L-Acoustics V-DOSC, Руководство оператора

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L-ACOUSTICS V-DOSC Manual Version 4 6/29/2005 Page 11 of 158
INTRODUCTION
The V-DOSC sound reinforcement system is different. We hope this manual will help you to
appreciate why and to understand the basic theoretical principles behind how V-DOSC works.
Understanding the concepts behind V-DOSC and Wavefront Sculpture Technology is just as
important as the many operational details related in this manual – the more you understand the big
picture, the more effectively you will use V-DOSC.
V-DOSC is a complete system approach – starting from the basic scientific question of how to
effectively couple sound sources then including aspects of performance prediction, sound design,
system installation, rigging, cabling, signal distribution, digital signal processing and system tuning. This
turnkey system approach allows for accurate and predictable results, however, in order to achieve the
best results you need to understand the theoretical concepts behind how the system works and adopt
a methodical approach to sound design and installation. For these reasons, specialized training is
necessary to obtain the best results with the system. Some people think that working with V-DOSC is
complicated but once you understand the procedures involved, you save time and - more importantly
- obtain better, more predictable results.
Apart from sound quality and the system design approach, there are many other benefits to
V-DOSC. Many readers are already aware of these – if not, hopefully they will become apparent
throughout the course of this manual.
WAVEFRONT SCULPTURE TECHNOLOGY FUNDAMENTALS
THE SOUND REINFORCEMENT PROBLEM
The first task of sound engineers and audio consultants is to design sound reinforcement systems for a
given audience area. Performance expectations in terms of sound quality, sound pressure level (SPL)
and coverage consistency have progressively increased over the years while at the same time the size
of the audience has grown, inevitably leading to an increase in the number of loudspeakers.
In the past, conventional horn-loaded trapezoidal loudspeakers were typically assembled in fan-shaped
arrays according to the nominal horizontal coverage angle of each enclosure in an attempt to reduce
coverage overlap that causes chaotic interference. With this type of arrangement, the optimum clarity
available in one direction could only be provided by the individual enclosure facing in this direction.
Attempts at “flattening the array” to achieve greater throw and higher SPLs resulted in severe
interference in an uncontrolled way, affecting coverage, pattern control, intelligibility and overall
sound quality. Even when arrayed according to specification (always an ''optimum'' compromise since
the polar response of individual horns varies with frequency), the sound waves radiated by individual
horn-loaded loudspeakers do not couple coherently thus the conventional system approach is
fundamentally flawed (see Appendix 1). Furthermore, the chaotic sound fields created by interfering
sound sources waste acoustic energy, thus requiring more power than a single, coherent source
would in order to obtain the same SPL.
As an illustration of this, imagine throwing some pebbles into a pool of water. If one pebble is thrown
into the water, a circular wave will expand concentrically from the point where it entered. If a handful
of pebbles are thrown into the water, we observe the equivalent of a chaotic wavefront. If we throw
in a single larger stone, having total size and weight equal to the handful of pebbles, then we again see
a coherent circular wave as for the case of the single pebble — only now with a much larger
amplitude. If all of the individual pebbles could be glued together, this would provide the same effect
as the larger stone...
This illustrates the thinking behind V-DOSC: if we can build a single sound source from a number of
individual speakers that can be separated for transport and handling, then we have achieved our goal,
i.e., to create a modular sound reinforcement system where the individual loudspeaker enclosures
couple correctly when arrayed together so that the system behaves as the equivalent of a coherent
line source array. This was the initial specification at the outset of the V-DOSC R&D program - to
design a single sound source that was completely modular, predictable and adjustable.