L-Acoustics V-DOSC, Operator'S Manual

Page: 147 / 158

L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 147 of 158
Figure 107: Destructive interference rings out of beamwidth for two kinds of line arrays :
condensed and standard.
The ideal situation is achieved when sound sources get so close to each other that they become
equivalent to a flat radiating ribbon or continuous line source. This solves the source separation
problem at higher frequencies where the wavelength is smaller than the size of the drivers (for
example,
λ
= 2 cm at f= 16 kHz) since the chaotic, multiple source wavefront is replaced by a
single well-defined wavefront.
With further analysis, it is shown in the first AES preprint that optimized coupling can be
achieved in two ways:
the first way is to minimize the spacing of sound source acoustic centers to less than half the
smallest wavelength (corresponding to the upper frequency of their operating bandwidth)
the second way is to shape the radiated wavefront of the sound sources into a flat isophasic
ribbon, with no more than 20% discontinuity of the radiating area.
In the AES journal paper ''Wavefront Sculpture Technology'', these two WST Criteria were re-
derived based on an intuitive approach using Fresnel analysis and in addition it was shown that:
♦
The deviation from a flat wavefront must be less than
λ
/4 at the highest operating frequency
(this corresponds to less than 5 mm of curvature at 16 kHz - the DOSC waveguide provides
less than 4 mm of curvature at this frequency).
♦
For curved arrays, enclosure tilt angles should vary in inverse proportion to the listener
distance (geometrically this is equivalent to shaping variable curvature arrays to provide
equal spacing of individual enclosure impact zones)
♦
Limits exist given the vertical size of each enclosure and the relative tilt angles that are
allowed between enclosures.
REFERENCES:
C. Heil, M. Urban, “Sound Fields Radiated by Multiple Sound Source Arrays”, preprint #3269,
presented at the 92
nd
AES Convention, Vienna, March 24-27, 1992
M. Urban, C. Heil, P. Bauman, ''Wavefront Sculpture Technology'', Journal AES Vol. 51, No. 10,
October 2003