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Room Eq Wizard and Feedback Problems
Old 2 weeks ago
  #1
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Room Eq Wizard and Feedback Problems

Hi everyone, I'm in need of some serious help!

So for the first time ever, I have decided that I am going to fix my room acoustics as accurately as I can. I've bought foam in the past, which I then realized was a waste of money for what I needed to do. I bought Owens corning 703 and put them anywhere. Most recently I got Ikea bookshelves and put a combination of Owens corning 703 and roxul safe'n'sound in them. But after my mixes still failing the car speaker test so many times I finally said I'm going to do this right!!
I bought a textbook, the Master Handbook of Acoustics, read most of the chapters, did not understand it fully but definitely learned some stuff. So now in my quest to understand acoustics and fix them in my room, I bought a Behringer ECM8000 and downloaded the REW software. I am trying to get a reading of my room, but my signal I believe is too low. When I try to raise the volume on my M-Audio Sound card, or increase the input on the mic, I get feedback. So how do I eliminate this? I know that the microphones output is going back to the speakers but how can I mute that part of the mic?? do I do that in the new software? or is there somewhere else that I can change it? If someone can give me some links that can help me out or some advice that would be much appreciated.
I am using MacOS, an M-audio Soundcard, Yamaha hs7s, and the Behringer emc8000.
Old 2 weeks ago
  #2
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Bring the levels up to the threshold of feedback and back it off just enough that it stops, then take a measurement. The software will complain about the levels but just click OK and move on. Once the biggest response peaks are flattened you will be able to get much higher gain without feedback.
Old 2 weeks ago
  #3
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Hey Paul, thanks for the reply
ok I've attached some graphs and well this is what I got, I have no treatment in my room at the moment, do these graphs seem like they're actually picking up the room? And when you say flattened, you mean with acoustic absorption right?
Attached Thumbnails
Room Eq Wizard and Feedback Problems-screen-shot-2020-01-30-9.22.10-pm.jpg   Room Eq Wizard and Feedback Problems-screen-shot-2020-01-30-9.22.17-pm.jpg   Room Eq Wizard and Feedback Problems-screen-shot-2020-01-30-9.22.56-pm.jpg   Room Eq Wizard and Feedback Problems-screen-shot-2020-01-30-9.26.01-pm.jpg  
Old 2 weeks ago
  #4
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That looks way to flat to be an actual acoustic measurement, check that the internal mic on the computer is turned off and that you are actually getting input from the external mic, you can use the RTA app in the software to test the mic in real time.

Have you generated a calibration file for the interface? Any half decent interface will be next to ruler flat but this is easy enough to do so why not, and the software has steps to guide you through it.
The Mic should also have a cal file but those provided by the manufacturer in this case are generic and of little value, if you don't have this file you can't do much about it so don't worry about it for now.

Also, apply smoothing to your measurements to get a single line response, I use 1/12 or 1/24. It is under the Graph pulldown menu on the top of the screen.
Old 2 weeks ago
  #5
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Is there a direct monitoring function on that soundcard? Turn it off.
Old 2 weeks ago
  #6
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thanks guys! I did all your suggestions... now is this graph looking like it's picking up an untreated room? I only swept though 20 hz to 500 hz though
Attached Thumbnails
Room Eq Wizard and Feedback Problems-screen-shot-2020-01-30-11.49.43-pm.jpg  
Old 2 weeks ago
  #7
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The mic should hear the speaker, but the mic absolutely should not be sent to the speaker. If you solved that, you’re on your way.
Old 2 weeks ago
  #8
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akebrake's Avatar
 

Quote:
Originally Posted by RobbieDames View Post
thanks guys! I did all your suggestions... now is this graph looking like it's picking up an untreated room? I only swept though 20 hz to 500 hz though
It seems like you managed to execute the two most common newbie mistakes with REW.

1. Direct Monitoring on/ mix control = acoustical feedback
Simplest way to check that: Tap the microphone. You should hear nothing in the speaker.

2. You have (probably) used a measurement file for calibration
Switch Soundcard calibration OFF. (and mic calibration)

Take new measurements at a decent level.
Too loud = Distortion. Too soft= Noisy.

One speaker at a time.

