Technology

NlightN Flat Panel Speakers Are Revolutionary!

"Much of the past 40-plus years of loudspeaker development has revolved around identifying, understanding, and then suppressing diaphragm resonances and their resulting coloration and 'smear.' So a new drive unit technology that, rather than attempting to eliminate diaphragm resonance, encourages and exploits it genuinely merits the over-used description 'revolutionary.' In a sentence, that's what (flat panel speaker) technology does. It tears up the loudspeaker rulebook, as we know it."
--An Introduction to NXT Technology

NlightN Flat Panels are a new class of speakers, referred to as the Distributed Mode Loudspeaker." The DML is the most revolutionary advance in speaker technology, since the advent of the moving coil speaker in the 1920s. It produces sound in a totally different way from conventional cone speakers: warm, clear, and balanced with excellent vocal intelligibility. NlightN speakers are able to perform where conventional cone speakers fail, because of the unique properties of the NXT SurfaceSound™ Technology that they utilize.

Ironically, this radical new speaker technology started out as a British Defense Agency project to create a "sound barrier panel" in jet fighter cockpits. These would-be noise isolation panels actually had the opposite effect and resonated sound. This serendipitous discovery has resulted in an evolution of the science of acoustics and produced an invention that will forever change the way we hear sound.

All of this has happened at a time when advances in digital sound production have seemingly reached the limits of conventional loudspeakers. The sound field produced by an NlightN Flat Panel Speaker is more natural with greater ambience and presence than a conventional cone speaker. The NlightN is the perfect complement for plasma display monitors and significantly enhances the performance of surround sound systems. It's just a matter of the physics!

The Physics

Distributed Mode Loudspeakers are able to achieve the ideal audio reproduction characteristics for digital sound through the use of wave propagation technology. Conventional cone speakers are structured to produce a more forceful magnet-driven particle propagation. Just as light can be characterized as both a particle (photon) and a wave (ray), we can also think of sound as a waveform (resonance) and particle (moving air molecules). This analogy is useful in conceptualizing the operational characteristics of a flat panel speaker.

The vibrations on the panel diaphragm can be compared to the concentric ripples produced by a stone dropped into a pond. However, a flat panel speaker resonates in a disordered, chaotic way, by emitting audio waves wherever the various vibrations reinforce each other sufficiently. The native resonances of the panel itself are not strong enough to corrupt the sound produced by the speaker. The sound that radiates from both sides of the panel closely resembles the audio signal received by the exciters.

Flat panel speakers are based on the concept of "Mode Distribution." This term describes the physics under which the technology operates. The basic principle is to achieve an optimal Modal Distribution through the efficient radiation of sound over a wide frequency range. This advanced technology allows us to produce an effective wide bandwidth speaker from a very thin, lightweight panel.

Structurally, the Distributed Mode Loudspeaker is a combination of an extremely stiff panel and a moving coil motor that serves as the "driver" (or transducer). The speaker works by setting up vibrations within the panel that in turns cause oscillation and the production of sound.

The Distributed Mode Loudspeaker moves the air differently than a conventional cone speaker. A rigid, lightweight panel is excited by a simple motor with a moving coil. This actuates the material's natural resonances to deliver a range of frequencies. The sounding board of a piano works in a similar manner.

The exciter is firmly mounted to the panel, and thus causes it to vibrate. These small but rapid vibrations, not unlike the vibrations in a violin body that's been similarly "excited" by the vibration of a string, are what make the sound. It's the bending of the panel that makes the noise, not any gross fore-and-aft motion of the diaphragm.

A New Transducer

Appropriately enough, the original company that perfected the Distributed Mode Loudspeaker technology is named, New Transducers, plc. A "transducer" is an electronic device that converts energy from one form to another. Common examples include microphones, thermometers, pressure sensors, antennae, and, of course, loudspeakers. Different speakers use different types of transducers.

The transducers used in most conventional cone speakers are voice coils. The flat panel speaker is designed to use a moving coil motor, called an "exciter," as its transducer. The exciters are able to actuate the resonating materials in the panel to produce sound which has the quantum mechanical (wavelike) behavior of systems whose classical (ray) equivalents are chaotic. This transducer-diaphragm design gives flat panel speakers the ability to radiate sound waves uniformly in almost all directions, including backwards, over the a very wide rage of the audible frequencies.

The Panel Verses the Piston

Conventional cone speakers are designed to utilize the piston-like movement of a paper diaphragm to create a beam of sound that is projected from a point source. By contrast, a Distributed Mode Loudspeaker uses small motors, called "exciters," to generate "bending waves" across the surface of a thin, stiff panel, which serves as a diaphragm. The exciters actuate the native resonances of the panel to produce a diffuse "sound field" that provides an immersive audio experience for the listener.

