Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 181 - AVS Forum
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Audio Theory, Setup, and Chat > Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs
mogorf's Avatar mogorf 02:47 PM 10-16-2013
Quote:
Originally Posted by AustinJerry View Post

As for the Spectrogram, I have viewed it on occasion, but I don't understand what it is showing, and haven't had the time to research it. When I read the REW Help files, I usually have a hard time following what John is saying.

Jerry, think of looking at your waterfall graph from above. Just like looking at Niagara Falls from a helicopter: cool.gifsmile.gif



markus767's Avatar markus767 02:51 PM 10-16-2013
Quote:
Originally Posted by Sean Spamilton View Post

What on earth could be doing this?

3rd and last time: please measure the nearfield response of driver and port of each sub.
AustinJerry's Avatar AustinJerry 02:51 PM 10-16-2013
Quote:
Originally Posted by kbarnes701 View Post
 

 

Thanks J. Would it help to stuff the mineral wool in the gap that is currently between the corner and the GIK bass trap?  They are currently across the corners at a 45 degree angle, so there is a nice, rwady-made space lurking behind every corner panel. I could easily do that, and it wouldn't be seen either. Worthwhile?

 

Interesting question.  I was under the impression that for a velocity trap, the air space behind the panel was important, which is why we straddle a corner and not place the panel flat on the wall.  Filling the air space would seem to defeat this purpose, IMO.


AustinJerry's Avatar AustinJerry 02:54 PM 10-16-2013
Quote:
Originally Posted by markus767 View Post


3rd and last time: please measure the nearfield response of driver and port of each sub.

 

Sean, we are trying to help you understand what is going on.  Even if you don't understand why Markus is requesting this, it is an easy measurement to take.  Let's see what conclusions can be drawn from the measurements.  Think of Markus as the doctor, and he has just asked you to stick your tongue out.  Do it.


jkasanic's Avatar jkasanic 03:02 PM 10-16-2013
Quote:
Originally Posted by AustinJerry View Post
 
Quote:
Originally Posted by kbarnes701 View Post
 

 

Thanks J. Would it help to stuff the mineral wool in the gap that is currently between the corner and the GIK bass trap?  They are currently across the corners at a 45 degree angle, so there is a nice, rwady-made space lurking behind every corner panel. I could easily do that, and it wouldn't be seen either. Worthwhile?

 

Interesting question.  I was under the impression that for a velocity trap, the air space behind the panel was important, which is why we straddle a corner and not place the panel flat on the wall.  Filling the air space would seem to defeat this purpose, IMO.

 

I was discussing what to use in my corners (e.g. rockwool straddling the corner vs. superchunk style corner bass traps) and Sanjay referred me to this post.  Sounds like members over at Gearslutz are using pink fluffy in their superchunk style traps with better results than rockwool or OC703 which previously was considered to be on par with an absorber straddling the corner (creating the air pocket).


AustinJerry's Avatar AustinJerry 03:13 PM 10-16-2013

OK, I need help from someone knowledgeable.  Here is a frequency response measurement:

 

 

Using the same measurement, I generated three waterfalls, varying the lower limit from 40dB to 45dB to 50dB.  Same measurement, but each waterfall obviously looks different.  What information do the differences convey to me?  The 5odB waterfall "looks better", but since they are all the same measurement, it can't be better.  Why am I having difficulty understanding this?

 

 

 

 

 

And here is a spectrogram using the same measurement.  Can someone walk me through how to interpret this graph?  Thanks!

 


AustinJerry's Avatar AustinJerry 03:19 PM 10-16-2013
Quote:
Originally Posted by jkasanic View Post
 

 

I was discussing what to use in my corners (e.g. rockwool straddling the corner vs. superchunk style corner bass traps) and Sanjay referred me to this post.  Sounds like members over at Gearslutz are using pink fluffy in their superchunk style traps with better results than rockwool or OC703 which previously was considered to be on par with an absorber straddling the corner (creating the air pocket).

 

I have seen this post.  Interesting that there is a door in the right rear corner of the room.  Evidently, he moves two stacked traps into the corner covering the door when he is watching movies, and then moves it back out of the way.  :eek:


Sean Spamilton's Avatar Sean Spamilton 03:24 PM 10-16-2013
Quote:
Originally Posted by AustinJerry View Post

Sean, we are trying to help you understand what is going on.  Even if you don't understand why Markus is requesting this, it is an easy measurement to take.  Let's see what conclusions can be drawn from the measurements.  Think of Markus as the doctor, and he has just asked you to stick your tongue out.  Do it.