Upload mdat here and we will comment.
Old 2 weeks ago
  #9
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Thanks akebrake, The first problem I' m pretty sure I fixed.. my sound card had a knob that needed to be off direct and all the way to usb (I attached a pic of my sound card), but the calibration I am not understanding. On a youtube tutorial it said to do a loopback but as you can see on my sound card I don't have many options there unless I unplug one of the monitors? Anyways I sent the mdat file.. I generated a waterfall plot but something doesn't seem right.. Please let me know
Attached Thumbnails
Room Eq Wizard and Feedback Problems-screen-shot-2020-01-31-2.02.49-pm.jpg   Room Eq Wizard and Feedback Problems-screen-shot-2020-01-31-2.02.39-pm.png  
Attached Files
File Type: mdat First Room Test.mdat (5.99 MB, 10 views)
Old 2 weeks ago
  #10
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Also when I do the test only these 2 meters are moving, but I feel like the in meter should be moving, or is this correct? Ive attached a picture
Attached Thumbnails
Room Eq Wizard and Feedback Problems-screen-shot-2020-01-31-3.11.27-pm.jpg  
Old 2 weeks ago
  #11
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Yes when doing the hardware calibration unplug everything connected to the soundcard except USB and install a loop cable between the mic input and a line output. Don't worry about connecting to both outputs and be careful with the levels as the line output could easily overdrive the mic input.
Old 2 weeks ago
  #12
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akebrake's Avatar
 

Quote:
Originally Posted by RobbieDames View Post
Also when I do the test only these 2 meters are moving, but I feel like the in meter should be moving, or is this correct? Ive attached a picture
Yes, the IN meter should be around -15 or so... your is -100 dB

It seems like you have no input signal at all, and all we see is noise.

You have to use the same Input & Output for measuring.
Output: Right Input: Right

Forget about the loop back calibration for now. (Not needed if the sound card is decent).

Hope that helps
Attached Thumbnails
Room Eq Wizard and Feedback Problems-meas-info.jpg  
Old 2 weeks ago
  #13
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Anyone willing to Skype with me, I am willing to pay for your time to help me get this right... Please inbox me if interested
Old 2 weeks ago
  #14
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Hey guys so I think these readings are accurate because after the tests I listened while observing the valleys and peaks with this speaker test:

https://www.youtube.com/watch?v=URrEtyFSENc..

but please let me know if it seems legit.. I took 8 measurements, 4 with the mic pointing at screen at listening position, dead centre, a little to the left, a little to the right and mid further back, then did the same thing with the mic pointing at the ceiling. I named the Measurements according to their position, but had to take 4 out because the file was to big to send here.. so I've attached an mdat with only 4 measurements but have screenshots of overlays of all 8. So in the mdat there is 2 measurements of middle and middle back with microphone pointing at screen and 2 more in the same positions but with the mic pointing at the ceiling.
Please let me know, and if possible can someone show me what a properly treated room should look like...

Thank you so much for your time
Attached Thumbnails
Room Eq Wizard and Feedback Problems-overlay.jpg   Room Eq Wizard and Feedback Problems-all-8.jpg  
Attached Files
File Type: mdat FEBRUARY OH TWOOO.mdat (12.67 MB, 9 views)
Old 2 weeks ago
  #15
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No that still isn't right, no way all the measurements should be that similar. Do a little experiment, open the RTA app in the software, hit the little red button to start it and then speak into the mic, you should hear and see your voice if everything is setup correctly.
Old 2 weeks ago
  #16
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ok so the first screen shot is what I think is the room response, seconds screenshot is me saying la la la repeatedly in the Behringer ecm8000 for the whole test, with no sound coming out of the mic and the last screenshot is just me running the measurement with no sound coming out of the speakers... let me know
Attached Thumbnails
Room Eq Wizard and Feedback Problems-screen-shot-2020-02-03-1.58.01-am.jpg   Room Eq Wizard and Feedback Problems-room.jpg   Room Eq Wizard and Feedback Problems-lalala.jpg   Room Eq Wizard and Feedback Problems-no-sound.jpg  
Old 2 weeks ago
  #17
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heres overlay with top being what I think is the room measurements, the middle purple test is my saying lalala, and the bottom is just no sound at all
Attached Thumbnails
Room Eq Wizard and Feedback Problems-screen-shot-2020-02-03-3.05.24-am.jpg  
Old 2 weeks ago
  #18
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akebrake's Avatar
 

Scaling way off

Quote:
Originally Posted by paul o View Post
No that still isn't right...
Agree

Quote:
..no way all the measurements should be that similar...
They are not similar, they only look similar.
From the bottom of the graph (-240 dB) to the top 180dB = 420db!

