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Long enough that it would be nice to get back OT.
Sure. But my thought was somewhat serious, though: why do we measure an empty seat? It's not empty when the system is in use. There is absorption, diffusion, and reflection caused by various parts of the human body, head, and clothing that are simply absent in such measurements. It's no different than why we re-calibrate when replacing our seats: the physics change.

Genuinely curious.
 

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I have always placed a very high importance on accurate placement of the mic for the first calibration measurement, and for subsequent REW measurements that rely on same-spot mic placement. On a whim, I created a small procedure that describes how I place the mic.
I’ll assume that is humor. Besides, mic in front of face would not be the proper placement. The mic needs to be in the center of your head. Good luck trying that.
Is this primarily for the purpose of time-alignment? Because I’ve never seen where basic frequency response measurements need that much fuss. But then, I think I’ve been fortunate enough to have an easy room...

Regards,
Wayne A. Pflughaupt
 

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Sure. But my thought was somewhat serious, though: why do we measure an empty seat? It's not empty when the system is in use. There is absorption, diffusion, and reflection caused by various parts of the human body, head, and clothing that are simply absent in such measurements. It's no different than why we re-calibrate when replacing our seats: the physics change.

Genuinely curious.

A number of reasons. First, there is no mic placement in the middle of one's head. Second, regardless of the extraordinary efforts you might go through, I don't think there would be a significant difference in the results. Can we just agree that it is a bad idea and move on? If it were really something to consider, don't you think the various REW guides would bring it up as a recommendation?
 

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Is this primarily for the purpose of time-alignment? Because I’ve never seen where basic frequency response measurements need that much fuss. But then, I think I’ve been fortunate enough to have an easy room...

Regards,
Wayne A. Pflughaupt
The importance of the first mic placement is the accurate calculation of trims and delays, which are critical to imaging and the sound stage.
 

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A number of reasons. First, there is no mic placement in the middle of one's head. Second, regardless of the extraordinary efforts you might go through, I don't think there would be a significant difference in the results. Can we just agree that it is a bad idea and move on?
It is a logical extension of the countless posts asking if someone should re-calibrate after moving a seat or a coffee table, should I cover my leather seats with something soft, etc. The answer is yes because those things do make a difference. Anyways, the recommendation is always to measure/EQ the room as it will be when the system is used. Our seats aren't empty when our systems are used. There are a few hundred pounds worth of bodies there taking up space that essentially changes the size, shape, and mass of the seats that the speakers will be interacting with to some degree. It has been my experience that when changing out seats for something new, my frequency response is all out of whack. So, it is simply a logical question that follows from standard practices.

I'll grant that you can't place the mic right in the middle of your head. And I can't say how much of a difference there would be. Maybe someone has tried it - I don't know. That is why I asked. But it seems logical that one would want the same environment when measuring and equalizing as what will be in play when listening. I hope at least you can understand where I'm coming from.
 

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It is a logical extension of the countless posts asking if someone should re-calibrate after moving a seat or a coffee table, should I cover my leather seats with something soft, etc. The answer is yes because those things do make a difference. Anyways, the recommendation is always to measure/EQ the room as it will be when the system is used. Our seats aren't empty when our systems are used. There are a few hundred pounds worth of bodies there taking up space that essentially changes the size, shape, and mass of the seats that the speakers will be interacting with to some degree. It has been my experience that when changing out seats for something new, my frequency response is all out of whack. So, it is simply a logical question that follows from standard practices.

I'll grant that you can't place the mic right in the middle of your head. And I can't say how much of a difference there would be. Maybe someone has tried it - I don't know. That is why I asked. But it seems logical that one would want the same environment when measuring and equalizing as what will be in play when listening. I hope at least you can understand where I'm coming from.
Be careful, telling by the responses you've got you're already inducing major cognitive dissonance in the OCD crowd :)

Yes you want to measure with all objects in place. But some objects move or aren't always there and therefore it becomes and exercise in futility.

With regard to measuring with yourself placed at the main listening position you would need to put microphones in your ears. If you have ever looked at the results of such measurements you'll see that the response is highly erratic and changes significantly even with tiny head movements. In the end you have to compare those measurements to some reference. What is that reference?
When measuring with an omnidirectional mic the task gets much easier as this is how the mixing/mastering environment was measured and optimized as well. Now the results will always be the same as your body would have changed the sound field in the mixing/mastering environment the very same way it will change it at home. Therefore your body doesn't need to be part of the measuring process.
 

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Do you have a scaling factor set up on your laptop? If you are using 200% scaling (for example) your 1920 x 1080 screen effectively looks like 960 x 540. Fixed y axis grid line increments wouldn't work well with the varying vertical span, meaning users would end up having to adjust the grid line spacing when the vertical SPL span or the window height changed. REW adjusts the grid line spacing so they don't get too sparse or too dense.
Thank you so much John. I had forgotten that with my ageing years at some stage a long time ago I must have opted to apply a 165% scaling factor to make reading font on my laptop easier.
All good now.
Cheers.
 

