Live Sound Reinforcement System fundamentals

Live Sound Reinforcement A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers that makes live or pre-recorded sounds louder and delivers those sounds to a large audience. Sound reinforcement systems can be found in night clubs, churches, concerts, board rooms and at graduations just to name a few.

Live Sound Reinforcement Sound reinforcement systems are sometimes referred to as PA systems which is similar to those found in schools, colleges and many businesses. Sound reinforcement also plays a critical role in life safety systems such as fire alarms systems that provide emergency evacuation functions. These speakers are designed for clear intelligibility.

Live Sound Reinforcement The most basic system involves an input, amplification and an output. This could be a microphone, an amplifier and a speaker.

Live Sound Reinforcement Here is a complete PA system in a hand held unit. Obviously this is the one of the most simplified examples, however it incorporates all of the basic requirements of sound reinforcement.

Live Sound Reinforcement An integral part of a sound system is the transducer. A transducer changes one kind of energy into another. A microphone changes sound waves into audio signals. A speaker changes audio signals into sound waves.

Live Sound Reinforcement The basic function of a sound system is amplification which can be accomplished in several different stages. An amplifier makes an electrical copy of an electrical signal and reproduces the copy into a stronger signal. The increase in signal strength is known as gain.

Live Sound Reinforcement In a basic system each component makes an electrical copy of an input audio signal and reproduces a desired output signal. These outputs go beyond just level control (volume, gain and fading) they are mixed, reshaped, and manipulated.

Live Sound Reinforcement These manipulated functions are known as signal processing. Modern sound systems are made up of a series of interacting components which can be interconnected on an as needed basis. Signal flow starts with the mixer.

Live sound reinforcement We can add more components as needed to this system.

Live sound reinforcement The mixer plays an important role in the live sound reinforcement system, it is the heart of the system.

Live Sound Reinforcement Microphones play an important role in determining the quality of the sound that will be delivered through the speakers. High quality mics combined with the appropriate directional pick up pattern can provide the best possible pick up of sound sources and eliminate unwanted sounds.

Live Sound Reinforcement Equalizers provide the ability to further hone in on specific frequencies and make adjustments to increase clarity or eliminate unwanted noise and feed back. EQs come in various configurations, the more channels the more control that is available throughout the frequency spectrum.

Live Sound Reinforcement We breifly discussed amplifiers and their role in making an electrical copy of the input signal, there are many different stages of amplification though. Preamplifiers boost a signal level prior to power amplification, many times this is done by the mixer. Power amplification provides an output signal strong enough to drive the speakers.

Live Sound Reinforcement Another component of a live sound system is the crossover, this component separates frequencies between the highs and lows of the frequency spectrum, (the frequency spectrum or audio frequency range will be covered later).

Live Sound Reinforcement Crossovers can be active equipment as in the previous slide or passive such as you would find in full range speakers. Passive crossovers are small circuits connected between speakers in a speaker cabinet.

Live Sound Reinforcement You’ve probably noticed that the majority of live sound equipment is rack mountable. Live sound systems are also housed in roll away cabinets for easy transport and set up.

Live Sound Reinforcement Some PA systems can be contained in one cabinet and provide a docking station for i-phones, i-pods and mp3 players. These systems can be used in conjunction with wireless mics

Live Sound Reinforcement Live sound reinforcement is covered by the NEC, article 640: Audio signal processing, amplification and reproduction equipment. This article does not cover any cable types associated with live sound like many of the other low voltage articles. We use similar types of cable though, the two primary cables are coax and twisted pair (18AWG, 1 pair).

Live Sound Reinforcement Coax is unbalanced transmission, all of the signal travels down the center conductor and the braid/shield is used to contain noise.

Live Sound Reinforcement Twisted pair cable is balanced transmission, equal but opposite signals on a pair of wires, the output of which is the sum of both signals.

Live Sound Reinforcement Besides the quality of the components in a live sound system, the cabling as usual, will greatly determine the output quality of the audio signals.

Live Sound Reinforcement Other components that are used in live sound systems are compressors and limiters, sound effects equipment, reverb units and delay echo, noise gates and downward expanders. DELAY ECHO COMPRESSOR DOWNWARD EXPANDER

Live Sound Reinforcement We will take a closer look at each stage of the sound system and the equipment previously discussed in more detail as we move forward with live sound reinforcement. This course will concentrate on the technical aspect of sound reinforcement as it applies to the installer.