d&b TI 385 d&b Line array design - Manual (Page 4)

1. Introduction
This Technical Information paper will explain the procedure
for designing and tuning d&b J, V, Q, T and xA-Series line
arrays, point source systems from the E, Q, T and xS Series
as well as column speakers from the xC Series in a given
venue using the d&b Array Calculator (ArrayCalc) from
version V7.x.x.
Before setting up a system read the respective
manuals and safety instructions.
2. The J-Series line array
The J-Series consists of four different loudspeakers: the J8
and J12 loudspeakers and the J-SUB and J-INFRA
subwoofers. The J8 and J12 are mechanically and
acoustically compatible loudspeakers providing two
different horizontal coverage angles of 80° and 120°. The
dispersion of both systems is symmetrical and well
controlled to frequencies down to 250 Hz, their bandwidth
reaching from 48 Hz to 17 kHz.
J-Series loudspeakers can be operated with d&b D12 or
D80 amplifiers. With D80 amplifiers d&b ArrayProcessing
is available.
In the vertical plane J8 and J12 produce a flat wavefront
allowing splay angle settings between 0° and 7° (1°
increments). An array should consist of a minimum of six
cabinets - either J8, J12 or a combination of both.
The J8 with its 80° horizontal dispersion and high output
capability can cover any distance range up to 150 m
(490 ft) depending on the vertical configuration of the
array and the climatic conditions.
The J12 offers a wider horizontal coverage which is
particularly useful for short and medium throw applications.
Using a combination of J8 and J12 cabinets enables the
user to create a venue specific dispersion and energy
pattern.
The J-SUB cardioid subwoofer extends the system
bandwidth down to 32 Hz while providing exceptional
dispersion control either flown or ground stacked in arrays,
or set up individually.
The J-INFRA cardioid subwoofer is an optional extension to
a J8/J12/J-SUB system. It is used in ground stacked
configurations and extends the system bandwidth down to
27 Hz while adding impressive low frequency headroom.
2.1 Number of cabinets required
The number of J-Series loudspeakers to be used in an
application depends on the desired level, the distances and
the directivity requirements in the particular venue. Using the
d&b ArrayCalc calculator will define whether the system is
able to fulfill the requirements.
Depending on the program material and the desired level,
additional J-SUBs will be necessary to extend the system
bandwidth and headroom. In most applications a J-SUB to
J8/J12 ratio of 1:2 is sufficient. Distributed SUB arrays may
require a higher number of subwoofers, such as a J-SUB to
J8/J12 ratio of 2:3.
When additional J-INFRA systems are used, one cabinet
provides the very low frequency extension for two J-SUB
subwoofers, thus generally reducing the total number of
J-SUBs required.
2.2 J-SUB subwoofer setup
J-SUB cabinets can be used ground stacked, as a horizontal
SUB array or integrated into the flown array, either on top
of a J8/J12 array or flown as a separate column.
Depending on the application the dispersion pattern of the
J-SUB cabinet can be modified electronically to achieve the
best sound rejection where it is most effective. In cardioid
mode, the standard setting of the D12 J-SUB setup, the
maximum rejection occurs behind the cabinet (180°) while
hypercardioid mode (HCD selected) provides a maximum
rejection at 135° and 225°. The HCD mode should also
be used when J-SUB cabinets are operated in front of walls.
When used with additional subwoofers, the J8/J12 system
should be operated in CUT mode to gain maximum
headroom at low frequencies.
J8 / J-SUB crossover setup
When maximum low end headroom is not an issue, the
J8/J12 system can also be operated in standard mode (full
range, i.e. CUT not selected) and additional J-SUB cabinets
in INFRA mode can be used to extend the system
bandwidth down to 32 Hz.
J8 / J-SUB crossover setup, full range
TI 385 (6.0 EN) d&b Line array design, ArrayCalc V8.x Page 4 of 54