As Requested three times: Old Sub:



New Sub:


AustinJerry's Avatar AustinJerry 03:36 PM 10-16-2013

Interesting differences.  I have four "matched" subs.  I have never actually taken a nearfield measurement of each to see how well they are actually matched.  I should do it sometime, but I'm scared of what the measurements will reveal.  I don't actually know how different supposedly identical subs can be before it is considered an issue.  Perhaps Markus will comment, since he has done extensice research with subwoofers.


AustinJerry's Avatar AustinJerry 03:42 PM 10-16-2013

OK, Sean, something is wrong.  I thought you were going to gain-match the subs?  The output of the old sub looks to be about 95dB, while the new sub is closer to 120dB.  How can they be gain matched?

 

Are you familiar with the gain matching process?

 

And when you re-present the graphs, please show them like this:

 

Graph 1:  Old and new sub nearfield driver

Graph 2:  Old and new sub nearfield port

 

This will facilitate comparing the two subs.


Sean Spamilton's Avatar Sean Spamilton 03:46 PM 10-16-2013
Quote:
Originally Posted by AustinJerry View Post

OK, Sean, something is wrong.  I thought you were going to gain-match the subs?  The output of the old sub looks to be about 95dB, while the new sub is closer to 120dB.  How can they be gain matched?

Are you familiar with the gain matching process?

And when you re-present the graphs, please show them like this:

Graph 1:  Old and new sub nearfield driver
Graph 2:  Old and new sub nearfield port

This will facilitate comparing the two subs.

I'll try it again following this: "the most rigorous method is to move each sub to the middle of the room, place a mic very close to the driver, and measure the SPL. Then move each of the other subs to the exact same position with the mic exactly the same distance away, and set the level to the same SPL as the first one. I place tape on the floor around the first sub, so I can ensure the subsequent subs are located in the exact same place. I don't move the mic between measurements. This works for identical subs, and the level knobs should be at the exact same point, assuming the amps are consistent from unit to unit. It also works for different subs, but then you should expect different settings on the amps."

Granted I didn't gain match from a nearfield position last time - perhaps this will be more accurate.
jim19611961's Avatar jim19611961 03:52 PM 10-16-2013
Quote:
Originally Posted by jkasanic View Post

I was discussing what to use in my corners (e.g. rockwool straddling the corner vs. superchunk style corner bass traps) and Sanjay referred me to this post.  Sounds like members over at Gearslutz are using pink fluffy in their superchunk style traps with better results than rockwool or OC703 which previously was considered to be on par with an absorber straddling the corner (creating the air pocket).

When pink fluffy is very thick (10"+), I prefer it over any other material. This of course applies to corner superchunks that are generally deeper still.

Some of my bass traps are 16-24" thick of pink fluffy. Marvelous stuff when very very thick.
jevansoh's Avatar jevansoh 04:00 PM 10-16-2013
Quote:
Originally Posted by kbarnes701 View Post

Quote:
Originally Posted by jevansoh View Post

 
 
PS Keith, I wouldn't spend a large amount of money on pre-fab "bass traps" at this point. You have all the panels you need. What I'd do is stuff as much (don't compress it) Safe N Sound equivalent (Rockwool/Mineral Wool) in any corner, weird space, and possibly even build soffits with a fabric covering - it sure would help in making suggestions if I could SEE your room smile.gif ) in open/available areas because that frequency is not too difficult to fix. Anything much below would be, and if you had a larger room my suggestion would be use Pink Fluffy but I'm confident you can both fix this problem and that it will cause audible benefit that is worth the time, trouble, and expense.

Thanks J. Would it help to stuff the mineral wool in the gap that is currently between the corner and the GIK bass trap?  They are currently across the corners at a 45 degree angle, so there is a nice, rwady-made space lurking behind every corner panel. I could easily do that, and it wouldn't be seen either. Worthwhile?

ABSOLUTELY YES!!! Always better than just air gap. Don't compress it though and use medium density (not Rockboard 80 for instance) for that amount of space.

If you do this in ALL corners it may just be enough on its own to fix your issue.

If I could only see pics of your room, I could make more specific recommendations. wink.gif

--J
AustinJerry's Avatar AustinJerry 04:00 PM 10-16-2013
Quote:
Originally Posted by Sean Spamilton View Post


I'll try it again following this: "the most rigorous method is to move each sub to the middle of the room, place a mic very close to the driver, and measure the SPL. Then move each of the other subs to the exact same position with the mic exactly the same distance away, and set the level to the same SPL as the first one. I place tape on the floor around the first sub, so I can ensure the subsequent subs are located in the exact same place. I don't move the mic between measurements. This works for identical subs, and the level knobs should be at the exact same point, assuming the amps are consistent from unit to unit. It also works for different subs, but then you should expect different settings on the amps."

