Here’s some hints and tips to make purchasing and operating a portable audio system easier while avoiding some of the problems you might face. Answering a few questions before you start shopping will help you focus on the types of products that will work best for your situation.
How many people do you want the sound system to handle?
A basic starting point for an indoor sound system is approximately 1 watt per person. This would be a good formula if you are only amplifying spoken word in a quiet environment. If you have music and singing, you’ll need to at least double the power. Of course, if the ambient noise level (read noisy congregation) is high, even more power will be required. Outdoor sound systems will require more power still, as there aren’t walls and ceilings to confine the sound waves.
What does the sound system need to amplify?
A system for speech alone doesn’t need to produce the entire frequency spectrum needed for music. There is little need for a subwoofer in a system used for spoken word. In fact, loudspeakers with smaller woofers will actually do a better job of reproducing the vocal frequency range.
Who will be operating this system?
Since this is a portable system, it will be set up and taken down for storage, and of course you must consider who will actually operate the system. Avoid complexity whenever possible, particularly when volunteers are on your crew. Color coding and other labeling are a must to help these folks quickly and reliably get the system up and running. Using a grease pencil, you can make marks around knobs or beside faders to help ensure they are properly set.
Choosing the gear
Now you can start shopping for the gear you’ll need for the system. Planning the system is best done by thinking through the audio path, starting with your microphones and ending with the loudspeakers.
1. The microphones.
How many will you need? This really depends on the type of service you conduct, and what needs amplifying. Pick the right microphone for the source. A handheld dynamic vocal microphone may not do a very good job picking up a choir or a piano. Microphones are one of the most important parts of your system as they actually do the conversion from acoustic to electrical energy, so choose these carefully.
2. The audio mixer.
The mixer will be responsible for combining all the sources and sending them out to the main speakers, and other places too. It will need to accommodate all the microphones and other sources (Keyboards, CD players, electronic drums etc.). Once you know the number of inputs, add a few extra just for good measure. This way, future expansion can easily be accommodated. You’ll also need to consider how many outputs are needed. Almost all mixers have a stereo output for your main speakers, but what about all the other needs? If you are using monitors for the performers, you’ll need an aux, or auxiliary send for each of them. Having a few extra auxiliary sends is really a must for adding things like reverbs and other special effects later. Also, don’t forget recording and other rooms or areas where you may need to send sound.
You can also get mixers with power amplifiers built in them. These powered mixers can really help simplify the system, combining separate components.
3. Amplifiers and Loudspeakers.
You have a couple of choices when choosing the amplifiers and loudspeakers. You can use powered, or active loudspeakers that have the amplifier inside the cabinet, or the traditional design that uses separate amplifiers and passive loudspeakers. There are benefits to both styles.
If your system is always used indoors, powered or active loudspeakers should be considered. Remember, they will each need AC power along with a signal cable. These cabinets will have some controls on them, so make sure they don’t accidentally get changed once you’ve set them.
Using separate amplifiers and unpowered or passive loudspeakers allow you to place the amplifiers in a safe place, keeping them cool and dry. There is only one cable from the amplifier to the loudspeaker, simplifying hookup. Incidentally, there are many more passive loudspeaker models in the market to choose from.
When choosing the correct model loudspeaker, first consider what you’re amplifying. Voice or speech reinforcement systems typically can use a smaller woofer and smaller cabinet. Music will almost certainly need more low frequency extension, so a cabinet with a larger woofer or possibly a separate subwoofer might be needed. Pay attention also to the dispersion of the loudspeaker. This specification is given both horizontally and vertically. Try to match the pattern to the audience area you need to cover. Note that loudspeakers with broad dispersion patterns won’t carry, or “throw”, as far as a model with a narrower pattern.
Whether active or passive, the goal here is to generate acoustic energy for the audience to hear. Since human ears are on our heads, it’s important get the loudspeaker up off the floor and aimed at the audience. Using tripod stands will make this both quick and safe.
The very best sound systems can be undermined by a failure in the smallest part of the system. Remember this when you shop for cabling, cases and other “infrastructure” items. These items will get the most use (read abuse), so plan on more frequent replacement. AC power conditioners should be used to protect the gear and performers as well.
Hopefully you have a better understanding of what’s needed to get the best performance from your sound system.