Over the past several months, I have been covering the various parts of the audio, video and lighting (AVL) signal chain and detailing how they affect overall application design. So far, I’ve looked at design considerations for both live and playback sources, covered audio, video and LED video processing, and addressed distribution. Now, we’re moving on to the important design considerations for AVL outputs, starting with amplifiers and speakers. In today’s post, we’ll look at the types of speaker form factors and coverage patterns, and in upcoming posts, we’ll look at other design considerations such as mounting, zoning and more.
Select Amplifiers and Speakers Together
When we discuss audio outputs, we almost by necessity must talk about amplifiers and speakers together. These two integral pieces combine to make the “output” section of the audio signal chain. The amplifier takes the distributed audio signal and boosts the voltage of the electrical signal, thus increasing the output volume. That speaker-level signal is then sent to the speakers input connector. The frequency dividing network (passive crossover) then distributes that signal through one or more drivers (also called transducers) that convert the electrical signals into soundwaves. Waveguides control the output path of the audio signals, so they follow specific coverage patterns, and then the sound is directed to the listener.
For all of these processes to work correctly, it’s important to make sure you coordinate the selection of your amplifiers and speakers. Otherwise, you run the very real risk of damaging your equipment. If you need to get the maximum output the speaker is capable of delivering, choose an amp with twice the power as the speaker’s root mean power (or RMS) rating, a measurement referring to the amount of continuous power the speaker handles. This lines up the peak signal capability of the amplifier with the peak signal capability of the loudspeaker. However, you should use a limiter to ensure the amp is never “clipped” (i.e., sends even more power to some components of the speaker and can blow them out). If you don’t need that much power, then a lower powered amplifier will suffice (one that gets you to the sound level you need). If you need help selecting the right amplifier, the “How much power can my speakers handle?” section of Crown’s “How Much Amplifier Power Do I Need?” whitepaper is a great place to start.
Of course, to match your amplifier and speaker, you need to decide what you need first. Much of this involves determining how loud the audio output will be. There are actually a number of factors that affect the sound pressure level (or SPL) in a particular space, including speaker sensitivity, signal variability and more. For an overview of this topic, read this article to learn more about how to ensure your sound system is loud enough.
Types of Loudspeakers
Beyond loudness, there are a number of other factors involved in selecting the right amplifier and speaker. However, we should define the basic types of speakers you might encounter first:
|Box Loudspeakers: These are the traditional box-shaped loudspeakers that have been used since James B. Lansing, founder of JBL, got his start with speakers back in the 1920s. Sometimes referred to as “point-and-shoot” loudspeakers, they come in a variety of sizes and are useful in a wide range of applications.|
|In-Ceiling Loudspeakers: These loudspeakers are designed for installation flush in the ceiling and pointed downward toward listeners.|
|Line Array Loudspeakers: These specially designed loudspeakers were created for easy stacking on top of each other. When combined together, they can cover a large area with better pattern control. The longer the array, the lower the frequency the vertical pattern extends to, reducing sound energy onto the stage and ceiling.|
|Column Loudspeakers: These are a hybrid of line array and box loudspeakers. Column loudspeakers combine multiple speakers to replicate the effect of an array, but in a fixed format in a single cabinet.|
|Application-Specific Loudspeakers: There are a variety of speakers that use unique form factors to meet the needs of a specific application, such as pendant speakers, landscape speakers and soundbars.|
The basic job of audio output is to ensure the audio reaches the people you are targeting at the appropriate volume. One part of this equation is loudness, as discussed above. The other part is audio reaching listeners, something that is largely determined by the speakers’ coverage pattern.
The coverage pattern is what measures the “shape” of the sound output from the speaker. This shape is determined by a variety of factors in the individual speaker cabinet and typically listed in speaker specifications under “Coverage.”
Ceiling speakers coverage is described as “conical” (cone shaped), with the volume loudest at the center. The stated coverage pattern describes the point the SPL drops to –6dB. This specification is listed as an angle in degrees, which describes how wide of an area the speaker will cover in sound. The wider the angle, the larger the coverage area at any distance from the speaker. So, if a speaker has a coverage of 120° conical, it will cover more floor space than a speaker with a coverage of 90° conical when mounted at the same height.
Of course, the coverage expands as you get farther from the speaker, but the SPL goes down as well. The –6dB point is typically 60⁰ off-axis. Ceiling speakers with more narrow coverage often have higher “sensitivity,” a term that refers to the SPL the speaker emits from a 1-watt input measured at a 1-meter distance. Because of this, a narrow-coverage speaker is a better choice for higher ceilings, where wider-coverage speakers are often better lower-ceiling installations, since fewer speakers may be required to cover the same area.
Coverage for box speakers may be rectangular or conical, with rectangular specifications listing both a horizontal coverage angle and a vertical coverage angle. Again, as with ceiling speakers, the larger the coverage pattern, the more space that will be covered at any given distance, but at a loss of sound pressure. Please note, I’m speaking in generalities here, and coverage patterns and sensitivity for speakers can vary widely, so it’s important to check the specifications and consult with a sound engineer when selecting the appropriate model for an application.
A specific line array cabinet works similarly to a box speaker, as it has rectangular coverage. However, the specification only lists the horizontal coverage, as the actual vertical coverage of the overall array installation depends on how many speakers you have in the array and how the overall array is configured. The more cabinets you have in the array, the larger the vertical coverage.
But there is a lot more to amplifier and speaker design than selecting the form factor and coverage pattern. We’ll look at some of those considerations in our next article on installation challenges.
Do you have insights on selecting the right amplifiers and speakers for a system design? Share them in the comments.