Crown Audio IQ-P.I.P.-MEM - Manual (Page 22)

Page 22 Reference Manual
IQ–P.I.P.-MEM Programmable Input Processor for IQ Systems
(shielded or unshielded). If fiber
optic wiring is required contact the
Crown Technical Support Group
(see page 4).
Here are some guidelines for
twisted-pair wiring:
• Use shielded twisted-pair
wire at least 26 AWG in size
when inter ference is a
problem. The wire should be
of good quality and should
have low capacitance—30
picofarads/foot or less is
good. (West Penn 452 or an
equivalent wire works well.)
The shield serves two
purposes: First, it helps
prevent the
IQ data signal
from transmitting to nearby
audio wiring. Second, it helps
prevent outside RF from
inter fering with the data
signal. However, in most
cases interference is not a
problem and, since
unshielded wire has lower
capacitance, it is a better
choice.
• Minimize the total capaci-
tance of each Crown Bus
loop. The total capacitance
should be less than 30
nanofarads. Allow for ap-
proximately 60 picofarads for
each IQ component in a loop.
This accounts for a slight
delay which occurs as data
signals pass through a
component.
• Add an IQ Repeater for very
long loops—greater than 1000
feet (305 m)—or when re-
quired by high-capacitance
wire. Although we recom-
mend a repeater for loops
longer than 1,000 feet, it is
often possible to go 2000 feet
(610 m) or more. The most sig-
nificant characteristic of the
wire is its capacitance. Lower
capacitance allows longer
loops. Unshielded wire usually
has less capacitance.
• Never use the ground wire
in a mic snake line. It may
sometimes be convenient to
run Crown Bus data signals to
and from stage monitor am-
plifiers along unused wire
pairs in a mic snake. Do not
use the ground wire which is
normally connected to pin 1
on an XLR connector or data
noise will be added to the au-
dio lines. Use only the signal
lines which normally connect
to pins 2 and 3 of the XLRs.
Note: Because typical mic
cables have high capaci-
tance, the maximum possible
Crown Bus loop distance will
be less.
Outside RF interference is seldom a
problem for a Crown Bus loop—
especially if shielded twisted-pair
wire is used. However, there are
extreme situations when fiber optic
wiring is recommended. For
example, locating a Crown Bus loop
next to an AM radio transmission line
may require fiber optic cabling. An
extremely long Crown Bus loop
distance may also require fiber optic
cabling.
There are three different types of
connectors used for Crown Bus
wiring: DIN connectors, RJ45 and
screw terminal plugs. The IQ–P.I.P.-
MEM uses a 5-pin DIN connector
for input and a 4-pin DIN connector
for output. Figure 4.9 shows how
they should be wired.