FUMC Sound Tech Course

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FUMC Sound Tech Course

• Course No. 2007-1
• Session 1

Oct 2007
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Thanks for your dedication to Christ and
FUMCinServing as Sound TechsTraining to Do
your BEST for Him
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Sound Techs Job

• Maximize Worship Experience for attendees
• Everyone can clearly hear Pastor/speakers on the
  Podium
• Song Service is musical and encourages
  participation
• No glitches that distract from mood of the
  Service
• Know sound equipment operation
• Protect sound equipment
• Set up sound equipment for services
• ( take down/put away also)
• Maintain sound equipment

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FUMC Sound Tech Course

• Session 1 the Physics of Sound
• Session 2 Equipment Mics, Amps, Speakers,
  Wiring
• Session 3 Equipment Mixers, EQs,
  Processors, etc.
• Session 4 Equalization, Compression, Loose
  Ends

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FUMC Sound Tech Course

• Physics of Sound
• Sound Waves frequency, wavelength, etc
• What frequencies matter?
• Human ear characteristics
• Sound propagation in Rooms
• Feedback other effects/frequency dependence
• Sound volume measurement

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What is Sound?

• Alternating compression and rarefaction waves in
  air
• Sound waves travel atthe Speed of Sound
• Waves impact our ears/ear drums/ear bones
• Nerve endings in Inner Ear convert pressure waves
  to electrical signals for the brain to process
• Sound is made by Moving air molecules
• Mouths
• Speaker systems
• Explosives
• No airNo sound

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Sound Waves
Frequency 1 / Period Units are Hertz (Cycles /
Sec)
Amplitude Signal level/Volume
Speed of Sound 1130f/sec (at Sea level) 5
sec delay approx 1 mile
Wavelength Speed of Sound / Frequency
Examples 50Hz 22.6 ft 2000Hz .57 ft 10000Hz
.11 ft
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Audio signal Phase is VERY Important
PHASE Phase is the time relationship of a wave to
a known reference. Expressed in degrees (0-360)
Signals add to Double Amplitude
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Typical Sound Frequency Ranges

• Human hearing range 20Hz 20,000Hz (Good ears!)
• Most sensitive human hearing range 500Hz -
  8,000Hz
• Most voice intelligence 300Hz 3,000Hz
  (telephones)
• AM Radio 50Hz 5,000Hz
• FM Radio 50Hz 15,000Hz
• CDs 20Hz 20,000Hz
• MP3s, etc Good but determined by specific sample
  rates
• Most Sound Reinforcement Systems 80Hz 12,000Hz
• AC Power Frequency (USA) 60Hz

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Voice Instrument Frequency Content
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Audio Frequency Demos
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Complex Sound Waveforms

• Sounds are not just simple, single Sine waves
• Normal sounds are composed of mixtures of Sine
  Waves of different frequencies
• Fundamental frequencies multiples of
  fundamental frequency
• Square wave Fundamental Odd harmonics
• Triangular wave Fundamental Even harmonics
• Harmonics also called Overtones
• Add fullness and character to single note sounds
• Provide individual sound identity
• Require Sound System to reproduce higher
  frequency sounds
• Basis for frequency analysis and response shaping
• Why Equalizers work
• Real Time Analyzers (RTA) Spectrum Analyzers

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Audio Test signals

• Signal sources
• Random noise
• Pink Noise Equal Power per octave
• Less energy at higher frequencies
• Better simulates human hearing music
• THE STANDARD sound test source
• White Noise Equal energy per Hz
• Power rises 3dB per octave
• Sine Square Waves

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Octaves, Equalizers (EQ)31 Band (1/3 Octave) EQ
20 25 31.5 40 Hz
1/3 Octave Bandwidth Filter
Octave a frequency range from f1 to 2 x f1
Octave
Octave
Octave
Octave
20 25 31.5 40 50 63 80 100 125 160 200 250 315
400 500 630 800 1K 1.2K 1.6K 2K 2.5K 3.1K 4K 5K
6.3K 8K 10K 12.5K 16K 20K
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Loudness MeasurementSOUND PRESSURE LEVEL(SPL)

• SPL measurement unit Originally the Bel (named
  for Alexander Graham Bell). Now the Decibel (dB)
  1/10 Bel is most common. Decibels are measured
  on a logarithmic scale. A Bel (10 dB) is defined
  as the ratio of SPL needed so that people would
  perceive a DOUBLING of the volume.
• Actually, each increase of 10dB on the scale
  represents a tenfold increase in loudness. 20 dB
  is 10 times as loud as 10 dB 30 dB is 100 times
  louder than 10 dB, etc.

