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Image 8-3
8.3
Measurement
8.3.1
Preparations
About
Following preparations should be done before performing correct measurement calibration of the measurement microphones.
Adjust the microphone preamp gain of all channels individually, so that all microphones induce the same voltage when being exposed
to the same SPL. Place all used microphones at close quarters on axis of a distant loudspeaker of the setup. Thus they are virtually
at the same position as seen from the distant loudspeaker. Play back pink noise with the Control Unit's player or feed pink noise to
the system's audio input and route the signal to that distant speaker using the Scene Designer. Adjust the preamp's gain of each
microphone to equal amplitude using the level meters on the preamp or the level meters in the settings tab of the System Tuning
extension.
Measurement Level
The speakers nearest to the reference point should induce a SPL of around 80dBC at the reference point. This level is sufficient
for good Signal to Noise Ratio (SNR) of the measurements under typical conditions. Try to achieve a SNR of at least 10dB. If the
installed loudspeakers are not powerful enough to reach reasonable levels the venue's noise floor has to be reduced.
The microphone positions nearest to the loudspeakers should be checked against clipping with a test run of sweeps in the System
Tuning extension. Proceed similar with the subwoofers because room mode distribution and pressure chamber effects often cause
microphone clipping even at low playback volume. The gain of subwoofer can be reduced globally using the subwoofer attenuation
option in the settings tab. An attenuation of -24dB is a good starting point for further adjustments. This attenuation setting applies
to the measurement routine only.
Microphone Placement
By measuring every speaker's transfer function at several positions different acoustic conditions of the room and speaker installation
as well as the speaker's directivity are taken into account. Averaging all measurements of a certain loudspeaker avoids equalization
of singular acoustical phenomena.
Therefore it is necessary to sample the whole desired audience area with microphone positions which have to be distributed evenly.
The height of the microphone capsule should be at the desired ear height of the future listeners. For a seated auditorium a micro-
phone height of 1.20m, for a standing auditorium 1.70m above floor level will work. If there are acoustically reflecting objects near
the microphones like e.g. the backrest of an armchair in seated venues, the microphones' tips should be at least 0.30m above those
barriers to prevent acoustical shadowing and minimize comb filter effects due to reflections.
The error thresholds for SNR and IRNR can be set by the user in the settings tab. The default values are 10dB for SNR and 45dB
for INR. To improve those ratios, increase the playback level of the stimulus, still paying attention to clipping. If you have reached
maximum output or input level, try to decrease ambient noise during measurement.
8.3.2
Running A Measurement
To run a measurement
1. Click the Start button in the Measurement tab
Note: The measurement signal is played back via the selected loudspeakers in chronological order in one loudspeaker group
after the other. The remaining duration of the measurement will be displayed at the bottom of the window.
2. Once a measurement run is finished, the measurements are analyzed regarding Signal to Noise Ratio, IR Noise Ratio and
Clipping of the measurement mic signal
-
Select lines with red cells
-
Adjust input gain on your mic preamp or output gain on the IOSONO CORE
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Repeat the measurement only for selected/red cells (image 8-4)
Note: In the window Measurement Summary each measured speaker is repre- sented as a rows and microphone inputs/mea-
surement positions as columns. The color of the matrix' cells indicate, whether all checks have been passed. Green
indicates a correct measurement while yellow and red indicates critical or failed checks. Furthermore there are check-
boxes adjacent to every row for repeating the measurement of each particular speaker. Right-click onto the matrix opens
a context menu offers selecting or deselecting all speakers to be measured again. Place the cursor on one of the matrix
cells to display the measurement check's results at the bottom of the window. Clicking the button at the bottom of the
dialogue will start the repetition of the marked measurements or proceed with the process when no repetitions are set.
3. If none of the checkboxes is marked, click Proceed
R5906746 IOSONO CORE 08/05/2017
8. Advanced System Tuning With The System Tuning Extension
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