# REW measurements in a noisy room



## Shadowtricks (Nov 13, 2014)

*Greetings!* This is my first post to the forum, I hope to get more into the community in the coming months.

*My intentions:* I’m attempting to create a small project studio (listening room) at the office where I will be composing music, doing post production sound for video, and possibly recording some voice overs. Most of the time I will be completing projects while alone in the studio. I have a long and thin room that is fairly small, with a giant recessed window the length of the wall to the right of the mix position, the floor dimensions/3d are below.

*Room:*
L: 176.5”
W: 70.25”
H: 97.5”

The recessed window forms a rectangular prism that is 176.5”x47.5”x10”, with its bottom windowsill 36” from the floor. I predict this will need to be filled with panels or other insulation. We shall see the differences in the L and R graphs.
Testing Photo
 

*Details:* I need to treat my room acoustically, and possibly do isolation work on the door.
So, I endeavor to bass trap my corners from floor to ceiling, and add some huge broadband absorbers on each of the walls and above. I am allowed to go into the drywall, but not the door. My primary concern is creating at least a low level “reflection free zone” in my stereo field so that I can mix projects more accurately. 

Problems I can’t correct in my room will have to be met by stocking a wide variety of expensive mixing monitor headphones comparing them with various monitors in my (probably) less than accurate stereo field. Nevertheless, I need any help I can get because this is my first time. We will be moving offices a lot in the future, so it would be great to get a good working understanding of this highly sophisticated practice.

I’ll try to add photos and as much detail of my procedures as I can, help is sooooo appreciated!!

Equipment List:
Macbook Air, Umik1, Steinberg UR28m, Fostex Pm0.5 MKII Powered Monitor Speakers, RadioShack SPL meter, required cabling

On to the testing!
Here’s the link to download my REW file: http://www1.zippyshare.com/v/24165199/file.html
Here is the link to the Graph Photo’s
http://s966.photobucket.com/user/djqazi/library/Acoustic measurements

Comparing Left and Right ear mono Measurements
 
Right ear position mono measurements
 
Left ear position mono measurements
 
Center stereo Low freq measurement
 
Waterfall - Stereo Low freq measurements 1600ms
 
Waterfall - Stereo Low freq measurements 600ms
 
ETC
 
 
Noise Floor Graph
 

*Testing:*
1.	Opened up new REW beta on my mac air connected to my Steinberg UR28m Soundcard and Umik1 Microphone. The Umik1 has a unique calibration file, which I applied. 
2.	Measured 38% into the room, found my sitting ear height (67.25”), and created a string of that length with a weight on the end. I taped down the positions of my left ear, center, and right ear along the 38% line where I will be sitting. 
3.	Set up my Umik1 on a mic stand and used the string and weight to position at center mix position. Unfortunately my noise floor is around 55db (office ventilation), so I will be measuring at 120db (with ear pro). I am not sure how accurate what I’m doing is. Please enlighten me how to feel about this noise floor. 
4.	Verified my SPL meter/mic calibration within REW. I did this by playing a sinetone at -20RMS level 1Khz. I then adjusted the main mix on my soundcard until I was reading a steady 80db. I then verified that level with my radioshack SPL meter. Looking good.
5.	I took a stereo measurement at the center mix position. I repeated the measurements for the left and right ear positions, soloing the speaker on that side. I attached my first mdat file to this post, as well as a screenshot of the noise floor my Umik1 experienced.

*Questions:*
1.	I have not addressed the curve of my speakers. I’m a little worried about doing this in my room, since it’s small and the reflection points are very close. Is this such a necessary step that I should take my setup outside and test them reflection free? Won’t wind or car noises get in the way? Can I skip this step since problems in my speakers’ response (in addition to room problems) can be helped with acoustic treatment?
2.	Is my high noise floor causing my graphs to be useless? Can I perform these tests with higher decibel levels to increase accuracy?
3.	Is the next step simply to begin applying treatment and see how the measurement graphs change?
4.	Can anyone link me to a site that lists the different “acoustic response models”. I seriously cannot find a straight answer on this. (Solved with this link: http://www.eetimes.com/document.asp?doc_id=1274937 )
5.	Should I take more measurements from other areas in the mix position?
6.	I want to set up a recording spot more towards the center of the room with one of those shields that wraps around the mic or more. How can I make measurements at that spot in order to make sure it is a “flat” spot to record from?
7.	How do you, and should I, be taking multiple sweeps of the material and combining them?

I promise I’ve been doing some research (mainly reading through many pages of forum threads and various linked media) but there is a lot of information to take in so if you would be so kind as to link me to that thread you read then please do.
I would like to give a HUGE thanks to any and all responses that will help me improve my sonic situation, much love friends!


