Performance

A speaker with a membrane!

Distributed Mode Loudspeakers (DML) are designed to deliberately encourage "modes" of vibration in the panel (diaphragm). As we have seen, conventional cone speakers are designed to suppress the natural resonances of the cabinet. Consequently, the acoustical properties of a DML are substantially different from a traditional loudspeaker.

A DML distributes the sound more evenly throughout the listening area, irrespective of frequency. The power that produces sound from the mechanical resistance of the panel is constant with frequency. As a result, the dimensions of the diaphragm do not affect the directivity. This means that the size of the panel can be increased without confining high frequency output to a narrow beam in the forward axis, as is the case with front firing conventional speakers.

Separating output directivity from the panel dimensions overcomes the traditional compromises loudspeaker designers have faced for more than 70 years. Smooth, dense modal behavior produces a predictable, scaleable behavior that, until now, has been the loudspeaker designer's unfulfilled dream.

The NlightN Flat Panel Speaker has a wide bandwidth or frequency range. Even so, it has its limitations. While it can efficiently produce 8 octaves of the sound that humans can hear, the panel is not able to efficiently reproduce frequencies below 100 Hertz. A conventional subwoofer can be combined with two NlightN speakers to produce a full spectrum, stereo sound system.

The conventional subwoofer and flat panel speaker together produce a diffuse sound field over the entire frequency range. The lower frequencies reproduced by the Subwoofer are transmitted through the resonances of cabinet and interaction with physical structures in the listening area. Conventional subwoofers radiate sound in much the same way that the NlightN does for the higher sound spectrum. The sounds from the two types of speakers combine synergistically to produce a nondirectional, immersive listening environment.

NXT press release.doc (product specs)

Loudness

One of the main differences between flat panel and conventional cone-type speakers is the psychoacoustic phenomenon of "loudness." Sound waves are mechanical variations in air pressure. The vibrating surfaces of the flat panel speaker produce wave motions of varying air pressure that resonate from both sides. This wave propagation of sound is less forceful than the cone speakers that produce sound through particle propagation. In conventional speakers, air molecules are "propelled" in a beam out of the cabinet into the listening area by the piston-like movement of the diaphragm (cone). By contrast, sound from the NlightN can be loud without hurting the ear drums, because the air molecules that are "excited" by the panel are simply traveling at a lower velocity.

Paradoxically, flat panel speakers have the ability to maintain the sound pressure level, or volume, over distance better than conventional cone speakers, even though much less power is required to reproduce the sound being transmitted. This demonstrates the physical principle of resonance: air molecules are more responsive to the natural vibrations produced on the surface of a resonating membrane (panel), than to a stream of air molecules that are propelled into the listening area by a stronger mechanical force.

A listener situated several meters from a flat panel speaker can still hear the sound without the person next to it being deafened. The better maintained, more uniform loudness has the benefit of reducing the usual disparity in sound intensity in the listening area between those who are close to the speakers and others further away. As well as making things more comfortable for the audience, this also reduces the risk of ear damage that can result from prolonged exposure to high-intensity sound.

The sound radiation pattern of the flat panel speaker at various frequencies shows a more even and larger sound emission when compared to conventional speakers. This is because the diaphragm of a DML vibrates in a complex pattern over it's entire surface. The loudness is smooth and not as variable over distance from the emitting source. This is close to the directivity of a true point source, meaning that NlightN Flat Panel Speakers has a nearly omnidirectional dispersion pattern.

Links

History of Loudspeakers

How Conventional Speakers Work

Dynamic Loudspeaker Principles

Loudspeaker Design Tradeoffs

The Flat Speaker Solution

Technical Articles

Loudness

Loudness: A Study of the Subjective Difference between DML and Conventional Loudspeakers (Pre-Print #4872)

Sheila Flanagan, Neil Harris (New Transducers Ltd, Huntingdon, UK)

Abstract

In the auditioning of Distributed Mode Loudspeakers (DML), listeners have remarked on the position independence of sound quality. This study compares the subjective loudness properties of DML and conventional loudspeakers. Auditory modelling of objective measurements and the results of psychometric experiments to determine the perceived loudness, are presented in this paper. Investigations into the psychoacoustic mechanisms to explain the phenomena are discussed.

Presented at the 106th Convention, Audio Engineering Society, 1999 May 8-11, Munich

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

Investigation Into the Relationship Between Subjective Loudness and Auditory Distance Perception (Pre-Print #5049)

Sheila Flanagan and Valerie Taylor

Abstract

This paper investigates the link between loudness and distance perception for a range of acoustic sources. Investigation into subjective loudness has shown a significant correlation between perceived loudness and loudspeaker type. Distance perception for a range of loudspeaker types are presented. Results show that the perception of distance rather than sound pressure level, strongly influences the subjective loudness judgment, and that distance cues vary with class of acoustic radiator.

Presented at the 107th Convention, Audio Engineering Society, 1999 September 24-27, 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

The NXT Technical Review 01, January 2002

Available for download at: http://www.nxtsound.com/technology/techReview.php