Granted I didn't gain match from a nearfield position last time - perhaps this will be more accurate.

 

Well, you can do an acceptable gain-match without moving the subs.

 

- Place the mic close (1"-2") from the dust cap.

- Run the AVR speaker level test tone for the sub channel.

- Adjust the speaker gain control (I would recommend setting 90dB as a starting point).

- Repeat the procedure for the second sub, making sure it reads the exact same SPL as the first.

 

We are assuming for the time being that your subs are identical.  The gain controls on the two subs will NOT necessarily be in the same position after the gain matching has completed.  Differences in plate amp tolerances, and in your case a different driver, will most likely result in DIFFERENT gain control settings.

 

After gain matching, there should not be a 25dB difference when you re-measure, like in the previous set of graphs.


Sean Spamilton's Avatar Sean Spamilton 04:03 PM 10-16-2013
Ok, well these look completely different from my old measurements, and very very similar, if not identical: ( I obviously did something wrong )




Sean Spamilton's Avatar Sean Spamilton 04:04 PM 10-16-2013
Do you think it would be too soon to go ahead and re-measure at those room locations I was having such a strange difference of responses at?
jevansoh's Avatar jevansoh 04:08 PM 10-16-2013
Quote:
Originally Posted by AustinJerry View Post

Quote:
Originally Posted by kbarnes701 View Post

 

Thanks J. Would it help to stuff the mineral wool in the gap that is currently between the corner and the GIK bass trap?  They are currently across the corners at a 45 degree angle, so there is a nice, rwady-made space lurking behind every corner panel. I could easily do that, and it wouldn't be seen either. Worthwhile?

Interesting question.  I was under the impression that for a velocity trap, the air space behind the panel was important, which is why we straddle a corner and not place the panel flat on the wall.  Filling the air space would seem to defeat this purpose, IMO.

An air space is a great way to enhance the absorption and get a free lunch but it is always better to use more treatment.

Sometimes mixing densities at certain thicknesses will create better absorption, too.

For instance, if you model a 10" x 30" (You can make this trap so easily and cheaply by simply hanging two pieces of R-30 vertically, side by side) trap and compare that to, for instance, a 10" x 34" of the same density, approximately 5000 rayl/s pink fluffy, you'll see minor improvement. Change that last 4" to a 12,500 density 4" rockwool and place it in FRONT of the pink fluffy and absorption DECREASES at certain frequencies. Place that same 4" of 12,500 medium density (safe n sound) rockwool BEHIND/against the wall with the pink fluffy in front and you'll gain a lot of low end absorption.

Another thing you can do is place 2x4 traps 4' across the corner (the 2' side would be the vertical side) and this greatly increases absorption and the amount of air space behind the traps. However, filling that airspace with the proper type and amount of treatment will always outperform only airspace.

Adding airspace is a great way to stretch your budget but will never outperform actual insulation/material if properly sized (density/rayl/s), placed, and installed (not compressed).

Hope this helps,

--J
jlpowell84's Avatar jlpowell84 04:12 PM 10-16-2013
Quote:
Originally Posted by jkasanic View Post

I was discussing what to use in my corners (e.g. rockwool straddling the corner vs. superchunk style corner bass traps) and Sanjay referred me to this post.  Sounds like members over at Gearslutz are using pink fluffy in their superchunk style traps with better results than rockwool or OC703 which previously was considered to be on par with an absorber straddling the corner (creating the air pocket).

I'm going to check out that link. Would it still be better flat on the wall or just with the open back space between the wall style?
jim19611961's Avatar jim19611961 04:14 PM 10-16-2013


http://www.stanleyhallstudios.co.uk/pacalc/pacalc.php?m=4&s11=2&d11=300&v11=5000&s21=2&d21=150&v21=16000&s22=1&d22=150

As one can see, pink fluffy 12" thick blows away OC703 6" with a 6" air gap. Or OC703 in any thickness with any air gap for that matter.
Sean Spamilton's Avatar Sean Spamilton 04:24 PM 10-16-2013
Having gain matched the subs again, pretty closely together as evidenced by the graphs above - I've gone ahead and rerun the tests - Taking measurements in the same location but varying the Old and New subs position .... And got the same thing:


jevansoh's Avatar jevansoh 04:25 PM 10-16-2013
Quote:
Originally Posted by jkasanic View Post

Quote:
Originally Posted by AustinJerry View Post

 
Quote:
Originally Posted by kbarnes701 View Post

 

Thanks J. Would it help to stuff the mineral wool in the gap that is currently between the corner and the GIK bass trap?  They are currently across the corners at a 45 degree angle, so there is a nice, rwady-made space lurking behind every corner panel. I could easily do that, and it wouldn't be seen either. Worthwhile?

