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Cable Requirements
Each HM-1 draws a maximum of 3 Arms and 5 Apk from
a 48 V power supply at peak SPL. The cabling between
the 48 V supply and the speaker adds resistance to the
circuit and produces a voltage drop at the speaker.
Decreasing the voltage at the speaker compromises the
peak SPL so cable resistance should be minimized.
For best sonic performance, avoid voltage drops greater
than 8 V at the speaker. Voltage drops greater than 15 V
may cause the speaker to mute or distort. The maximum
round-trip resistance for a cable attached to a single
HM-1 should be no higher than 1.6 Ω, which keeps the
voltage drop below 8 V during the maximum current
draw of 5 Apk.
The following table helps select cable gauges for various
cable lengths.
M
a
i x
m
u
m
C
a
b
e l
1
8
A
W
G
#
H
M
1 -
s
t a
e
n
d
f o
c
a
b
e l
f
( t
m
)
1
1
2
5
3 (
. 8
2
6
3
1 (
. 9
3
4
2
1 (
. 2
4
3
2
(
. 9
5
2
5
(
. 7
A single HM-1 attached to a 100 ft 18 AWG cable (1.27 Ω
total) produces a 6.4 VDC loss at the speaker (41.6 V)
during maximum audio bursts (5 A, 0.5 s). This results in
a small loss in peak SPL.
Audio Input
The input impedance of an HM-1 is 10 kΩ. Pins 2 and 3
carry the input as a differential signal. Pin 1 and the case
are connected to the HM-1 chassis. The power cable can
be jacketed in the same sheath as the signal cable with-
out adding noise to the input signal.
For best EMI immunity, it is desirable to use a twisted
pair shielded cable with the twisted pair connected to
pins 2 and 3, and the shield to pin 1. However, an
unshielded twisted pair cable can be used effectively,
even if it is jacketed with the power cable.
L
e
n
g
h t
f
r o
<
8
V
d
o r
p
1
6
A
W
G
1
4
A
W
f
( t
m
)
f
( t
m
) 0
2
0
0
6 (
. 1
) 0
3
3
0
1 (
0
) 2
1
0
0
3 (
. 0
) 5
1
6
5
5 (
) 8
6
7
2 (
. 0
) 4
1
1
0
3 (
) 8
5
0
1 (
. 5
) 2
6
6
2 (
) 6
4
0
1 (
. 2
) 2
6
3
1 (
The input is RF and ESD protected, capacitive coupled,
±50 V common mode to ground, +4 dBu nominal, +21
dBu max. Clipping occurs at the input at 12 Vpk. The
Common Mode Rejection Ratio (CMRR) is greater than
80 dB.
The HM-1 is available with either an XLR or a terminal
strip input connector.
Interfacing Options
Two types of interface panel are available for the HM-1.
One uses an XLR connector for the audio input, and a
four-pin terminal connector for the power supply input
and subwoofer output. The other interface panel type
uses a seven-pin terminal connector for the audio input,
power supply input, and subwoofer output. Both versions
use a two-pin terminal connector for the fan power
output.
The wiring for the terminal connectors is inserted into a
G
keyed plug that fits only into the correct terminal
)
connector. This section discusses both interface panel
types.
. 0
) 6
. 0
) 3
XLR Connector
. 3
) 5
The XLR connector is standard for most audio devices.
Pins 2 and 3 carry the input as a differential signal (pin 2
. 0
) 1
is hot) and pin 1 is connected to the chassis. The power
. 9
) 2
supply input and subwoofer output connections are each
made with a two-pin plug. Each plug is keyed such that it
can be inserted only into the correct location. For example,
the power supply plug does not fit into the subwoofer
output.
Rear panel with XLR connector
5
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