That's a huge dynamic range and measurements looks similar due to lack of amplitude detail.

We rather use 50dB vertical scaling for SPL & Waterfall etc.
An uploaded mdat is more useful for investigation.
Attached Thumbnails
Room Eq Wizard and Feedback Problems-room.jpg  
Old 2 weeks ago
  #19
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akebrake's Avatar
 

Quote:
Originally Posted by RobbieDames View Post
ok so the first screen shot is what I think is the room response...
Looks like two speakers running and mic is not in the middle. That will result in a strange combfilter response.
Measure L & R spkr separately. (unplug or swich spkr off)
Mic in your normal listening position.

Also...Pls supply a sketch or photo of the room where one can see the set up (pos of spkr & mic) also the dimensions of the room.

Below is what your "Middle facing screen" meas looked like with adjusted (by me) scaling and estimated SPL.
Attached Thumbnails
Room Eq Wizard and Feedback Problems-estimated-.jpg  
Old 2 weeks ago
  #20
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OK I have attached my dimensions in the attachment as well as pictures of the room.. I used to have Ikea bookshelves with a combo of Owen corning 703 and safe n sound, but have removed it all to do this right... the desk is in the middle of the width of the room and the desk is 2 feet away from the back wall...
Attached Thumbnails
Room Eq Wizard and Feedback Problems-room-dimensions.png   Room Eq Wizard and Feedback Problems-front.jpg   Room Eq Wizard and Feedback Problems-left.jpg   Room Eq Wizard and Feedback Problems-right.jpg   Room Eq Wizard and Feedback Problems-back.jpg  

Room Eq Wizard and Feedback Problems-back-right.jpg   Room Eq Wizard and Feedback Problems-back-left.jpg   Room Eq Wizard and Feedback Problems-far-left.jpg   Room Eq Wizard and Feedback Problems-far-right.jpg   Room Eq Wizard and Feedback Problems-owens-corning.jpg  

Room Eq Wizard and Feedback Problems-bookself-safensound.jpg  
Old 2 weeks ago
  #21
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thanks again for the help guys!!!
Old 2 weeks ago
  #22
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Oh and here are the speakers done separately as you requested Akebrake...
Attached Thumbnails
Room Eq Wizard and Feedback Problems-screen-shot-2020-02-03-1.28.30-pm.jpg   Room Eq Wizard and Feedback Problems-screen-shot-2020-02-03-1.28.32-pm.jpg  
Old 2 weeks ago
  #23
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Quote:
Originally Posted by RobbieDames View Post
Oh and here are the speakers done separately as you requested Akebrake...
mdats please
Old 2 weeks ago
  #24
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here you go
Attached Files
File Type: mdat one speaker at a time.mdat (12.65 MB, 13 views)
Old 2 weeks ago
  #25
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akebrake's Avatar
 

Quote:
Originally Posted by RobbieDames View Post
here you go
Thanks!

IMHO the first question to ask: Is my measurement valid?

Unfortunately your Soundcard Cal curve is in error (pic 1)
I don’t know how you managed to create that one...?
It should rather look like a straigt line. (Example in pic 2)

Calibrated measurements are approximately the ”inverse” of the calibration and that explains partly the strange Frequency Response here. (Pic 3)
So, one can probably ignore Loop back/ SC Cal. Switch it off.

Then: Looking into the Distortion Tab. How much THD? (Total Harmonic Distortion)
Your measurement shows 20% or more below 100Hz. Probably runs into clipping. (Sound Card Cal is not active in the Dist plot)

When sweeping loud (with small speakers) it’s easy to get a distorted response and also run into signal clipping. THD should be around 1% (Not 20%...) 1% translates to -40 dB below fundamental. pic4

REW 5.20 (beta 10 and later) also displays a Noise Floor in the Distortion plot.
Most rooms are around 30 dB SPL (not 5) unless an extremely quiet area in the countryside, no wind, no rain, no traffic, no fans or machinery. That way one can ”guesstimate” the actual sweep level (if the SPL is not calibrated).
I’ll guess like 95dB in the peaks.

