SIASmaart School

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SIA-Smaart School Applications Seminars

• Welcome
• This PowerPoint presentation can be downloaded
  at
• http//www.RaionalAcoustics.com/Training

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What are we going to cover?

• System Alignment Overview
• Reading the Phase Trace.
• Our TF Friends
• Averaging
• Coherence
• Magnitude Thresholding
• System Alignments Crossovers, Setting Delays,
  Subs, etc.
• What Ever Else You Want . . . .

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System engineering is managing interactions

• Acoustically
• Multiple Drivers, Speakers, Systems
• Reflections/Acoustics

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Signal Addition

• Jean Baptiste Joseph Fourier
• All complex waves are composed of a combination
  of simple sine waves of varying amplitudes and
  frequencies

Time Domain Freq.
Domain
(Amp vs Time)
(Amp vs Freq)?
Waveform
Spectrum
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The Big Question

?
or
or
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Addition of Sine Waves of Same
Frequency and Equal Amplitude
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System Engineering Key Concept

• Interactions are greatest where signals are equal
  level - Crossover Points

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System Engineering Key Concept

• Interactions are greatest where signals are equal
  level - Crossover Points
• Phase determines the interaction
• Phase Shift (Filters)?
• Polarity (Wiring)?
• Delay (Time Alignment)?

Align from Loudest Quietest Systems
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Arrays
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ArraysPoint Destination
Equal Time Arrival
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Arrays Planer
Equal Time Arrival
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Arrays Point Source
Equal Time Arrival
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Reading the Phase TraceIts About Time
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Math You Need

• T1/
• 1/T

250 Hz T 4 ms
100 Hz T 10 ms
T .1 ms 10 kHz
T .1 ms 10 kHz
20 Hz T 50 ms
T 1 ms 1 kHz
T .5 ms 2 kHz
500 Hz T 2 ms
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Our Friend the Comb FilterorWhere Did All
That Ripple Come From?
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Period and Frequency
T 4 ms
1/4 ms 250 Hz
1 ms
2 ms
3 ms
4 ms
O ms
T 3 ms
1/3 ms 333 Hz
1 ms
2 ms
3 ms
4 ms
O ms
T 2 ms
1/2 ms 500 Hz
1 ms
2 ms
3 ms
4 ms
O ms
T 1.5 ms
1/1.5 ms 666 Hz
1 ms
2 ms
3 ms
4 ms
O ms
T 1 ms
1/1 ms 1000 Hz
1 ms
2 ms
3 ms
4 ms
O ms
T .5 ms
1/.5 ms 2000 Hz
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Phase Shift vs. Frequency Group Delay 1 ms
1 ms
250 Hz
²ø 90
1 ms
2 ms
3 ms
4 ms
O ms
333 Hz
²ø 120
1 ms
2 ms
3 ms
4 ms
O ms
500 Hz
²ø 180
1 ms
2 ms
3 ms
4 ms
O ms
666 Hz
²ø 240
1 ms
2 ms
3 ms
4 ms
O ms
1000 Hz
²ø 360
1 ms
2 ms
3 ms
4 ms
O ms
2000 Hz
²ø 720
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1ms (-3 dB) Reflection
Reflection 1 ms late
Comb Freq. 1/1 ms 1000 Hz
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Reflection Arrival vs. Comb Freq.
1 ms
1 kHz
2 ms
500 Hz
4 ms
250 Hz
10 ms
100 Hz
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Reading the Phase TraceIts all about your
measurements time reference
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Smaart Measurement Delay
Time
System Delay
Input
Measurement Signal
Smaart Delay
Reference Signal
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Phase Trace Slope Shows Delay
Phase Trace Slope
Time
Meas
System
Smaart
Ref
Measurement Signal Lags Reference Signal
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Phase Trace Slope Shows Delay
Phase Trace Slope
Time
Meas
System
Smaart
Ref
Measurement Signal Aligned to Reference
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Phase Trace Slope Shows Delay
Phase Trace Slope
Time
Meas
System
Smaart
Ref
Measurement Signal Leads Reference Signal
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The Phase Trace
Reading the Phase Wrap
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Slope vs. Delay
Linear Scale
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Slope vs. Delay
Log Scale
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Polarity Reversal
Same Slope Same Timing
Traces 180 Degrees Apart
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System Alignment
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An analyzer is only a tool YOU make the
decisions

• You decide what to measure.
• You decide which measurements to use.
• You decide what the resulting data means.
• And you decide what to do about it.

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Any idiot can get squiggly line to appear on the
Smaart screen. Our goal is to learn how to
make ones we can make decisions on.
Remember Computers do what we tell them to do,
not what we want them to do.
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To use Smaart for system alignment, we must first

• Verify that we are making our measurements
  properly.
• Verify that it is an appropriate measurement for
  our purpose.

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Dual-Channel Measurement Issues
System Delay x ms
Output Signal
Input Signal
Ref Signal

• Propagation Time
• Linearity - Does response change with level?
• Noise
• Averaging Thresholding
• Coherence

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Coherence
How stable/consistent is your data? Coherence
indicates the linearity/quality of each data
point in your transfer function measurement.

