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What do sudden deep cuts in the measurements mean?
Old 1 week ago
  #1
Gear Head
 

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What do sudden deep cuts in the measurements mean?

What do sudden deep cuts in the measurements mean?

This is a measurement from a stereo system, i.e. two speakers playing simultaneously.



I also noticed that if I move the measurement microphone slightly, then I can make some of the cuts disappear. So does this mean that they're phase cancellations that occur around the listening position?

How can such be treated? By moving the listening position slightly or by moving the speakers? Or adjusting their angle or what?
Old 1 week ago
  #2
Lives for gear
 

Phase cancellations are caused by reflections coming from the room boundaries and objects within the room. The best thing to try is to install first reflection absorbers. A first reflection is a reflection that only bounces from one surface.
Old 1 week ago
  #3
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You can view those reflections on an IR or ETC graph. But with two speakers running, the other speaker can appear like a reflection, plus all of it's reflections make it impossible to tell anything really.
Note that when two sources add coherently the result will be say +6dB peak. But two coherent sources out of phase will cancel very deeply. As you can see.
A narrow notch may not be present at all at the other ear. Also it has been believed that the ear will not distinguish anomalies narrower than 1/3 of an octave.

Often, a low notch like that is caused by a reflection from the Front Wall or the Floor. The higher ones could be first order reflections as Opus has said. Even a desk can be a null causing reflector at higher frequencies.

DD
Old 1 week ago
  #4
Gear Head
 

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Quote:
Originally Posted by DanDan View Post
Also it has been believed that the ear will not distinguish anomalies narrower than 1/3 of an octave.
So does that mean that viewing the measurements at 1/3th octave smoothing is enough for acoustic measurements and treatment?

That'd make doing the treatment a lot easier.

However, for correcting the response with EQ I've found that simply manually sweeping sine waves and listening gives accurate results. This can be automated by programs such as REW that can generate EQ settings from the measurements.
Old 1 week ago
  #5
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DanDan's Avatar
Analysis

Quote:
viewing the measurements at 1/3th octave smoothing is enough for acoustic measurements and treatment?
This should give a sense of what is actually audible, although it applies to the general population. I think 1/6 might be more appropriate for professional listeners. We need less to no smoothing to see anomalies that we are working on. For instance of you suspect say a floor of causing a 100Hz notch, Zoom to say 50-150Hz no smoothing. Move the mic towards the floor to see if the frequency of the null rises.

DD
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