SR/Live Sat, October 11, 2008

Is it really possible to effectively pack 10 pounds of stuff into a 5-pound bag? Further, can all of that “stuff” be painstakingly formed into a cohesive unit capable of meeting critical challenges and professional expectations?

EAW set out to affirmatively answer these questions – and more – with the new NTL720, an extremely compact, self-powered line array loudspeaker system. The result is a culmination of sorts, a package that integrates fresh and genuinely exciting design developments with a lion’s share of the most significant technological advances that have been pioneered over the past three decades. Though so small (9.4 x 24 x 14.3 inches) and light in weight (less than 50 pounds even with onboard tri-amplification) it has been nicknamed the “baby” line array module (BLAM for short), the NTL720 is outfitted with a true three-way design that delivers full-sized performance.

From the outset, EAW committed that its new baby would provide maximized vocal clarity via a correctly executed three-way design with superior mid-range performance – regardless of the miniscule footprint. From there, the development team defined a long, detailed list of other absolute “musts” to be accomplished for the NTL720 to be worthy of exceeding requirements in virtually every medium-format live and installed sound application. Every item on that list has a big check mark next to it, and as noted, all of these individual technologies are united as a seamless system easily optimized under a user-friendly software interface.

A LOOK INSIDE
Let’s start with a look at the horn and driver components and technologies of the NTL720 before moving along to other crucial aspects. When the (stainless steel) grille is removed from the front of the cabinet, the first thing that stands out is that the entire front face of the enclosure is filled by a full-sized mid/high horn providing 110-degree (horizontal) by 12-degree (vertical) dispersion.

The extreme size of this horn – an approach first applied to our lauded KF730 and 760 line arrays and KF750 concert systems – has proven to insure broadband pattern control, particularly in the entire MF/HF pass-band. High frequencies are produced by six 1-inch dome tweeters, configured in two vertical columns (each with three tweeters) mounted on a manifold that feeds a single slot in the center of the horn. This is highly effective in controlling vertical dispersion, and with equivalent output of a 1-inch-exit, 44-millimeter voice coil compression driver. The HF section serves the 1.5 kHz to 21 kHz frequency range.

Flanking the HF section, dual 6- inch cone woofers handle the MF range, also loading on to the large horn. A primary design goal was to minimize the space between the MF and HF components in order to enhance coherency and improve overall off-axis response. Further, a symmetric layout of the MF drivers (placed on both sides of HF) would promote a symmetric horizontal offaxis response.

Openings needed to be incorporated in the horn for these MF drivers. The easiest approach would have been to provide openings the same size as the MF cones, but this creates a large void in the HF horn wall, causing HF energy to “escape” into this void, reflect off of the MF cone, and arrive later in time than the direct energy.

A slot in the horn was another possible approach, reducing the void in the horn and somewhat minimizing interference to the HF while also decreasing the distance between the acoustic centers of the MF drivers. Yet a large percentage of the horn wall is missing since the void in the horn wall is still relatively large as compared to the overall size of the horn.

The solution deployed on the NTL720 stems from a great deal of research during the development of the acclaimed AX Series of largeformat installation loudspeakers. Called Concentric Summation Array (CSA) technology, it calls for several smaller openings in the horn, with a close look at the horn surface revealing these openings to be “randomized” cutouts in diamond-shaped patterns. The cutouts decrease the acoustic center of the mids while also decreasing the percentage of open area at any point along the horn. The result is greatly minimized interference to the HF.

Another EAW focus over the past several years has been beam forming and array shading; in other words, the creation of precise beam shapes combined with the ability to steer them as desired for more tightly focused coverage, particularly at longer distances. As a result, all transducers in the NTL720 are highly efficient and capable of very high output – and packed into the smallest space possible – while the large-mouth horn enhances pattern control. Called Phased Point Source Technology (PPST), it was first developed for the EAW KF900 Series of extreme long-throw loudspeakers. Briefly, PPST works in tandem with digital processing to create a unified source sound impulse at all points within the coverage area. Building upon our previous use of phase and frequency “shading” techniques to manipulate beam profiles and to blend vertically dissimilar subsystems, the outcome is further integration of loudspeaker modules within an array into a single acoustical element. In tandem with PPST principles, EAW’s Divergence Shading technology, utilized in the KF760 large-format line array, has been applied to further achievement of even sound pressure levels over distance. With Divergence Shading, the pressure remains constant throughout the source while the curvature of the wavefront is varied. A flatter wavefront produces higher pressure at distance while a tightly curved wavefront produces lower pressure at distance. Because the input is constant across the source, the rate-ofchange of pressure magnitude is small, resulting in smooth frequency response.