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Need help interpreting REW results
Old 3rd June 2020
  #1
Here for the gear
 

Need help interpreting REW results

Hi,

First post here.
I´m currently building a home studio and did a REW measurement a few hours ago.
The majority of the room (sidewalls, rear wall, front corners and ceiling) is already treated with Rockwool.
As I´m not an expert, I cannot interpret these results as good or bad.

Attached are the results and the room.

Many thanks in advance!
Attached Thumbnails
Need help interpreting REW results-studioplan.jpg  
Attached Files
File Type: mdat Home Studio.mdat (3.15 MB, 35 views)
Old 4 weeks ago
  #2
Something is wrong in your measurement. Distortion levels are the same as your measuring level which is too low.
Your noise levels in the mids from 300hz-500hz is too high.

Also try measuring at a higher level like 75db-85db.

Also measure left and right seperately.
Old 4 weeks ago
  #3
Is the speaker's acoustic axis at the same level as the measurement microphone (high-frequency rolloff)?

You have some weird pre-impulse -10 ms before the main impulse, is that another speaker? See @ thethrillfactor .

There is a very loud desk reflection. Cut down on the size of your desk or cover it with thick foam (10 cm+).

There is another loud reflection at ~12 ms, is that the rear wall? Is the rear wall treated floor to ceiling or are there any holes?

Spectrogram is noisy but if I set the threshold high enough, the room doesn't seem to be very modal. A better measurement would be nice though.

I think you may sit away too far from the front wall which could explain the loss of volume in bass.

Sounds like a lot of problems but not a bad start at all.
Old 4 weeks ago
  #4
Here for the gear
 

Alright, just did a new measurement. L, R and L+R and moved the listening position closer to the rear wall.
Now the graph looks more like a right measurement, don't know what was the issue the first time...
Attached Files
File Type: mdat new measurements.mdat (8.67 MB, 26 views)
Old 4 weeks ago
  #5
Overall SPL symmetry I think is really good now.

Desk reflection is still really loud. I would recommend you work on that, it's a nice effect when it's gone.

The hole around 118 Hz may be some kind of interference?

31 and 40 Hz may still be a little modal but I think overall, decay times are pretty even.

Really good result for a small room, maybe you would like having some diffusion in the room now, I don't know how dry it is.
Old 4 weeks ago
  #6
Quote:
Originally Posted by johannburkard View Post
Is the speaker's acoustic axis at the same level as the measurement microphone (high-frequency rolloff)?

You have some weird pre-impulse -10 ms before the main impulse, is that another speaker? See @ thethrillfactor .

There is a very loud desk reflection. Cut down on the size of your desk or cover it with thick foam (10 cm+).

There is another loud reflection at ~12 ms, is that the rear wall? Is the rear wall treated floor to ceiling or are there any holes?

Spectrogram is noisy but if I set the threshold high enough, the room doesn't seem to be very modal. A better measurement would be nice though.

I think you may sit away too far from the front wall which could explain the loss of volume in bass.

Sounds like a lot of problems but not a bad start at all.
A spike before an impulse at 0 is usually a Distortion spike according to the REW manual.
Attached Thumbnails
Need help interpreting REW results-screen-shot-2020-06-06-5.39.56-pm.png  
Old 4 weeks ago
  #7
Quote:
Originally Posted by zyodmusic View Post
Alright, just did a new measurement. L, R and L+R and moved the listening position closer to the rear wall.
Now the graph looks more like a right measurement, don't know what was the issue the first time...
On your filtered ETC 10,000/8,000/6300 hz on the left and right side has huge spikes you need to suppress.

The excess group delay at 115hz which shows up as a null in frequency response is SBIR.
Attached Thumbnails
Need help interpreting REW results-screen-shot-2020-06-06-6.01.29-pm.jpg   Need help interpreting REW results-screen-shot-2020-06-06-6.01.39-pm.jpg   Need help interpreting REW results-screen-shot-2020-06-06-6.01.50-pm.jpg  
Old 4 weeks ago
  #8
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Quote:
Originally Posted by thethrillfactor View Post
On your filtered ETC 10,000/8,000/6300 hz on the left and right side has huge spikes you need to suppress.

