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Sound systems are of vital importance in Places of Worship. People need to hear what is going on clearly so that they can take part in meetings and services. Additionally, the correct operation of a sound system could be important for safety as announcements might be given to a congregation in an emergency.
The design of a Public Address or Sound Reinforcement system is as important as the daily use and running of the system.
System Design
It is important that a PA or sound reinforcement system is designed for the purpose for which it is intended. Before deciding on the equipment that is required, ask yourself if the system is for:
- Speech reinforcement (sound from microphones only)
- Background music (for example playing a tape as people enter)
- Foreground music (for example, playing a CD as part of Worship)
- Worship bands (where the system must be capable of handling guitars, keyboards and other instruments)
The demands on the system increase down the list – as speech system is often simpler and cheaper than a system for a worship band. The ability of the system to reproduce sound increases down the list, along with the amount of output power that the system is capable of producing.
Additionally, it is likely that the number of microphones and other inputs will increase down the list. In most Churches and Places of Worship, all locations where people speak from would need a microphone.
Microphones
There is a bewildering array of microphone types and technologies available. It is suggested that a "Cardiod" microphone is used as this is most suited to PA work, but "Hyper-Cardioid" might be better if there is a feedback problem or the room suffers from reverberation. Highly directional microphones such as "shotgun" and "rifle" microphones are usually unsuitable for sound reinforcement systems.
For general use in Places of Worship, "condenser" microphones are best. They are usually more sensitive than other kinds of microphone and are less prone to electrical interference. These microphones are available in a number of different shapes, including discrete microphones that look like a pencil and "boundary" microphones that are perfect where the microphone must not be seen. The main disadvantage is that these microphones need a power supply either from the mixing desk (called "phantom power") or a battery within the microphone.
The main alternative to condenser microphones are "Dynamic" microphones. These often have the more traditional microphone "ice cream cone" shape. The main disadvantage is that the quality of sound gets muddier as you speak into the microphone more closely. They are usually unsuitable for use when using induction loops and often give poor results when people use them at close range (though they are frequently used in this way).
Radio microphone systems are available at very low cost, but reliability is of primary importance in any PA system. Radio microphone systems should be "true diversity" as this improves reliability. Either UHF or VHF systems can be used, with economic systems usually being VHF and quality systems usually UHF. Note that licences might be needed for some systems and four frequencies are available licence free on each of the UHF and VHF systems.
It is not normally necessary to position microphones on drum kits and similar instruments. In some situations, a microphone might be useful directly in front of guitar and bass amplifier cabinets. Quieter instruments, such as flutes, benefit from reinforcement in all but the smallest of buildings, where it is not necessary
The cables used for microphones should be "balanced". This kind of signal uses a 3-pin "XLR" plug rather than a 6.35mm jack plug. Most modern microphones are classed as "low impedance" - "high impedance" microphones should usually be avoided for modern systems.
Amplifier and Mixer
An amplifier is the core of the sound system. As a guide, for speech reinforcement in most buildings, a 100-watt amplifier is more than adequate. For a worship band, this might need to be a 400-watt amplifier. In larger buildings with more loudspeakers, more amplification is likely to be needed.
Usually one amplifier us used to run a pair of speakers, but if more speakers are needed, a special kind of system can be used. A 100-volt (alternatively a 70-volt) line system allows multiple speakers to be connected to one amplifier. The main problem with this arrangement is that the sound quality is not as good compared to "low impedance" speaker systems and are suitable for speech and background music sound reinforcement only.
Low impedance speakers are usually quoted as 4, 8, or 16 ohm and are best for quality sound reproduction. The main disadvantage is that good quality speaker cable is needed as there can be a loss of the signal to the speakers if too thin cable is used, which lowers the quality of the sound.
Mixers allow the connection of microphones, CD players and other equipment to the amplifier. These have controls on them to adjust the volume and tone for each signal and some have other features such as special sound effects. An auxiliary output should be used to connect an induction loop to the sound system.
