The earliest PA systems took the form of completely separate components—woofer (LF or low-frequency) cabinets, high-frequency (HF) horns, amplification, crossovers, and room equalization.
The next generation of PA systems integrated HF horns and woofers to create systems that looked better and were easier to hang and aim. The fixed physical relationship between HF and LF elements in these systems allowed for the design of simple passive crossovers for separating the signals between HF and LF elements. The result was a relatively flat performance. Connection to an external amplifier was simple, and in the hands of a competent systems integrator, these newer systems offered improved performance over the earlier generation of component-based systems.
But amplifier technology was rapidly advancing to a point where amplifiers were becoming more powerful than the components they were driving could handle. At the lowest frequencies, amplifiers could drive components over their excursion limits, burning out the voice coils of these components as the long-term RMS output of these amplifiers exceeded the capabilities of the drivers they were connected to.
To correct for this, and to optimize the performance of the loudspeaker systems overall, processor-based systems came into vogue. These processors offered high-pass filtering (HPF) to protect from over-excursion, high-order crossover slopes to separate LF and HF signals (thereby ensuring that the HF drivers were not driven to over-excursion), along with RMS and peak limiting designed to the specific loudspeaker system. The processors usually took some feedback from the amplifier to set the limiting points correctly, regardless of the size or brand of the amp used to power the system. These processor-based systems were good sounding and virtually bullet-proof—the only way to break them was to wire the amp racks incorrectly or bypass the feedback loop from the amp to the processor.
Bring on the power
The next logical step in performance and reliability for a loudspeaker would be to build the amplifier and processor directly into the loudspeaker. Of course, this is easier said than done. The heat and vibration caused by a moving woofer and voice coil made for a less than ideal environment for amplifier and processor electronics.
Early powered loudspeakers were typically underpowered or very heavy, due to the large power transformers required in traditional analog amplifier and power supply designs. However, modern amplifier technologies have now evolved to the point where highly efficient amplifier topologies are suitable for—and are finding their way into—loudspeakers in growing numbers. With power supply development and the availability of high power switched mode power supplies (SMPS), we're now able to deliver high power without the weight, as these do not require transformers. (An added benefit is that these SMPS can automatically detect input voltage of 110 or 220 volts, and will self-adjust accordingly. This allows manufacturers to reduce the number of variants and SKUs needed without compromising quality.)
Another consideration with powered loudspeakers is keeping the cabinet sealed. The loudspeaker that is able to project sound for 50, 100 feet or more is moving air to do so. The inside of that loudspeaker cabinet is a pretty inhospitable environment with very high air pressures being developed. In a non-powered loudspeaker, this is fairly easy to manage—only a small hole for a connector is needed in an otherwise airtight cabinet. But creating a powered loudspeaker is not quite as simple as cutting an amplifier-sized hole in a cabinet and dropping an amp in. In a powered loudspeaker there are a lot of electronics in the box that need to be protected from the air pressure and vibration. There are also typically more connectors (power, signal, network), as well as LEDs, buttons and switches. All of these can cause air leaks, and even a pinprick hole in the back of a speaker can make a lot of noise, easily audible from 20 feet away. All connectors must be sealed, and all circuit boards amply supported to handle vibration—perhaps even a separate enclosure within the speaker to hold the amplifier and keep it airtight.
What's so good about it?
Nowadays, we have not merely integrated amplification, we have dedicated amp and signal processing per driver. What's more, these are now factory-installed and tested for absolute maximum performance and reliability.
From a manufacturer's perspective, the benefit of a self-powered loudspeaker is that we're in complete control. We know exactly what amp is driving which components; we can be more critical in our design of DSP, EQ, crossover and limiter parameters, since we don't have to account for a wide array of third party amps and DSPs, all with varying performance and specs. In short, we can get the best out of our loudspeaker by creating a completely known, closed-loop system, and provide the best protection—meaning the user has less to worry about.
