Fundamentals of Audio Production

1. Fundamentals of Audio Production Chapter Twelve: Live Sound Reinforcement Fundamentals of Audio Production. Chapter 12 1

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 12

10. Crossovers Fundamentals of Audio Production. Chapter 12

11. 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 12

12. Pre-fader versus post-fader Fundamentals of Audio Production. Chapter 12

13. 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 12

14. Monitor mixing Fundamentals of Audio Production. Chapter 12

15. Monitor mixing Fundamentals of Audio Production. Chapter 12

16. 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 12

17. Monitor mixing Fundamentals of Audio Production. Chapter 12

18. 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 12

19. 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 12

20. 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 12

21. 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 12

22. 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 12

23. Types of shielded cabling Fundamentals of Audio Production. Chapter 12

24. XLR connectors Female (left) and male (right) use 3 contacts, with pin “1” connected to shield Fundamentals of Audio Production. Chapter 12

25. Connectors 1/8-inch tip-ring-sleeve 1/4-inch tip-ring-sleeve 1/4-inch tip-sleeve Fundamentals of Audio Production. Chapter 12

26. Connectors RCA connector is popular in consumer electronics – but not widely used in professional systems Fundamentals of Audio Production. Chapter 12

27. Connectors Speakon (left) is used for speaker connections, DIN (right) is used for connecting MIDI signals Fundamentals of Audio Production. Chapter 12

28. 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 12

29. Impedance matching Fundamentals of Audio Production. Chapter 12