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I have an on-going issue with my center channel speaker's response curve:



The issue I am trying to address is the 12dB dip centered at 253Hz, and approx. 100Hz wide. The conventional wisdom is to vary the placement of the center channel speaker, re-measure, and determine whether the dip is sensitive to different placements. The speaker is on a dedicated speaker stand, with the front baffle 42" from the back wall, and with the driver height 23" from the floor.



My experimentation with placement (so far) has been limited to moving the speaker forwards and backwards, and moving the MLP forwards and backwards. I have not tried raising or lowering the speaker (because the stand has no adjustment), nor have I tried moving the speaker to the left or right (because I want to preserve the precise symmetry of my speaker layout).

I came across this interesting web site: SBIR Calculator

When I fill out the forms and click Compute, I get the following two results:





I am looking for some guidance on interpreting the results. Do any of the calculations shed any light on what might be causing the 253Hz dip for the center channel? If yes, it is not obvious to me. Any advice would be appreciated.
 
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I have not tried raising or lowering the speaker (because the stand has no adjustment), nor have I tried moving the speaker to the left or right (because I want to preserve the precise symmetry of my speaker layout).
Uhm, wouldn't it be much more productive just to try that?
 

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Uhm, wouldn't it be much more productive just to try that?
Probably, but my question was whether anyone could see in the results anything that might suggest that the current placement is an issue. To change the speaker height, I would need to find a new speaker stand. The current stand is 18” high, and the tallest stand that I have found in my internet search is 22”. The speaker can only be raised 8” before it would block the TV monitor.

I guess testing out 22” would be the logical next step.
 

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Probably, but my question was whether anyone could see in the results anything that might suggest that the current placement is an issue. To change the speaker height, I would need to find a new speaker stand. The current stand is 18” high, and the tallest stand that I have found in my internet search is 22”. The speaker can only be raised 8” before it would block the TV monitor.

I guess testing out 22” would be the logical next step.
Sure, you can choose to ignore the productive approach and try guessing instead. Not really what this thread is about, is it? Good luck.
 

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Sure, you can choose to ignore the productive approach and try guessing instead. Not really what this thread is about, is it? Good luck.
If vertical changes do nothing to alleviate the 253Hz dip, what are other tests you might suggest? Left/right adjustments adversely impact the soundstage, so I am reluctant to do this.
 

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If vertical changes do nothing to alleviate the 253Hz dip, what are other tests you might suggest? Left/right adjustments adversely impact the soundstage, so I am reluctant to do this.
Well, you first want to find out what's causing the issue, don't you? Then you can decide what to do about it. For some issues there is no fix.
 

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If vertical changes do nothing to alleviate the 253Hz dip, what are other tests you might suggest? Left/right adjustments adversely impact the soundstage, so I am reluctant to do this.
I'm aware you have ceiling treatments but what about the ceiling fan? Maybe the blades are causing reflection? Try it with fan moving or remove the blades to see if it helped at all. Its gonna be reflection of something. Could it be the tv? Put a blanket over the tv and see if the sbir from the tv isn't causing this. Only 2 things I can see to try without costing anything but little time.
 

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I'm aware you have ceiling treatments but what about the ceiling fan? Maybe the blades are causing reflection? Try it with fan moving or remove the blades to see if it helped at all. Its gonna be reflection of something. Could it be the tv? Put a blanket over the tv and see if the sbir from the tv isn't causing this. Only 2 things I can see to try without costing anything but little time.
I have done extensive tests with the ceiling fan. It causes some minor reflections on the ETC measurement, but has no effect on the frequency response. And I have ruled out front wall SBIR based on the for,USA for calculating SBIR. As Markus has pointed out, the next logical thing to try is vertical positioning.
 

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Probably, but my question was whether anyone could see in the results anything that might suggest that the current placement is an issue. To change the speaker height, I would need to find a new speaker stand. The current stand is 18” high, and the tallest stand that I have found in my internet search is 22”. The speaker can only be raised 8” before it would block the TV monitor.

I guess testing out 22” would be the logical next step.

Just as an FYI, I have the same speakers stands as you, the Sanus Steel Series. I had bought the 22" SFC22 center speaker stand, but wanted another 4" of height to fit perfectly under my TV. So I ordered the SF26 (26" bookshelf speaker stands) and replaced just the 2 vertical tubes of the 22" with the 26" tubes, perfect. You said you could raise your center by 8" (18" + 8" = 26") which might be a consideration if your measurements are indeed better at that height.:)
 

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