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FUMC Sound Tech Course Session 3

FUMC Sound Tech Course Session 3

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FUMC Sound Tech Course Session 3

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  1. FUMC Sound Tech CourseSession 3 Microphones, Speakers & Spkr Systems, Amplifiers

  2. This is a BLOCK DIAGRAM

  3. Handheld/Vocal Close range for individual singer/speaker UniDirectional - Cardioid or Hypercardioid pattern Feedback rejection Lavalier Close range Omni or Cardioid pattern Small Stand/Drop Mounted Group pickup Longer range Recording (high quality) Cardioid pattern Over-the-Ear Pastors, Speakers Noise & Feedback rejection Contact Guitar, Piano Pressure Response Boundary mic Shotgun Long range Noise cancelling High noise environments Actually 2 mics – out of phase Microphone Types

  4. Transducer Types • Dynamic • Made like miniature speaker w/ coil & magnet • Warm response – Preferred by singers • Condenser • Made to form a capacitor (condenser) • Gold sputtered diaphragm acts as capacitor plate • Requires amplifier & voltage supply (phantom power) • Excellent frequency response • Small vs. Large Diaphragm • Electret condenser • Permanently charged diaphram • Small & cheap

  5. Transducer Types - Continued • Ribbon • Metal ribbon suspended between magnet poles • Flat frequency response - Great recording mics • Expensive • Carbon • Earliest type, used in telephones until recently • Carbon granules form resistance element • Poor frequency response but very rugged • Piezoelectric • Diaphragm connected to piezoelectric material • Cheap – low cost mics of a few years ago • Crystal or Ceramic mic

  6. Mic Pickup Patterns • Omnidirectional (Omni) • Equally sensitive in all directions • Cardioid (heart shaped) • Directional • Most popular • Very little pickup directly behind • Hypercardioid • Reduces side pickup • Has some pickup directly behind • Proximity effect • Bass boost when mic is very close to source • Only in directional mics (not omni)

  7. Important Mic Specs • Sensitivity • Ex: -47dBv @ 94dB SPL • Maximum SPL (overload) • Ex: 140 dB SPL • Frequency Response • Ex: 50-15,000 Hz +/- 6dB • Look for response curve • Impedance • Low • Most Pro mics, < 150 Ohms • Tolerate long cable runs • Balanced output • High • Low Cost Piezo/crystal mics • 25,000 Ohms or greater • Unbalanced Cables up to 20 ft

  8. Wireless Mics System consists of: • FM Transmitter (Tx) • FM Receiver (Rx) • Best are Dual Diversity ( 2 separate receivers in the case w/ 2 antennas. Output auto switches to the Rx with best signal ) • Best are UHF frequency range (500-900 MHz) – Less interference • Lower cost are VHF (150-200 MHz) – More crowded=More interference • Best are tunable frequency, otherwise are fixed frequency • Controls • Transmitter • On/Off, Mute, Frequency select, Mic Sensitivity • Receiver • Frequency Select, Audio Output level, Squelch level • Metering-RF signal strength, Audio level, Muting, Battery low

  9. Sennheiser Wireless Mics • FUMC uses Handheld & Lavalier styles • Operation • Handheld Mic - Push Red On/Off button for 2 sec & ONLY with fleshy part of your finger…..NOT the fingernail • Check Rx Signal Strength Meter…Should be Mid-to-Full Scale • Check Rx AF Meter…Should go up as you talk or tap mic • Check Rx MUTE Indicator if no audio out • Check that Rx & Tx are on the correct frequency • Check Tx Sensitivity if too much or not enough volume • Put in freshly charged NiMH batteries for use & put batteries back in Charger after use. Charged batts will run approx 8 hrs • We use 3 frequency bands: 500MHz, 600MHz & 700MHz. See the freq charts for each mic’s assigned frequency.

  10. Speakers • Convert electrical sound signals back to Sound Waves • Electromagnetic Transducers • Fixed Magnet w/ Moving Coil • Large magnet = higher power • Semi-rigid cone w/ corrugated surround • Piezoelectric Transducers • High Frequency Drivers (Tweeters)

  11. Low Frequency Drivers Low frequencies require moving lots of air • Electromagnetic Transducer • Large Diaphragm Area • Long Diaphragm Excursion (Long Throw) • High power handling • Heavy Magnet structure • Large Diameter Voice Coil w/ large wire • Rigid frame • HEAVY!

  12. High Frequency Drivers • Types • Cone, Dome, Piezoelectric, Horn • Short cone movement • Low power required • EASILY DAMAGED by high volumes, Amp clipping • Consumer speakers use Cone, Dome, Piezo HF Drivers • Provide as wide dispersion of sound as possible • Pro Speakers use Horn HF Drivers • Provide CONTROLLED dispersion of sound • Common units are 40V X 60H and 40V X 90H degrees Typical Constant Directivity Horn

  13. Pro Speakers (Cabinets) • 2 or 3 Drivers per cabinet • Called “2 Way” or “3 Way” • Low Frequency Driver (woofer) • Mid-Range Driver • Hi Frequency Driver (Horn) • Bass Reflex Cabinet • Box is “tuned” to LF Driver with Ports to extend low frequency response Typical 2-Way Pro Speaker

  14. Crossovers • Separates out proper audio frequencies to send to each Driver • Passive (High level) • RLC network inside speaker cabinet • One Amplifier output wire pair drives entire cabinet • “Brute Force” method • Not most efficient • Active (Low level) • Electronic Crossover separates the various frequency bands • Separate Power Amplifiers for Low, Mid, High frequency Drivers • Multiple amp output wire pairs to speaker cabinet • Efficient • Used in Concert & Touring systems

