Our aim would be to use a fan as a speaker, generating sound in open loop to follow a target audio signal.. We would like the average airflow to be manually tunable, like a normal fan, while pressure waves in the frequency range between 20Hz and 20kHz are controlled in open loop to follow a target audio signal. This is certainly possible for sound at low frequencies, but we would like to take advantage of the fast switching frequency and the power of the TAPAS board to push the volume and the frequency range and demonstrate a usable speaker.
The setup would be fairly simple: a 300W permanent-magnet synchronous motor (to maximise sound volume), an impeller, a secure mount for the assembly, a TAPAS board, a generator of audio signals (e.g. a PC with a headphone port) and a potentiometer to set the average speed of the fan.
The TAPAS board should run a control loop at 500kHz, sampling the audio signal and motor current, and controlling the latter to follow the profile of the audio signal, minus an offset. The offset is calculated in a slower control loop (~5Hz), with lower priority, where the potentiometer voltage is sampled and the slow target for the acceleration of the fan, which is proportional to the average motor current, is set.
Our team is composed by myself and Katherine Puttick. While only one board is required, we could really use two boards to work in parallel.
This idea submission is among the finalists and will be presented at the CKI Conference in Erlangen.