Bending Wave Technology: An Audio Game Changer
By Craig Hubbell, President and CEO, Tectonic Audio Labs
In the case of loudspeakers, bending wave technology disrupts a 100-year-old tradition of loudspeaker technology being dominated by the dynamic loudspeaker drive unit. In 1925, General Electric engineers Chester Rice and Edward Kellogg introduced a ‘new type of hornless loudspeaker’ based on a conical paper diaphragm with attached voice coil energized by a large magnet structure. Nearly all conventional moving coil drive units in market today still bear a strong resemblance to their design. Fast-forward 72 years to 1997, when the UK Ministry of Defense was conducting research on using composite panels to reduce noise in aircraft cockpits. They discovered that instead of making the cockpit quieter, the noise level got louder, and the UK Ministry of Defense realized they had a potential loudspeaker technology that could be commercialized.
A company called NXT was formed to research and commercialize this novel approach to loudspeaker design. In fact, 40 mathematicians, physicists and engineers buckled down to tackle the problem. Thanks to their work, the strong link between the size of a speaker and its bandwidth was finally broken by utilizing a complex arrangement of optimally spaced bending wave modes in a flat, composite panel to produce sound. In 2012, Tectonic Audio Labs acquired the rights to Distributed Mode Loudspeakers (DML) for sound reinforcement and has been producing loudspeakers with bending wave technology ever since.
What makes bending wave technology different is that in traditional speakers, pistonic (rigid body) vibrations of the cone diaphragm produce the sound. However, in Tectonic’s DML loudspeakers, the sound is produced by complex bending wave vibration patterns. Loudspeakers featuring this technology utilize bending waves excited into complex modal patterns to produce sound. This is in contrast to the push-pull pumping action of a pistonic cone speaker. Bending wave modal vibration patterns stimulate the air into motion and the complexity of the pattern ensures wide directivity and a predominantly diffuse radiation character. Distributed Mode Loudspeakers radiate sound from many dozens of bending modes smoothly distributed across the frequency range.
Tectonic also applies its expertise in bending wave technology to loudspeaker drive unit components that improve the audio quality and intelligibility of just about any product that uses a loudspeaker. Typical examples include; soundbars, TVs, conferencing systems, as well as IoT devices ranging from smart automobiles to smart home gadgets including smoke alarms and appliances. To address these markets, Tectonic produces components called Balanced Mode Radiators (BMRs), which are designed to provide wide directivity through the highest frequencies from a single transducer, ensuring clear intelligibility throughout a room or other listening environment.
Described compactly, a BMR is the practical realization of the ideal acoustic radiator; a free, flat disk driven by a perfect force. This ideal radiator has flat on-axis Sound Pressure Level (SPL) and a smooth, extended sound power response (SWL). Unfortunately, there is no such thing as a perfect force so to drive the disk effectively a voice coil must be added which introduces mass. A BMR balances for the effect of the added voice coil mass and recovers the ideal radiator performance.
Here’s how it works. At low frequencies, the diaphragm moves as a rigid piston, but at higher frequencies, where the piston behavior is starting to beam, the bending wave modes are deliberately introduced (modes are standing wave vibration patterns). This carefully controlled modal behavior, superimposed with the underlying piston movement, ensures that the drive unit does not ‘beam,’ maintaining wide directivity up to the highest frequencies.
BMR benefits include clear intelligibility throughout the room, elimination of the cross-over in the highly sensitive vocal region, system simplification (e.g. consolidation of bass, midrange and tweeter into a single BMR drive unit) and better human-to-machine interaction in the case of IoT devices. Key features include wide dispersion of sound, off-axis speech intelligibility and design simplicity.
In terms of directivity, by utilizing carefully optimized bending wave modal behavior in the drive unit diaphragm, a BMR can maintain wide directivity up to the highest frequencies, even in BMR drive units with relatively large radiating diameters where a conventional drive unit would be significantly beaming its higher frequencies into a narrow cone.
Off-axis speech intelligibility is achieved by maintaining the wide directivity from a single drive unit even at high frequencies. A BMR maximizes the intelligibility with the minimum number of sources. Of course, multiple sources can be used (e.g. two or three conventional drive units); however, this can cause complex interference patterns in the sound radiated into the room, phase interactions and timing smear – all of which adversely affect speech intelligibility and musical enjoyment.
And, thanks to the full range of coverage produced from a BMR drive unit, a single drive unit, and thus a single amplifier channel can be used, saving weight and cost, allowing designers the freedom to explore aesthetic flexibility.
Bending wave technology offers a new era of sound quality and has already begun infiltrating speakers near you. For example, airports and train stations, concert halls and smart home IoT devices like smart speakers already feature the innovative technology. Tectonic is disrupting the market by providing audio technology that conveys significant benefits to product companies as well as consumers through its unique performance characteristics that apply to many current audio applications and usage.
(c) EEWeb, 2019.
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