The idea of an inexpensive, compact yet expandable platform for polar measurement of electroacoustic devices has been in our minds for a long time. The aim of this project is not to replace commercial available products such as the industry standard Outline ET250-3D turntable which we do recommend for the polar measurement of loudspeaker boxes. Nevertheless we always found a market niche void in the polar measurement applications of small and light electro-acoustical devices.
Development of such turntable device in the past required significant investment. Specific mechanical and motor control design skills were needed, leading to both costly and time consuming process. Recent developments in mechatronics and 3D printing allows to design and build a cost effective solution.
Our aim is to create a device which can be easily built with off-the-shelf parts, and at the same time can be tailored to specific customer’s needs using minimal modifications. This can be achieved using a ball bearing swivel plate with a belt driven mechanism. The belt is connected to a pulley on a NEMA 17 stepper motor controlled by an Arduino microcontroller running Grbl firmware.
In our example we used a small yet inexpensive swivel plate which can be easily found in online shops. We designed a GT2 belt gear and a simple but robust frame using OpenBeam 15 x 15 mm profiles and 3D printed parts. As electronics we use an Arduino Uno and a CNC motor control shield with an A4988 Stepper Motor Driver.
The result went beyond our expectation, with a compact yet sturdy frame which is open to customizations. If needed the turntable top plate can be adapted to fit the device under test dimensions and/or shape. In fact the whole device can be customized using different mechanical parts, with the only constraint that the software control is carried out using Grbl compatible G-Code.
A simple customization to adapt a microphone stand
Two OpenBeam rails can be mounted on top of the plate, and using a 3D printed adapter a microphone boom can be fit. The adapter can easily slide on the rails allowing different microphone size to rotate the microphone exactly around its capsule.