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post #3781 of 9620
Quote:
Originally Posted by jim19611961 View Post


I think whats at work here is phasing.

http://www.eetimes.com/design/audio-design/4015884/Using-the-Decibel--Part-3-Combining-decibels-and-using-log-charts

In the above link (table 2-9), you can see that when two signals combine, the resulting amplitude differs with respect to phase. 0 degrees = +6db, 90 degrees = +3db, 120 degrees = +0 db, 180 degrees = cancellation.

If the distance from the sub to the listening position is different from the mains to listening position, then their will be phase issues. And they will be different for different frequencies on the basis that their corresponding wavelengths are different. So in this case, I think the best approach is to measure with mains AND sub operating, and making small changes in location in the sub and remeasuring. Getting each to look good driven separately is a good starting point, but if the cumulative FR curve due to phase is bumpy, then you must tackle the problem measuring both working together.

 

Jim, when you say making small changes in location in the sub, are you referring to actually moving the subs, or are you referring to adjusting the sub timing delays in the AVR menu (what we have been calling the "sub distance tweak")?  Or try both?

Gear mentioned in this thread:

post #3782 of 9620
Quote:
Originally Posted by AustinJerry View Post


On a separate topic, for Markus, or anyone who has feedback, is there a way to use REW to determine the actual room modes for an irregularly-shaped room?  We have been using the Room Mode Calculator to calculate the axial standing waves, but I think this tool assumes a rectangular room.

Another question along the same lines, what influence does interior build features play on top of a "regular rectangular" shaped room to influence room modes? For example, I have a soffit around the entire ceiling/wall perimeter of my room, as well as 7 Cherry wood columns. Is it safe to assume the basic axial modes would still exist (as calculated) with the overall rectangular room dimensions, or does that go to crap with these other items in the equation?
post #3783 of 9620
Quote:
Originally Posted by AustinJerry View Post

Good feedback, Markus, thanks.  Let's revisit this when I have the new measurements.

On a separate topic, for Markus, or anyone who has feedback, is there a way to use REW to determine the actual room modes for an irregularly-shaped room?  We have been using the Room Mode Calculator to calculate the axial standing waves, but I think this tool assumes a rectangular room.

My listening room has a 16.3' left side wall, and a 12.9' right side wall, with the back of the room opening out into a foyer.  I can plug either of these two measurements into the Calculator, but I think the actual modes will be somewhat different.

Take measurements smile.gif This is the most practical approach in determining a room's unique behavior.
Irregular shaped rooms don't exhibit less modes, only the spatial distribution differs.
post #3784 of 9620
Quote:
Originally Posted by AustinJerry View Post

Jim, when you say making small changes in location in the sub, are you referring to actually moving the subs, or are you referring to adjusting the sub timing delays in the AVR menu (what we have been calling the "sub distance tweak")?  Or try both?

I am not sure which will be better or more effective. But since dialing the AVR delay setting is easier than moving the sub around, I might try that first smile.gif
post #3785 of 9620
Quote:
Originally Posted by AustinJerry View Post

...is there a way to use REW to determine the actual room modes for an irregularly-shaped room?  We have been using the Room Mode Calculator to calculate the axial standing waves, but I think this tool assumes a rectangular room.
The calculator not only assumes a rectangular sealed room, but also assumes perfect reflectivity from the walls and zero transmission loss through the air. This is why the calculator is sometimes off by a few hertz when compared to actual in-room measurements (though still close enough to be a useful tool).

For rooms that aren't rectangular and closed, the easy thing to do is look for patterns in the measurements. For example, when Saturn94 posted his measurement, there were various peaks and dips. What caught my eye were the particular dips around 60Hz, 120Hz, 180Hz, 240Hz, 300Hz.

Without knowing room dimensions nor subwoofer/speaker placement, I would guess that they were due to room modes. Can't imagine those dips would be due to the boundry cancellation problem discussed a couple months back.
post #3786 of 9620
Quote:
Originally Posted by sdurani View Post

The calculator not only assumes a rectangular sealed room, but also assumes perfect reflectivity from the walls and zero transmission loss through the air. This is why the calculator is sometimes off by a few hertz when compared to actual in-room measurements (though still close enough to be a useful tool).

Transmission loss through air is insignificant at low frequencies. Please see http://sengpielaudio.com/calculator-air.htm
The problem with most mode calculators is that they assume the source to be located in a room corner and the listener in the opposite corner. Not very realistic.
post #3787 of 9620
Quote:
Originally Posted by markus767 View Post


How does L+R+Sub behave when measured a couple of inches to the left and the right?