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How loud is LOUD?
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HIGH SOUND PRESSURE LEVELS(SPL)

• Damage to Hearing -
• The maximum exposure time for unprotected ears
  per day is 8 hours at 90 dB according to The
  Occupational Safety and Health Administration
  (OSHA) guidelines. For every 5 dB increase in
  volume, the maximum exposure time is cut in half.
  
• 95 dB - 4 hours
• 100 dB - 2 hours
• 110 dB - 30 min
• 120 dB- 7.5 min
• Many hearing professionals believe that these
  permissible levels are still too high for hearing
  safety.
• Warning! Be careful using earphones earbuds.
  All of the sound is directed into your ear canal
  and it is easy to achieve high SPLs.
• Warning! Hearing loss from prolonged high SPLs is
  PERMANENT!

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Frequency Response Curve
Audio Signal Output
Frequency (Hz)

• Every piece of audio equipment has a Frequency
  Response curve which depicts how the particular
  piece of equipment changes the levels of all the
  frequencies fed into it.
• For multiple pieces of equipment connected in a
  chain, the Frequency Response curve of each
  equipment effects the total response of the
  chain.
• We say equipment has Flat response when it has
  even response across a band of frequencies (like
  the audio frequency band)

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Do we have flat ears?
Fletcher-Munson Curves (Human ear freq response
vs loudness)
SPL Meter Weighting Curves Use A for lower
SPLs below 65 dB C for high SPLs above
85 dB
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Decibels dB

• Power ratios (in dB) 10 logarithm P2/P1
• Log 2 .3 Double power 3dB increase
• Log 4 .6 4x power 6dB
• Log 10 1.0 10x power 10dB
• dBW Power level referenced to 1 watt
• 3 dBW 2 watts
• 10 dBW 10 watts
• 30 dBW 1000 watts
• 6 dBW ? watts
• - 3 dBW ? watts

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Sound Propagation in Free Space(outward from a
point source)

• SPL Inverse Square Law
• SPLs attenuate at a rate proportional to
• 1 / R² (where R is radial distance from the
  sound source)
• Therefore
• SPL 20 log R1/R2
• Sound levels decrease by 6dB for every Doubling
  of distance from the source (speaker)
• Example If SPL 80dB at 1m from speaker,
• SPL 74dB at 2m
• SPL ? dB at 4m
• SPL ? dB at 16m

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Sound in Rooms
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So What?

• Low frequencies spread out all over the room
• High frequencies are directional
• They can be controlled, as we shall see later

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Sound in Rooms

• Absorption Coefficient Measure of energy
  absorbed by wall materials
• Reflected Energy 100 - percentage absorbed
• Reflections lead to
• Reverberation in a large room

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Sound Reflection (Reverberation)in a Room
Reflections produce Constructive and Destructive
combination of sound waves based on the room
dimensions and the sound wavelengths
(frequencies) and give rise to an uneven room
frequency response.
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Room Resonances

• Rooms act like large tuned enclosures
• They have resonant antiresonant frequencies
  (maybe many)
• Determined by size, shape, building materials,
  furnishings
• They have an inherent frequency response just
  like your mics, amp speakers
• Resonant frequencies do bad things to you as a
  Sound Tech
• Acoustical design of rooms is extremely important
• Reverberation time of approx 1 sec is optimum

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EQing Room/System Response
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Feedback(CONSTANT Enemy of the Sound Tech)

• Feedback is caused by extraneous input getting
  into mics, which is amplified sent to speakers,
  which gets back into the mics.etc. etc.
• Feedback when playing a CD or DVD?
• Feedback occurs at specific frequencies, not over
  a broad frequency range
• Resonances of the Room greatly affect feedback
• EQing the Room minimizes resonances and nulls
• Input Pink Noise into sound system. Use Real
  Time Analyzer to measure Room response. Adjust
  Equalizers to flatten Room response

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ENDof Session 1
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• Questions?

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Ohms Law Power

• 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)
• Power I x V V² / R I² x R

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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)