De-Mystifying the Amplifier: A Look Inside Meyer Self-Powered SpeakersBy Phil DeLancie
This article provides an inside look at a core component of Meyer self-powered technology:
Which Amp Does My Speaker Use?
Meyer produces amplifiers in two lines: the UltraSeries and the MP Series.
The newer amplifier line, the UltraSeries, was created for the new Self-Powered UltraSeries, featuring the UPA-1P and UPA-2P speakers and the UM-1P and UM-100P stage monitors. The MP Series of amplification is found in most powered Concert Series models, including the MTS-4 loudspeaker and the 650-P subwoofer.
Both amplifier designs are housed within the speaker cabinet, in addition to the transducers, active crossovers, frequency and phase response correction, and driver protection. This yields a self-contained unit requiring only power and line-level input signal for operation. Both use Meyer's Intelligent AC circuitry to provide automatic voltage selection, which eases setup in international touring.
The MP series uses a two-channel complementary MOSFET design (operating class AB/H) to deliver 620 watts per channel into eight-ohms with less than 0.02% distortion. The package includes EMI filters and surge suppressors to minimize spurious noise, and dual circuit breakers to protect against powerline fault conditions. The biamplified UltraSeries, meanwhile, offers a burst output capability of 350 watts per channel. The amp uses high-current complementary-symmetry MOSFET output stages in class AB/bridged configuration with a unipolar switched-mode power supply.
Keeping the Amp Cool and Clean
According to Meyer technical support manager John Monitto, most environmental hazards facing sound installations boil down to heat and moisture, each of which poses its own challenges. In the case of heat, operation in high ambient temperatures can expose limitations in a system's heat dissipation strategy. Self-powered systems enjoy some inherent advantages here, because heat sources are not concentrated together in amp racks, but rather spread out among all the cabinets in the system. The amplifiers are also protected from the contamination problems often encountered in traditional setups, where build-up of dirt and dust can compromise cooling, and in severe cases lead to fault conditions. Further, each Meyer self-powered cabinet is specifically designed to ensure a dedicated air path across the electronics which exceeds peak cooling needs.
The MP series uses a dual-fan design to draw air across an internal heatsink. Only one fan is used under most operating conditions, but if temperatures within the unit rise above 74° Celsius (165° F), the second fan kicks in, increasing airflow through the system. To minimize contaminate deposition on sensitive amplifier and control componentry, the MP's air supply is filtered by being drawn first through the front grille foam and then through a secondary piece of open cell foam at the cooling air inlet.
UltraSeries systems include an internal fan, but rely for cooling primarily on a massive external heatsink on the rear panel. In some settings, high ambient temperatures - caused by weather, limited space or restricted airflow - can reduce the cooling potential of the heatsink. For these situations, Meyer offers an optional fan kit to increase the movement of air across the heatsink. Mounted on the cabinet rear face, the fan draws its power from the electronics package and thus requires no additional AC feed.
TruPower Limiting Ensures Safe, Extended Peak Power
Even with the optimized cooling strategies designed into the MP and Ultra enclosures, there may be occasional situations where electronic thermal protection is required. The fact that each of the self-powered designs is created from the start as an integrated system with known load characteristics allows Meyer to dispense with the kind of one-size-fits-all protection circuitry that often compromises the sound quality and reliability of conventional amplifier designs.
Instead, says Meyer engineering manager for R & D Peter Soper, dedicated TruPower speaker protection circuits allow Meyer cabinets to deliver full peak power for extended periods without the threat of running into sonically damaging thermal protection circuitry, and can even afford the ability to operate in higher ambient temperatures than many traditional power amplifiers.
In the UltraSeries UPA-P amplifiers, for example, this intelligent thermal limiting activates when the heatsink temperature exceeds 85° C (185° F), lowering protection limiter thresholds by 6 dB. The over-temperature protection circuit resets itself when the heatsink cools to below 75° C (167° F).
Sound Protection from Weather and Water Damage
In addition to heat, the other main environmental concern in the field is moisture. Self-powered loudspeakers are, of course, considerably less likely to be subject to damage from flood waters or spilled drinks than their floor standing counterparts. But beyond that inherent advantage, Meyer offers a number of additional protection options. Rear panel electronics may be shielded with optional rain hoods made of tough ABS plastic that mount using existing screw locations. The hoods allow wiring hook-ups and cooling air flow while preventing water from getting into the electronics, and are strongly recommended for outdoor applications.
For more extreme environments where continued exposure to the elements is expected, fully weather protected enclosures are recommended. Designed with the requirements of installed systems in mind, the weather protected cabinet starts with epoxy treatment to all end grains. Marine epoxies are used for all joinery, and stainless steel or powder-coated hardware is used throughout, with special sealants and caulking around potential leak points. Finally, a special latex enamel is used for the finish which allows for cabinet expansion and contraction without cracking.
The weather protected option should be considered in all cases where an installation is expected to see prolonged periods of weather exposure, says Soper, such as outdoor pole mounting and other permanent outdoor applications. The standard cabinet is preferred when units will be transported a lot-the epoxy paint used on standard cabinets holds up better to abrasion and road use-or when there is some degree of protection from the elements such that the cabinets will not be subject to prolonged, direct, water exposure.
Technology You Can Trust
The development teams for the MP and Ultra lines drew on both field experience and laboratory testing to confirm that their designs hold up under real world stresses. Early in the development cycle, says Soper, the MP series amplifier was placed in an environmental chamber which allows for control of temperature and humidity. The unit was subjected to temperatures from 0 up to 50° C, as well as humidity all the way to 100%, where condensation occurred on portions of the chassis and circuitry. Lessons learned from these tests were incorporated not only into the MP design, but into the UltraSeries as well. Extensive field testing, says Soper, has assured us that both these products possess the same degree of immunity from environmental concerns.
In the rare case where servicing is required, both the MP and UltraSeries reflect a modular approach to design that is intended to maximize the ease of troubleshooting and repair in the field. Readily accessible on the cabinet's rear face, amplifier modules mount into enclosure with a few Phillips-head screws, and connect to the loudspeakers with a single connector. All sub-assemblies can be field replaced by following Meyer's simple recommended service procedures. In most cases, a screwdriver and a set of spare modules are all it takes to keep Meyer's self powered loudspeakers singing in the rain.