Some amplifiers, especially 100-volt line amplifiers, have a built-in mixer. It is good practice to use a separate mixing desk where possible, as these offer more control over the signal, such as equalisation (bass and treble controls) and balance or pan controls, for stereo systems.
Loudspeakers
Loudspeakers should be placed in front of the congregation but not behind microphones. Do not put speakers at the back of the room and direct them back onto the congregation as this increases the chance of feedback and can be uncomfortable to listen to.
For many situations, a stereo pair of speakers is adequate and this would be good for foreground music and possibly a worship band. In larger buildings, and more traditional settings, 100-volt line driven column speakers are preferable. A larger number of lower powered speakers directed to the congregation would help prevent feedback and reduce reverberations in the room as this would make listening to the system harder.
It is essential to ensure that the speakers and amplifier match each other. Consider the impedance of the speakers, the power and if any special equipment is suggested by the manufacturer (which is typical of high-end loudspeakers). An amplifier should usually be capable of producing twice the RMS measured power of the speaker maximum.
It might also be necessary to install "foldback" speakers when the system is to be used by a worship group. This would enable the members of the band to hear the music clearly as they are playing.
Fit the speakers using purpose designed brackets and fix them in accordance with the manufacturer's guidance. It might be necessary to install safety bonds to retain the speaker should the fixing bracket fail.
Induction Loop Systems
Audio Frequency Induction Loop Systems (AFILS) are needed in most situations under the Disability Discrimination Act. They allow hearing aid users to pick up the signal from a loop of wire connected to a piece of equipment known as a "driver". The driver gets a signal from the main PA system and a number of other microphones from around the room.
The important thing to remember with induction loops is that the hearing aid user will only hear the sounds you pick up using microphones. Everyone who speaks must use a microphone and a microphone is usually needed to pick up ambient sounds such as singing and choral speaking, prayers and so on. It is also important to ensure microphones are used correctly to ensure the clarity of the sound the system user will hear.
Listening devices are available to allow someone without a hearing aid to listen to the induction loop, which is invaluable for checking that the system works. Some of these also have a signal strength meter to test that the loop complies with design requirements and is working effectively.
Feedback and other problems
Feedback is a howl that is sometimes heard from PA systems at loud volumes. A microphone being turned up too high or the speakers being in the wrong place is a usual cause of feedback.
Most feedback problems have a simple cause – the sound from a speaker enters a microphone and is amplified again by the system. To prevent this, it should not be possible to see the front of a speaker when you look from where the microphone is located.
The exact pitch (or frequency) that you get feedback depends on the equipment in use and the acoustics of the room. Good quality equipment is less prone to feedback problems. Room acoustics are more difficult to control, but equalisers are a good idea for persistent feedback problems. A "parametric equaliser" is preferable for feedback reduction over a "graphic equaliser", and most "feedback eliminators" work on this principle.
Another kind of feedback is when a microphone cable is run next to a speaker cable or an induction loop cable. The signal from the speaker cable or induction loop is picked up by the microphone cable. For this reason, avoid running microphone and speaker cables together – usually, they should only cross at right angles.
Distortion can come from many different sources, including systems where domestic and commercial specification equipment is mixed. Cables being too close to mains electrical cables and stage lighting equipment can cause mains hum. Hum can also be because of "earth loops" and these are easily rectified using an "earth lift" adaptor – never remove the electrical earth connection from the mains plug.
Radio noise is usually caused by "unbalanced" microphone cables or poorly designed equipment. For this reason always use a good quality balanced microphone cable with lapped or braided screening. Radio Frequency Interference filters are also available but these should be a last resort and are not normally very effective.
Running the system
Most systems benefit from someone being with the controls to ensure that the microphones and other inputs are set at an appropriate volume and to check that no feedback occurs. Another benefit, especially for induction loop users, is that the quality of the sound would be better as sound would not be amplified from a number of microphones at the same time.
Care should be taken to ensure that the system is correctly powered on (starting with the inputs, mixer desk ending with the amplifier). The system needs to be powered off in the reverse order as this protects the system from damage.
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