Week 29 - Advanced System Tuning - Phase Alignment Flashcards
What is the transfer function and what does it allow measurements of?
Transfer function is a comparison of the input of the system to the output of the system
In SMAART, this allows for measurements of magnitude, phase, and impulse response
What is magnitude?
Magnitude is a comparison of the amplitude of the two signals being sent to the transfer engine
The magnitude window shows the gain/loss or deviation from the center 0DB Line
What is coherence and what are some reasons for a low coherence reading?
The coherence trace displays the stability of the transfer function over the frequency range. This is telling you if your measurement is accurate
If your coherence is low, you most likely have an issue with either the delay time, reverberations, or the signal to noise ratio of your measurement signal
What is ground bounce?
Reflections from a speaker off the ground, affecting our measurements
How can we diminish the effects of ground bounce?
Best: Adjust the height with each measurement in an average
Alternate methods:
Block reflections with a road case/baffle/other item
Measure with the mic low to the ground
What is an inverted trace and when would we use it?
An inverted trace simply displays the measurement upside down.
This is helpful when applying an EQ curve to the PA
When do we use delay locator
When performing a transfer function, delay locator must be done before any measurements are taken
It must also be done any time that the test microphone is moved
What is impulse response, and how do we use it when phase aligning?
CMnd + I to open in SMAART
Impulse response is the time domain response of a system under test to an impulsive stimulus
If the measurement signal is polarity reversed from the reference signal, it will display a negative voltage. This is due to a polarity reversal somewhere in our system (Amp wiring is a good place to check first)
Excursion upwards, polarity coherence
Excursion downwards, nah
What do we actually use impulse response measurements for?
Setting the delay time for the transfer engine
Identifying polarity reversals
What is the phase window?
Similar to the magnitude window, the phase window shows the phase relationship between two signals across the frequency range.
The Y axis shows the 360 degrees of a waveform
What would we use phase measurements for?
Time aligning one sound source to another
Time aligning subs to the main PA at the crossover point
Time aligning delay speakers or front fill speakers to the main PA
What are spatial crossovers?
Takes measurements for phase where two zones are equal amplitude
This is where any phase interactions will be greatest
What are spectral crossovers?
Focus on phase interactions where multiple drivers interact
Focus on where subs and mains have equal amplitude, focus on where phase traces are equal
How do we time align multiple speakers?
Find the delta, the difference in arrival time between the two speakers
What are the three primary steps to system tuning?
Verification:
Each driver/speaker is working
Polarity
Response:
Level
EQ
Timing (With attention to spatial and spectral crossover points)