 

Here are three measurements, the first at the MLP, and the second and third 12" to the right and left.  Unfortunately, since I continue to work on my early reflections, there have been significant changes to treatments since the graphs I posted yesterday, so the actual response curves look quite different.  However, I think the measurements demonstrate a reasonable uniformity to the bass response up to 85Hz (crossover is at 80Hz), at least across these three positions.  The graph represents Left+Right+Subs.

 

 

 

 


Edited by AustinJerry - 6/27/13 at 5:15pm
post #3788 of 9620
My UMM-6 mic has stopped working. mad.gif I still have an EMM-6 and a legacy kit, but it is somewhat more difficult to use, but will do until I decide whether to replace the UMM-6.

Since CSL is now selling a calibrated UMIK-1, and since the UMIK-1 has slightly better integration with REW, is there any reason I shouldn't order this mic? (Other than the fact it is back-ordered)
post #3789 of 9620
Jerry, I can't read the labels on your graphs.
post #3790 of 9620
Quote:
Originally Posted by markus767 View Post

Jerry, I can't read the labels on your graphs.

 

Please use the correct terminology:  you can't read the Titles, or the Legends?  When you click on a graph, does it open up in your browser to a larger size?

post #3791 of 9620
Quote:
Originally Posted by AustinJerry View Post

Quote:
Originally Posted by markus767 View Post

Jerry, I can't read the labels on your graphs.

 

Please use the correct terminology:  you can't read the Titles, or the Legends?  When you click on a graph, does it open up in your browser to a larger size?

 

I can read them but they aren't as clear as usual. Did you squish the jpegs or something?

post #3792 of 9620
Quote:
Originally Posted by AustinJerry View Post

My UMM-6 mic has stopped working. mad.gif I still have an EMM-6 and a legacy kit, but it is somewhat more difficult to use, but will do until I decide whether to replace the UMM-6.

Since CSL is now selling a calibrated UMIK-1, and since the UMIK-1 has slightly better integration with REW, is there any reason I shouldn't order this mic? (Other than the fact it is back-ordered)

 

Wasn't there a reason we all went for the UMM-6?  Something to with the calibration files?  Rings a vague bell.

 

I assume yours has gone into terminal decline after its head got snapped off?

post #3793 of 9620
I recall calibration files (which appears to be resolved if the mic is coming directly from CSL rather than having to send it out for calibration?) as well as the UMIK-1 not measuring below 15 or 20Hz. I believe this may have also been addressed so some of the advice may be outdated?
post #3794 of 9620
I didn't think my Can't Remeber Stuff (CRS) disease was contagious, but I guess it is! smile.gif

Mark
post #3795 of 9620
Quote:
Originally Posted by kbarnes701 View Post

Wasn't there a reason we all went for the UMM-6?  Something to with the calibration files?  Rings a vague bell.

I assume yours has gone into terminal decline after its head got snapped off?

Both mics are available from CSL with custom calibration files now, so that reason has been removed.

I don't know what happened to the mic. I removed the gaffer tape and inspected the wires, and everything seems to be intact. Both of my computers refuse to recognize the mic when I plug the cable in.
post #3796 of 9620
Unless the UMIK has changed it originally came with only a 0 degree calibration file with no provision for calibrated 90 degree usage
post #3797 of 9620
Quote:
Originally Posted by AustinJerry View Post

Please use the correct terminology:  you can't read the Titles, or the Legends?  When you click on a graph, does it open up in your browser to a larger size?

I just can't read the damn numbers - I'm getting old smile.gif
post #3798 of 9620
P.S. When you resize a REW window, the font size of the labeling stays the same. When you export a graph from REW, any font is scaled down depending on the image size you chose.
post #3799 of 9620
Quote:
Originally Posted by ggsantafe View Post

Unless the UMIK has changed it originally came with only a 0 degree calibration file with no provision for calibrated 90 degree usage

 

post #3800 of 9620
Quote:
Originally Posted by AustinJerry View Post

I don't see any difference.

I do when I look at your original files. Do the following test: click "capture" when the REW window is full screen, then click "capture" with the REW window at half the size. Look at the two images, text size is different.
post #3801 of 9620

Several weeks ago (post 3553) I reported that I had taken down the treatments at the first reflection points on the side walls, and that I couldn't tell any difference using the ETC measurement.  Since then, based solely on my belief that the ETC graphs were not correct, I re-deployed treatments on the side walls and re-measured.  I am now able to see a slight difference in the reflections, nothing dramatic.

 

 

 

 

The reflection at ~4.5m is the ceiling fan, which I have yet to figure out what to do about.  The discouraging thing about hunting and killing early reflections is that after a whole lot of work, the results can be disappointingly insignificant.  I am close to admitting that reducing early reflections to -20dB < 20ms is an unattainable goal for me.

post #3802 of 9620
Quote:
Originally Posted by AustinJerry View Post

Several weeks ago (post 3553) I reported that I had taken down the treatments at the first reflection points on the side walls, and that I couldn't tell any difference using the ETC measurement.  Since then, based solely on my belief that the ETC graphs were not correct, I re-deployed treatments on the side walls and re-measured.  I am now able to see a slight difference in the reflections, nothing dramatic.