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## JohnM (Apr 11, 2006)

Noise floor is fine, nothing to worry about. Ignore stuff below 25 Hz in the measurements.

For the other questions you'll get more knowledgeable responses in the Home Audio Acoustics forum, I'll move the thread there.


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## Shadowtricks (Nov 13, 2014)

Thanks JohnM, that's great news. Much appreciated.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Shadowtricks said:


> *Questions:*
> 1. I have not addressed the curve of my speakers. I’m a little worried about doing this in my room, since it’s small and the reflection points are very close. Is this such a necessary step that I should take my setup outside and test them reflection free? Won’t wind or car noises get in the way? Can I skip this step since problems in my speakers’ response (in addition to room problems) can be helped with acoustic treatment?


Unless the room is especially reverberant (and this is virtually impossible in a tiny room), you’re primarily hearing the speakers directly, not the room, at least down to something between 300-500 Hz (depending on the size and liveness of the room). So if by “addressing the curve of the speakers” you mean equalization, if the speakers show any serious deviations from flat response you might want to address that. No reason to take an outside measurement, you want the graph to show what the room might be contributing.




> 2. Is my high noise floor causing my graphs to be useless? Can I perform these tests with higher decibel levels to increase accuracy?


As long as the measurement signal is above the noise floor, you’re fine. For instance, you can see in your waterfall where the signal fades down into the noise floor. Speaking of, waterfalls are typically more useful with a 300-500 ms window. It appears that the signal has fully decayed (i.e. into the ambient noise) by 300 ms or so, which is what could be expected in a tiny room.




> 3. Is the next step simply to begin applying treatment and see how the measurement graphs change?


Treatments don’t have a huge effect on response. They primarily reduce reflections, which will enhance imaging. For sure, reducing reflections will have an effect on a graph, primarily reducing comb filtering so that (for example) a 1/24-smoothed graph would look more like one that’s 1/12-smoothed. But treatments won’t do anything for any response characteristics inherent in the speakers. If they did, you could put any speaker you like in a well-treated room and they would all sound the same!

The exception would be bass traps. They can reduce peaks and depressions in response, in addition to reducing decay times (aka ringing).




> 5. Should I take more measurements from other areas in the mix position?


Never hurts, but in your situation the mix position is “where you live,” so I don’t see what it would benefit you.




> 6. I want to set up a recording spot more towards the center of the room with one of those shields that wraps around the mic or more. How can I make measurements at that spot in order to make sure it is a “flat” spot to record from?


There isn’t going to be any spot in the room that is flat. I’m not totally unfamiliar with recording studios, but I don’t know what a “shield that wraps around the mic” is...




> 7. How do you, and should I, be taking multiple sweeps of the material and combining them?


See #5 above. REW does have a averaging feature, though.

Regards,
Wayne


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## Shadowtricks (Nov 13, 2014)

Wow thanks for the thorough responses Wayne!

The device I was referring to in 6 is an "Acoustic Isolation Microphone Absorber Shield". Not sure how good they actually make vocals sound, but it might be combined with other portable panels to improve the quality of the vocal tracks. Here's a link: http://www.amazon.com/Pyle-PSMRS11-Acoustic-Isolation-Microphone/dp/B00IJSBCOI

I'll be taking more + longer tests today before I purchase the insulation, but I have a preliminary plan for my response model. Please let me know if there are major holes in my thinking!
I'll certainly play around with the placement before I start going into the drywall.
I've decided upon using the RFZ (reflection free zone) model for my room. Right now I'm working out how much absorption I need and at what frequency ranges.
Basically, Im going to use regular pink insulation to fill the entire 10.5" cavity made by the room length window.
I'll use 6" thick Roxul RHT 80 to trap my corners from ceiling to floor (8')
I'll use 4" thick Roxul RHT 80 to make 4'x4' early reflection panels on the sides, front and back walls, and ceiling
Finnaly I'll use 3" thick Roxul RHT 80 to make an 8'x2' panel to glue to my door, and add better sealing somehow.

I chose RHT 80 because it appears to have the highest absorption coefficients across the band. Also I'm pretty sure I wont need to frame them.

http://www.bobgolds.com/AbsorptionCoefficients.htm

Thanks again for the super helpful responses Wayne and John!


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## Wayne A. Pflughaupt (Apr 13, 2006)

Since this is a home theater forum, you might want to check the Tape Op Message Board for advice from recording professionals and hobbyists. The have a sub-forum on studio acoustics.

Regards,
Wayne


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