Public Address System Buyer’s Guide

A public address system is a set of audio equipment that allows you to electronically amplify and distribute sounds over a designated area. If you’re in the market for a PA, before you make a purchase, here are several things you should first consider:

• Size of the venue
• Number of people in the audience
• Whether you're indoors or outdoors
• Type of sound you're amplifying - a graduation speech is very different from a heavy rock band

Will you be setting your system up in a school or office building? Or do you plan to use it outdoors or in a larger arena? Maybe you’re even looking for a portable PA to transport from venue to venue.

It’s imperative you determine which audio output will best fit your needs. The system that’s perfect for a tiny karaoke bar certainly won’t get the job done at a larger scale event.

Public Address Systems for Small Audiences

If you’re setting up a PA system at a small or mid-sized venue, for instance a church, bar, or school gymnasium, you will need a fairly simple, minimalistic set up that generally provides between 50 and 250 watts of power. The most modest system will consist of just a microphone, mixer amplifier, and full-range speakers with a woofer and tweeter, in one enclosure. 

Public Address Systems for Large Audiences

For a larger audience, you’ll obviously want a more powerful and complicated system. Bigger venues, especially live concert settings where sound clarity and coverage are of the utmost importance, utilize two PA systems: the main system and the monitor system.
Main systems are comprised of a series of powerful amplifiers. The largest clubs will require amplifiers that provide 3,000 to 5,000 watts of power, while outdoor venues could require as high as 10,000 watts. These bigger PA systems will also use a higher range of speakers, including subwoofers, and also a crossover to split the signal among separate woofers, tweeters, and midrange speakers for cleaner, more precise sound.

A monitor system, manned by an engineer who controls the tone, level and volume, reproduces the sound created on stage and directs it back to the performers so they can hear how they sound. If you’re at an indoor venue, these monitor systems typically should provide between 500 and 1,000 watts of power, and thousands of watts for an outdoor performance.

Portable Public Address Systems

If you’re looking for a mobile system to bring from event to event, obviously weight and size are key factors to consider. Compact, self-contained, personal PAs are lightweight and not intended for permanent installation. Often these convenient systems can get their power by plugging into an outlet or from a battery.

Battery-powered PAs generally range from about 15 to 100 watts. If access to AC power is available, then you might want to consider a higher-powered unit with better range that is easy to pack up and transport. These portable units usually include an amplifier, mixer and built-in speakers that can handle up to six channels.

Public Address Systems: Important Factors to Consider

• Power
• Input channels
• Frequency
• Mixer controls

Public Address System Power

To determine how powerful your PA should be, a good rule of thumb is to aim for one watt per audience member. For example, if you expect a crowd of 100, you’ll want at least a 100 watt system. And remember, you should never turn your system up as high as it will go because it could distort the sound you're producing. Also, your speakers and amplifiers should each provide the same amount of sound. Otherwise, you could possibly damage both pieces of equipment. 

Public Address System Inputs

Input channels allow you to plug additional equipment - microphones, CD players, instruments, etc - into your PA system. Smaller systems will have from one to six channels.

Public Address System Frequency

Vibrations of an object or surface - such as a speaker cone - are how sounds are created. Frequency - how often these vibrations, or waves, pass through a certain point - measures the tone, or pitch, of a sound. The human ear responds to frequencies that are approximately 20 to 20,000 cycles-per-second, measured in Hertz (Hz).

For a point of reference, here are a few common frequencies:

• Lowest “C” note on a piano = 32 Hz
• Average speaking voice = 250 Hz
• Testing tone of a television station when it goes off the air for the night = 1,000 Hz
• Treble tone control on a stereo turned up = 5,000 Hz – 8,000 Hz
• Crash of a cymbal = 15,000 Hz. 
• See the chart below for more common frequencies.

A speaker's frequency response indicates how much of that range can be reproduced. Woofers are the largest of a speaker's drivers, producing lower frequency sounds between 40 and 2,500 Hz. Tweeters are smaller in size and produce higher tones. Some speakers also have a midrange driver, which handles the range between 500 and 4,000 Hz. 

Two-way speakers contain two drivers - a woofer and tweeter. These are typically found in smaller and/or portable PA setups. Larger, more complicated PA systems utilize three-way speakers with three drivers - a tweeter and woofer, as well as midrange driver - to reproduce a higher quality sound in a larger venue. For even better sound, speakers with subwoofers reproduce the lowest bass frequencies - 20 Hz - crisply and clearly.

Public Address System Mixers

The mixer controls various settings, such as the volume of each individual input channel, pan, bass, midrange and treble, as well as any onboard effects - reverb, chorus, delay, echo, etc. The controls are also used to monitor the amplifiers and speaker lines to ensure the best sound reaches the loudspeakers. They also separate and control each zone and ensure the sound created by each input channel blends together evenly.

Smaller setups, and even many portable PAs, come with a basic mixer to manage volume and other levels, while larger setups will often use several mixers and feature more onboard effects.