The reflection at ~4.5m is the ceiling fan, which I have yet to figure out what to do about.  The discouraging thing about hunting and killing early reflections is that after a whole lot of work, the results can be disappointingly insignificant.  I am close to admitting that reducing early reflections to -20dB < 20ms is an unattainable goal for me.

Still using the absorbers with scatter plates at first reflection points?
post #3803 of 9620
Quote:
Originally Posted by jim19611961 View Post


Still using the absorbers with scatter plates at first reflection points?

 

No.  I moved those bass traps to the intersection of the front wall and the ceiling where I figured the scatter plates would have the least impact on reflections.  In retrospect, I think I wasted $150 by adding that option to three panels.  I don't want to throw the panels away though.

 

The side walls are now standard GIK 244 panels, and I kept the two 244 panels that were originally on the side wall mounted at the intersection of the side wall and the ceiling.  Once I install a bass trap, I don't want to remove it--ever.  I am now up to sixteen 24x48 bass traps:

 

- Two each in the front left and right corners

- Three at the intersection of the front wall and the ceiling

- Two in the back left corner

- Two at the intersection of the side wall and the ceiling

- Two on the ceiling

- Two on the right side wall

- One free-standing panel on the left side in front of the fireplace

 

Not much room left for treatments....

post #3804 of 9620
Quote:
Originally Posted by AustinJerry View Post

No.  I moved those bass traps to the intersection of the front wall and the ceiling where I figured the scatter plates would have the least impact on reflections.  In retrospect, I think I wasted $150 by adding that option to three panels.  I don't want to throw the panels away though.

The side walls are now standard GIK 244 panels, and I kept the two 244 panels that were originally on the side wall mounted at the intersection of the side wall and the ceiling.  Once I install a bass trap, I don't want to remove it--ever.  I am now up to sixteen 24x48 bass traps:

- Two each in the front left and right corners
- Three at the intersection of the front wall and the ceiling
- Two in the back left corner
- Two at the intersection of the side wall and the ceiling
- Two on the ceiling
- Two on the right side wall
- One free-standing panel on the left side in front of the fireplace

Not much room left for treatments....

Looking closer, I see some 10 -15 db differences. Pretty significant if you asked me. Have you compared your latest to your very first tests? The ones before any treatment? Should be eye opening smile.gif

Since you know about the ceiling fan at 4.5ms, you only have two spots left above -20db (around 5 & 11ms). In due diligence, you will find these as well. The 11ms may be secondary reflections rather than a first, making it harder to track. if you discouraged, take a break. You can always come back to it with fresh ideas and renewed vigor later.
post #3805 of 9620
Quote:
Originally Posted by jim19611961 View Post

Looking closer, I see some 10 -15 db differences. Pretty significant if you asked me. Have you compared your latest to your very first tests? The ones before any treatment? Should be eye opening smile.gif

Since you know about the ceiling fan at 4.5ms, you only have two spots left above -20db (around 5 & 11ms). In due diligence, you will find these as well. The 11ms may be secondary reflections rather than a first, making it harder to track. if you discouraged, take a break. You can always come back to it with fresh ideas and renewed vigor later.

There is no question that I have come a long way. It's just the last stretch that seems to be so difficult. Good advice about taking a break for a while, and thanks for your feedback, as always.
post #3806 of 9620
Quote:
Originally Posted by AustinJerry View Post

OK, now I get it.  The smaller screen size is actually more legible.  I never paid any attention to this before, and the REW screen size was most likely randomly different for different sessions.
You can also change the font size REW uses on its graphs in the View preferences.
post #3807 of 9620
Quote:
Originally Posted by JohnPM View Post

You can also change the font size REW uses on its graphs in the View preferences.

John, how do you know all these good tips? wink.gif
post #3808 of 9620
Quote:
Originally Posted by giomania View Post

I didn't think my Can't Remeber Stuff (CRS) disease was contagious, but I guess it is! smile.gif

Mark

My CRS disease is worse because I Can't Remember Sh/t.
post #3809 of 9620
Quote:
Originally Posted by AustinJerry View Post



Glad to see they made those changes - since the lack of a 90 degree file was one of the primary reasons (along with incorrect calibration files) that I traded in my UMIK-6 (actually sold it to CSL) for the UMM ! back in January.
post #3810 of 9620
Quote:
Originally Posted by ggsantafe View Post

Unless the UMIK has changed it originally came with only a 0 degree calibration file with no provision for calibrated 90 degree usage

 

That was what I was vaguely remembering!  

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