FUMC Sound Tech Course Session 3

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FUMC Sound Tech CourseSession 3

• Microphones, Speakers Spkr Systems, Amplifiers

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This is a BLOCK DIAGRAM
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Microphone Types

• 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

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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

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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

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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)

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Important Mic Specs

• Sensitivity
• Ex -47dBv _at_ 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, lt 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

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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
  crowdedMore 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

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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 MeterShould be
  Mid-to-Full Scale
• Check Rx AF MeterShould 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 mics
  assigned frequency.

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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)

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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!

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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
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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
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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

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Crossover Frequency Response Curves
Idealized 2-way crossover response
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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

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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 _at_ 1 meter with a 100 watt amplifier?
• What is SPL _at_ 4 meters with a 100 watt amplifier?
• What is SPL _at_ 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 _at_ 500
  watts)

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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

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FUMC Speaker Systems

• 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

Main Amp
Mixer
Electronic (active) Crossover
Passive X-Over
Sub Amp
Sub
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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

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Microphone Stand Etiquette

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

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Power Amplifiers

• Convert low audio voltage/high impedance levels
  to high voltage/low impedance to drive speakers
• Input 4dBV _at_ 600 Ohms
• Output 100-400V _at_ 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)

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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
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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

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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!

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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 _at_.05 THD
• Intermodulation Distortion (IM)
• Non-linear mixing of 2 audio frequencies

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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

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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
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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)

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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)
• IE/R
• Power I x V V² / R I² x R

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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