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Help Needed With Room Null
Old 1 week ago
  #1
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Help Needed With Room Null

I just finished building some big new front corner traps and a cloud. The good news is that my decay time is way down and the sub region is much more even but I have two big NEW nulls between 100-200Hz! They didn't show up in old measurements but perhaps they were always there and covered up by other modes somehow. I just want to smooth them out if possible and it should be possible considering they're above 100Hz.

My room is roughly 13x15x10. I have what feels like a decent amount of absorption in the room, which you can see in the pictures. Everthing pictured has 4-6 inches of OC 703 and if it is deeper than that there is R-19 behind it. All 8 corners have bass traps. The back wall is fully covered, reflection zone fully covered, and the front wall is mostly covered except for the windows. The side walls are largely bare.. one side there is a door and the other side wall has a fireplace.

Take a look at my measurements and I'd be grateful for any suggestions. The collective wisdom on this forum has helped me get this far. I'm not sure where to go from here to help with the remaining nulls. I have genelecs with SAM and I own Sonarworks but neither are turned on for these measurements and I know they won't help improve a null.

Thank you for any help!
Attached Thumbnails
Help Needed With Room Null-screen-shot-2019-06-10-9.56.17-pm.jpg   Help Needed With Room Null-front-wall.jpg   Help Needed With Room Null-rear-wall.jpg  
Attached Files
File Type: pdf FFT Waterfall 5Hz-200hz.pdf (145.8 KB, 20 views) File Type: pdf 20-500 Freq Chart.pdf (22.7 KB, 20 views) File Type: pdf FFT Waterfall 10Hz-22k.pdf (133.0 KB, 14 views)
Old 1 week ago
  #2
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Hello,

On the pictures, it seems you have measured with a mic not pointed towards the ceiling?

Have you measured the both speakers together?
Old 1 week ago
  #3
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Quote:
Originally Posted by dinococcus View Post
On the pictures, it seems you have measured with a mic not pointed towards the ceiling?
Makes no difference for low/mid-range measurements, which is what the OP seems to be focusing on (variations dependent on mic angle tend to start around 5kHz).

I've tested this in my own room out of curiosity. Low/mid-range frequency response results remain exactly the same no matter whether the mic is angled vertically or horizontally. Variation in the higher-range response (>5kHz) is less than 1dB in my case... but my room is heavily treated and so the reflections are dampened.
Old 1 week ago
  #4
Old 1 week ago
  #5
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Quote:
Originally Posted by dinococcus View Post
Haha! I see you are adopting the patented Jens-Style response™

That's a long thread and I'm not sure what you are referring to within it, but happy to be enlightened
Old 1 week ago
  #6
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If it makes you feel any better I'll just say I've similarly found that with room treatments it's not simply a case of more = better, and that it's possible to make things worse. For myself my plan is to make measurements with/without various panels to get an understanding of their effects and to ultimately decide what it's best to use where. I'm new to this though so I'll be interested in what the more experienced folks may have to say in response to your problem.
Old 1 week ago
  #7
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EastNashRocker's Avatar
 

Quote:
Originally Posted by dinococcus View Post
Hello,

On the pictures, it seems you have measured with a mic not pointed towards the ceiling?

Have you measured the both speakers together?
Thanks for pointing this out. I've been testing out FuzzMeasure but I may go back to REW. My understanding is that with FM I'm supposed to point the mic horizontally but I could be mistaken. I can go back and take a measurement with the mic positioned vertically. My issues appear to be between 100-200Hz. Is it really worth removing treatment to get a better frequency response? My decay time is the best it's is ever been and I'd would hate to sacrifice that.. but those nulls are no joke.

Any thoughts/suggestions about how to treat those would be great.
Old 1 week ago
  #8
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Can your post your .mdat? Nice symmetrical setup otherwise so you should be able to get good results.

One thing that I'm thinking: The pros in here talk about how some materials become reflective at certain depths.... Maybe that's what's happening here? Too much absorption turns the absorbers into reflectors and the null is a regular interference?
Old 1 week ago
  #9
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Quote:
Originally Posted by EastNashRocker View Post
Thanks for pointing this out. I've been testing out FuzzMeasure but I may go back to REW. My understanding is that with FM I'm supposed to point the mic horizontally but I could be mistaken. I can go back and take a measurement with the mic positioned vertically. My issues appear to be between 100-200Hz. Is it really worth removing treatment to get a better frequency response? My decay time is the best it's is ever been and I'd would hate to sacrifice that.. but those nulls are no joke.

