Amped Up: Active Speaker Designs
Less Cost for a Total System?
For years, when one thought of active speakers, they thought of studio monitors. Today, when one picks up a trade magazine it is obvious that about every speaker manufacture has an active loudspeaker line.
I often hear people ask, “What’s so special about active speakers? Why would you want to put all of your eggs in one basket? What are the advantages of active speakers? Aren’t active speakers overpriced?” Read on, let’s find out.
Active speakers have been around for over twenty years. Paramount studios was one of the first to have custom built active speakers built for them by AB Systems in the late 1970’s. Meyer Sound was the first to perfect and successfully market active speakers. These days JBL, Tannoy, Mackie and EAW are at the picnic and reaching for their piece of the pie.
ACTIVE OR POWERED
What’s the difference? Active speakers are also known as powered speakers. I refer to them as “active”, because there is much more happening inside the box besides amplification. An active speaker consists of a box, drivers, electronic crossover, compressor/limiters, delay, equalization and amplifiers.
The truth is powered speakers should sound better than conventional speaker designs. All of the crossover points, equalization, time alignment, compression, limiting and amplification matching are finalized to meet the manufacturer’s intended sound.
The key here is the intended sound quality! We all feel that we can do a better job tweaking the speaker than the manufacture, don’t we? What most people don’t understand is where the break point is.
Today, custom speaker processors give speaker manufactures more control over crossover points and equalization but certainly not with power amplification to speaker component matching. Proper gain or power (wattage) matching is one of the most important elements of making a speaker sound good and insuring the longevity of speaker components.
I come from the old audio school of thought that there is no such thing as too much “available” power. There is, however, such a thing as wasting money on power. You don’t need 5KW power amps for the high frequencies.
Don’t forget though, that under powering any speaker can be as harmful as overpowering. The key to success is controlling or harnessing amp power. Quality active loudspeakers match amplifier power (wattage) to component need (i.e. power handling). The manufacturer already did the math for you.
BOLD, BUT TRUE
Powered speakers, as a total sound system design, cost less than equivalent conventional component PA systems. For this bold statement to be true, one must consider everything that makes up a PA such as: crossovers, equalizers, compressor/limiters, speaker processors, amplifiers, rack space and cabling.
Material cost of an active speaker remains the same when compared to a passive type box.
Further, active and passive designs both require crossover networks, equalization, compressor/limiting, time alignment and POWER. Don’t under estimate this reduction in truck space. With powered speakers there is much less gear to haul. Most importantly, once your loudspeaker system goes “active”, the total system cost is reduced. Lets break this down into fundamentals, and see how this is achieved.
The audio phrase “front-end” refers to the first part of the signal path. In this case, it is the input. Depending on the speaker application, this input will be at line level, mic level, or both.
A good front-end design is essential to prevent those nasty RF signals from bleeding in the audio signal. It is pretty embarrassing when you get a call from the local church complaining that a local trucker, on his CB radio, bled thru the sound system during the sermon saying “Some Smoky is on his a—-“.
For many small jobs, an obvious cost savings comes when no mixer is required. Still, every advantage comes at a price. As such, from a design and material cost viewpoint, quality front-end design is one of the few areas where of active speakers add direct cost.
The back end of the electronics in an active speaker is where processing, such as active crossovers, EQ points, compressor/limiters and delay, takes place. These multiple functions are why considerable savings can be via internal processing compared to external digital speaker processing.
With an active speaker, electrical parameters are pre-determined by the manufacturer. This is not all digital processing wizardry either. Precise non-variable filter networks can be implemented using low cost analog components. In fact, it is still cheaper to use analog components compared to operating in the digital domain.
As soon as there is a need to have external processing adjustments, this may no longer be true. However, if parameter tweaking is ever allowed, the main purpose of an out-of-the-box, acoustically aligned speaker would be effectively eliminated
Eventually, the digital domain will become more cost effective over analog, especially when audio signal remains all-digital from the mixer to the loudspeaker front-end. The high cost of digital is the conversion from analog to digital and from digital back to analog.
DSP and the microprocessor are the inexpensive part of a digital audio design. As of today, it is still more cost effective to use analog components, for active speakers, rather than digital.
There are two different approaches to power supply designs for all amplifiers, switching and conventional (transformer). Both serve a strategic purpose.
The big difference between the two approaches is cost and weight. Conventional transformer types are more cost effective for power requirements under 200W.
Switching power supplies are always lighter in weight and are more cost effective for power requirements over 200W especially in the 1KW and above range. The downfall for switching power supplies, if there is one, is that it is harder and more expensive to get safety and CE certifications.
The essential difference between stand-alone amplifiers and active speakers is the required wattage the power supply has to deliver. Traditional component amplifiers must be designed to handle various external loads. This requirement inevitably causes component amplifiers to be overbuilt.
With active speakers, speaker load is predetermined, as is the maximum current load. If current load is predetermined, you can reduce the requirements of the supply thus, reducing the design cost. As soon as the external elements faced by stand-alone amplifiers are removed, a designer needs only to implement the exact amount of circuitry required.
Maximum current requirements are then fixed and cannot be altered from an outside source. Once you know this, the need for short circuit protection, additional output transistors, larger pre-drivers and massive heatsinks are practically eliminated.
Another active speakers advantage over stand-alone amplifiers is weight loss (i.e. less metal). The elimination of large heavy heatsinks and power supply transformer seriously reduces overall system weight. The need for an expensive, heavy rack mount chassis is also eliminated, and should yield further cost reductions, right? One could only hope!
I am not trying to say that active speakers are the solution to every audio application. There will always remain a need for traditional PA systems. My point is that anyone designing a new system should always consider active speakers as a total system option.
I suspect you will find out that you might soon find you have some extra cash in your pocket at the end of the day. Another potential payback will be fewer down-the-road headaches, as the PA system will keep that original factory sound longer and the number of end-user “adjustments” will evaporate.
Jeff Kuells is a Performance Audio Engineer and Audio Manufacturing Consultant. Previously Director of Engineering for a major amplifier manufacturer, Kuells can be reached via e-mail at email@example.com
September/October 2001 Live Sound International