tecnogadget
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Although I've been using Umik1 for years, at first I always seem to have it right, but then the results end up driving me crazy with the same doubt:
What combination of microphone positioning and calibration file gives us the real response our ears perceive at the listening point above the transition frequency? Especially if one wants to take measurements to perform room and Eq correction, tailoring the speaker response with a target curve.
DIRAC LIVE Manual:
The same is true for almost any mainstream room eq software like Audyssey. They all recommend using the 90º cal file and point the mic to the ceiling.
More specialized software like Acourate, Audiolense, Focus Fidelity, recommends using the microphone horizontally pointing at the center between the main channels and 0º calibration file.
IN PRACTICE
The issue arises when a person has a multi-channel system for enjoying movies but at the same time uses it as a stereo system for listening to music. Ideally, you choose a preferred target curve and EQ all channels to follow the same curve (in my case, Harman or Olive/Toole).
A UMIK1 and most measurements microphones are omnidirectional, but this does not mean they are 100% omnidirectional in all frequencies. So when your surround and back surround speakers are positioned behind your listening position, if pointing the microphone horizontally toward the center between the front channels, the microphone would be oriented backwards with respect to the surrounds, which would be causing a kind of "acoustic shadow".
Here are some in-room measurements I have taken, plotted only from 1kHz onwards to focus on the difference in microphone orientation and not on room modal interactions or loudspeaker response:
As you can see, in both cases there ends up being a difference of about 5dB in the treble region between one way of orienting the microphone and the other, with their respective calibration files ( all measurements have been made without eq, hence no target curve applied yet)
Which makes me absolutely doubt which is the real response I should take for the target curve, since a difference of +-5dB would absolutely change the tonal balance and puts us on the fine line between dull and bright.
If it were a question of loudspeaker response measurement, vs. room response measurement, it is easier to agree that the former would be done horizontally at 0º and the latter vertically at 90º.
The conclusion I draw from my measurements is that for room/speaker eq, if we measure horizontally at 0º the direct sound of the speaker takes precedence, and if we measure vertically at 90º reflections and diffuse field are added into the measurement...and unless I am wrong, this is the way our ears end up hearing the music.
Should we limit to one method or the other, or does it make sense to consider a hybrid model? One that considers the room as two halves from the listening position
-Alternative option 1: Measure the main and center speakers with microphone pointing horizontally to the front and cal file 0º, and measure the surround speakers with microphone pointing to the ceiling and cal file 90º.
-Alternative option 2: Measure the main channels and center speaker with microphone pointing horizontally to the front and cal file 0º, measure the surround channels with microphone horizontal and cal file 0º but pointing backward from the listening position, this way we achieve a better line of sight between the surrounds and the microphone.
What combination of microphone positioning and calibration file gives us the real response our ears perceive at the listening point above the transition frequency? Especially if one wants to take measurements to perform room and Eq correction, tailoring the speaker response with a target curve.
THEORY
DIRAC LIVE Manual:
The same is true for almost any mainstream room eq software like Audyssey. They all recommend using the 90º cal file and point the mic to the ceiling.
More specialized software like Acourate, Audiolense, Focus Fidelity, recommends using the microphone horizontally pointing at the center between the main channels and 0º calibration file.
IN PRACTICE
The issue arises when a person has a multi-channel system for enjoying movies but at the same time uses it as a stereo system for listening to music. Ideally, you choose a preferred target curve and EQ all channels to follow the same curve (in my case, Harman or Olive/Toole).
A UMIK1 and most measurements microphones are omnidirectional, but this does not mean they are 100% omnidirectional in all frequencies. So when your surround and back surround speakers are positioned behind your listening position, if pointing the microphone horizontally toward the center between the front channels, the microphone would be oriented backwards with respect to the surrounds, which would be causing a kind of "acoustic shadow".
Here are some in-room measurements I have taken, plotted only from 1kHz onwards to focus on the difference in microphone orientation and not on room modal interactions or loudspeaker response:
As you can see, in both cases there ends up being a difference of about 5dB in the treble region between one way of orienting the microphone and the other, with their respective calibration files ( all measurements have been made without eq, hence no target curve applied yet)
Which makes me absolutely doubt which is the real response I should take for the target curve, since a difference of +-5dB would absolutely change the tonal balance and puts us on the fine line between dull and bright.
If it were a question of loudspeaker response measurement, vs. room response measurement, it is easier to agree that the former would be done horizontally at 0º and the latter vertically at 90º.
The conclusion I draw from my measurements is that for room/speaker eq, if we measure horizontally at 0º the direct sound of the speaker takes precedence, and if we measure vertically at 90º reflections and diffuse field are added into the measurement...and unless I am wrong, this is the way our ears end up hearing the music.
Should we limit to one method or the other, or does it make sense to consider a hybrid model? One that considers the room as two halves from the listening position
-Alternative option 1: Measure the main and center speakers with microphone pointing horizontally to the front and cal file 0º, and measure the surround speakers with microphone pointing to the ceiling and cal file 90º.
-Alternative option 2: Measure the main channels and center speaker with microphone pointing horizontally to the front and cal file 0º, measure the surround channels with microphone horizontal and cal file 0º but pointing backward from the listening position, this way we achieve a better line of sight between the surrounds and the microphone.