,
• ambitools >= v1.3.

Hardware:

• A 3D printer with filament,
• A MiniDSP MCHStreamer,
• 10x Adafruit PDM microphone breakout boards,
• 4x 10 mm M3 screws with nuts,
• 1x M6 threaded rod for the mic stand.

Procedure

Compile the STL files

In SMALL repository open the openSCAD file /cad/sma_rigid.scad. You should see something like this:

Printing the spherical shells

Assembling the microphone array

Example of use

More infos