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Thursday, April 29, 2010

Designer Notebook: Inside The Development Of The New EAW KF740 Line Array

This Designer Notebook was submitted by EAW. Live Sound/ProSoundWeb makes every effort to eliminate any use of marketing-inspired hyperbole.

From the outset of the development process, the new KF740 line array module has been conceived as a medium-sized, flexible package capable of meeting the widest possible range of touring and installation applications, while providing exceptional sound quality as well as efficiency.

Further, it needed to provide full-range performance as a stand-alone line array system as well as be easily integrated into existing KF Series line array structures.

Other primary factors on our list included light weight, fast flyability and convenient cartage - all especially important for portable applications.

We started the design process at a logical point by incorporating the most valuable characteristics of other KF Series modules, led by consistent broadband pattern control, which we view as one of the more critical attributes to the performance of a professional loudspeaker system.

Lack of pattern control inhibits the creation of functional arrays and limits the ability of a loudspeaker to properly cover a given audience area.

However, maintaining it across the frequency range is not an easy task. Proper pattern control requires that the source size is proportional to the wavelength produced by those sources.

In essence, larger wavelengths require larger sources. Horns provide the means to effectively increase the size of a source.

Pattern Control
In 2001, EAW introduced the first completely horn-loaded 3-way line array module, the KF760, with the goal of providing the highest possible degree of pattern control throughout its frequency spectrum.

In fact, the KF760’s front surface is entirely occupied by horns, and this same approach was engineered into a much smaller package, the KF730, which offers 110-degree horizontal dispersion (and 12 degrees vertical).

With the new KF740, a large MF/HF horn also occupies the entire front area of the enclosure to provide control at the lowest range of the mid frequency devices.

Horizontal dispersion is 90 degrees by 12 degrees vertical. HF (1,220 Hz to 20 kHz) is supplied by dual 1.4-inch-exit compression drivers, flanked by dual 8-inch cone drivers delivering MF (255 Hz to 1,373 Hz).

Top: Woofers in the KF740 are arranged in dual phase-aligned pairs, mounted to the sides of the enclosure. Bottom: The horn has an assortment of diamond-shaped openings that minimize the interference presented to the HF.

The desire for extremely tight pattern control was also a focus of the LF design, where response is extended down to 50 Hz.

The KF740 LF section utilizes four 10-inch woofers, in dual phase-aligned pairs, mounted to the sides of the enclosure. Spacing a pair of transducers is much more effective than using a single transducer when pattern control is required at low frequencies.

For example, within its bandwidth in a KF740, an ideal single 10-inch woofer’s response is completely omnidirectional. However, adding a second woofer and spacing it appropriately allows the two woofers to create off-axis cancellation.

This cancellation occurs at the wavelengths that are roughly twice the spacing of the woofers and below the point at which the individual woofers begin to exhibit directivity.

By placing the woofers on the sides as well as the front, the KF740 utilizes the entire width of the enclosure to space the woofers as far apart as possible. This allows the KF740 to maintain pattern control at a lower frequency than that which would otherwise be achieved by only using front-firing woofers in the same size enclosure.

And, the enclosure is sealed so the 10-inch transducers enhance the accurate reproduction that is extremely responsive to any necessary equalization.

Transient Response
Another key factor in loudspeaker design is transient response, and this is optimized with a proprietary technology called Concentric Summation Array (CSA) technology.

Essentially, CSA is an assortment of diamond-shaped openings for the mid frequency device that randomize and minimize the interference presented to the high frequency device.

Although not concentric, or coaxial, the KF740 uses the same technology to minimize the interference in the high frequency range.

Rather than one large aperture for the mid frequency, the opening is broken into several smaller diamond-shaped openings providing a consistent and minimal percentage of open area.

This reduces the amount of HF energy (emanating from the high frequency transducers) that can enter the void formed by the mid frequency devices and hence reflect back out at a later time.

HF response is significantly improved as the amount of reflected energy is reduced.

In addition, the apertures that fall in front of the central part of the MF cone are also located farthest back in the horn bell and therefore are closest together horizontally.

Because the upper frequency range of the MF generates from the central part of the cone, the configuration prevents unwanted beaming at the upper range of the mid-frequencies.

Then there is the aspect of horizontal symmetry. In our view, single section pass-bands on one side of the enclosure or the other produces output that is inherently asymmetrical.

Although the listeners are often a great distance from the loudspeaker array, the asymmetric design is hard to ignore and generally quite audible.

It might seem intuitive, then, to place the HF section in the middle of the cabinet, flanked by the LF section to one side, and the MF section to the other.

Above, non-processed response measurement of the KF740; below, the processed response measurement.

But this can cause abnormal summation characteristics between the MF section and the LF section due to the additional spacing between these sources.

Our approach with the KF740 and all EAW line array modules, on the other hand, keeps the spacing between individual pass-bands to a minimum.

The design is completely symmetric, creating identical sound reproduction on both sides of the loudspeaker/array.

Further, a passive low-pass filter drives the side-firing woofers to help prevent unwanted lobing, as well as to foster integration of the LF pass-band with the MF pass-band.

