====== Recognition of disturbing spatial reflections in the pulse response ======

For a good stereo image, a balanced ratio of direct and diffused sound is necessary. Above all, early reflections caused by the room or the interior contents can have a disturbing effect. The sound is reflected from the room or the room contents and mixes with the direct sound from the speaker. Good stereo localization is guaranteed if the first 0.02 seconds (20 milliseconds) consists of undisturbed direct sound (Footnote 1)

With Acourate, one can determine both the strength and source location of disturbing reflections. Depending on the cause of reflections, these can then be diminished by different methods. On walls one can place absorbers, on the floor, high-pile carpets, possibly even furniture can be moved. The success or failure of these measures can then be compared again with a new measurement with Acourate.

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(If there is no data from a log sweep measurement, a log sweep must first be created.)\\
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{{:wiki:anhang:anleitungen:reflexionen:01_anl_reflexionen.png?nolink&}}

1. Open the file Pulse44L.dbl, then click button no.2 at Active Curve to load the next file Pulse44R.dbl as second curve.\\
2. Select the time chart by View - Time to display only the time behaviour of the recorded pulses\\
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{{:wiki:anhang:anleitungen:reflexionen:02_anl_reflexionen.png?nolink&}}

3. Left mouse-click into the chart left side of the pulse start, then right mouse-click about 0.2 seconds later\\
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{{:wiki:anhang:anleitungen:reflexionen:03_anl_reflexionen.png?nolink&}}

4. Select the magnifying button to zoom into the marked area\\
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{{:wiki:anhang:anleitungen:reflexionen:04_anl_reflexionen.png?nolink&}}

5. At the right side of the time chart the position of the maximum pulse value is displayed\\
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{{:wiki:anhang:anleitungen:reflexionen:05_anl_reflexionen.png?nolink&}}

6. Enter the position of the max. pulse value into the edit field below the time chart, confirm by Enter key\\
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{{:wiki:anhang:anleitungen:reflexionen:06_anl_reflexionen.png?nolink&}}

7. <font 12.0pt/inherit;;inherit;;inherit>Right-click on a peak further to the right in the Time window.</font>\\
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{{:wiki:anhang:anleitungen:reflexionen:07_anl_reflexionen.png?nolink&}}

8. <font 12.0pt/inherit;;inherit;;inherit>On the right side of the time window, you can see the distance the reflected sound traveled in addition to the direct sound until it arrived at the listening position.</font>\\
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{{:wiki:anhang:anleitungen:reflexionen:08_anl_reflexionen.png?nolink&}}

<font 12.0pt/inherit;;inherit;;inherit>Reflections which only come from the left or right channel have a particularly negative effect because they disturb the necessary symmetry for the functioning of the stereo system</font> .\\
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{{:wiki:anhang:anleitungen:reflexionen:09_anl_reflexionen.png?nolink&}}

9. <font 12.0pt/inherit;;inherit;;inherit>Once you have measured the distance that the sound additionally requires, the cause can be determined as follows: Stretch a string from the tweeter of the loudspeaker to the listening position, lengthen the string by the specified distance and determine which areas can be touched with the string: The Blue line is the path of direct sound from the speaker to the measuring microphone. The red line is the longer path of the diffuse sound. Instead of a cord, using a laser range finder is helpful. This way, even reflection points from the ceiling of the listening room can be measured easily.</font>

=====  Footnote 1  =====

<font 12pt/inherit;;inherit;;inherit>Undisturbed direct sound is considered to be -20 dB down from the peak impulse. You can see this in Acourate by choosing the ETC curve display at the bottom of the time window. Now hover the mouse over a reflected impulse that is within the first 20 ms after the main impulse. Observe at the top left of the window the dB value of the reflection compared to the main impulse.</font>

{{:en:wiki:anhang:anleitungen:clipboard_image.jpg?nolink&400x671  |Early_Reflection_ETC}}