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Advanced Training 2009

Advanced Training 2009. Topics to be covered Noise Grounding Safety System Gain Considerations Auxiliary Fed Subwoofers. What Causes Noise?. Induced Electricity from External Electrical or Magnetic Fields -Lights -HVAC -Motors -Fans Ground Currents

garrett-tillman
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Advanced Training 2009

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  1. Advanced Training 2009 Topics to be covered Noise Grounding Safety System Gain Considerations Auxiliary Fed Subwoofers

  2. What Causes Noise? Induced Electricity from External Electrical or Magnetic Fields -Lights -HVAC -Motors -Fans Ground Currents -Improper Grounding Methods -Faulty Equipment -Faulty Connections!!

  3. How to Fix Noise Induced Noise -BALANCED CABLES!

  4. Unbalanced Cable Tips • Keep cables as short as possible. • Use cables with heavy gauge shields. • Bundle signal cables. • Maintain good connections. • DO NOT ADD unnecessary grounds. • Use ground isolators at problem interfaces. Expensive and exotic cables, even if double or triple shielded, made of 100% pure unobtainium, and hand-made by a team of virgins, will have NO significant effect on hum and buzz problems!

  5. How to Fix Noise Ground Currents -Signal Ground Lifts -Transformers

  6. Ground Lift For shielded balanced audio cables, the shield should ALWAYS be grounded at the driver — whether or not the receiving end is grounded.

  7. Transformer Isolation

  8. Properly Operating Equipment

  9. Defective Equipment

  10. NEVER, EVER use devices such as 3 to 2-prong ac plug adapters, a.k.a. "ground lifters," to solve a noise problem! • Interrupting any portion of Equipment Ground (for example, by breaking off the ground pin of an AC plug or using a "ground lift" plug), or adding a series impedance (like an inductor or "choke") that reduces fault current is unsafe, and could cause electrocution.

  11. Defective Equipment with Lifted Ground

  12. Consequences • Between 1980 and 1989: 153 people died by contacting short-circuited, damaged, or improperly installed wire or equipment. • For the year 1990, the National Safety Council reported that electrocutions were the fourth leading cause of work-related traumatic death. • Improperly connected grounds in audio equipment may lead shock back to Monitor Engineer, FOH Engineer, etc….YOU!!

  13. Power considerations • Ensure that all circuits used share a common ground i.e. come from the same breaker panel • Mics must be pin 1 grounded to the nearest console • NEVER lift equipment ground for ANY reason. It’s against the law and unsafe!

  14. System Gain Structure • Two widely used methods: Unity Gain and Optimal Gain • Unity Gain: Setting all ratios to Unity or 1/1. Level is unchanged • Optimal Gain: Set clipping point of all pieces in the signal chain equal.

  15. Pros and Cons • Unity gain: • Maximum headroom • Slightly higher noise floor • Optimal Gain: • Reduced Headroom • Lower noise floor

  16. Headroom? • Difference between peak and RMS values • The closer a circuit is to clipping, the greater the distortion • Leave at least 6dB of headroom • Avoid earlash • Amps have less available headroom above +4 dBu, but are designed to run at higher levels

  17. Back to system gain structure • Set amp inputs wide open • All gear in the signal chain set at Unity • Control system volume at the console

  18. ConventionalSubwoofers • Currently Our System is Set Up in the Following Fashion

  19. Conventional Sub Downfalls • Lower harmonics tend to muddy up the low end. • High Pass Filters on Channel strip generally have gentle slopes of 12 dB • Low Frequency Stage Volume can enter through VOX

  20. System Auxiliary Fed Subwoofers Presets are in the Ashly for Aux Fed Sub Setup

  21. Aux Fed Sub Advantages • Only Signals with “meaningful” low frequency content will be sent to subwoofer • Other content will be rolled off at a steeper rate • Gain Structure Remains Intact

  22. Aux Fed Sub Disadvantages • Need to fade master fader, and aux fader • Additional Crossover is sometimes needed Aux Fed Sub Instruments -Bass Guitar -Kick Drum -Low (Floor) Tom -Low mic on Piano -Low mic on Leslie (Organ) -Electronic Keys -CD/TAPE Playback

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