EAW KF740 Technology Brief Nathan Butler Principal Engineer Page 1 of 8
In 2001, EAW revolutionized the professional loudspeaker industry by introducing the first completely horn loaded, 3-way line array module, the KF760. Maintaining EAW s heritage for consistent pattern control, the KF760 s front surface was entirely occupied by horns. Later in 2003, EAW built upon the success of the KF760 by offering the same consistent pattern control in a much smaller package, the KF730. Like the KF760, the KF730 offered exceptional pattern control for a box of its size. It did this by borrowing the concept of the large mid frequency/high frequency horn from the KF760 and utilizing a pair of side-firing woofers. In 2009, EAW will continue this tradition with the introduction of the KF740, a line array system featuring excellent pattern control, compact size and exceptional sound quality. Pattern Control Consistent broadband pattern control is one of the more critical attributes of a professional speaker system. Inconsistent 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 entire frequency range is not an easy task. Proper pattern control requires that the source size is proportional to the wavelength being produced by those sources. In essence, larger wavelengths require larger sources. Horns provide the means to effectively increase the size of a source, as does the spacing of the transducers. Like the KF730, the KF740 utilizes woofers 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. As an example, below is the polar plot of an ideal single 10 woofer. Figure 1. Horizontal polar of an ideal, single 10 woofer. The 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. Page 2 of 8
Figure 2. Horizontal polar of a pair of ideal 10 woofers spaced horizontally. By placing the woofers on the sides as well as the front, the 740 utilizes the entire width of the enclosure to space the woofers as far apart as possible. This allows the 740 to maintain pattern control at a lower frequency than that which could be achieved by only using front-firing woofers in the same size enclosure. The 740 carries this pattern control throughout the entire operating range as illustrated below. Figure 3. KF 740 horizontal color polar plot. Thin black line indicates -6 db. Page 3 of 8
Like the KF760 and KF730, the large mid frequency/high frequency horn occupies the entire front area of the loudspeaker enclosure allowing for the most control at the lowest range of the mid frequency devices. Figure 4. Front view and cross section of KF740 system showing the single, large horn. Symmetry One aspect of line array systems is that they are often hung as single columns, one on each side of the performing space. As such, horizontal symmetry is critical. Too often, line array modules are designed with inherent asymmetries, placing single section passbands on one side of the enclosure or the other. Although the listeners are often a great distance from the loudspeaker array, the asymmetric design cannot be ignored and is generally quite audible. The pass-band to which the listener is closest is often prominent. It is because of this that some manufacturers allow their systems to be hung upside down. Others, aware of this problem, choose to place the high frequency section in the middle of the cabinet, flanked by the low frequency section to one side and the mid frequency section to the other. This can cause abnormal summation characteristics between the mid frequency section and the low frequency section due to the additional spacing between these sources. Like many EAW systems, the spacing between individual pass-bands in the KF740 is kept to a minimum. Additionally, a passive low pass filter drives the side-firing woofers. This prevents any unwanted lobing from these devices and facilitates integration of the low frequency pass-band with the mid frequency pass-band. Furthermore, like the Page 4 of 8
KF760 and KF730, the design is completely symmetric, creating identical sound reproduction on both sides of the speaker/array. Figure 5. Cross section of KF740 system showing its symmetric design. Another critical aspect of this design approach is that the KF740 has a perfect 50/50 weight distribution left to right. This allows arrays of KF740s to be hung perfectly level from a single point off the center of the fly bar. Output The KF740 takes advantage of some of the latest developments in transducer technology. The dual 1.4-inch exit high frequency compression drivers utilize a 62 mm titanium diaphragm that is specially treated to provide additional hardness and improve extreme high frequency response. The dual 8-inch mid frequency transducers are driven by massive 75 mm voice coils. In addition, the large, sealed aluminum chassis provides additional thermal dissipation. Both provide extended power handling over typical 8-inch devices. The sealed midrange chassis also provides optimal tuning, maximizing output and preventing any unwanted modulation from the low frequency devices. Four 10-inch low frequency transducers complete the package. The KF740 enclosure is sealed, so the 10-inch transducers provide accurate reproduction that is very responsive to any necessary equalization. Each of the eight transducers used in the KF740 utilize neodymium magnets, reducing weight while increasing efficiency. Finally, dual Neutrik 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. Dimensions Considering what is contained within the KF740, its size is remarkably small. Its profile is identical to that of the KF730, measuring 330 h x 446 d (mm). The KF740 has grown over the KF730 only in width, which is roughly 1019 mm. Page 5 of 8
Figure 6. KF740 mechanical drawing (preliminary). In addition, the KF740 remains remarkably lightweight. Thanks to neodymium magnets and thorough 3-D cabinet design, the KF740 weighs just 49 kg (107 lbs). Transient response Several years ago, the EAW AX series introduced Concentric Summation Array (CSA) technology. This involves the use of a coaxial transducer loaded onto a single horn. The fundamental technology 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. Page 6 of 8
Figure 7. Detail view of KF740 mid frequency apertures. This reduces the amount of high frequency energy (emanating from the high frequency transducers) that can enter the void formed by the mid frequency devices and hence reflect back out later in time. In short, the high frequency response is vastly improved as the amount of reflected energy is reduced. In addition, the apertures that fall in front of the central part of the mid frequency cone are also located farthest back in the horn bell and therefore closest together horizontally. Since the upper frequency range of the mid frequency is generated from the central part of the cone, this configuration prevents unwanted beaming at the upper range of the mid-frequencies. Focusing, first introduced in the NT products in 2005, has changed the way we think about the components used in professional speaker systems. No longer does a compression driver need to lack detail, nor does a horn need to exhibit honk. A 12-inch two way no longer is assumed to sound better than a 15-inch two way. The proper application of unique digital filters has allowed some of these previously accepted shortcomings to be corrected, if not eliminated. All of these effects are the result of irregularities in the time response. Like the NT series, the KF740 improves the time response, providing studio monitor-like reproduction when driven by the UX8800 digital processor. Page 7 of 8
Figure 8. KF740 without Focusing (left) with Focusing (right). The plots above, depicting frequency on the y axis and time on the x axis, illustrate how the time response of the KF740 is improved with the use of Focusing. Higher energy is represented by darker shades of grey. On its own, the KF740 exhibits a fine response. However, there is no denying the improved response that can be achieved; indicated by fewer dark areas later in time which indicate late or reverberant energy. Summary Like many products before it, the KF740 maintains EAW s heritage for consistent pattern control. It achieves this while remaining lightweight and compact, and still providing output levels on par with larger systems, something only the best transducers can allow. Only after months of rigorous design does the KF740 achieve these performance levels. Barely larger than a KF730, the KF740 should prove capable of providing reinforcement for all but the largest of venues. Page 8 of 8