The excess group delay at 115hz which shows up as a null in frequency response is SBIR.
Okay, so how do I deal with those spikes? More absorption?
Secondly, is possible to treat the SBIR with absorption behind the speakers on the front wall? And is there a way to calculate how thick the panels should be for 115hz?

Thank you!
Old 4 weeks ago
  #9
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akebrake's Avatar
 

Quote:
Originally Posted by zyodmusic View Post
Okay, so how do I deal with those spikes?
Your measurement "quality" still looks a bit strange IMHO.

1. Distortion is a bit high. Are you sweeping loud? As your real Noise floor is probably is around 30 dB SPL (not 0 dB) I guess your sweep level is close to 100...

Need help interpreting REW results-info-dist.jpg

2. What kind of speakers?

3. What kind of Microphone?

4. Try ONE sweep instead of 4. (L & R separately of course)
USB on different units might introduce clocking errors.

5. Make sure Direct Monitoring is OFF or you'll get feedback.

6. Immediately after a sweep is done check the Scope -window (REW 5.19) to see if the level is OK without dropouts, clipping etc)

7. Show us a photo of your set up.
Front wall w Speakers, Desk, Mic/ clamp, chair?

Best
Attached Thumbnails
Need help interpreting REW results-info-dist.jpg  
Old 4 weeks ago
  #10
Here for the gear
 

Quote:
Originally Posted by akebrake View Post
Your measurement "quality" still looks a bit strange IMHO.

1. Distortion is a bit high. Are you sweeping loud? As your real Noise floor is probably is around 30 dB SPL (not 0 dB) I guess your sweep level is close to 100...


2. What kind of speakers?

3. What kind of Microphone?

4. Try ONE sweep instead of 4. (L & R separately of course)
USB on different units might introduce clocking errors.

5. Make sure Direct Monitoring is OFF or you'll get feedback.

6. Immediately after a sweep is done check the Scope -window (REW 5.19) to see if the level is OK without dropouts, clipping etc)

7. Show us a photo of your set up.
Front wall w Speakers, Desk, Mic/ clamp, chair?

Best
1. Before measuring, i set the "check levels" to around -20db. Is that too loud?

2. Yamaha HS7

3. Sonarworks Calibration Mic (XREF 20)

4. New measurement attached.

5. Is off

6. Level seems to be fine..

7. Attached


Thank you!
Best
Attached Thumbnails
Need help interpreting REW results-img_0376.jpg   Need help interpreting REW results-img_0378.jpg   Need help interpreting REW results-img_0379.jpg  
Attached Files
File Type: mdat new measurements2.mdat (8.64 MB, 11 views)
Old 4 weeks ago
  #11
Quote:
Originally Posted by zyodmusic View Post
1. Before measuring, i set the "check levels" to around -20db. Is that too loud?

2. Yamaha HS7

3. Sonarworks Calibration Mic (XREF 20)

4. New measurement attached.

5. Is off

6. Level seems to be fine..

7. Attached


Thank you!
Best
The distortion figures are better, but the third harmonic is strong especially when you measure both speakers together.

Why that is would have to be checked out. It might be ok.

I attached the overlays of the distortion figures from before and now.
Attached Thumbnails
Need help interpreting REW results-screen-shot-2020-06-08-12.42.08-pm.jpg   Need help interpreting REW results-screen-shot-2020-06-08-12.42.31-pm.jpg  
Old 4 weeks ago
  #12
@ zyodmusic very solid amounts of treatment here.
Old 4 weeks ago
  #13
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akebrake's Avatar
 

Testing testing

Thanks for the photos! Wow, that’s a clean set up!
Nice symetrical room with large traps and Cloud.

Now you have a unique opportunity to check exactly what a fairly large desk is doing to the Frequency Response...

First, try lowering the monitor level (Focusrite) a little.

1. With the Mic & Spkr in the usual position make a couple of sweeps. (Save)
2. Place your Mac & Fousrite on the floor in stead (to the side) plus chair.
3. Remove the desk.
3. Take a couple of new measurements. Upload here.