Any thoughts/suggestions about how to treat those would be great.
IMHO, i think at a cancelation due to the floor. The frequency range is typical of this issue.
Check by a measure with the speaker near the floor.
Old 1 week ago
  #10
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Quote:
Originally Posted by johannburkard View Post
Can your post your .mdat? Nice symmetrical setup otherwise so you should be able to get good results.

One thing that I'm thinking: The pros in here talk about how some materials become reflective at certain depths.... Maybe that's what's happening here? Too much absorption turns the absorbers into reflectors and the null is a regular interference?
The .mdat should hopefully be attached. I measured with the mic pointing towards the ceiling for REW but I am by no means an expert at using or analyzing these graphs. Thank you for taking a look at it!!

I think you're right about absorbers being able to turn into reflectors. What I've read is that more than 4-6 inches of OC 703 can start to reflect instead of absorb. Anything in my room more than 6" deep has soft R-19 behind it to hopefully avoid the possibility of reflecting.
Attached Files
File Type: mdat Left Plus Right 6-11-19.mdat (3.27 MB, 10 views)
Old 1 week ago
  #11
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Quote:
Originally Posted by dinococcus View Post
IMHO, i think at a cancelation due to the floor. The frequency range is typical of this issue.
Check by a measure with the speaker near the floor.
dinococcus - That is a fantastic idea! It could totally be caused by the floor.. goodness knows I have absorption everywhere else

Do you think a floor bounce from my speakers is causing the dip or is it from a null related to the entire floor? The reason I ask is because I could put some small 703 absorbers on the floor between my listening position and the speakers. I have some spare insulation laying around. I'll test it out.

In case the pictures in the first post are hard to see I have an oriental rug on top of a hardwood floor (over a basement if that makes a big difference). My desk is tiny (25"x16") because I've simplified my setup and I wanted to remove the big desk bounce I was getting with my previous setup.

When you mention checking by measuring with the speaker near the floor.. does that mean leave the mic in the listening position and run the test tone with one speaker on the floor? What will these results tell me. Sounds interesting, I've never tried anything like that before. Thanks!
Old 1 week ago
  #12
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If the floor is the source of the null, it's a bad news. A sub is the solution.
Old 1 week ago
  #13
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Quote:
Originally Posted by EastNashRocker View Post

When you mention checking by measuring with the speaker near the floor.. does that mean leave the mic in the listening position and run the test tone with one speaker on the floor? What will these results tell me. Sounds interesting, I've never tried anything like that before. Thanks!
The mic stays at the listening position, at the ears level and pointed towards the ceiling.
Old 1 week ago
  #14
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Quote:
Originally Posted by dinococcus View Post
If the floor is the source of the null, it's a bad news. A sub is the solution.
I have two subs in the room already. A pair of genelec 7350a's to go with the 8341's. I had one sub for a year but getting a second sub and testing them out in a dozen places led to a pretty nice low end.

The trouble I'm having now is that I've added new corner traps and a cloud that have revealed (or caused?) a dip between 100-200Hz. This problem area wasnt an issue with the subs before the new absorbtion got added and is above the crossover range of the subs.
Old 1 week ago
  #15
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The floor is an hypothesis easy to check
Old 1 week ago
  #16
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akebrake's Avatar
 

Quote:
Originally Posted by EastNashRocker View Post
...Do you think a floor bounce from my speakers is causing the dip or is it from a null related to the entire floor?
There are several dips in that area. Floor bounce creates one of them but we also have ceiling and wall bounce. Slightly later, modal resonances will form and we measure all of it in a very complex mix.

Help Needed With Room Null-floor-bounce-rew4.jpg
Figures are from REW Room Sim (with some arrows added by me)

Suggestions:
1. If you have a mic cal file use it.

2. Always measure L and R speaker separately.

Why? We like to investigate the Room and Spkr Symmetry. E.g if one side of the room differs from the other. Like: Left wall is brick and Right wall is plywood.
Also differences caused by doors, openings, windows, wardrobes, furniture...

3. Separate meas. means: Mic does not have to be exactly equidistant from the speakers.

4. Update your REW software.
REW is continuesly updated and new features added.
Now we have 5.20 beta 12 (You’ve got 5.19 beta 8)

Best

PS Just noted you mentioned two subs!
Are your uploaded L+R measurement: L+R 8341’s + subs?

