The revolutionary approach to sound.

David Schwartz and his Laser-Accurate microphone prototype, which trades mechanical moving parts for the measurement by a laser of the movement of particulates suspended in air.

There have been several key milestones in the evolution of the microphone, from the development of the basic transducer in the 19th century, to the introduction of the condenser microphone in the 1920s, followed by FET microphones in the 1960s and the more recent multichannel microphones used for surround audio applications.

Laser-Accurate technology from Schwartz Engineering & Design may be the next milestone in microphone technology: instead of the conventional diaphragm whose resonance creates electrical impulses against a coil or a back plate, Laser-Accurate technology uses a laminar stream of air in a chamber in which microscopic smoke particles are suspended. When excited by changes in air pressure, the movement of these particles is detected by a laser beam that continuously passes through the chamber aimed at a photoelectric cell opposite the laser source. According to company president David Schwartz, it has the potential to be the “perfect microphone,” capturing sound unadulterated by the mechanical motion of the diaphragm and the inevitable time lags caused by that movement.

Conventional microphone design has numerous inherent idiosyncrasies: the speed with which a traditional diaphragm can react is innately limited by its physical size and shape, and the variety of those mechanical elements inevitably adds tonal coloration — distortion — to the sound it’s recording. In the Laser-Accurate mic, the diaphragm or plate is replaced with microscopic particles dispersed in a gas-filled chamber in which the laminar flow of the gas is constant. Detection of the displacement of the airstream and particles by a laser and optical receiver creates a completely non-intrusive method by which to measure the movement of air. There is no significant mass that stands between the source of the sound and the transduction of it to an electrical signal.

A clear, vertical plastic tube has a small smoke generator at the bottom and a fan at the top. The fan pulls the smoke in an even stream past a laser beam, which is pointed at a sensor. When you speak into the small slot in the tube, it disturbs the smoke stream, affecting how the sensor picks up the beam.

The latest prototype of the Laser-Accurate microphone was demonstrated at the recent Audio Engineering Society convention in New York. Although signal level and sound quality were significantly below what you’d expect from a professional-quality studio microphone, it was clear that the technology succeeds in concept. Schwartz says that, in his design, the limits of signal-to-noise and frequency response are the limitations of the optical system, as opposed to an existing mechanical system (as with conventional mics) that has reached its full potential. The current prototype system uses a 650 nm, 5 mW laser and a PDA100A silicon detector from Thorlabs. Smoke is currently generated using fluid that’s used in model trains, although Schwartz is experimenting with a water nebulizer. Vapor density and the optical properties of the particles themselves play a role on the way the optical receiver picks up the sound.

Schwartz Engineering and Designs plans to offer the patented technology to manufacturers on a licensed basis.