In our ongoing look at the audio, video and lighting (AVL) signal chain, I’ve been detailing how each section affects the overall application design. In previous posts, I looked at live and playback sources, audio, video and LED video processing, and distribution. When we moved on to design considerations for AVL outputs, I started with amplifiers and speakers in what will be a three-part sub-series. Last time, I looked at speaker form factors and coverage patterns. Today, I’m moving on to some general installation considerations, and then next time, I’ll look at the difference between high impedance (70V/100V) and low impedance (4 ohm/8 ohm) speaker systems.
Selecting the Right Place to Mount Your Speaker
While many of the design considerations for audio output are the same for both installed environments and portable/touring applications, there are some obvious differences. For permanently installed systems, the largest unique concern is with the mounting location. There are a number of different places you can mount a speaker, and each provides its own unique challenges and considerations.
For example, we mentioned ceiling speakers in the previous post. When people hear this term, they most often think of circular, in-ceiling speakers that are designed for mounting in the ceiling with only the grill showing. These speakers can be mounted in a variety of ceilings, with mounting options available for a wide range of materials. However, depending on the application, you may prefer other ceiling mounting options. While you can certainly use circular, in-ceiling speakers for dropped ceilings, for example, you can also use lay-in speakers, like the JBL LCT 81C/T, that are designed specifically for dropped ceiling applications. These speakers lay directly into a two-foot-by-two-foot suspended grid ceiling and don’t require cutting ceiling tiles. Alternately, for certain applications where sound is directed at a specific location within a larger space, especially in locations with large ceilings and a potential for echo, pendant speakers are a better fit for ceiling mounting. In other words, there is a wide range of ways you can mount speakers from the wall to the ceiling to the floor, with specialized speaker designs and mounting for each. The goal for picking a speaker is to fully consider the coverage you want to achieve and then pick the mounting location and coverage pattern to match.
Getting Proper Coverage When Your Mounting Location is Predetermined
Of course, in certain applications, the mounting location is already preset. In applications that are designed for performances and events with a performer, the sound is generally expected to come from the same direction as the performance. House of Worship facilities and concert venues want the sound to come from the central point of focus (that is, the stage or presentation area). For example, a sound engineer might have the option to adjust the aiming angles of the speakers, but he or she has to use existing rigging or structural suspension points. Such installations may be logistically problematic for a number of reasons, and may not be the most desirable, but they must occasionally be used. Audiences ideally want to localize the sound source to the stage. The addition of a proximity speaker, placed above or near the presenter or sound source, can help ‘pull’ the image back to this point of origin. As humans, we tend to localize the source to the first arrival. Adding delay time to the speakers beyond this proximity location makes for a more natural listening experience.
That said, even in other installed speaker applications (such as public address systems), it still might not be possible to mount the speaker in the ideal location to get suitable coverage without echo. This may be due architectural issues that limit where the speaker can be installed or it may be due to aesthetic concerns (often, it’s both). In these cases, speakers with beam steering capabilities, like the JBL Intellivox and CBT Series, provide a good alternative, as they can adjust the directionality of the sound either through software control (Intellivox) or with physically adjusting the speaker itself (CBT Series).
Using Zoning to Handle Multiple Coverage Areas
In addition to looking at where the speakers are installed in a space, you also need to look at how many different spaces you have that need speakers. Specifically, you need to consider sound “zones”—the different areas where you might need to individually control the volume or content people hear. For example, different spaces might have different ambient noise levels, depending on the size of the space, building materials, number of people, etc., and that might require different volume levels and frequency adjustment for each area.
Alternatively, certain areas, such as the lobby of a restaurant, might have seating announcements while other areas, like the dining areas, might only want background music. In either case, zoning allows the system designer to send different content to each area. Each different zone requires a separate amplifier channel (or two channels for stereo applications), so it’s important to understand zoning when planning your audio output design.
Outdoor Installations and Other Public Areas
When speakers are going to be installed in public areas, particularly outdoors, there are some additional concerns that should be addressed as well. You should never install indoor-only equipment in an outdoor environment. Speakers that installed outdoors should be outdoor rated. To gauge how effective the device will operate in outdoor environments, you can look to the device’s IEC rating, which rates how much the device protects against dust and water getting into it and causing damage.
You also need to address life safety considerations. Organizations, such as shopping centers, hotels, casinos, theme parks, airports, train stations and other buildings that open their grounds to others, especially the general public, are typically held to a higher government standard. These places face a large number of government regulations to ensure sufficient care has been taken regarding fire detection, public address systems and more. Speech communicated over the speakers need to be highly intelligible if they are used to distribute life safety messages in noisy environments, a capability that is measured using a number called the speech transmission index (STI). Achieving a specific STI number for voice evacuation systems is a requirement than differs regionally. Check out this article on life safety to learn more.
Of course, this is just the tip of the iceberg when it comes to designing a speaker installation. To get the best performance out of your system, it’s always best to consult with an audio engineer. Hopefully this post has helped you consider some of the important topics you need to look at when designing an AVL system.
Do you have insights into proper speaker installation? Share them in the comments.