  15. Crossover Frequency Response Curves Idealized 2-way crossover response

  16. Speaker Specs • Frequency response • Ex: 60 – 15,000 Hz +/- 6dB • Impedance (nominal) • Ex: 8 Ohms, 4 Ohms • Most spkrs either 8 or 4 Ohms • Power Handling (Watts) • RMS = Constant sine wave • Program = Double RMS • Peak = 4 X RMS

  17. Speaker Specs (cont) • Sensitivity • SPL output level with 1 watt input power (normally at 1 meter from Spkr) Ex: Sensitivity = 95 dB (Sensitivities range from 85 dB to 100+ dB) • Example (using above speaker sensitivity) • What is SPL @ 1 meter with a 100 watt amplifier? • What is SPL @ 4 meters with a 100 watt amplifier? • What is SPL @ 16 meters with the 100 watt amplifier? • Speaker Beamwidth • Degrees (Horizontal & Vertical) vs. frequency • Maximum SPL Output • XX dB at rated input power (Ex: 125 dB @ 500 watts)

  18. Speaker System Design • Use multiple speaker cabinets & Arrange in Arrays to provide the required room coverage • Direct sound at the audience, NOT at walls • Minimize sound reflections • Provide as constant SPL (& frequency response) as possible across room • Use Main cabinets in front and “fill” cabinets as necessary • Use Time Delay units to drive rear & fill cabinets to account for closer fill speaker placement

  19. All FUMC Venue speaker systems are 3-Way • Main Cabinets are 2-Way (low frequency driver covers 80-250 Hz + high frequency Horn covers 250-20KHz • Uses an internal Passive Crossover • Subwoofer Cabinet covers 80 Hz and lower • An Active (electronic) Crossover set to an 80 Hz frequency takes the Mixer output signal and sends 80 Hz and below to SubWoofer Amplifier and 80 Hz and above frequencies to Main Amplifier FUMC Speaker Systems Main Amp Mixer Electronic (active) Crossover Passive X-Over Sub Amp Sub

  20. Monitor Speakers (Wedges) • Allow singers & bandsmen to hear music & themselves • Usually on stage in front of performer (aimed at performer) • Mix is different from main House mix

  21. Microphone Stand Etiquette • Fold out legs • RELEASE Tension knob before moving boom • Stand will be RUINED if boom joint is forced

  22. Power Amplifiers • Convert low audio voltage/high impedance levels to high voltage/low impedance to drive speakers • Input: +4dBV @ 600 Ohms • Output: 100-400V @ 8/4/2 Ohms • High Current output • Final component in the chain, just before speakers • Internal Components • Power Supply • Transformer / Rectifier / Series Regulator • High frequency chopper • Input amplifier stage • Power amplifier stage • Protection circuits (clip/overload protection)

  23. Power Amplifier Specs • Frequency Response • Frequency range passed by the device • Ex: 20-20,000 Hz +/- 2 dB • Power Bandwidth • Frequency range over which the amp puts out at least ½ its rated power Typical Power Bandwidths

  24. Power Amp Specs • Power Output level • Output Impedance • Speaker impedances the amp will support • Usually 8 ohms, 4 ohms, or even 2 ohms • Output current required goes up with lower speaker impedance • Amp that will drive 2 ohm loads is top rung

  25. Power Amp Specs • Clipping • Pushing an amplifier beyond the limits of its output capability • Makes a sine wave into a square wave • Adds harmonic frequencies to original audio signal • Speaker damage!

  26. Power Amp Specs • Distortion • Output signal that was not identical to the input signal • Distortion ADDED to the “perfect” input signal • Total Harmonic Distortion (THD) • Ex: 100 watts @.05% THD • Intermodulation Distortion (IM) • Non-linear mixing of 2 audio frequencies

  27. Power Amp Output Modes • Stereo • 2 Channels driven with different signals – 2 outputs • Mono (Parallel) • 2 Channels driven with same signal – 2 outputs • Bridge • 2 Channels driven with same signal – 1 output • Maximizes power output of amp • Channels are fed inputs out of phase so channels add power • Minimum output impedance is doubled • 2 Ohm minimum in Stereo or Mono becomes 4 Ohm minimum in Bridge mode

  28. Multiple Speakers Total Impedance = Z1 + Z2 + Z3 Total Impedance = 1 1/Z1 + 1/Z2 + 1/Z3 Examples: 2ea 8 Ohm speakers in Parallel = 4 Ohms 3ea 8 Ohm speakers in Parallel = 2.7 Ohms 4ea 8 Ohm speakers in Parallel = 2 Ohms

  29. Audio Equipment Measurementsof Interest • Power: Watts = Amps x Volts • Resistance: Ohms, Kilohms, Megohms • Impedance: “Complex Resistance” • Similar to Resistance • Ohms • Voltage: Volts, Millivolts, Microvolts • Current: Amps, Milliamps (1/1000 amp)

  30. Ohms Law • I = V / R (Current = Voltage / Resistance) • Other forms are also valid • R = V / I • V = I x R • E is often used instead of V (for voltage) • I=E/R • Power = I x V = V² / R = I² x R

  31. Guess the Frequency Game • Important that you can pick out frequency content so you can EQ properly. • Choices: • 50 Hz • 100 Hz • 315 Hz • 1000 Hz • 2 KHz • 3.15 KHz • 6.3 KHz • 10KHz