Best
Old 4 weeks ago
  #14
Gear Head
 

Quote:
Originally Posted by zyodmusic View Post
1. Before measuring, i set the "check levels" to around -20db. Is that too loud?

2. Yamaha HS7

3. Sonarworks Calibration Mic (XREF 20)

4. New measurement attached.

5. Is off

6. Level seems to be fine..

7. Attached


Thank you!
Best

Do you have a measurement before treatment?

Your 1-0-0 is still very long ringing. Seems like the 40 cm at the back wall + the corner traps at the front wall are not enough.

What was used - Munich = Rockwool Sonorock?
Old 4 weeks ago
  #15
Here for the gear
 

Quote:
Originally Posted by Kurt B View Post
Do you have a measurement before treatment?

Your 1-0-0 is still very long ringing. Seems like the 40 cm at the back wall + the corner traps at the front wall are not enough.

What was used - Munich = Rockwool Sonorock?
Yes, i did some measurements when the room was empty. I´ll attach them.
Tho at this time my listening position was more in the middle of the room.

Yes, i used Sonorock for all of the absorption. As you see in the pics, I don't really have the front wall absorbed yet - besides the corners - would that help with mode?
Old 4 weeks ago
  #16
Gear Head
 

Quote:
Originally Posted by zyodmusic View Post
Yes, i did some measurements when the room was empty. I´ll attach them.
Tho at this time my listening position was more in the middle of the room.

Yes, i used Sonorock for all of the absorption. As you see in the pics, I don't really have the front wall absorbed yet - besides the corners - would that help with mode?

You already can see how powerful SBIR is at your 116 Hz Dip. (sidewall - speaker distance)

If you put your speakers away from the front wall - to put thick porous treatment on it - you will get another dip.

In small rooms it is usually (not always) a good start to get the most out of the back wall and leave the speakers really close to the front wall.

If you haven't done this a few times (treated some rooms) then do not try to do too much at once.

Go from the worst problem to the next problem.

First treat the lowest room mode - as this needs the most space or time to figure out how to do it if you need some pressure based help.

And by using mostly porous treatment only - a lot of problems are already gone by treating the lowest mode.

In your case 40 cm of sonorock (28kg density + 6kpa) are not enough to work really all the way down to 30 or 40 hz.

If you can - try to pull that back wall treatment a little further out from the wall.
Try to make an airgap of around 20 cm behind it.

From the pics it looks like you treated the whole back wall from side to side and top to bottom.
This is important by dealing with air gaps behind absorbers. You need a sealed surface of absorption to gain anything from spacing the absorbers away from the wall.
All this space a 100 x 60 cm panel away from the wall is senseless as long as there are not a lot of other panels around it covering the whole wall.
Put a complete package of rockwool in the middle of your room - it will have a murder airgap around it there - make a measurement to see how good this works...
By covering a whole wall - it is a different story - here are air gaps sometimes useful.

Put that treatment at the back wall a little bit out - that would be your cheapest try - and look at waterfall and spectrogram what it does to the ringing of your lowest mode.
If it is still not enough you can try it at the front wall.
Google "Genelec SBIR" and use Google Pictures. You will find a chart that gives you a rough idea of what distance causes which dip related to wall distance.
Make sure that the treatment you put behind the speakers is able to handle those SBIR related issues. Do not go to far directly behind the speakers as it becomes really hard to treat the lower frequencies related to SBIR.

It does not make sense to give you any general numbers what is good and what not.


Try before you buy!

That means do not build anything to last if you are not sure that it works probably.

If you have to treat the front wall - just lean the Rockwool at the wall - try out how thick you need it before you build a frame and if it works at all.
Old 4 weeks ago
  #17
Here for the gear
 

Quote:
Originally Posted by Kurt B View Post
You already can see how powerful SBIR is at your 116 Hz Dip. (sidewall - speaker distance)

If you put your speakers away from the front wall - to put thick porous treatment on it - you will get another dip.

In small rooms it is usually (not always) a good start to get the most out of the back wall and leave the speakers really close to the front wall.

If you haven't done this a few times (treated some rooms) then do not try to do too much at once.

Go from the worst problem to the next problem.