Another benefit of the symmetrical approach is a 50-50 weight distribution left to right, which helps balance arrays as they hang from a single point off the center of the fly bar.

Finally, sonic quality starts with the components, with the KF740 incorporating our latest developments in transducer technology. All offer neodymium magnets, with the dual 2.5-inch (again, 1.4-inch-exit) HF compression drivers utilizing a specially treated titanium diaphragm that provides additional hardness and improves response.

The two 8-inch MF cone drivers are driven by 3-inch voice coils, with their sealed aluminum chassis providing additional thermal dissipation while also preventing any unwanted modulation from the LF devices. The four 10-inch LF transducers are outfitted with 2.5-inch voice coils.

Digital Procesing
Proprietary EAW Focusing technology, provided by the UX8800 digital processor, offers specially tailored alignment and driver processing algorithms that further optimizes performance.

It eliminates the traditional characteristics of “honk” and “splashiness” that can plague horn-loaded loudspeaker designs.

The honk of a horn is normally heard in the lower frequencies of its band pass, while splashiness (an attribute of compression drivers) is usually heard at the highest frequencies and obscures the fine detail in instruments, such as cymbals.

Likewise, cone drivers have inherent resonances in their upper frequency range that result in “muddiness” in the middle of the vocal range.

These HF and LF behaviors combine to produce a sonic signature commonly referred to as “coloration.”

The roots of EAW Focusing began with a proprietary, software-based spectrograph for acoustical analysis. This spectrograph, along with other analysis tools, was used to investigate the unprocessed responses of HF and LF subsystems in various directions and at various levels.

The analysis allowed various performance anomalies to be isolated from each other.

In this way, those anomalies that were linear, time invariant, spatially consistent, and therefore correctable, could be distinguished from anomalies without those characteristics, and which were therefore not correctable.

The EAW UX8800 digital processor that delivers EAW Focusing parameters to the KF740.

The next step was to apply appropriate DSP to the correctable anomalies. Another analysis was performed on the standard, universally used DSP algorithms.

This test proved that these standard algorithms simply did not produce filters with response shapes, temporal behaviors, or resolutions with anywhere near the required precisions or accuracies necessary to correct those anomalies to which they were being applied.

To solve this dilemma, we undertook development of custom DSP algorithms specifically engineered to provide the required filters for correcting loudspeaker anomalies.

The resulting filters had to possess the required precision and accuracy in both the frequency and time domain.

At the same time, any uncorrectable anomalies would have to be ignored by the filters. The anomalies and resonance problems cured by EAW Focusing are very specific to each loudspeaker design.

Completing this package, the vertical output can be tailored to match the requirements of any space by varying the splay at the rear of the enclosures as directed by EAW Resolution software.

The resultant configuration repeatedly produces a continuous, coherent wave front of extended range, high-resolution audio over the entire defined coverage area.

Scale & Packaging
It was also very important to us that the KF740 be as lightweight and efficient as possible.

Especially at the present time, given the state of the economy, minor considerations such as cartage have become especially big factors in the purchasing process for sound companies.

Extensive 3-D modeling was deployed to develop a rugged yet lightweight exterior-grade Baltic birch plywood enclosure, protected by wear-resistant textured coating and powder-coated steel grille.

In combination with the neodymium transducers, each module checks in at just over 100 pounds.

Its profile is identical to that of the KF730 in terms of height and depth (13 inches by 17.5 inches), while the KF740 is about 40 percent wider at 40.1 inches.

These compact enclosures require a minimum of truck space, and caster pallets for easy transport are available.

The dual Neutrik Speakon STX Series NL8 connectors on the rear panel provide access to each of these sections separately. The low frequency sections; side and front, are wired separately but can be driven by the same DSP channel.

The integral rigging system is constructed of structural high-strength aluminum to meet the weight goals, strong enough to hang a 16-module array at a 10:1 design factor.

After completing the design using a solid modeling program, we utilized Finite Element Analysis software to conduct virtual pull tests that provided invaluable information in furthering the integrity of the rigging, followed by actual physical failure testing.

The Neutrik NL8 connectors on the rear panel provide access to each section separately.

We also advise that all arrays be structurally verified with EAW Resolution software, which calculates (in real time) the stress load on all rigging points of every enclosure. This is critical because every array is different.

Users can quickly and easily construct vertical arrays ranging from 4 to 16 enclosures. In most cases, choosing the correct points on the multi-position fly bar will aim the array, although some angled configurations will require pull back using an inverted fly bar. Boxes are quickly secured with precision quick-release rigging pins.

The rigging system permits box-to-box angles of 12, 9, 6, 3, and 1.5 degrees, while always keeping module faces contiguous. Under normal conditions, easily hung arrays can cover listening areas ranging from approximately +10 degrees to -70 degrees along the vertical axis.

The rigging also accommodates “radical” array configurations that can cover any vertical angle. Accessory adapter bars for easy configuration within KF730 and KF760 arrays are also available.

Inherent within all of our goals was one consistent theme: to maintain and further the EAW heritage of consistent pattern control while attaining output levels comparable to larger systems.

Preliminary customer response indicates that with the new KF740, we’re on the right track.

Nathan Butler serves as principal design engineer at EAW.

EAW Website