*******

Let’s pretend the Soundcard isn’t broken. Calibration OFF. (pic 5)
Now the R ONLY Waterfall measurement looks more like an untreated room with some bass problems...

I suggest you move the spakers close to the front wall and make some more sweeps with say 6dB less level. (less distortion)

Hope that helps
Attached Thumbnails
Room Eq Wizard and Feedback Problems-r-only-sc.jpg   Room Eq Wizard and Feedback Problems-soundcard-ok-cal-.jpg   Room Eq Wizard and Feedback Problems-r-only-cal-off.jpg   Room Eq Wizard and Feedback Problems-default-thd-noise.jpg   Room Eq Wizard and Feedback Problems-r-only-wf-no-cal.jpg  

Old 2 weeks ago
  #26
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Thanks Akebrake! But based on those measurements, even thought there are some screwups, there are problems in the bass, of course. I will keep trying to get a better reading on REW but until then what would you do to fix this room if you were going to DIY with a budget of like 3000, that would guarantee, with or without the readings, that it would improve the sound of the room. I was planning to purchase OC703 from Gik or something, not sure yet, but like what thickness would be good for bass traps, clouds, panels against front wall. how wide should they be? should they go from floor to ceiling.. I re attached my room pics.
Attached Thumbnails
Room Eq Wizard and Feedback Problems-all-8.jpg   Room Eq Wizard and Feedback Problems-back-left.jpg   Room Eq Wizard and Feedback Problems-back-right.jpg   Room Eq Wizard and Feedback Problems-back.jpg   Room Eq Wizard and Feedback Problems-far-left.jpg  

Room Eq Wizard and Feedback Problems-far-right.jpg   Room Eq Wizard and Feedback Problems-front.jpg   Room Eq Wizard and Feedback Problems-left.jpg   Room Eq Wizard and Feedback Problems-right.jpg  
Old 2 weeks ago
  #27
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Also I just took an old bass trap I made a while ago (real ugly looking) and threw some OC703 panels in the other corner to see if it did anything to the reading... even though my reading is still not perfect... but did it do something? I sent a screenshot of one of the old measurements, pics of the room with what I threw in there and then the measurement after done after I put the OC703 in the room...
Attached Thumbnails
Room Eq Wizard and Feedback Problems-screen-shot-2020-02-04-2.49.06-pm.jpg   Room Eq Wizard and Feedback Problems-img_6618.jpg   Room Eq Wizard and Feedback Problems-img_6619.jpg   Room Eq Wizard and Feedback Problems-screen-shot-2020-02-04-2.49.11-pm.jpg  
Old 1 week ago
  #28
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Robbie, you seem to be having a lot of trouble getting valid results with your REW measurements. You might find this helpful: How to calibrate and use REW to test and tune your room acoustics That walks you through the process of putting it all together, calibrating it, and using it to get valid results.

- Stuart -
Old 1 week ago
  #29
Quote:
Originally Posted by RobbieDames View Post
but did it do something?
Look at the spectrogram before you look at the SPL diagrams. Things will start to move there first in my experience. You can also use the overlays tool with the RD60 tab.
Old 1 week ago
  #30
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Quote:
Originally Posted by RobbieDames View Post
...I sent a screenshot of one of the old measurements, pics of the room with what I threw in there and then the measurement after done after I put the OC703 in the room...
With just a couple of 2x4ft traps in the front corners the difference will be quite small... Agree with Johann. It might be visble in the Spectrogram and an overlaid RT60 plot.

(But that means you have to practice REW a lot in order to interpret something meaningfull out of the measurement.

From your uploaded pics it’s difficult to spot a difference because:
1. One needs a lot of treatment to improve the Frequency Response.
and you have only added a very small area.

2. Your vertical scaling is still 420dB...
Use 50dB range instead, say 35to 95dB. Adjust that in the ”limits”-box. (watch post 18 again)

3. The before curve is still ”calibrated” (in error) and the after curve is without calibration...
One needs the same scaling etc. in order to compare plots. And preferable using the same set up mic position. The only difference should be the added traps.

4. Upload mdats!
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