You've got some measurement job ahead...
Attached Thumbnails
Help Needed With Room Null-sim-l-only.jpg   Help Needed With Room Null-floor-bounce-rew3.jpg   Help Needed With Room Null-floor-bounce-rew4.jpg   Help Needed With Room Null-wf-l-r-spkr.jpg   Help Needed With Room Null-l-r-wave-1-8-lin.jpg  

Old 1 week ago
  #17
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Thanks akebrake, take a look at the .mdat attached. I took the measurements you recommended. It sounds like you'll be able to discern more information from this than me. The frequency chart and the waterfall charts mostly make sense but I know I'm not getting a full picture. There are some differences between the left and right speakers but they look pretty similar for the most part.

Let me know what you think and if there are more measurements that'll be helpful
Attached Thumbnails
Help Needed With Room Null-betterviewofroom.jpg  
Attached Files
File Type: mdat 6.12.19 Room Measurements.mdat (12.88 MB, 9 views)
Old 1 week ago
  #18
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Quote:
Originally Posted by dinococcus View Post
The floor is an hypothesis easy to check
dinococcus - In my pervious post there is a .mdat with a measurement of speaker sitting on the floor. The frequency response has a boost below 100Hz but my issues between 100-200Hz look almost identical to the measurements with the speaker on the stand. Take a look at it when you get a chance, I'm not sure what I'm supposed to be learning from putting the speaker on the floor.. but I did try what you suggested. Perhaps the issue is not the floor?

I also tested having 4" of 703 flat on the floor between me and the speakers in the reflection area. This also had little impact on the 100-200Hz range.
Old 1 week ago
  #19
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re: subs - are those subs in the corners of the front wall, below the traps? if your room is symmetrically/rectangular, you might want to consider a dual sub system, flown on the ceiling, which would get you pretty much the same amount of lf (very even distribution/spl) everywhere in your room.



p.s. from looking at the pic, those two screens are certainly not doing any good...

Last edited by deedeeyeah; 1 week ago at 07:34 PM.. Reason: p.s. added
Old 1 week ago
  #20
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Quote:
Originally Posted by EastNashRocker View Post
dinococcus - In my pervious post there is a .mdat with a measurement of speaker sitting on the floor. The frequency response has a boost below 100Hz but my issues between 100-200Hz look almost identical to the measurements with the speaker on the stand. Take a look at it when you get a chance, I'm not sure what I'm supposed to be learning from putting the speaker on the floor.. but I did try what you suggested. Perhaps the issue is not the floor?

I also tested having 4" of 703 flat on the floor between me and the speakers in the reflection area. This also had little impact on the 100-200Hz range.
The floor was easy to check. It's a pity.
Old 1 week ago
  #21
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Quote:
Originally Posted by deedeeyeah View Post
re: subs - are those subs in the corners of the front wall, below the traps? if your room is symmetrically/rectangular, you might want to consider a dual sub system, flown on the ceiling, which would get you pretty much the same amount of lf (very even distribution/spl) everywhere in your room.



p.s. from looking at the pic, those two screens are certainly not doing any good...
deedeeyeah - yep the two subs are in the corners of the front wall located below the bass traps. When you mention that I should get a dual sub system, what does that mean? I already have a dual sub setup. I've never heard of a setup for home studio mixing that includes subs flown from the ceiling.. do you know of an article or anything I can read about this? You mentioned the two screens.. if you're talking about the fabric in front of the subs that is just for looks.
Old 1 week ago
  #22
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EastNashRocker's Avatar
 

Quote:
Originally Posted by dinococcus View Post
The floor was easy to check. It's a pity.
No worries, checking the floor bounce was a good idea and worth a try. Let me know if there's anything else that comes to mind. Thanks!
Old 1 week ago
  #23
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Quote:
Originally Posted by EastNashRocker View Post
deedeeyeah - yep the two subs are in the corners of the front wall located below the bass traps. When you mention that I should get a dual sub system, what does that mean? I already have a dual sub setup. I've never heard of a setup for home studio mixing that includes subs flown from the ceiling.. do you know of an article or anything I can read about this? You mentioned the two screens.. if you're talking about the fabric in front of the subs that is just for looks.
'dual sub' does not just mean using two subs; sound coming from a dual sub system should not be obstructed by any furniture, hence my suggestion to mount subs on the ceiling (i've installed such a system a few years back in the control room of a national broadcaster) - a bit much to guide you through all the details if you don't know any yet; if interested, i suggest you look up the term (amongst others, klein und hummel had a system which they called 'aram')...

