October 2018

White Paper Coaxial Ribbon LineSource
The next step towards perfect audio reproduction.
Article By Newform Research

  Music reproduction, whether in the home or in large public venues, is plagued by the acoustic effects of the physical space (room) in which it takes place.  Reflections and standing waves distort the accuracy of the sound at the listening position from that initially produced by the loudspeakers. Control and minimization of room effects is one of the critical frontiers of music reproduction. Delivering the soundwave faithfully to the listener's ears in a typical listening environment is the objective of this development. The ideal loudspeaker would deliver consistent, accurate, high quality sound to any point in the listening space. Newform's Coaxial Ribbon LineSource delivers consistent, high quality sound to a larger portion of the listening space than has been possible before.

This approach is inherently free from the flaws of conventional dome based point source loudspeakers and incorporates features which allow an ideal (ideal = the best practically achievable, but almost certainly not perfect) installation to be quickly achieved in many different rooms for many different listeners.

The traditional loudspeaker consists of a larger cone diaphragm bass transducer possibly a cone or dome midrange and a cone or dome high frequency tweeter.  This configuration has a number of significant acoustic drawbacks in its ability to deliver the soundwave, that the separate drivers initially create faithfully, through the acoustic space to the listener's ear. The overlapping hemispherical dispersion patterns of these dome/box loudspeakers using single, small round diaphragms of different sizes for different frequencies staggered on a flat baffle assures cancellation patterns in many directions from the baffle. It also assures that large numbers of room resonances are excited and that reflected sound arrives at the listener's ear from many different sources at different times degrading the integrity of the original wave created at the diaphragms.

A line source loudspeaker is one with multiple identical drivers arranged vertically in a line or one vertical long driver. The resultant long, narrow diaphragm creates a pattern of dispersion radically different from that of a round diaphragm.  Instead of being hemispheric, the dispersion pattern of a line source radiator is resembles a column or cylinder. Round and broad but with limited and well defined height.

A long narrow driver such as a Ribbon or thin electrostatic transducer also produces a pattern of dispersion that effectively extends the "near field" response, i.e. the response of the loudspeaker before it is affected by interaction with the room, further into the listening area.  The distance the near field effect is projected depends on the length of the effective diaphragm and the frequency it is producing.

Line source loudspeakers (classic electrostatic and Ribbon speakers) have much more controlled vertical dispersion and therefore excite fewer detrimental room interactions but as previously implemented have introduced several other deficiencies of their own.  These deficiencies stem from the alignment on the same plane of the drivers in two or more parallel vertical lines. By placing radiating surfaces beside each other, the waves created will arrive at different horizontal points in the room at slightly different times causing many amplitude and phase anomalies (comb filtering) which degrade the perceived accuracy of the music.  

Only in one very narrow area are these anomalies minimized giving rise to the term "head-in-a-vice sweet spot".  Slight movement of the listening head produces distinctly different acoustical performance. This also precludes more than one listener from enjoying ideal response.

The traditional parallel line source configuration gives rise to the same kind of interference in the horizontal plane that is inherent with conventional dome/cone speakers in the vertical plane.

Besides phase differentials, other anomalies include baffle bounce and diffraction.  Baffle bounce occurs when a wave from a driver (typically high frequency) radiates to the side of the driver and "bounces" off of the baffle or the diaphragms of other adjacent drivers.  Diffraction occurs when the sound wave encounters a radical change in the baffle surface along which it is radiating – either a corner of a loudspeaker enclosure or the edge of a panel speaker.

For conventional or parallel line source loudspeakers, phase coherence due to the physical offset of the drivers cannot be corrected over a large listening area by electrical means.  A coaxial line source holds much higher potential for delivering phase and frequency response accuracy in a large area in any listening space.

Newform's Coaxial Line source loudspeakers with a Ribbon (long and narrow film transducer), placed directly in front of the low frequency transducer line array, have the following advantages:

1) Extremely even horizontal dispersion

2) Very limited vertical dispersion

3) Minimized baffle bounce since the high frequency driver is located ahead of the baffle of the midbass drivers and any high frequency sound reaching the midbass baffle will have very low energy

4) Minimized baffle bounce since the high frequency driver is located ahead of the baffle of the midbass drivers and any high frequency sound reaching the midbass baffle will have very low energy

5) Diffraction will be minimized by the small size and contoured shape of the high frequency drivers baffle (front plate). 

