| HM-1 Self-Powered Loudspeaker System Questions & Answers |
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The Meyer Sound HM-1 is a very compact, full-range self-powered loudspeaker system designed to serve in a broad range of professional applications from foreground/background music and distributed systems to theatrical sound.
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. Built-in electronics include integral complementary MOSFET bridged class A/B biamplifiers with 400 watts total power output, an active crossover, driver protection voltage limiters, and frequency and phase response alignment circuitry. This powerful combination of components provides flat, full-range response from 42 Hz to 20 kHz (half space, or free field with optional subwoofer) and 116 dB peak SPL with symmetrical 100° constant-directivity coverage.
The HM-1 accepts a single, unipolar power source in the range of 35 to 52 VDC, accommodating a broad range of local and national electrical code requirements. Meyer Sound offers an accessory AC adaptor, the PS-1, which can power up to two HM-1's, or one HM-1 and one HM-1 Subwoofer. Compact and very lightweight, the PS-1 may be installed in proximity with the loudspeaker cabinet or placed in a remote equipment room.
PS-1 AC Adaptor (for powering up to 2 HM-1's)
What are the intended applications for the HM-1?
Combining very compact size with true full-range reproduction and significant peak output capability, the HM-1 can be used anywhere that clear, coherent sound quality, smooth coverage and unobtrusive cabinetry are desired. In foreground/background systems, the HM-1 provides excellent music reproduction with the ability to deliver crisp, highly intelligible speech. Theatrical sound applications include onstage effects as well as under-balcony or front fill systems. In cinema applications, the HM-1 makes an excellent surround speaker, accommodating full-range signals and affording very wide coverage to assure consistent sound across the theater seating area. For live performance, the HM-1 can serve as both a distributed reinforcement speaker and as a mini stage monitor.
What makes the HM-1 different from other small coaxial loudspeakers?
The HM-1 incorporates a number of design innovations that separate it from the competition and afford substantial practical advantages.
In contrast to most small speaker systems, the HM-1 cabinet venting is tuned at 40 Hz to provide excellent low-frequency response. The concentric tweeter mounting structure is optimized to minimize back-wave interference and IM distortion, both of which are significant problems with other concentric designs. And sophisticated phase-correction circuitry assures true point-source performance while minimizing the off-axis cancellations that plague many conventional dual-concentrics. The result is extraordinary fidelity and coherence, with the ability to achieve smooth, seamless coverage.
What are the benefits of making the HM-1 self-amplified?
Self amplifying frees the consultant and contractor from the limitations and headaches associated with conventional loudspeaker designs, enabling them to construct clean, efficient systems that install in a fraction of the time.
Amplifier racks are eliminated, reducing assembly labor and minimizing the chances for miswiring. There's no need to select, install and adjust crossovers or system equalizers: these functions are already included and are factory-aligned for optimum performance. Line-level signal distribution is easily handled using conventional small-gauge wiring, and coverage zones can be flexibly configured simply by assigning signal feeds. Expanding the system is as easy as hanging another unit and daisy-chaining connections, so coverage can be fine-tuned on-site with minimum time and labor requirements. Finally, self-amplifying eliminates the need for constant-voltage transformers in distributed systems, avoiding distortion that can damage intelligibility and assuring uncompromised low-frequency response for optimum music reproduction.
What about reliability and service?
Each HM-1 electronics package is individually burned-in and tested prior to installation, ensuring far greater reliability than most off-the-shelf amplifiers and signal processors can provide. But should an amplifier fail, all you need to service the unit is a phillips screwdriver and a spare amp package. Connections within the HM-1 cabinet are made with a multi-pin snap-on connector, so changing an amplifier is as easy as replacing a loudspeaker driver. And the HM-1 is backed by a limited three-year warranty, so youÐre covered by the factory in the unlikely event that problems arise.
How should the signal input connection be wired?
The HM-1 is available with either a three-pin XLR-type input connector or, for fixed installations, a multi-pin terminal block receptacle. In either case, the HM-1 input accepts either balanced or unbalanced inputs at +4 dBu nominal operating level, and presents a 10k ohm input impedance. The input is capacitvely coupled, accepts up to ±50 volts common mode and is RF and ESD protected. Twisted pair shielded cable is recommended for best EMI immunity, but an unshielded twisted pair can be used with excellent results.
