User manual MARTIN AUDIO WLXGS

[. . . ] PREMININARY INFORMATION WLX, WLXGS User's Guide The Martin Experience All material © 2007. Subject to change without notice. Wavefront WLX and WLXGS HybridTM Subwoofer Preliminary information Introduction The powerful WLX HybridTM subwoofer is designed to complement Wavefront W8L Series touring systems to provide deep bass with maximum efficiency. WLX Rigging options Standard WLX subwoofers are equipped with integral flying hardware. A non-flying version is available ­ the WLXGS (= WLX Groundstack). Standard WLX subwoofers may be flown from a standard W8LC grid via a single point W8LC lifting bar. W8LC Grid W8LC Lifting Bar All material © 2007. [. . . ] They can be symmetrically coupled by placing them label-tolabel. All material © 2007. Subject to change without notice. Symmetrically coupled 2-wide columns show a slight improvement in mid-bass amplitude and polar response - but the effect becomes insignificant in large, flat fronted arrays or widely spaced stage apron systems. 2-wide symmetrical columns of WLX/WLXGS may be horizontally arrayed to improve mid-bass coverage. Array shapes vs coverage WLX or WLXGS subwoofers may be stacked and arrayed in various configurations to increase sound pressure and tailor coverage. The sound pressure increase is intuitive but the significance of subwoofer array shapes and sizes is often overlooked. The following table shows the sound pressure boost and coverage provided by a variety of flat fronted arrays: All material © 2007. Subject to change without notice. Array Approx Boost (wrt single unit) - Horizontal coverage Wide Vertical coverage Wide +12dB Wide Narrow +12dB Narrow Wide +24dB Narrow Narrow In these examples "wide" means that there are no coverage nulls within the forward 180º at mid-bass crossover frequencies. Wide coverage arrays have significant output beyond 180º making them more prone to room colouration. "Narrow" means that coverage will drop significantly before 180º coverage is reached at the mid-bass crossover frequency. General rules: The larger the array the more directional it becomes A larger, directional system will be less affected by the room We get a 6dB far field sound pressure boost every time we double the number of cabinets. Stacked WLX or WLXGS subwoofers should always be blocked, strapped and anchored from above by a qualified rigger. All material © 2007. Subject to change without notice. Coverage angle for tightly packed flat fronted arrays -6dB Coverage Here is a simplified formula for calculating the main coverage angle of a tightly packed flat fronted array. * = approximate speed of sound in m/s. Varies with temperature (see Section 2a). Arcsin means "the angle whose sin is . . . " Flat fronted cluster coverage patterns will be confined to one main lobe whose mid-bass crossover directivity is proportional to the size of the cluster. All material © 2007. Subject to change without notice. The medium sized array (left) has significant output to ±90º whereas the large array's ±90º output is dramatically reduced. A note on coverage nulls It is useful to be able to calculate where these first response nulls will occur for various frequencies as they indicate areas where coverage, transient response and directional information would be poor without fill systems. For symmetrical arrays nulls will occur either side of the on-axis line. We can calculate the overall "null-to-null" angle using the simple formula: As a very rough guide, the null-to-null angle will be approximately twice the -6dB coverage angle. Interpreting polar plots i) It is conventional to "normalise" polar plot on-axis amplitudes so that different polar shapes may be readily compared. In practice, the large array (right example) would have a higher on-axis amplitude than the medium array. ii) It is also conventional to plot polar amplitudes on a logarithmic scale. This is fine when working in sound pressure level terms but is not suitable for superimposing a polar plot onto a venue plan. Venue plans are drawn to a linear scale so polar plots with linear amplitude scales would be more suitable. Real-world off-axis lobe amplitudes and shapes would vary considerably depending on boundary loading, echoes, reverberation and other audio sources affecting the same space. Vertical -6dB coverage The following table gives the approximate vertical coverage angles of typical WLX/WLXGS arrays ignoring boundary effects (see later). WLX/WLXGS High 3 4 8 16 Vertical coverage 47Hz 94Hz Wide Wide Wide 69º Wide Wide 69º 33º 188Hz 98º 69º 33º 16º Use tall stacks for long shots. Useful for long distances in low-roofed venues with raked seating up to the height of the stack. [. . . ] Subject to change without notice. Polar variations with frequency Whether particular frequency components add or subtract in the far field will depend on the loudspeaker system spacing, the angular offset of the listener with respect to the centre line, and the wavelength. The following polar responses show what happens when subwoofers are placed 8. 6m apart and are driven in unison at various frequencies: 100Hz The polar plot shows the far field polar response of the two subwoofers when driven in phase with the same 100Hz signal. Subwoofer interaction causes irregular coverage either side of the centre line. Response nulls (cancellations) occur at the sides because the spacing is an odd number of half-wavelengths causing this frequency component to cancel in the far field. 80Hz The above shows the same system at 80Hz. [. . . ]