Aside from the obvious performance advantages, there can be some added cost savings to choosing a self-powered loudspeaker where appropriate. With the amplifiers and processing now located within the speaker cabinet, there is no longer a need for a dedicated amplifier room, which takes up limited space and requires costly labor to assemble correctly. The nominal heat these self-powered systems produce is distributed around a much larger area as well, thereby eliminating the need for expensive air conditioning and climate control. And the short conduits for line level signal cable are far less expensive than the lengthy ones required to house bulky and expensive speaker cables. All these potential cost savings can often be reallocated toward upgrading other parts of the signal chain, or to simply reducing the cost of the project overall.
The challenges
One concern many people voice regarding self-powered loudspeakers is their reliability and serviceability. In practice, however, the failure rate of modern amps and transducers, particularly in the case of self-powered loudspeakers, is exceptionally low to begin with. Moreover, we have found that amplifiers tend to fail along a similar frequency as loudspeakers. In fact, many failed amplifiers are themselves the cause of loudspeaker failure. So while it's easier to replace an amp that has failed when it is mounted in an amp rack, the chances are fairly good that when that amp fails, you will also find yourself climbing a ladder to repair a loudspeaker, as well. And in practice, is that really any different from replacing a lighting fixture? After all, light bulbs burn out far more frequently than amps, and most facilities have some method of accessing their lighting fixtures when needed.
It's the network
One desirable feature that is available on a number of modern self-powered loudspeakers is remote supervision and control via a network of some type (e.g., CobraNet, etc.). With the ability to connect that network to the Internet, the installing contractor can potentially be forewarned of a service issue without a site visit, enabling them to provide repair before your operators even become aware that there is a problem.
Another advantage to networked systems is flexibility. With non-powered loudspeakers, typically a number of speakers are linked together on single amplifier and DSP channel, meaning that they can only be controlled as one unit. With powered loudspeakers, particularly those with networked control and DSP built in, each loudspeaker can be individually tailored to meet the need of its space and location. Compromises are removed, and better performance can be achieved.
Most manufacturers have introduced a range or two of powered loudspeakers, some with networking, some without. Renkus-Heinz offers powered, networked loudspeakers across almost all of its products, providing the ability to network an entire system, from the mains, to the delays, under balconies, foyer and lobby, etc.
For example, in a typical project the balcony fill system may use a single “delay ring” of multiple loudspeakers, all delayed by a single channel of DSP. The delay time chosen must be a compromise, since not all speakers will be ideally located. With a self-powered, networked DSP solution, each individual loudspeaker can have its own delay and EQ, individually optimized.
Where might they not be appropriate?
While powered loudspeakers are an ideal solution for the majority of projects, there are occasionally projects where the existing infrastructure (cabling, amp room, etc.) are already in place and fully functional, and only the speakers need an upgrade. In such cases, it may be easier and cheaper to just run a couple of extra speaker cables and change the speakers than to provide power and network connections at each location. Of course, you won't get the benefits of individual control for each speaker, but as we all know, sometimes we're faced with a compromise between budget and performance.
What's the latest?
Finally, there is a new class of loudspeakers that demands to be self-powered. These are the new “steerable” column or steerable array loudspeakers. These new systems take the concept of close-coupled electronics and control to the ultimate level, with speakers that offer dedicated amplifiers and signal processing for every driver in the array. This of course makes external amplification impractical, if not impossible, even for smaller systems. Steerable arrays require self-powering. In a column of 16 drivers, with each needing its own amp and DSP, it would be impractical to do this outside the box. Instead of needing one channel at 1,600W, we now need 16 channels of 100W, and 16 channels of DSP. Just the cabling alone needed to do this in a rack and run it to a speaker would be formidable. Containing it inside the speaker allows for shorter cable runs, lower gauge wiring, simpler connections, and more efficient electronic design.
From a systems integration perspective, these steerable arrays can offer practical as well as performance advantages over conventional self-powered loudspeakers, largely due to their ability to direct sound to where it is needed, while avoiding reflective surfaces. Often these steerable systems can be mounted flat against a wall surface, thereby minimizing the expense of getting power and signal to their locations.
Self-powered loudspeakers have the potential for maximum performance and reliability when compared with non-powered loudspeakers, and should be considered when their acoustic parameters of output and coverage match your design criteria.
