The “personal PA,” like the Anchor Audio Bigfoot (which will be the subject of a review in a future blog post), has taken the world of live sound by storm. It’s now possible to have a PA system that can blast out sound, be easy to set up and tear down, and fit in a car. But myths abound about PAs, so we’re here to help sort out the confusion.
1. Analog is better than digital. Let’s get this out of the way first. With guitar amps, analog, tube-based designs can color and distort the sound in ways that are subjectively pleasing. However, the goal of a PA system should be clean, distortion-free, reliable sound, with high power levels. It’s also important to remember that digital, Class-D amplifiers are smaller, lighter, more reliable, generate less heat, and provide more power in a more portable package than typical analog amplifiers (Fig. 1). Some early Class-D models had a reputation for “brittle” sound, but like all digital technology, power amps have improved exponentially since they were introduced.
2. 3-way speaker systems are always better than 2-way systems. While this can be true, it often isn’t. A properly designed 2-way speaker, with separate low- and high-frequency drivers, can provide a balanced, powerful sound that covers the full frequency range. It’s harder to design a 3-way system, because it requires two crossovers. This can introduce more errors than the single crossover used in 2-way systems. The way the speakers generate sound is also different. 2-way systems have to coordinate only two sound sources (the high- and low-frequency drivers), whereas a 3-way system has to coordinate three sound sources. That said, there are great 3-way systems and not-so-good 2-way systems, but the overall sound quality depends on more than just the number of speakers. There’s no reason why a 2-way system can’t provide exactly what you need. (By the way, note that the same issues apply to studio monitors and hi-fi speakers.)
3. To evaluate a system’s power, look at the specification for watts. Unfortunately, most wattage specs are meaningless. When comparing two systems, unless you know the protocol that was used for testing the speakers, it’s an apples-and-oranges situation. Other differences are speaker efficiency (an inefficient speaker will turn power into heat more readily than an efficient speaker), and the acceptable amount of distortion. For example, an amp could be rated at 100 watts with 0.5% distortion, or at 250W—but with 10% distortion. Without knowing this kind of information, you’ll be doing something akin to testing a car’s gas mileage by comparing one that’s speeding down a highway, with another coasting downhill in neutral.
You can put two systems with the same wattage spec side by side, turn them up to maximum, and feed in the same input level—yet one can sound cleaner and louder than the other. This is probably because they used different testing procedures. The louder, cleaner one probably based its rating on the maximum clean power level before distortion. This makes sense, because once an amp gets past the point of distortion, a properly designed system will have a limiter kick in, so the system won’t play louder anyway. With the one that doesn’t sound as loud, the design might allow the amp to distort before the limiters engage, or the power rating could even be based on no protection circuitry (like a limiter) engaged at all. The result is essentially a theoretical value—it’s like saying an amp can deliver 2000 watts, but forgetting to add that this much power would blow up the speakers. And remember, output depends on speaker efficiency as well as wattage.
Until the industry adopts a standard test procedure for personal PAs, take wattage ratings as a guide, not gospel. It’s not that companies are necessarily trying to pull the wool over your eyes; it’s just that different companies measure wattage differently. Your best option is to stick with reputable, known brands, and put different systems through their paces in a performance situation—you’ll find out which ones deliver loud, clean sound, and which ones don’t.
4. Whether a system can cover a venue depends on its power rating. Although this is partially true, dispersion (given in degrees) is an equally important spec. This can also influence your buying decision, because wide dispersion at high volume levels is harder to achieve than narrow dispersion—but you may not need wide dispersion in a rectangular-shaped venue, where the sound system is projecting from one of the shorter sides of the rectangle. Narrower dispersion means the system will be able to concentrate more sound over a narrow “sweet spot,” and it won’t matter that the volume drops off rapidly away from that sweet spot. On the other hand, speakers with wide dispersion spread sound more evenly throughout a room, which gives greater coverage for a given amount of power (Fig. 2).
For solo acts, you need a PA and a guitar amp. This is only a half-myth. Today’s multieffects for guitar, like the Line 6 Helix and Kemper Profiler amp, nail a variety of iconic amps and cabinets. They don’t need to go through a guitar amp; in fact, what they really want to feed is a flat-response, full-range amplification system like a PA. So if your PA system has a spare input, plug in the multieffects’ output, and you’re good to go.
However, the reason why this is a half-myth is because some guitar amps have “signature” sounds that are difficult to duplicate digitally, and perhaps more importantly for some guitarists, playing through an amp has a different “feel.” If that’s the case, it’s a tough call whether you want to retain that feel, or forego that in favor of a simple, more reliable, more compact setup that still sounds to your audience very much like, if not identical to, a guitar amp.
So there are the five myths. Just remember, your ears are the most remarkable piece of “test equipment” ever created: the test is in the listening. But also remember that the personal PA field is very competitive, so when dealing with reputable brands (i.e., not knock-offs), you’re not going to find bad products—and as a rule of thumb, PA systems in the same general price range will likely perform similarly. Because the technology is quite mature, your buying decision may depend more on whether a PA system has the features you need (number of inputs, mounting options, size and weight, etc.) than a raw wattage spec.