fundamentals of audio production. chapter 12 11 fundamentals of audio production chapter twelve:...
TRANSCRIPT
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Fundamentals of Audio Production. Chapter 12
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Fundamentals of Audio Fundamentals of Audio ProductionProduction
Chapter Twelve:Chapter Twelve:
Live Sound ReinforcementLive Sound Reinforcement
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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
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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
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Controlling feedback
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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
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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
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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
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Tuning the system
PC-based RTA display, left and right channels
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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
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Crossovers
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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
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Pre-fader versus post-fader
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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
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Monitor mixing
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Monitor mixing
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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
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Monitor mixing
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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
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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
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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
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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
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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
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Types of shielded cabling
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XLR connectors
Female (left) and male (right) use 3 contacts, with pin “1” connected to
shield
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Connectors
1/8-inch tip-ring-sleeve
1/4-inch tip-ring-sleeve
1/4-inch tip-sleeve
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Connectors
RCA connector is popular in consumer electronics – but not widely used in professional systems
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Connectors
Speakon (left) is used for speaker connections, DIN (right) is used for connecting MIDI signals
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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
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Impedance matching