The libraries of the 21st century are no longer merely repositories for books. Libraries now provide an increasing range of different services. Libraries have also become a key meeting place for an exchange of ideas and information. With a growing need for means to reach larger groups in a library setting, the public-address system remains one of the best investments for such a task. The applications of a public address system are endless. But even if you will be purchasing a PA system for a similar environment as one listed, how do you know which one to choose? This guide will help you narrow our selection down by answering some simple questions, and ultimately choosing the PA system that will be perfect for your needs.

Who will be using the PA system?

You may already own a microphone, or you're planning on adding your new PA system to a shared environment where multiple users will supply their own mics. In these situations, select a system that does not include a microphone. However, if you’re building a presentation system from the bottom up, you may want a product that includes a microphone. Most come with a wired microphone, but all are compatible with wireless mic systems. Also, some PA systems include two or more microphone inputs, thus enabling more than one speaker to use the system simultaneously.

What features would assist your presentations?

  A PA system that is AC powered doesn’t have to be recharged, and in some cases allows more volume. However, it does not give you access to the quick and easy portability of a PA system.

  Some systems come with media players that can play their source material while also using the microphone jack for vocal applications (also known as a “voice over”). These include a CD and/or tape player that is built to be more rugged than common audio players, with added skip protection. Nevertheless, PA systems do include input jacks for additional media sources, if you’d like to supply your own.

What is the difference between wired and wireless microphones?

Wired microphones are simply microphones that are plugged into your PA system. There are two types of wireless mics: lapel mics and handheld mics. Lapel mics usually come as two separate pieces, a “body pack” that works as a transmitter and a receiver that plugs into your PA system. A handheld wireless microphone looks just like a wired mic and acts as the transmitter.

How large will your audience be?

The audience size that a PA system’s audio output can cover is affected by several variables, including amplifier wattage, mixer voltage, and the size of the woofer speaker (to reproduce the lower frequencies of your source material, be it voice or music). We’ve conveniently listed our selection of PA systems as being ideal for small, medium, or large audiences. If the size of your audience will fluctuate from application to application, many systems have companion speakers (listed as the PA systems’ related product(s)), to expand your crowd coverage. Building on this idea, PA speakers can also be daisy-chained (which is similar to adding one companion speaker, only it involves a total of two or more output devices).

How many watts do you need?

A general rule of thumb when determining how many Watts you need is 1 Watt per person in your audience . Depending on the venue you are working in, this may change. When working outdoors, or in other areas where you will need to over come loud conditions you will need at least 250 Watts. For smaller rooms, you will most likely not need more than 50 Watts.

Additional Information

PA systems can amplify sound at approximately 100 to 140 decibels, or dB. This is a measurement of the sound pressure level, or SPL, and is determined by a combination of microphone sensitivity, mixer pre-amp voltage, main amplifier wattage, and speaker efficiency. As a comparison to these figures, here is a simple list of common every day sounds, and their respective decibel levels:

• Threshold of hearing: 0 dB
• Rustling leaves: 20 dB
• Quiet whisper: 30 dB
• Normal conversation: 60 dB
• Loud singing (three feet away): 75 dB
• Food blender: 90 dB
• Power mower: 107 dB
• Chain saw (three feet away): 117 dB
• Amplified rock & roll (six feet away): 120 dB
• Jet plane (100 feet away): 130 dB

Glossary of Key Terms

• AC/DC powered: A/C(alternating current) meaning it must be plugged into a wall, or D/C (direct current) meaning batteries can be used.
  Balanced Speakers: Allows less induced noise.
• Decibel: The degree of loudness.
• Impedance: Measured in ohms, impedance refers to the resistance of a circuit or device to AC. More power (watts) will flow through a speaker with a low impedance than one with a high impedance.
• Ohm: The measurement of electrical resistance and system impedance. It is a measure of the degree to which electrons are limited in both velocity and quantity in passing through a circuit.
• Unbalanced Speakers: More susceptible to induced noise problems but are less expensive than balanced speakers.
• Watts: A measurement of power. Basically, the more watts your speakers have the louder your sound will be. If you try to play extremely loud sounds out of a low watt sound system you may blow your speakers.