HM-1 rear panel with XLR Connector
HM-1 rear panel with 7-Pin Connector
How can the HM-1 be mounted/rigged?
The HM-1 cabinet sides, top or bottom can be drilled to accommodate a variety of mounting hardware, and for larger quantity orders it can be supplied pre-drilled to accept popular fittings. The driver assembly is magnetically shielded and may be placed in proximity with television or computer monitors without affecting image quality.
Because the rear-panel heatsink can reach temperatures of up to 85° C, a minimum of approximately three inches of unrestricted free air space should be allowed behind the cabinet. The HM-1 utilizes convection cooling, so to encourage the chimney effect there should be a provision for free flow of cool air from below the cabinet and for warm-air exhaust above it. For applications where the HM-1 must be mounted in a closed soffit or false ceiling, an optional fan assembly is available. The cooling fans mount directly to the cabinet rear face and are powered from an integral rear-panel variable-speed drive output.
How does placement affect the HM-1's acoustical performance?
Because of its very small size, the HM-1 is highly sensitive to loading and its low-frequency performance benefits substantially from adjacent boundaries. In free space, the HM-1 is flat within ±2.5 dB at one meter on-axis from 90Hz to 20 kHz, and -6 dB at 42 Hz. With half-space loading the HM-1 is maximally flat achieving ±2.5 dB from 42Hz to 20kHz, and placement at a wall-to-ceiling junction or in a corner will yield further low-frequency boost.
Where substantial low-frequency output is required in free field applications, an optional subwoofer can be used to achieve ±2.5 dB response tolerance to 42 Hz with increased low-frequency acoustic power. The subwoofer employs a passive crossover network and is driven directly from a low-frequency amplifier output connector located on the HM-1 rear panel. With subwoofer, the systemÐs maximum SPL output also increases to 120 dB at one meter.
HM-1 Space-Loading Chart
Can I locate the PS-1 AC Adaptor in a remote equipment room?
Yes, in most practical applications, remote power yields substantial benefits. Because the HM-1 operates with relatively low DC supply voltages, low-voltage wiring techniques may be used, eliminating the need for conduits and greatly simplifying installation. Direct-current power also greatly reduces the potential for 50/60 Hz noise coupling in the signal conductors. Since the HM-1 amplifier and signal-processing circuits are designed to tolerate supply voltage variations of up to twenty-five percent, relatively light-gauge cables and long wiring runs are easily accommodated.
When the power source is installed in a remote location, DC may be routed to the HM-1 using wiring jacketed with the signal source conductors. The HM-1 DC input is furnished with a diode bridge, so there's no need to keep track of wiring polarity - further simplifying the work of installing and connecting cable runs.
Can I power a large number of units with rack-mounted, high-current DC supplies?
Yes, in large installations it may be more convenient and cost-effective to use industrial power supplies capable of delivering up to 5 kilowatts. To ensure safe operation, a distribution bus with break-outs to separately-fused 20 amp branch circuits is recommended. Complete instructions and specifications for such power distribution systems are provided in the HM-1 Installation Guide.
Click here for a sample HM-1 System Diagram
Isn't this really a case, then, of simply replacing amplifier racks with power supply racks?
In a word, no.
An industrial power supply capable of 5 kilowatts output typically will occupy three rack spaces and weigh in the neighborhood of sixty pounds. Such a supply may easily be wired to a simple power distribution breaker panel mounted at the rear of the rack, providing five separate 20A branch circuits. Each branch will power up to five HM-1's, so this compact, lightweight rack will supply up to twenty-five loudspeaker in any zone configuration that you desire.
Now, compare this system with one that uses separate power amplifiers, crossovers and equalizers to do the same job. Assuming biamplification (for equivalent performance) and minimum amplifier output loads of four ohms per channel (two speakers per amplifier), a total of thirteen power amps will be required. Add separate crossovers and equalizers for each coverage zone, and the rack space allotment increases further. Moreover, all of these components must be interconnected, then tested to assure correct polarity, high-and-low frequency channel assignments, crossover settings, amplifier channel gains and so forth - dramatically increasing labor costs and providing ample opportunities for error.
In short, a remotely powered HM-1 system requires far less rack space than an equivalent conventional system and is simpler, easier to install, easier to troubleshoot and inherently more reliable.
