Nexo Alpha System - Manual (Page 20)

α α α
P 20
USER MANUAL
VERSION :1.01
DATE : 06/10/10
• resulting
directivity
At low frequencies, because wavelength is much larger than the spacing between sources, interference
cannot result in cancellation ; however, directivity index will increase.
In the mid and high frequency range, where wavelength is comparable to spacing between sources, the
directivity polar plots will show dips and lobes. The amplitude of these lobes will depend on the
directivity of the individual sources and on their angulation.
However, lobes and dips will only appear on single tone signals (sine wave) ; on third octave or full
octave excitement, they will be smoothed.
3.4.2. S MALL A RRAYS ( LESS THAN 4 A LPHAS M3 / M8)
The amplitude of the dips and the lobes is minimised when angling the cabinets at their nominal
coverage angle. If the angle is less than the coverage, the interference region will be larger, and if the
angle exceeds that value, there will be a « hole » between the cabinets.
It is therefore strongly recommended when using a small amount of cabinets to angle them at their
nominal coverage angle (Alpha M3 : 35°x35°, M8 : 75° x 45° ; EM/EF : 75° x 30°).
The only situations where such arrays can be assembled with very little angle are long throw
applications (very small vertical coverage).
3.4.3. L ARGE A RRAYS (4 A LPHAS M3 / M8 AND ABOVE )
Construction of large arrays derives from important SPL requirements rather than large listening angles:
although the Alpha M3 is a high Q cabinet, 4 boxes are enough to cover a 140° horizontal plane...
Therefore, large arrays will usually assemble cabinets at less than their nominal coverage angle.
Measurements and simulations show that when using a large amount of cabinets, the individual
behaviour of a cabinet will determine the roll-off on the limits of the coverage zone, and the architecture
of the array will be responsible for the behaviour in the coverage zone.