Advantages of the Newform Research monopole Ribbon in this application:

1) Use of a tall Ribbon driver eliminates the multitude of vertical nodes and cancellations inherent in a line array of small high frequency drivers for example 1" dome tweeters.

2) Use of the Newform monopole Ribbon is a necessity to avoid excitation and distortion of the high frequency diaphragm by strong low frequency waves created by the midbass drivers directly behind it. A dipole Ribbon (open back) will be "fluttered" by the midbass low frequency output.

3) Offer greater fidelity in a larger area of listening space than any other loudspeaker configuration.

4) With the Ribbon in front, this co-axial configuration is highly scalable – the ceiling is the limit with no acoustic downside.

The Perfect Loudspeaker?
So, having minimized and eliminated some of the major remaining deficiencies of modern loudspeakers, have we achieved perfection? Well, not quite. The experienced loudspeaker enthusiast will point out two issues.

Number one is the placement of the Ribbon ahead of the mid-basses which will cause a depth phase alignment shift.  This is certainly the case but the audibility of this kind of delay is very hard to ascertain.  If a digital crossover is being used, then timing (delay) can be adjusted by approximately 0.5 milliseconds and the drivers are then extremely closely aligned in all three planes which has never been possible before.

The second issue is reflection off the rear of the Ribbon towards the midbass enclosure of frequencies under 1kHz. Even in early prototypes with our standard R-Series Ribbons, (all tests done using 7" ScanSpeak midbasses) we did not hear any degradation we could ascribe to this effect. One would think it would have to exist as the backs of the R-Series are flat and about 3 1/4" wide.  Perhaps since the midbass wavelengths are well over a foot, and the back of the Ribbon is within 0.5" of the cones, the air flows around the Ribbon body very well.

In any case, the coaxial Ribbon configuration was conceived from the start as using a new, narrow, lower acoustic profile Ribbon.  Thus, we developed the 2" wide Oval Ribbon to be used in coaxial applications. The neodymium Oval is narrower and beveled at the rear to maximize flow and radically reduce any trace of reflection.

The Newform Research Coaxial Ribbon Line source technology eliminates several major problems inherent in conventional loudspeakers and is a significant step forward in the reproduction of sound in the home.

Progression
First horizontally aligned LineSource – the usual problems.  Very good sound but horizontal comb filtering and high frequency bounce off the midbass baffle were glaring when compared to existing models.

Try the Ribbons in front – Bingo!  A new world of room control!  Height matters but image is too large for normal seated listening distances.  But good for small medium sized public spaces. Eight 18cm ScanSpeaks  dynamics and glorious bottom end – drove with a 600 Watt prototype Spectron digital amp – hurt hearing but uplifted soul.

A smaller soundstage champ in a two foot height.  15" Ribbon with four  5.25" Peerless subwoofers.  Potent package!

Oval formed cabinets and vastly more attractive presenters.

Coaxial Ribbon LineSource Pyramid – a favorite but incredibly difficult for us to build.  Also too heavy.

Super Module (Skeleton Speaker)  the best loudspeaker Newform has made.  Baffle bounce, floor bounce, diffraction – all minimized.

(Bias Alert!)

Gets out of the way of the music better than just about anything. Better than the venerated R645v3 below – our most popular speaker. Scan Speak Revelator 5" mid-basses in the upgrade unit don't hurt either.

R645v3  dual 18cm ScanSpeak and 45" ceramic magnet Ribbon – the woodstove look! 

Fabulous soundstage with the Ribbon in free air but occasional placement issues with Ribbon and mid-basses looking at completely different reflective environment strata when placed next to a stuffed sofa for example and Ribbon seeing the hard walls above.

Newform Research Inc.
10 Macfarlane Street
Parry Sound, Ontario
P2A 2N2 Canada

Voice: (705) 835-0081
E-mail: ribbons@newformresearch.com 
Website: www.NewformResearch.com