As Dr Graham Banks, Research Director at NXT, explains:

A flat panel speaker doesn't "radiate by pushing the air directly. We introduce bending waves into light, stiff structures. This radiates in a completely different way. Instead of pushing all the air at the same time, it pushes it in a pseudo-random fashion. One describes this as 'uncorrelated,' but in fact, it is 'pseudo-uncorrelated.' "
--ZD Net News

Bending waves are actuated by small motors attached to the panel, which serves as a diaphragm for the speaker. Those waves travel on the surface of the panel in like manner to the waves produced after a stone is thrown into water. The rigidity of the flexible panel increases from the center out to the edges like the basilar membrane in the human ear. The short waves (high frequencies) resonate in the inner area of the membrane, and the long waves (low frequencies) move towards the edge of the panel.

For proper function, a bending wave radiator needs a material with specific acoustic properties. The distribution and frequency of the resonances excited in the material is called mode density; it is this mode characteristic that gives the principle its name, the Distributed Mode Loudspeaker.

In most situations, because it disperses sound more evenly throughout the listening area, NlightN Flat Panel Speakers are able to offer much better performance than traditional speakers.

Reduction of the Amplifier Load

The moving mass of a conventional cone loudspeaker gives rise to large reactive component presented to the driving amplifier. This can impose stress on the power amplifier and impede its performance. Inherent in the NXT flat panel speaker technology is the substantially resistive load that it presents to the amplifier. This friendly load has brought major benefits to the NlightN, removing many of the usual design constraints imposed by the common difficulty of the amplifier/loudspeaker interface associated with conventional loudspeakers.

Links

NXT: When a Little Chaos is Good For You

An Introduction to NXT Technology

Quantum Vibroacoustics

NXT Sound website, Technology Index

History of NXT, plc

Glossary of Transducer Terms

Acoustic Animations

Vibrational Modes of a Rectangular Membrane

Sound Fields Radiated by Simple Sources

Sounds: Allow the wave to expand

How We Hear

Technical Articles

Distributed Mode Loudspeaker Technology

The Distributed-Mode Loudspeaker (DML) as a Broad-Band Acoustic Radiator (Pre-Print #4526)

Neil Harris and Malcolm Omar Hawksford

Abstract

The principles of a new class of acoustic radiator (DML) are described and the counter-intuitive result for broad-band frequency independent acoustic radiation established. It is demonstrated that a low-loss panel with optimal modal distribution produces a flat power response. A simple mechanical model is presented to calculate the mean velocity within the panel as a function of frequency and intrinsic properties.

Presented at the 103rd Convention, Audio Engineering Society, 1997 September 26-29, New York.

The study report can be downloaded from the internet ($10) at the AES website. Search by Pre-Print number. http://www.aes.org/publications/preprints/search.html

Distributed Mode Loudspeaker Resonance Structures (Pre-Print #5217)

Dr. James Angus (University of York)

Abstract

The distributed mode loudspeaker's performance is analyzed with reference to its resonance structure. In particular the effect of the wave propagation type, shear or bending, over the frequency range is examined. The paper also examines the effect of diffusing boundaries on the resonance structure.

Presented at the 109th Convention, Audio Engineering Society, 2000 September 22-25, Los Angeles.

The study report can be downloaded from the internet ($10) at the AES website. Search by Pre-Print number. http://www.aes.org/publications/preprints/search.html

The Intrinsic Scalability of the Distributed Mode Loudspeaker (Pre-Print #4742)

Graham Bank

Abstract

A Distributed Mode Loudspeaker (DML) operates by introducing bending waves into a panel, which has specified mechanical properties. Although the dimensions of the panel will affect the bandwidth, the sound radiated from such a panel will be diffuse in nature, and the directional characteristics should be substantially independent of its size. Both the theoretical justifications as well as some practical comparisons are given.

Presented at the 104th Convention, Audio Engineering Society, 1998 May 16-19, Amsterdam, The Netherlands.

The study report can be downloaded from the internet ($10) at the AES website. Search by Pre-Print number. http://www.aes.org/publications/preprints/search.html

Distributed-Mode Loudspeaker Simulation Model (Pre-Print Number #4739)

Jörg W. Panzer and Neil Harris

Abstract

This paper demonstrates the implementation of the Distributed Mode Loudspeaker into an electro-mechano-acoustical network simulator based on the lumped element method. To be able to take into account the mechanical coupling to the frame, the DML is separated in electro-mechanic and in mechanic-acoustical transducer-modules. In this way the necessary flexibility in modeling is maintained as well as a straightforward application for panel and system design.

Presented at the 104th Convention, Audio Engineering Society, 1998 May 16-19, Amsterdam, The Netherlands.

The study report can be downloaded from the internet ($10) at the AES website. Search by Pre-Print number. http://www.aes.org/publications/preprints/search.html

Exciter Design for Distributed-Mode Loudspeakers (Preprint Number 4743)

Martin Roberts

Abstract

The exciter component in a distributed mode loudspeaker (DML) can have a profound effect on the overall performance of the system. This paper introduces the equivalent circuit analysis of the combination of electro-dynamic exciter and distributed mode panel and discusses how exciter parameters can influence DML performance. Measurements are given which show how these influences are manifested.

Presented at the 104th Convention, Audio Engineering Society, 1998 May 16-19, Amsterdam, The Netherlands.

The study report can be downloaded from the internet ($10) at the AES website. Search by Pre-Print number. http://www.aes.org/publications/preprints/search.html