User manual ELECTRO-VOICE SUBWOOFER ARRAYS A PRACTICAL GUIDE

[. . . ] Subwoofer Arrays A Practical Guide Vers i on 1 E l ectro- V oi ce, B urns vi ll e, M i nnes ota, U S A © Bosch Security Systems Inc. A pri l, 2009 Subwoofer Arrays A Practical Guide Jeff Berryman Rev. 1 / June 7, 2010 TABLE OF CONTENTS 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Acoustical Concepts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] Figure 21 shows the coverage of a flown center cluster of 12 EV Xsub woofers in an arena venue. The woofers are hung in a straight line, an optimized set of beamforming delays are applied. As well, level shading has been applied. The result is a subbass coverage pattern that maintains constant tonal balance over the entire listening area and In this example, the delays have been applied in pairs. That is, each adjacent pair of woofers has a drive channel. This is more economical than having a separate drive and amplifier channel for each woofer. However, should a separate drive channel per woofer be available, even better coverage would be possible. 15 SUBWOOFER ARRAYS · A PRACTICAL Blue 40Hz Red 60Hz Green 90Hz GUIDE REV. 1 / JUNE 7, 2010 Blue Red Green 40Hz 60Hz 90Hz Figure 21. Xsub x12 center flown in arena. Delay and Gain Top to Bottom 5 5 2 2 1 1 0 0 1 1 1 mSec mSec mSec mSec mSec mSec mSec mSec mSec mSec mSec -3 3 0 0 0 0 0 0 0 0 -3 dB dB dB dB dB dB dB dB dB dB dB 16 SUBWOOFER ARRAYS · A PRACTICAL GUIDE REV. Gradient Arrays A gradient array is an arrangement of loudspeakers driven at different amplitudes and phases in such a way as to cancel sound radiation in unwanted directions. Gradient arrays only work when their dimensions are small with respect to wavelength. They are the opposite of beamformed and endfire arrays, which must be large in order to work. The reason for this is that gradient loudspeakers work by controlling pressure differences between the different parts of the sound wave, and must therefore be small enough to work "within" the wave. Figure 22. Gradient Gradient loudspeakers are the loudspeaker counterparts of ordinary directional microphones, which work by picking up pressure differences between different parts of the sound wave. The gradient technique is the only practical way to implement subbass pattern control with small arrays. When set up carefully and correctly, gradient arrays can provide a range of useful patterns that will give significantly better bass coverage than could be achieved using simple arrays of comparable size. 8. 1. Example Figure 23 shows a pair of EV Xsub subwoofers in a basic gradient configuration. The boxes are positioned back to back, 4" (10cm) apart. The rear box is driven in reverse polarity and is delayed by 4. 65 mSec. The resulting array has a cardioid directional pattern. Although in this example the loudspeakers are mounted back to back, it need not always be so. As long as the there is enough space between front and rear cabinets to allow the rear loudspeaker's sound to emerge, the rear cabinet can be mounted facing forward or backward. [. . . ] Figure 37 shows the case in which the subwoofers are driven from a separate mix. In this case, subbass contour EQ is implemented by a pair of equalizers, one on each mix. Both equalizers should always have the same setting. This can be done manually, or by using a multichannel equalizer, or, in the case of software-controlled equalizers, but linking channels in software. 30 SUBWOOFER ARRAYS · A PRACTICAL GUIDE REV. [. . . ]