Interesting question.  I was under the impression that for a velocity trap, the air space behind the panel was important, which is why we straddle a corner and not place the panel flat on the wall.  Filling the air space would seem to defeat this purpose, IMO.

I was discussing what to use in my corners (e.g. rockwool straddling the corner vs. superchunk style corner bass traps) and Sanjay referred me to this post.  Sounds like members over at Gearslutz are using pink fluffy in their superchunk style traps with better results than rockwool or OC703 which previously was considered to be on par with an absorber straddling the corner (creating the air pocket).

I personally have a relatively large room at 20' x 25.7' x 8.6' and have created four very easy to build, inexpensive, and extremely great performing traps using the following method.

My traps are basically 4 pieces of R-30 (R-30 normally measures about 10" thick x 15" wide) put together to total a 20" x 30" trap. This is a square (not cut into triangles and stacked) soffit style trap that is hung vertically so there is no compression or cutting of a million pieces, fooling with netting, etc.

I simply made frames out of 2x2 furring strips that are about 22" x 32" square and 8' tall to fit under my actual soffits from the floor with one support in the middle or so (Six 8' 2x2 furring strips at about $1.50 each in the US will yield one 20" x 30" x 8' trap) and then stapled black broadcloth (56" wide from Wal-Mart for $2.97 per yard) to the two sides that show.

Since I use fluffy insulation and it can have bumps and not be perfectly flush, I made the frame 1.5" larger than the actual trap inside all the way around by using the 2x2's (but the INSIDE dimensions of the frame are the same size as the trap @ 20" x 30" so you don't even have to staple the insulation - it just fits snugly inside the frame) and this allows room to add a barrier (IE: Plastic or very thin wood) to reflect the higher frequencies for areas I don't want/need broadband absorption and want a TRUE bass trap and to allow me to staple the fabric nice and flush for a perfectly straight appearance with no insulation pushing the fabric out and making it bulge in certain places.

It appears I have very expensive soffit traps or bumpouts (they can also be easily resized and used as columns for dedicated ht's) in my corners when in reality I have very effective bass traps for about an hour or two of work per trap and a total cost of well under $50 per trap including ALL materials (wood, insulation, staples, and fabric).

I recommend using http://www.stanleyhallstudios.co.uk/pacalc/ to try different designs that are easy and cheap to build to see how effective they'll be.

You can play around with changing the impedance (having two different densities and which one works better in front of the other) adding air space and comparing to insulation in place of the same amount of air space to see just how effective these inexpensive traps made out of pink fluffy or for folks with less space, lower density mineral wool such as safe n sound can be.

I would never purchase pre-made panels because it's just too expensive for what actually goes into them, even taking into consideration the small amount of labor.

Save that budget for Diffusors which are NOT easy to make properly or for more sophisticated bass traps with more complicated science and design/materials behind them but not a fabric wrapped piece of insulation. wink.gif

--J
jevansoh's Avatar jevansoh 04:29 PM 10-16-2013
Quote:
Originally Posted by AustinJerry View Post

OK, I need help from someone knowledgeable.  Here is a frequency response measurement:




Using the same measurement, I generated three waterfalls, varying the lower limit from 40dB to 45dB to 50dB.  Same measurement, but each waterfall obviously looks different.  What information do the differences convey to me?  The 5odB waterfall "looks better", but since they are all the same measurement, it can't be better.  Why am I having difficulty understanding this?











And here is a spectrogram using the same measurement.  Can someone walk me through how to interpret this graph?  Thanks!



If someone doesn't beat me to it I will try my best to explain this in detail later tonight when I have more time.

Right now it's supper time and I'm a hungry hungry hippo! wink.gif
jim19611961's Avatar jim19611961 04:30 PM 10-16-2013
Quote:
Originally Posted by jevansoh View Post


I recommend using http://www.stanleyhallstudios.co.uk/pacalc/ to try different designs that are easy and cheap to build to see how effective they'll be.

--J

+1
jkasanic's Avatar jkasanic 04:59 PM 10-16-2013
Quote:
Originally Posted by jevansoh View Post

I personally have a relatively large room at 20' x 25.7' x 8.6' and have created four very easy to build, inexpensive, and extremely great performing traps using the following method.

My traps are basically 4 pieces of R-30 (R-30 normally measures about 10" thick x 15" wide) put together to total a 20" x 30" trap. This is a square (not cut into triangles and stacked) soffit style trap that is hung vertically so there is no compression or cutting of a million pieces, fooling with netting, etc.

