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Interpreting REW output from speakers System Audio, Dynaudio and Neumann

rolfrander

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I am new to room measurements, and I am not quite sure how to interpret this.

I have compared 3 sets of speakers, positioned at approx the same place (all three are placed and not moved between measurements, so there is ca 20 cm between them):
  • Red: Dynaudio Emit 20
  • Blue: System Audio SA510, The Dynaudio and the SA are connected to a Marantz NR1603.
  • Green: Neumann KH80DSP

Details regarding the setup:
  • This is a stereo-measurement.
  • Before each test I adjusted the volume to 80dB SPL using pink noise at -15 dBFS.
  • The graph has 1/12 smoothing.
  • The room is practically square (approx 4,4 meters, height 2,4) and there is no treatment other than some furniture. There are wooden panels on walls and ceiling and a thick carpet on the floor.
First: the well at 50Hz.
At first I thought this was an error, it seemed consistent across different positions, and being at exactly 50Hz I guessed this might be some mains filtering in the AD-converter of my soundcard. So I changed from using a RadioShack SPL-meter as input to a new UMIK-1 with calibration file. But the well is still there. Measuring just one channel makes this a lot less deep. I see something similar in the REW room-simulator, but at a higher frequency.

Questions:
  • is there really a cancellation at 50Hz, or does it just look like that because of peaks at 40 and 70?
  • The wavelength at 50Hz is 6,86m, approx 1,5 times the measurements of the room, does the standing wave cancel itself?
  • What can be done to fix this?

Then there is the roll-off after 10K, this seems to fall a lot more than other REW-plots I have seen. Questions:
  • Is this an error in the test, or an attribute of the room?
  • How can I check this?
Then there is something going on between 80 Hz and 160 Hz, I'll get to that later...

Other than this, the measurements seem reasonably flat above 300Hz, is there a need for any treatment except the bass-issues?

Measurements:

1708784796434.png


Room sim: this is as exact I can get different distances, but of course the actual room is more complicated than the simulation.
1708784424614.png


Moving the simulated speakers a few centimeters adds a deep well:
1708784499155.png
 
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