Fundamentals of Audio Production. Chapter Fundamentals of Audio Production Chapter Twelve: Live Sound Reinforcement

Fundamentals of Audio Production. Chapter 12 2 Live sound terminology Terms are often interchangeable Public address (PA) systems – most often describes systems for voice –i.e. sports venues, paging systems Sound reinforcement – describes systems for live music –i.e. concerts and live performances

Fundamentals of Audio Production. Chapter 12 3 Controlling feedback Feedback is the result of the speakers’ output being picked up by microphones and re-amplified by the system Feedback is self-sustaining oscillation of the system Feedback is controlled by proper placement of the microphones is relation to the speakers

Fundamentals of Audio Production. Chapter 12 4 Controlling feedback

Fundamentals of Audio Production. Chapter 12 5 Controlling feedback Use of cardioid microphones helps eliminate feedback by rejecting sound from the front-of-house speakers and monitors The null or off-axis side of the microphone should be place toward the live speakers

Fundamentals of Audio Production. Chapter 12 6 Tuning the system Each room has unique modes resulting from its dimensions and shape Modes may cause some frequencies to “ring” or resonate – other frequencies may be difficult to propagate or hear Precise “tuning” of the system with a 1/3 octave equalizer can compensate for room modes by boosting or cutting some frequencies

Fundamentals of Audio Production. Chapter 12 7 Tuning the system Systems may be tuned by playing white noise, and then measuring the response with a real time analyzer RTAs capture the sound using a calibrated accurate microphone RTAs provide a visual display of the frequency response

Fundamentals of Audio Production. Chapter 12 8 Tuning the system PC-based RTA display, left and right channels

Fundamentals of Audio Production. Chapter 12 9 Loudspeakers and monitors In many large systems, the signal from the console is split by external crossovers, then routed to appropriate high, mid, or low frequency enclosures in the speaker array

Fundamentals of Audio Production. Chapter Crossovers

Fundamentals of Audio Production. Chapter Monitor mixing In small to medium systems, the sound is mixed for the on-stage monitors on the front of house console “Pre-fader” signals from individual microphones may be mixed and routed to the monitors without being affected by the main faders

Fundamentals of Audio Production. Chapter Pre-fader versus post-fader

Fundamentals of Audio Production. Chapter Monitor mixing In large complex live systems, the monitor mix is created on a separate console, usually located just off-stage The signals from the microphones are split at the snake box, and routed to the two separate consoles

Fundamentals of Audio Production. Chapter Monitor mixing

Fundamentals of Audio Production. Chapter Monitor mixing

Fundamentals of Audio Production. Chapter Monitor mixing In ear monitors, or ear buds, have become popular alternatives to on-stage floor wedges Keeps stage sound levels lower Requires a limiter to assure that feedback or other loud transients do not damage hearing

Fundamentals of Audio Production. Chapter Monitor mixing

Fundamentals of Audio Production. Chapter Sound check The system is tuned to the room Gain and output levels are set Automated consoles recall settings from previous shows or set changes Caveat: Some performers will play much louder during performance than sound check

Fundamentals of Audio Production. Chapter Avoiding equipment damage Amplifiers should be turned on last after consoles and all other outboard equipment Amplifiers should be turned off first before powering down consoles and other gear This will avoid speaker-damaging “pops” from the power surges

Fundamentals of Audio Production. Chapter Level management More and more venues are placing restrictions on sound pressure levels Some because of noise ordinances in local municipalities Some because of the fear of liability for hearing damage to patrons Many live sound engineers keep a sound pressure level meter at the FOH console

Fundamentals of Audio Production. Chapter Ground loops Ground loops cause hum in the system due to differing potentials on different power circuits If possible, all equipment should share a common earth ground point If hum is present, connecting the console and amplifiers to the same circuit may eliminate it

Fundamentals of Audio Production. Chapter Connections Professional systems use balanced connections Wiring contains two conductors for hot (+) and cold (-) signal, plus a shield Unbalanced cabling only uses one conductor and a shield Unbalanced connections are more susceptible to hum and interference

Fundamentals of Audio Production. Chapter Types of shielded cabling

Fundamentals of Audio Production. Chapter XLR connectors Female (left) and male (right) use 3 contacts, with pin “1” connected to shield

Fundamentals of Audio Production. Chapter Connectors 1/8-inch tip-ring-sleeve 1/4-inch tip-ring-sleeve 1/4-inch tip-sleeve

Fundamentals of Audio Production. Chapter Connectors RCA connector is popular in consumer electronics – but not widely used in professional systems

Fundamentals of Audio Production. Chapter Connectors Speakon (left) is used for speaker connections, DIN (right) is used for connecting MIDI signals

Fundamentals of Audio Production. Chapter Impedance matching The method by which speakers are connected to the amplifier will affect the impedance or “load” on the amplifier Mismatching the load on the amplifier can rob the system of power, or cause damage to the amplifier

Fundamentals of Audio Production. Chapter Impedance matching