By Craig AndertonWhere you place your PA speakers has a huge influence on how the sound reaches your audience
With “personal PA” systems becoming increasingly popular for medium-size venues like cafes, houses of worship, and conference centers, it’s important to know how to get the most out of these systems. Much of a PA
Definition:
(Public Address) A sound system intended to provide audio coverage to large groups of people. setup’s effectiveness depends not only on the gearDefinition:
Musical or performance equipment. itself, but where you place the speakers, mixerDefinition:
Combiner, controller, and router for multiple audio or video signals., mics, and performers.
Although you need to consider technical issues (for example, you don’t want to place a power ampDefinition:
Abbreviation for either Ampere or Amplifier. next to a heat source, or drape mic cables over transformers), you also need to think about the impact on the audience. Speaker placement is especially important because the sound needs to reach every corner of a venue, with no “dead spots.” We’ll explore the optimum placement for speakers, but first, please observe these rules regarding PA connections for power and audio.
- Rule #1: Make all your connections—both audio and power—first.
- Rule #2: Turn on the amplifierDefinition:
1. A device that increases the voltage or power of a signal. 2. In music performance, a device such as a guitar amplifier that includes speakers and controls to increase the sound level of acoustic or electric instruments. or powered speakers. Plugging or unplugging either audio or power connections while the system is on can produce loud pops. These are bad for your speakers, bad for your ears, and terrible for your audience. - Rule #3: Power-up your system with the mixer’s master volume control (or powered speaker level controls) at zero—full off. Turn up the gainDefinition:
The amount of amplification provided by an amplifier circuit, expressed in dB or numerically as in "3X" = "3 times". only when you know that all is well.
Now that’s out of the way, let’s figure out where to place the speakers.
Positioning the Speakers
Most small-format PAs use a large subwooferDefinition:
A low-frequency speaker, typically optimized for response below 120 Hz, for augmenting full-range sound systems. for the low frequencies and a smaller unit with high-frequencyDefinition:
A value, expressed in Hertz, that indicates how many cycles of a periodic signal occur in one second. drivers (Fig. 1). The latter may be a column that mounts directly on top of the subwoofer or a smaller speaker that mounts on a separate tripod. Often, these PAs allow for “daisy-chaining” multiple units for greater coverageDefinition:
In film making, additional footage shot from additional cameras that's useful for editing and backup. and wider sound dispersion. In other words, you can interconnect two or more systems to cover the left, right, and center areas of where the audience sits.
Place all speakers in front of any mics used by the performers, preachers, or presenters (i.e., the speakers should be closer to the audience or congregation), with as much distance as possible between the mics and speakers. The closer the mics are to the front of the speakers, the higher the chances of feedbackDefinition:
1. A squealing, chirping, or ringing sound when a microphone feeding a loudspeaker picks up audio from that loudspeaker. Also called howlround. 2. The state where a device's output connects back to the input.. Caution anyone using a wireless mic (or a conventional mic with a long cable) not to step in front of the speakers. It may help to put tape down on the stage or floor that draws a line between the speakers. Advise anyone using a mic not to cross over that line.
In any event, avoid using microphones with an omnidirectionalDefinition:
A pattern describing a microphone, radio antenna, or loudspeaker that radiates or picks up in all directions equally. pickupDefinition:
1. Transducer attached to a musical instrument that converts mechanical vibrations into an electrical signal for recording or amplification. 2. The part of a phonograph that translates mechanical motion from grooves into electrical signals for subsequent amplification. pattern, which picks up sound from all directions. A cardioidDefinition:
A microphone's heart-shaped directional pickup pattern. mic like the Shure SM58S, which picks up sound from the front but rejects sound from the back and sides, works well for liveDefinition:
Live broadcast of an event or program without substantial delay or editing. sound. A hypercardioidDefinition:
A directional microphone pickup pattern, narrower than a cardioid or supercardioid pattern, with a small out-of-phase node at the rear. mic like the Audix OM3 has even greater back and side rejection. You always want the sound from the person using the mic to be much louder than any residual noise picked up from the speakers.
Some personal PAs mount the speakers on tripods. When using speaker-mounting tripods, the speakers should be at least just above the highest people in the audience—and tightened down so they can’t move or rotate on the tripods. This is particularly important with systems like the Peavey Escort 3000, which don’t use a subwoofer but instead, include the low-frequency and high-frequency drivers in the same enclosure (Fig. 2). As a rule of thumb, if a tall person walks in front of the speaker, the speaker should be higher than that person; in some venues, mounting the speakers even higher may provide better coverage.
This is important because high frequencies are very directional, so if everyone in a room can see the high-frequency drivers in a speaker, they can probably hear the high frequencies. Low frequencies are not only less directional, they can even bend around objects in a room. This is why systems invariably place the bass speaker on the floor, and the high-frequency speakers on stands, tripods, or extenders that attach to the subwoofers.
