Meyer Sound Self-Powered Loudspeaker HM-1 User Manual
Page 4
4
Current Ratings
The wide dynamic range of audio signals normally causes
a high peak-to-RMS ratio in an amplifier’s DC supply
currents. The HM-1 has internal storage circuits to minimize
the peak-to-average ratio, which
• reduces the peak power rating required by the
supply;
• allows efficient use of switched-mode power
supplies which have similar peak and continuous
ratings.
The following table lists the current and power draw for
a single HM-1 at light, moderate, and maximum operating
levels.
1
-
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4
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Each HM-1 draws 0.4 ADC, 20 W in a quiescent state.
The RMS current is measured over a 500 ms integration
time. The peak current is measured over a 10 ms integration
time.
Each HM-1 can drive a slaved Meyer subwoofer from a
connection on the amplifier panel. Adding the subwoofer
increases the amplifier’s output current, which increases
the power supply current. The current and power ratings
for an HM-1 and a subwoofer are listed in the following
table at light, moderate, and maximum operating levels.
r
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A
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2
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5
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2
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6
9
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1
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6
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8
6
1
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R
W
8
8
2
K
A
E
P
An HM-1 with subwoofer draws 0.4 ADC, 20 W in a
quiescent state.
Voltage Ratings
The voltage operating range for the HM-1 is 48 VDC
nominal, 52 VDC absolute maximum, and 35 VDC
minimum without shutoff.
Allowing operation down to 35 VDC provides two
benefits. First, a moderate voltage drop (up to 8 V) for
long DC power cables has a minimal impact on audio
performance, enabling the use of light-gauge cables for
most installations.
Second, since some switched-mode power supplies
slowly foldback the voltage if they experience current-
limit, power supplies with lower power (current) ratings
can be used efficiently. Since supplies with lower power
ratings typically experience current-limit when the HM-1
is at continuous limiting, some voltage drop and loss of
headroom is acceptable provided the voltage does not
drop below 35 VDC. At 35 V, the maximum current draw
is 25% lower than the values stated in the preceding
tables.
NOTE: If the HM-1 will not be driven at continuous limiting,
a power supply that satisfies the moderate specifications
for voltage and current can be used safely without risk of
sonic degradation or interruption.
It is important to understand how the selected power
supply responds to current-limit, particularly for
switched-mode supplies. Some supplies trip off and must
be reset manually, while others remain off for a period of
time and reset automatically. In both cases, the HM-1
suffers audio interruption. In the third, and preferable
case, supplies that feature voltage foldback allow brief
periods of current-limit without audio interruption; for
this reason, we recommend using such supplies.
The HM-1 does not require tight voltage regulation and
operates down to 35 V although peak SPL values are
reduced. This operating voltage flexibility allows for
wiring loss and voltage foldback without interruption
or degradation of the audio signal.
Many high power industrial supplies (1–5 kWatt) are
available for 19” EIA racks that are suitable for large
installations with equipment rooms. Distribution panels
with branch circuits can be used economically with up
to 8 HM-1s on a branch. Contact Meyer Sound for
information on tested and approved supplies.