Stereo Imaging

Stereo Imaging refers to the ability of a set of speakers to accurately reproduce sound so that, with eyes closed, you can distinctly recognize and localize the sounds of the various instruments and voices in any recording. The positions of the voices and instruments should be easily identifiable and shouldn't seem to change with frequency variation. The speakers themselves should seem to disappear, replaced instead by a spatial arrangement of music sources, or soundstage.

With the superior sound field dispersion of an NlightN Flat Panel Speakers, the stereo imaging and balance remain in tack throughout the listening area. Due to the total absence of transient noise, the panel speaker cannot be heard or localized, as is the case with all conventional cone speakers. Whether listening to music for pleasure or working in a professional recording studio, you can listen for hours on end without experiencing the dreaded "listening fatigue."

Diffuse Acoustic Radiator versus Direct Radiating

NlightN Flat Panel Speakers provide superior stereo imaging. They maintain a wide radiation pattern with a diffuse output that reduces destructive room interactions. The flat panels sound pretty much the same everywhere in the room, creating an impressive presence and ambience. Stereo imaging is at least as well-defined and stable, as with conventional directional loudspeakers listened to from the stereo "sweet spot."

Outside this small area of optimum stereo, the NlightN panel is much superior to a conventional cone speaker, because of its better maintained off-axis performance and the reduced interaction with objects in the room. Compared to conventional speakers, the panel speakers radiate sound at a wider angle and more homogeneously, thus enlarging the optimum listening area distinctly.

The flat power output of the flat panel speaker and the fact that it doesn't behave like a point source means that the technology actually changes one of the fundamental laws that govern the way in which speakers work. For any point source, the relationship between distance and volume can be represented as an inverse square. As one moves away from the speaker, the volume of the sound will decrease by a square of the distance from the source. This is not the case with Flat Panel Speakers and that is why the superior stereo imaging of the NlightN is preserved in a much wider area.

Conventional speakers produce a blurred stereo image, rather than the precise, tightly defined soundstage. With conventional speakers, standing wave resonances within the listening area are more pronounced. Interaction with room boundaries is worsened. And the tonal balance varies significantly as you change listening position. These factors make speaker placement a much more critical determinant of stereo imaging capability.

The NlightN Flat Panel Speakers behave quite differently, because of the diffuse nature of their radiation. The sound does not emanate from a fixed, well-defined point in space. As a result the distribution of sound within a room is actually much more even with an flat panel speaker than with a conventional cone speaker.

Polar Response Patterns

Sound radiates from a speaker meaning that it moves out from a starting point into a given space. Direct radiating speakers project sound in a single direction, and are referred to as "unipolar." Conventional speakers are unipolar.

The NlightN is a "dipolar speaker" that radiates sound from the front and rear of the panel, out of phase. Dipole speakers provide a very open, enveloping soundstage without allowing you to pinpoint the location of the speakers themselves.

With sound waves coming from both the front and rear of a speaker, the sound waves are not all directed at the listening position. Some of the waves are reflected off walls and other room boundaries before reaching the listener. The resulting sound is spacious creating a wide soundstage and a larger sweet spot than direct radiating designs. The sound is more diffuse or spread out through the listening area.

Dipolar speakers generate sound to the front and rear with very little information emanating to the sides of the speaker. The sound waves reflect off walls, ceilings, and objects in the room before reaching the listener. The resulting sound field is broad and enveloping, and the speakers themselves are very difficult to localize or find by ear.

Surround Sound Applications

The revolutionary NlightN Flat Panel Speakers are perfect for multi-media use and enhance the surround sound experience by producing a larger stereo "sweet spot." The speakers have mounting holes and can be hung on the wall, like a picture frame, as the perfect audio complement for a plasma display television.

Flat Panel Speakers are perfect for home theatre, since the inherently diffuse nature of their sound radiation assures the required surround-channel diffusion. Listeners are not conscious of the surround speakers as distinct entities. Because of their wide directivity, NlightN speakers can be placed around a room in a much more flexible way. This is particularly valuable given the growing acceptance of DVD technology with its associated 5.1 audio systems.

Since the NlightN speakers have a flatter power output across the entire frequency spectrum and produce a more uniform radiation pattern (where the off-axis sound is more similar to that of the on-axis sound), a careful alignment of speakers is no longer necessary.

In a conventional surround-sound speaker system, there is a specific focal stereo "sweet spot" that is created by the placement of the front, rear, center and bass channels. Anyone who sits out of the stereo "sweet spot" will not receive the true surround sound image. The sound will be dominated by a left, right, or the speaker nearest to the individual.

