A Public Address system, or PA system, consists of three basic components in order to convey sound effectively to an audience. A microphone acts as the pick-up device, converting sound waves from voices or instruments into electronic signals. The signals go through an amplifier for processing and are converted via loudspeaker to be heard at a reasonable volume without distortion at the location of the speakers.
However, there is more to a PA system than the basic elements. Compatibility and product quality affect price. Discrete items bundled together do not favour a smooth sound or a good-looking rig.
Indoor and Outdoor PA System Requirements
Small intimate venues like village halls will have different requirements to a large theatre. An outdoor tent has different demands to an open-air concert. Just as the size will determine the components of a PA system, so too does the type of sound transmission. Spoken voices require different treatment to musical instruments.
There is a direct correlation between venue size and power requirements. Manufacturers may differ in the descriptions of the size of the system regarding the wattage, but it is fair to call systems under 30 Watts as mini PA systems, those between 30 Watts and 50 Watts as small PA systems, between 50 Watts and 150 Watts as medium or mid-size PA systems, and above 150 Watts as large PA systems.
Indoors, the enclosed cubic volume is important when assessing the right size of PA system for the venue. A high-ceilinged room with otherwise similar dimensions to another room has more space to fill with sound and requires a system with greater power and amplification to do so. Outdoors where noise drifts, there is little opportunity for bounced sound, and in the absence of audio reflection more volume is required and thus more power.
The acoustics also determine the system requirements. Some places with heavy furnishings, thick carpet and curtains will absorb sound rather than bounce it. A large audience will also absorb sound, which is why it is important to have sufficient capability in the PA system to cope with extra amplification and volume from the components at the turn of a dial.
An evening’s presentation might be about speech-giving, but most organisers will arrange a little light relief either through live or recorded music for background ambience. A PA system needs greater amplification for music because of the different frequencies that instruments deliver. They are usually higher and lower than speech patterns and as such, require a system which is sensitive enough to cope with the range in the spectrum.
More wattage is required for music. Expect to use double the requirements for a speech only presentation in order to capture the highs and lows of the wider frequency even for pre-recorded music. Stereo is also expected for music’s complexity to sound natural. Speakers which can be adjusted will produce a more favourable sound when woofers, tweeters, and horns address low, high, and mid-range frequencies.
For music gigs and live performances with a wide range of instruments, the demands are only met by complex configurations in the equipment involving bigger items in greater number.
Portable PA Systems
For presentations and productions offered in a variety of venues, the PA system needs to travel. Even in a school where there might be a permanent set-up in an assembly hall or theatre, there are occasions when the system needs to be located elsewhere. Sports days, summer fairs, and outdoor events held on an ad hoc basis are examples of situations where portability is an issue.
Audience Size and Wattage
Audience size, in an ideal environment without too many variables, determines power requirements. Usually sound technicians operate on a ratio of 1:1 (Watt to person). In a venue with an expected capacity of 120 in the audience, as portable PA systems usually have stereo speakers the two channels will require 60 Watts each to match the optimum listening experience. Where 500 people make up an audience, the total Wattage requirement is 500 Watts.
Fitting the system to the type of production also involves numbers. The amount of input and output channels need to accommodate the number of microphones, speakers, DVD/CD/tape recording devices and auxiliary devices used. There needs to be enough quarter-inch and XLR jacks to serve the output channels. One microphone will suffice if no one other than the main speaker uses it, but if questions go to the floor, at least one other microphone is required.
The issue of microphone portability may be addressed through the use of wireless technology for hand held, headband, collar, or lapel (lavaliere) mics with RF transmitters. Their receivers require plugging into a PA amplifier. Wireless mics are preferred when a slick performance is required with interaction or audience participation and offer terrific flexibility and mobility. To avoid interference, each wireless mic needs to have a separate operating frequency.
Cables, stands, and cases are more than accessories and make up parts of a portable PA package that can be added to on an ad hoc basis as needs require.
Additional specialist items can augment the basic PA system package. Mixers with the ability to provide special effects can enhance a drama or music production.
Fixed PA systems, or custom-built fitted configurations, ordinarily serve venues where they have regular use. Theatres, churches, and clubs or restaurants with music depend upon the sound quality of the production or performance given. Paying customers or avid students will want to hear everything clearly.
As a fixed or permanent fixture, the benefits can be streamlining, concealment, and optimum positioning of speakers for the venue’s acoustics. Podiums with in-built devices offer a professional appearance and can be fitted with extras such as lamps, shelving, and lighting so that a lectern has everything a speaker needs at hand. No visible wires or cables keep the look neat and maximise the safe space that can be utilised in a venue.
Whether fixed or portable, there is the option of an independent, self-contained wireless function for PA systems’ companion speakers. Typically, these include a CD player, integral wireless mic receivers, and tape player.
How to Find PA Systems on eBay
The eBay site features new listings every day. Pro Audio Equipment from retailers worldwide offers a fantastic selection for purchase. On the home page, choose All Categories and find Musical Instruments. Expand the category to reveal Pro Audio Equipment and select. Type PA System into the long search box and click on the most appropriate suggestion to match the search. When the choices appear, searches can be refined by checking boxes on the left for specific items.
Portable PA systems simply mean the equipment is not a fixed installation. The portability of the items may require wheeled trolleys to safely shift heavy speakers, consoles or lengths of cable. At the smaller end of the scale, PA systems less than 50 Watts are readily portable without haulage equipment and can be transported in the boot of a car easily. When not in use, they can be stored in small spaces. For larger scale productions the amount of equipment grows exponentially. Cables, companion speakers, stands and housings, batteries, chargers, and protective covers and casings all contribute to the number or essential accessories. Although components can be successfully mixed and matched product support and helpful information is easier to come by when the items are part of a compatible suite produced by the same manufacturer. Wireless options are the most versatile though expertise is required to ensure frequency settings on radio transmitters is optimised. Collecting the equipment after the performance has finished is essential. Small radio packs are easily mislaid so a good inventory is crucial. DJs, lecturers and performers whether amateur or professional can check specifications online to see if the equipment fulfills the requirements of the job.