First treat the lowest room mode - as this needs the most space or time to figure out how to do it if you need some pressure based help.

And by using mostly porous treatment only - a lot of problems are already gone by treating the lowest mode.

In your case 40 cm of sonorock (28kg density + 6kpa) are not enough to work really all the way down to 30 or 40 hz.

If you can - try to pull that back wall treatment a little further out from the wall.
Try to make an airgap of around 20 cm behind it.

From the pics it looks like you treated the whole back wall from side to side and top to bottom.
This is important by dealing with air gaps behind absorbers. You need a sealed surface of absorption to gain anything from spacing the absorbers away from the wall.
All this space a 100 x 60 cm panel away from the wall is senseless as long as there are not a lot of other panels around it covering the whole wall.
Put a complete package of rockwool in the middle of your room - it will have a murder airgap around it there - make a measurement to see how good this works...
By covering a whole wall - it is a different story - here are air gaps sometimes useful.

Put that treatment at the back wall a little bit out - that would be your cheapest try - and look at waterfall and spectrogram what it does to the ringing of your lowest mode.
If it is still not enough you can try it at the front wall.
Google "Genelec SBIR" and use Google Pictures. You will find a chart that gives you a rough idea of what distance causes which dip related to wall distance.
Make sure that the treatment you put behind the speakers is able to handle those SBIR related issues. Do not go to far directly behind the speakers as it becomes really hard to treat the lower frequencies related to SBIR.

It does not make sense to give you any general numbers what is good and what not.


Try before you buy!

That means do not build anything to last if you are not sure that it works probably.

If you have to treat the front wall - just lean the Rockwool at the wall - try out how thick you need it before you build a frame and if it works at all.
Thank you for the detailed information!
I already took all the space in the back wall unfortunately. Making it thicker would block the door, so 40cm is the thickest i can go...

Yeah, i still have some sealed rockwool packages, so i´ll try an place them on the front wall and see what's changing....
Old 4 weeks ago
  #18
Here for the gear
 

Quote:
Originally Posted by akebrake View Post
Thanks for the photos! Wow, that’s a clean set up!
Nice symetrical room with large traps and Cloud.

Now you have a unique opportunity to check exactly what a fairly large desk is doing to the Frequency Response...

First, try lowering the monitor level (Focusrite) a little.

1. With the Mic & Spkr in the usual position make a couple of sweeps. (Save)
2. Place your Mac & Fousrite on the floor in stead (to the side) plus chair.
3. Remove the desk.
3. Take a couple of new measurements. Upload here.

Best
Will do that, thank you!
Old 3 weeks ago
  #19
Here for the gear
 

Quote:
Originally Posted by akebrake View Post
Thanks for the photos! Wow, that’s a clean set up!
Nice symetrical room with large traps and Cloud.

Now you have a unique opportunity to check exactly what a fairly large desk is doing to the Frequency Response...

First, try lowering the monitor level (Focusrite) a little.

1. With the Mic & Spkr in the usual position make a couple of sweeps. (Save)
2. Place your Mac & Fousrite on the floor in stead (to the side) plus chair.
3. Remove the desk.
3. Take a couple of new measurements. Upload here.

Best
Ok, just did some new measurements.
Linked it via .zip, because the file size was too big.

1. Base measurement (R+L)
2. Macbook and Focusrite placed on the floor (R+L)
3. Macbook and Focusrite placed on the floor + no chair (R+L)
4. Macbook and Focusrite placed on the floor + no chair + no desk (R+L)
5. Macbook and Focusrite placed on the floor + no chair + no desk (L)
6. Macbook and Focusrite placed on the floor + no chair + no desk (R)
7. Macbook and Focusrite placed on the floor + no chair + no desk + 56cm Rockwool behind the speakers (R+L)

The Rockwool definitely improved the SBIR, however on the other side i now have the dip in the midnighs...

Best
Attached Files
File Type: zip new measurements4.mdat.zip (13.64 MB, 7 views)
Old 3 weeks ago
  #20
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akebrake's Avatar
 

Midnighs Dips

Quote:
Originally Posted by zyodmusic View Post
The Rockwool definitely improved the SBIR, however on the other side i now have the dip in the midnighs...
Thanks for your effort! Ill look closer to the files morrow.
Pls describe size and where the new RW is added. Speaker in a new position?