Some powered monitors (but generally not column-based ones) allow stacking units for wider coverage and more power, while other systems “split the difference” by being more modular. For example, the Bose L1 Model II System – Double B1 Bass Package includes two subwoofers (Fig. 3). Although one subwoofer is all that’s needed for most applications, being able to stack the subwoofers provides more powerful bass for DJs, electronic drums, and bands.
Stacking subwoofers is easy, because they usually sit on the floor. However, if you plan to stack powered monitors, make sure the combination is stable, out the way of the audience and performers, and can’t tip over. The last thing you want is a lawsuit because someone knocked a speaker column over on a child. It’s your responsibility to set up speakers so that their location won’t cause problems.
For the best coverage with two speakers (note that in most cases, two speakers aren’t there to provide stereoDefinition:
A two channel signal simulating a sound space, typically played through two speakers., but to increase the coverage of a monoDefinition:
Short for Monophonic. An audio program, recording, or hardware device/software routine that produces or processes a signal with only one channel. signal), mount them toward the left and right sides of the stage, and angle them slightly toward the middle of the room. One common method to choose the optimum angle is to pretend there’s a line that goes down the middle of the audience. Aim the speakers at a point approximately 75% of the way toward the farthest end of the room (Fig. 4).
Because sounds bouncing off a side wall are generally less of a problem than sounds bouncing off a wall behind (or in front of) the speaker, this type of setup can also help produce the best possible sound for people in the front and back of the room.
Positioning with Respect to Walls
Because the typical room is filled with reflective surfaces, the audience will hear sounds reflected off the walls, ceilings, and various objects—not just the sound coming out of the speakers themselves. This can be problematic because the reflected sounds will arrive later than the direct soundDefinition:
1. Sound arriving directly from the source, not reflections. 2. When spelled DirectSound, a mostly obsolete native Windows audio driver., which makes speech less intelligible, and with music, makes it more difficult to differentiate among instruments.
Sound travels at about one foot per millisecond (a thousandth of a second, or ms). Most listeners don’t object to delays under about 30 ms, but delays longer than 30 ms produce an audible echoDefinition:
A repeat of an audio signal. effectDefinition:
A device or software program that modifies some aspect of audio or video. With audio, the term is used interchangeably with signal processor. that can be distracting. Ideally, for an audience member, the difference in distance between the speaker and the nearest reflective hard surface (which produces the loudest reflection) will be 30 feet or less. In most rooms, this isn’t always possible, but it’s a goal worth trying to achieve.
However, distance can also be your ally. Even if the reflection path is longer than 30 feet, if there are a lot of people, drapes, objects, and the like between the audience and the wall, the reflections will weaken considerably. Reflections are most problematic in smaller spaces with reflective surfaces.
Another point to consider is where you place the subwoofer in a room because this can influence the amount of bass. Bass frequencies have a long wavelengthDefinition:
The distance between crests of a wave. For example, in air a 1000 Hz tone has a wavelength of slightly less than 1 foot., so placing the subwoofer in a corner will cause the bass to reflect off the walls, thus reinforcing the main bass signal. This trick can make one subwoofer seem like two. Placing a subwoofer a few inches away from where a wall meets the floor can produce similar results, but the results aren’t as dramatic as placing the subwoofer in a corner.
Where to Place the Monitors for the Performers
Because the performers or presenters are standing behind the speakers, they won’t hear themselves. In many cases, this doesn’t matter—but it usually does matter for musical ensembles, who need to hear each other as they perform.
In-ear monitors are the preferred choice by many professionals. The sound is clear, the mix can be customized for each person on stage, and feedback isn’t a concern. However, some performers prefer “wedge” monitors (Fig. 5). These point up to the performer at a 45-degree angle, away from the audience and other people on stage; with a quality cardioid or hypercardioid mic, the pickup pattern will tend to reject the sound of the monitors.
It’s All About the Setup
Experimenting with speaker placement before the event can be very helpful. But be aware that as people fill up a venue, the acoustics will change—for example, if it’s a cold winter night and people are wearing thick coats, the fabric will absorb sound. If the audience consists primarily of children, you may not want the high-frequency drivers mounted as high on their stands or tripods.
Fortunately, many PA systems now offer remoteDefinition:
A broadcast from the field, not from the studio. A Remote Control. control apps, as well as the ability to stream in audio from a smartphone or tablet (or feed audio in from a 1/8” stereo jackDefinition:
A connector, normally female, that works in conjunction wit a plug. Usually located in a piece of equipment, or as part of a cable.). This means you can play music as you walk around the venue, and use the app to adjust the PA’s controls for the best possible sound.
Of course, a personal PA isn’t going to fill a stadium with ear-splitting volume—but proper speaker placement will help you get the most out of any PA system, large or small.
