Meyer Sound Self-Powered Loudspeaker HM-1 - Manual (Page 3)

3
Introduction
The Meyer Sound HM-1 is a very compact, full-range
self-powered loudspeaker system designed to serve in a
wide variety of installed sound reinforcement and re-
production applications. The HM-1 incorporates sig-
nificant design innovations that combine unprecedented
performance with several practical advantages. In
contrast to conventional small speaker systems, the
vented cabinet is tuned at 40 Hz to provide flat, full-
range response with half-space loading. The concentric
tweeter mounting structure is optimized to minimize
both back-wave interference and IM distortion. A
constant-directivity high-frequency horn affords a 100
°
beam width, and sophisticated phase-correction circuitry
assures true point-source performance without the off-
axis cancellation effects that normally plague dual-
concentric designs.
By implementing distributed amplification, the HM-1
affords substantial advantages in reliability and ease of
installation when compared with constant-voltage (70 V)
distributed systems. The HM-1 accepts a unipolar 48 VDC
power source, which reduces induced noise significantly.
The 48 VDC power may be supplied using twisted-pair
wiring jacketed with the signal source conductors,
eliminating the need for wiring conduits. Its amplifier
and signal-processing circuits are designed to tolerate
supply voltage drops of up to 25%, accommodating
light-gauge cables and long cable runs. Internal energy
storage circuits minimize the system's peak-to-average
supply current demands, allowing efficient use of
switched-mode regulated supplies.
The HM-1 is a two-way system comprising a 7” graphite
cone low-frequency driver, and a concentrically-
mounted 1” soft-dome high frequency driver with
constant-directivity horn, in a vented cabinet; the drivers
are magnetically shielded. The enclosure contains two
200 Watt amplifiers, an active crossover, driver protection
voltage limiters, and frequency and phase response
alignment circuitry. A laser-trimmed differential input
stage affords superior common-mode rejection to ac-
commodate simple twisted-pair signal distribution.
Front-panel LEDs indicate power, signal limit, and
thermal overload; a rear-panel circuit breaker provides
overall DC power protection.
The HM-1 enclosure is coated with a textured black or
white finish, and a variety of factory-installed mounting
configurations may be ordered. Optional accessories
include a remote switched-mode power supply, a
variable-speed cooling fan assembly controlled from a
rear-panel drive output, and an auxiliary subwoofer,
powered by the HM-1 low-frequency amplifier, that
extends the frequency response to 42 Hz in free field.
Power Requirements
The HM-1 requires a 48 VDC external power supply,
which provides these benefits:
• Low voltage wiring simplifies installation.
• Utilizes telecom 48 V supply and bus standard.
• Eliminates 50/60 Hz AC noise coupling in wiring.
The HM-1 can be powered by the Meyer PS-1 AC adapter
or a supply that conforms to the 48 VDC specifications
detailed in this section.
Meyer PS-1 AC Adapter
Using the Meyer PS-1 AC adapter is the simplest way to
power a pair of HM-1s, or a single HM-1 with a sub-
woofer. The AC adapter can be purchased through Meyer
Sound and comes with two 10 ft power cables. The AC
adapter has two output connectors that are wired together
inside the supply, allowing either one connector to
drive two speakers at the end of a single cable, or one
connector and cable per speaker.
Do not connect the outputs of multiple PS-1 AC
adapters together!
For installations up to 10 HM-1s, using multiple PS-1
AC adapters is often the simplest and most cost-effective
solution. Since the limited output power for each supply
acts as circuit protection for light gauge cables, it is not
necessary to install circuit breaker distribution panels.
Using the PS-1 does, however, limit each 48 V line to two
speakers. The dimensions of the AC adapter are 10” x 5” x 3”.
Contact Meyer Sound for further information on the
PS-1 AC Adapter.
!
Do not use a ground-lifting adapter or cut the AC
cable ground pin.
Power Supplies for Large Systems
If an installation includes a large number of speakers, or
requires many speakers to operate from a single 48 V
line, a single high output power supply should be
considered. The following sections provide current and
voltage specifications for the HM-1’s power requirements.