SpHEAR

The *SpHEAR Project

The *SpHEAR (Spherical Harmonics Ear) Project is a collection of 3D models and ssociated code for building, testing and calibrating full surround Ambisonics microphones. All 3D models are written in Openscad with the code licensed under the GPL 3+ license (GNU Public License version 3 or higher), and the 3D models licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license.

The 3D models are almost completely parametric and are designed to be able to be printed on low cost widely available 3D printers (at CCRMA we use an Ultimaker 2 Extended printer, using PLA material). The design is modular and tries to avoid using overhangs and support structures. That is why each microphone assembly is made of a number of independently printed capsule holders interconnected by legs that interlock and hold the structure together. The capsule holders and the mount are glued together to create a 3D structure that securely holds all microphone capsules. A mount that can be clipped into a standard microphone stand is part of the design.

Printing a microphone assembly is only the first step in a long and complicated process. This also includes finding and buying the required microphone capsules, assembling the electronics (requires precision skill with the soldering iron) and finally calibrating the multi-capsule microphone to get the best performance out of it (you will need at least a single driver sound source and a calibrated microphone).

The whole process is not easy and requires knowledge of acoustics and electronics, plus a healthy dose of patience and the ability to perform tasks with precision and care. This repository will eventually include more detailed instructions, electronic schematics, suggested and tested parts and software and procedures for calibrating and measuring the microphone, including models for test and calibration rigs.

At this point the 3D models include the TinySpHEAR, a four capsule first order Ambisonics microphone, the Octathingy, an eight capsule second order design by Eric Benjamin and Aaron Heller and preliminary designs for 12 and 20 capsule designs (the BigSpHEAR_12 and BigSpHEAR_20 models). The models will be expanded as testing proceeds. Contributions are welcome.

TinySpHEAR

The TinySpHEAR microphone is a traditional 4 capsule tetrahedral first order Ambisonics microphone.

The four capsule holders come in two flavors, one for the upper two capsules and another for the bottom two capsules that connect into the microphone mount. The capsule holders have legs with fingers that interlock and hold the structure together. There are two styles of usable interconnections, horizontal legs (easier to print and assemble, a bit bigger) and vertical legs (more difficult to print and assemble but more compact).

Both pictures are renderings of a microphone with 10mm capsules.

There is a third style of legs intended to print the whole microphone structure in one go in a more sophisticated 3D printer, but this has not been tested.

A couple of configuration variables in the source file can be used to switch to a "print" rendering where the individual parts of the structure are laid flat on the printing surface.