• Given as a value between 0 to 1 (0 - 100)?
• 100 Highest Coherence great data
• 0 Lowest Coherence bogus data

Coherence Scale
100 (Top of Plot)?
0 (Middle of Plot)?
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Coherence

• Three causes of bad coherence
• Bad measurement
• Check measurement delay
• Check measurement signals
• Check measurement set-up
• Check equipment

Look for broad ranges of bad coherence.
Particularly in HF if Smaarts delay is set wrong.
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Coherence

• Three causes of bad coherence
• Bad measurement
• Poor Signal to Noise Ratio
• Turn up measurement level
• Turn down noise

If due to external noise, coherence should
improve with measurement SPL.
At what SPL should I measure?
How loud is loud enough?
(For accurate measurements)?
Slowly turn up your measurement signal level . .
. When the coherence trace no longer improves,
youre there!
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Coherence

• Three causes of bad coherence
• Bad measurement
• Poor Signal to Noise Ratio
• Poor Direct to Reverb Ratio
• Move mic closer to source
• Move source closer to mic
• Damp reverberance

Real World Coherence.
It is common to get a bad Coh spike where you
see a cancellation,
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You Are Responsible For Checking Your Measurement

• Ask yourself, Does this make sense?
• If it doesnt, check your measurement
• You are responsible for checking the validity of
  your measurement Smaart is responsible for
  crunching numbers and drawing pretty lines.

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Transfer Function ModeRecommended Settings
Input Meters Optimum input level is _at_ -12
Where the meter turns
yellow Coherence Threshold 10 - 15 Just
enough to remove the truly bogus data Averages
Acoustic Measurements 64()? Electronic
Measurements 8 -16 More averages better s/n
trace stability Magnitude Threshold 16 bit
Input Device 35 24 bit Input Device 55 FFT
Parameters Acoustic Measurements FFT
FPPO Electronic Measurements FFT 16k or 32k
Remember to set your delay!
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ArtSystem Engineering
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Art Engineering

• Art is the goal
• Engineering makes the goal possible

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Art is the goal.

• Art is a subjective experience.
• If you dont know where youre going, how will
  you know when you get there?
• The system needs to fit the goal
• Your artistic goals set your priorities
• One size does not fit all.
• Make the right compromises

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System EngineeringThe Alignment Process

• Eliminate technical problems
• Fix wiring errors
• Patching errors
• Polarity reversals
• Grounding/Hum problems
• Detect / replace bad components
• Blown drivers
• Bad amplifier channels
• Faulty electronics

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System EngineeringThe Alignment Process

• Eliminate technical problems
• Increase efficiency
• Gain structure
• Better dynamic range
• Good addition through crossovers
• Maximize power-bandwidth
• Proper limiter settings / system protection

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System EngineeringThe Alignment Process

• Eliminate technical problems
• Increase efficiency
• Increase consistency
• Consistent in Level and Tonality
• Everyone gets the same show
• Mix translates well to audience
• System responds to equalization

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System EngineeringThe Alignment Process

• Eliminate technical problems
• Increase efficiency
• Increase consistency
• Adapt to changing environments
• Changes in temperature and humidity
• Changes in acoustics with addition of audience
• Detection of problems during performance

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System EngineeringThe Alignment Process

• Eliminate technical problems
• Increase efficiency
• Increase consistency
• Adapt to changing environments
• Give objective feedback/reinforcement
• Quantify what youre hearing
• Peaks vs dips
• True center frequency and bandwidth
• Help for tired ears

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System Alignment
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Systems
Input
Output
System

• From single devices to complex combinations of
  equipment and acoustical environments
• Loudspeakers (in an acoustic environment)?
• Equalizers
• Consoles
• Microphones
• Complete Sound Systems

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Systems
System 1
System 2
System 3
Input
Output

• Total system response is the sum of responses of
  the individual system elements
• Links in a chain - weakest link
• Align from Individual Combined Systems

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System Engineering Key Concept

• Interactions are greatest where signals are equal
  level - Crossover Points

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System Engineering Key Concept

• Interactions are greatest where signals are equal
  level - Crossover Points
• Phase determines the interaction
• Phase Shift (Filters)?
• Polarity (Wiring)?
• Delay (Time Alignment)?

Align from Loudest Quietest Systems
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Our goal is to fix our systemnot the trace on
the screen.
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Key Concept

• Solve problem at source
• The closer to the source . . .
  the more effective the solution.

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System Engineering Key Concepts

• Use the right tool
• Every item in your tool box is a hammer . . .
  except your wood chisels, theyre
  screwdrivers.

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Tools in Order of Use

• Acoustic Design / Treatment
• Equipment Choice / Maintenance
• System Design - Design to align

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Tools in Order of Use

• Acoustic Design / Treatment
• Equipment Choice / Maintenance
• System Design - Design to align
• Level
• Delay

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Tools in Order of Use

• Acoustic Design / Treatment
• Equipment Choice / Maintenance
• System Design - Design to align
• Level
• Delay
• And lastly . . . EQ

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Problem
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Solution(s)?
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Setting Delays
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Setting Delays
Delay set at point B
A
Main
Delay
Delay speaker leads
Distance Time Remember Doubling
Distances
Main speaker leads
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1 ms 1 kHz 1 ft
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Example Delay vs.
Physical Positioning
Delay _at_ 15 ms
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Example Delay vs.
Physical Positioning
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System engineering . . .Is optimizing your
compromises

• Its all give and take.

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System EngineeringThe Serenity Prayer . . .

• Grant me the SerenityTo accept the things I
  cannot change
• Courage to change the things I can,
• And Wisdom to know the difference.

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System Example