In the quest for optimal home audio, enthusiasts have long experimented with various setups, from traditional headphones to modern soundbars. However, understanding how sound waves interact with your living space has remained a complex challenge. Enter PlasmatronX, who devised an ingenious method to visualize and study sound waves using Schlieren imaging and ultrasonic frequencies.
The traditional approach to acoustic modeling involves placing microphones at numerous points in a listening area, a tedious and time-consuming process. PlasmatronX sought a more efficient solution by leveraging Schlieren imaging, a technique that reveals density changes in transparent media, such as air. However, Schlieren imaging typically struggles with audio frequencies, prompting PlasmatronX to scale down the problem—literally.
Scaling Down Sound Waves
To make the visualization feasible, PlasmatronX shifted the sound waves into the ultrasonic frequency range. By scaling the frequencies up by a factor of 4:1, a 10kHz sound becomes a 40kHz ultrasonic wave. This approach allowed for the use of a standard Schlieren setup, which includes an 8-inch telescope mirror and a razor blade to create a knife-edge effect.
The heart of the system is a Computer Acoustic Tomography (CAT) arraymounted on a turntable. This array can be configured with various ultrasonic transducers to mimic different speaker setups, such as a 7.1 surround sound system or a compact soundbar. The turntable allows for 360-degree imaging, capturing the behavior of sound waves from all angles.
The Role of the Raspberry Pi Pico 2W
The entire system is controlled by a Raspberry Pi Pico 2Wwhich generates the ultrasonic signals and communicates via Bluetooth with a Raspberry Pi 4. The Pi 4 handles the camera, stepper motor for the turntable, image processing, and timing of the audio signals. To capture the dynamic ultrasonic waves, a stroboscope is employed, synchronizing with the sound waves for clear visualization.
The ultrasonic signals are amplified through a DIY 8-channel amplifier and fed into both ultrasonic transducers and larger ‘cat-repellent speakers’ sourced from AliExpress. This setup enables the visualization of sound waves as they propagate through the scaled-down environment.
Testing and Observations
With the system in place, PlasmatronX set up scaled-down versions of a 7.1 surround sound system and a miniature soundbar. The visualization revealed striking differences between the directed beams of the soundbar and the more dispersed waves of the surround sound system. However, the subjective experience of listening pleasure remains a personal judgment.
One of the most notable findings was the impact of soft furnishings on sound wave behavior. While PlasmatronX did not specifically match the frequency response of materials like curtains, the visualizations clearly showed how these items deaden sound, particularly affecting the shaped beams of the soundbar. This insight underscores the importance of room acoustics in achieving optimal sound quality.
Despite the valuable insights gained from this project, PlasmatronX ultimately decided to stick with headphones for personal audio needs. However, the detailed visualizations and data collected provide a wealth of information for anyone looking to optimize their home audio setup.
The entire process, from setup to visualization, is documented in a comprehensive video. For those interested in replicating this project, PlasmatronX has made the code available on GitHub, inviting others to explore and build upon this innovative approach to acoustic modeling.