Flat panel speakers create a diffuse sound field, which eliminates the effects of a dominant sounding speaker. It is more difficult to perceive sounds from a specific direction or location. The result is a much-improved home theater presentation with fewer stereo "sweet spot."

When a flat panel speaker is used with a plasma display monitor or video projector, the words of the characters on screen will be perceived as originating directly from their mouths, rather than from an individual speaker, as is currently the case with conventional speakers. This subtle perceptual feature of the NlightN is very significant, since the human brain is more likely to understand and remember what it processes when the audio and visual elements are unified and congruent with each other.

Links

Sound Radiation and Speaker Formats

Measuring the Directivity Patterns of a Loudspeaker with and without a Baffle

Technical Articles

Measurement Aspects of Distributed Mode Loudspeakers (Pre-Print #4970)

Vladimir P Gontcharov, Nicholas P R Hill, Valerie J Taylor (New Transducers Ltd, Huntingdon, UK).

Abstract

The complex radiation pattern generated by distributed mode loudspeakers makes a single-point measurement an inadequate representation of the sound field. In this paper we discuss simple multiple-point measurements as appropriate characterisation tools. These techniques are used to determine the total power, together with its directivity, and are equally applicable to both distributed mode and conventional cone loudspeakers.

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

Distributed Mode Loudspeaker Polar Patterns (Pre-Print #5065)

Dr. James Angus (University of York)

Abstract

The Distributed Mode Loudspeaker's polar response is analysed with reference to it's radiation mechanism. In particular the polar response below and above the supersonic plate propagation boundary is examined. The paper shows that a quasi omnidirectional response is possible.

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

Diffusivity Properties of Distributed Mode Loudspeakers (Pre-Print #5095)

Vladimir Gontcharov and Nick Hill (New Transducers Ltd, Huntingdon, UK)

Abstract

A method involving the evaluation of the Cross-Correlation Function has been developed to describe the diffusivity of direct sound radiation. The dependence of the spatial correlation of the radiation field on sound source properties and frequency has been investigated. This work has highlighted the diffuse nature of the sound field of a Distributed Mode Loudspeaker and the correlated output of a conventional cone loudspeaker.

Presented at the 108th Convention, Audio Engineering Society, 2000 February 19-22, Paris.

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 Radiation Mechanisms (Pre-Print #5164)

Dr. James Angus (University of York)

Abstract

The Distributed Mode Loudspeaker's performance is analysed with reference to it's radiation mechanism. In particular the effect of the wave propagation type, shear or bending, over the frequency range is examined. The paper shows that a flat frequency response is achieved by Distributed Mode Loudspeakers.

Presented at the 108th Convention, Audio Engineering Society, 2000 February 19-22, Paris.

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

Stereophonic Localization in the Presence of Boundary Reflections, Comparing Specular and Diffuse Acoustic Radiators (Pre-Print #4684)

Neil Harris and Sheila Flanagan (New Transducers Ltd, Huntingdon, UK) and Malcolm O J Hawksford (University of Essex, UK)

Abstract

Experiments on sound localization using specular radiators are often performed under near anechoic conditions which do not correspond closely to normal listening environments. A hypothesis is proposed that localization precision as a function of room acoustics is minimized by the use of diffuse acoustic radiators such as DML panels. This proposition is investigated and the results from a series of psychometric tests presented to establish the conditions under which this approach is valid.

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

Stereophonic Localization in Rooms, Comparing Conventional and Distributed-Mode Loudspeakers (Pre-Print #4794)

Neil Harris and Sheila Flanagan (New Transducers Ltd, Huntingdon, UK) and Malcolm O J Hawksford (University of Essex, UK)

Abstract

Results of a series of subjective listening tests support the hypothesis that diffuse acoustic radiators, such as distributed-mode loudspeakers (DML), lessen the degradation caused by room acoustics on stereophonic localization. In early tests, a pair of DMLs performed at least as well as quality two-way cone-in-box loudspeakers. Further experiments to confirm the hypothesis are reported.

Presented at the 105th Convention, Audio Engineering Society, 1998 September 26-29, San Francisco.

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

Diffuse Field Planar Loudspeakers in Multimedia and Home Theatre (Pre-Print #4545)

Martin Colloms, (Consultant, London, UK) and Christien Ellis (New Transducers Ltd, Huntingdon, UK)

Abstract

By combining diffuse radiation with a constant power output versus frequency, new opportunities are presented by this powerful mix of acoustic properties which is exhibited by a new class of sound reproducer. This has important implications for sound field uniformity. The behaviour is modelled and compared with the test results from a trial video system using a planar multi-channel sound system.

Presented at the 103rd Conference, 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

The NXT Technical Review 01, January 2002

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