It’s useful to note the benefit of operating a powered loudspeaker system at
higher voltages (when possible). At 240V AC, current consumption is half
that of
1
20V AC and the resultant voltage drop for a given cable size and
length decreases by a factor of 4.This means that the cable can be four times
longer when used at 240V AC than at
1
20V AC.
Higher voltages are
more efficient!
(
1
) Input Impedance and Level
The APL-
1
0, -
1
2, and -SB were designed to receive a balanced-line signal on
their 3-pin female XLR type connector. They are also equipped with a 3-pin
Male XLR output connector, labeled “loop-through,” intended for the pur-
pose of daisy-chaining multiple powered speakers together on a common sig-
nal feed.These input and output connectors are hard-wired in parallel; that is
to say, no active or passive buffer exists between the two connectors, they
are simply wired in parallel.This means that the loop-through connector will
always remain functional, even if AC power is interrupted to a speaker
“upstream” of other speaker(s) on the same feed circuit.
The input impedance is
1
0k-ohm, active balanced, and is intended to receive
a n4 dBv input level (+4 dBv = full power). Because it’s common
practice to loop quite a few powered speakers together on a shared feeder
circuit, care must be taken to insure that the signal source is capable of driv-
ing the group of powered loudspeakers. For example, ten APL-
1
2s present a
1k
-ohm load to the signal source. This is well within the capability of most
line-level output drivers, but depending on the output impedance of the
source, some loss in level may occur.The formula to calculate such loss is:
For example, let’s say you’re driving ten APL-
1
2s with a
1
00-ohm source
impedance.The formula to calculate loss would then be:
NOTE: It is important to be aware of the potential losses that may occur
from combining multiple powered speakers on the same feed circuit. This is
particularly important when attempting to adjust audio levels among a large
system that employs multiple feed circuits with different numbers of pow-
ered speakers on each feed.
Audio Signals
1
4
V
S
R
S
R
Ix
V
I
Voltage Loss (dB) = 20 * Log
[
]
R
Ix
R
Ix
R
S
+
(
)
Where: R
S
= Source Equipment Output Impedance
R
Ix
= Combined Input Impedance of all APL Speakers
Note: V
S
= Unloaded Source Equipment Signal Voltage
V
I
= Loaded Signal Input Voltage to APL Speakers
Voltage Loss (dB) = 20 * Log
[
]
= – 0.83 dB
1000+100
1000
(
)