I simply made frames out of 2x2 furring strips that are about 22" x 32" square and 8' tall to fit under my actual soffits from the floor with one support in the middle or so (Six 8' 2x2 furring strips at about $1.50 each in the US will yield one 20" x 30" x 8' trap) and then stapled black broadcloth (56" wide from Wal-Mart for $2.97 per yard) to the two sides that show.

Since I use fluffy insulation and it can have bumps and not be perfectly flush, I made the frame 1.5" larger than the actual trap inside all the way around by using the 2x2's (but the INSIDE dimensions of the frame are the same size as the trap @ 20" x 30" so you don't even have to staple the insulation - it just fits snugly inside the frame) and this allows room to add a barrier (IE: Plastic or very thin wood) to reflect the higher frequencies for areas I don't want/need broadband absorption and want a TRUE bass trap and to allow me to staple the fabric nice and flush for a perfectly straight appearance with no insulation pushing the fabric out and making it bulge in certain places.

It appears I have very expensive soffit traps or bumpouts (they can also be easily resized and used as columns for dedicated ht's) in my corners when in reality I have very effective bass traps for about an hour or two of work per trap and a total cost of well under $50 per trap including ALL materials (wood, insulation, staples, and fabric).

I recommend using http://www.stanleyhallstudios.co.uk/pacalc/ to try different designs that are easy and cheap to build to see how effective they'll be.

You can play around with changing the impedance (having two different densities and which one works better in front of the other) adding air space and comparing to insulation in place of the same amount of air space to see just how effective these inexpensive traps made out of pink fluffy or for folks with less space, lower density mineral wool such as safe n sound can be.

I would never purchase pre-made panels because it's just too expensive for what actually goes into them, even taking into consideration the small amount of labor.

Save that budget for Diffusors which are NOT easy to make properly or for more sophisticated bass traps with more complicated science and design/materials behind them but not a fabric wrapped piece of insulation. wink.gif

--J

I would love to see pics of your traps. You really need to figure out the picture upload operation on the site! It's definitely easier than making your own traps! tongue.gif
AustinJerry's Avatar AustinJerry 05:16 PM 10-16-2013
Quote:
Originally Posted by Sean Spamilton View Post

Having gain matched the subs again, pretty closely together as evidenced by the graphs above - I've gone ahead and rerun the tests - Taking measurements in the same location but varying the Old and New subs position .... And got the same thing:

 

Well, forget the mystery and go with old in front and new in back.

 

Edit:  The level-matching was certainly successful!


jim19611961's Avatar jim19611961 05:24 PM 10-16-2013
Quote:
Originally Posted by Sean Spamilton View Post

Having gain matched the subs again, pretty closely together as evidenced by the graphs above - I've gone ahead and rerun the tests - Taking measurements in the same location but varying the Old and New subs position .... And got the same thing:


The magenta colored plot looks pretty good if they are crossed over before that +8db peak around 75hz.
Sean Spamilton's Avatar Sean Spamilton 05:35 PM 10-16-2013
Quote:
Originally Posted by AustinJerry View Post

Well, forget the mystery and go with old in front and new in back.

Edit:  The level-matching was certainly successful!

It sure was. And I figured as you did I'd go with the best results, old in front new in back. I re ran Auddessy Calibration and measured again. This is what I got:



Awesome! lol. I can only surmise that when running my original measurements, the subwoofer distances were set differently - even with Auddessy off the Denon receiver uses what distances Aud Sets. Since the distances were calibrated for 2/5 and 4/5 positioning, when I ran the measurements it obviously used the delays for the subs set from before - and output the previous graphs. When I reran setup, it changed the distances from the subs to the MLP, and gave me what you see above. So now I'm lost.
Sean Spamilton's Avatar Sean Spamilton 05:44 PM 10-16-2013
This is what I get individually with the new distances set in auddessy ... What distances should I have input into the Denon when finding the ideal position for the subs? Do I have to change the distance to the MLP manually every time change the sub position?


jkasanic's Avatar jkasanic 05:48 PM 10-16-2013
Did you try 1/4 and 3/4 points??
AustinJerry's Avatar AustinJerry 05:55 PM 10-16-2013
Quote:
Originally Posted by Sean Spamilton View Post

This is what I get individually with the new distances set in auddessy ... What distances should I have input into the Denon when finding the ideal position for the subs? Do I have to change the distance to the MLP manually every time change the sub position?

I don't understand how the measurement of both subs after the Audyssey calibration can look worse than the two subs without Audyssey. Did you run the calibration without moving the subs?
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