Cheers
Old 3 weeks ago
  #21
Here for the gear
 

Quote:
Originally Posted by akebrake View Post
Thanks for your effort! Ill look closer to the files morrow.
Pls describe size and where the new RW is added. Speaker in a new position?

Cheers
I used the sealed Rockwool packages and placed it directly behind the speakers. 100cm in height (I put it on a woodblock so the speaker is directly in the middle of the package)
60 cm wide and around 50 cm thick, so I moved the listening position (speakers+desk+chair) 50cm from the frontwall.

Thank you!
Old 3 weeks ago
  #22
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akebrake's Avatar
 

Change one thing at a time

Quote:
Originally Posted by zyodmusic View Post
...
3. Macbook and Focusrite placed on the floor + no chair (R+L)
4. Macbook and Focusrite placed on the floor + no chair + no desk (R+L)
In order to evaluate the room +treatment one likes to clen up (remove furniture etc. that screw up the reflection pattern) to see what challenges one still might have...

Make notes or mark that ("reference") current Spkr /Mic positions w tape on the floor.

RE: Desk Test
I choosed to compare
test 3: jun15 16:26:20v (L+R; No Mac/no Focusr / No Chair) Blue curve
test 4: jun 15 16:30:31 (L+R; No desk) Red curves

Pic 1 is AllSPL 1/24 Oct smoothed and Overlaid
Pic 2 ETC 0.1ms smoothed and Overlaid

The strong 1 ms desk-reflection causes a comb filter like signature clearly visible in the higher frequencies. With desk removed the floor reflection (lower level)
shows more clearly.

Best

BTW
You’ve already got a several nice tips from Johann, Thrill and Kurt B.
Read these posts again and think hard about what they say ;>)
Attached Thumbnails
Need help interpreting REW results-l-r-all-spl-no-desk-vs-desk.jpg   Need help interpreting REW results-etc-desk-vs-no-desk-0.1-ms.jpg  
Old 3 weeks ago
  #23
Quote:
Originally Posted by zyodmusic View Post
Ok, just did some new measurements.
Linked it via .zip, because the file size was too big.

1. Base measurement (R+L)
2. Macbook and Focusrite placed on the floor (R+L)
3. Macbook and Focusrite placed on the floor + no chair (R+L)
4. Macbook and Focusrite placed on the floor + no chair + no desk (R+L)
5. Macbook and Focusrite placed on the floor + no chair + no desk (L)
6. Macbook and Focusrite placed on the floor + no chair + no desk (R)
7. Macbook and Focusrite placed on the floor + no chair + no desk + 56cm Rockwool behind the speakers (R+L)

The Rockwool definitely improved the SBIR, however on the other side i now have the dip in the midnighs...

Best
Is tough to compare measurements because you are measuring at different levels. Your rockwool measurement is 3-4 db lower then your other combined measurements. Why is that?

Try to maintain the same level when making measurements. Also your measurement shows you are measuring around 55-65db? That is too low.

If you are looking at the levels into the noise floor which is 60db below it will throw off the RT60 topt and spectogram. 40db down looks clean but if you go down further it stats to show the decays which look too long for mid and hi frequencies.

Also when looking at the distortion figures your 3rd harmonic distortion is high on different measurements. This is usually a sign of some sort of clipping somewhere. Is this why you are measuring so low?

Analyzing the rockwool measurement, on the surface its looks like its actually making it worse. Because you have to move the speakers to fit the Rockwool its created other SBIR issues between 3.4khz-6.92khz. But that could also be because the speakers are now uneven and when you do a sum measurement you get a phase cancelation( excess group delay shows possible SBIR). Its better to measure them separately with the rockwool and without and compare.

Lastly in general a narrow null even though at times it can be -20db deep is actually better then a wide null that is -10 db deep in the lows.

A narrow null can just be at the listening location and if you measure a foot either left or right of it or even behind(which everyone should actually because you rarely keep your head in one spot like in a vise) that deep null could shrink or even disappear.
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