but there are other ways to get good sound from your subs; dsp can get help you to better integrate them. pls note that subs perform vastly different regarding their directivity than tops so you may want to spend some time reading up further literature? check for 'sub arrays'. huge topic (which is mainly about pattern control - it's mportant nevertheless as this is getting achieved by manipulating the phase and hence can affect the performance of the entire speaker system) - here's a hint: subs should be positioned within a quarter of the wavelength of the highest frequency they produce (unless room dimensions/nodes dictate otherwise - but when is that...?);

i suggest you measure your room with just one sub running to find out whether their distance negatively affects the fr; i assume putting one at the front wall and one at the rear wall would get you better results than your current setup. delaying the rear sub is mostly helpfull/mandatory.

and no, the screens/displays i was referring to are your flat screens: sound 'bends' around speakers and your monitor screens/displays will cause reflections in their current position...
Old 1 week ago
  #24
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EastNashRocker's Avatar
 

Quote:
Originally Posted by deedeeyeah View Post
'dual sub' does not just mean using two subs; sound coming from a dual sub system should not be obstructed by any furniture, hence my suggestion to mount subs on the ceiling (i've installed such a system a few years back in the control room of a national broadcaster) - a bit much to guide you through all the details if you don't know any yet; if interested, i suggest you look up the term (amongst others, klein und hummel had a system which they called 'aram')...

but there are other ways to get good sound from your subs; dsp can get help you to better integrate them. pls note that subs perform vastly different regarding their directivity than tops so you may want to spend some time reading up further literature? check for 'sub arrays'. huge topic (which is mainly about pattern control - it's mportant nevertheless as this is getting achieved by manipulating the phase and hence can affect the performance of the entire speaker system) - here's a hint: subs should be positioned within a quarter of the wavelength of the highest frequency they produce (unless room dimensions/nodes dictate otherwise - but when is that...?);

i suggest you measure your room with just one sub running to find out whether their distance negatively affects the fr; i assume putting one at the front wall and one at the rear wall would get you better results than your current setup. delaying the rear sub is mostly helpfull/mandatory.

and no, the screens/displays i was referring to are your flat screens: sound 'bends' around speakers and your monitor screens/displays will cause reflections in their current position...

deedeeyeah - Thanks for the advice with the subs. I can look and see if I still have the .mdat from when I got and tested/placed my second sub. I tried them up off the ground, opposing walls/corners, and all the traditional front wall placement areas. If I could afford two more it would be a fun experiment to float them from the ceiling

Everything in the sub region already sounds fantastic in my albeit small room. Genelec makes the process of automating phase alignment, timed delay, and DSP correction really easy these days. The highest crossover for the subs is 100Hz and my issues are above that in the 100-200Hz region. There's a hole I can hear there while mixing. If you look at the .mdat that I posted you'll see that I have the same issues in that range with or without the subs turned on.

Let me know if you have any other thoughts or suggestions on how I could diagnose my 100-200Hz issue or potentially fix it. Thanks for the help, I've reached the end of my room treatment knowledge trying to solve this problem.
Old 1 week ago
  #25
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Quote:
Originally Posted by akebrake View Post
There are several dips in that area. Floor bounce creates one of them but we also have ceiling and wall bounce. Slightly later, modal resonances will form and we measure all of it in a very complex mix.


Figures are from REW Room Sim (with some arrows added by me)

Suggestions:
1. If you have a mic cal file use it.

2. Always measure L and R speaker separately.

Why? We like to investigate the Room and Spkr Symmetry. E.g if one side of the room differs from the other. Like: Left wall is brick and Right wall is plywood.
Also differences caused by doors, openings, windows, wardrobes, furniture...

3. Separate meas. means: Mic does not have to be exactly equidistant from the speakers.

4. Update your REW software.
REW is continuesly updated and new features added.
Now we have 5.20 beta 12 (You’ve got 5.19 beta 8)

Best

PS Just noted you mentioned two subs!
Are your uploaded L+R measurement: L+R 8341’s + subs?

You've got some measurement job ahead...
akebrake - What up! I did the measurements (and REW update) you recommended and posted the .mdat. I wanted to see if you'd be willing to take a look at it? I'm having trouble diagnosing the issue in the 100-200Hz region.

All my direct reflection points (except for the floor) are treated with broadband absorption. I tried dinococcus' idea of putting a speaker on the floor to measure and I tried putting 4" of 703 on the floor in the area when there'd be a 'floor bounce' but neither test had an effect one way or the other on the nulls between 100-200Hz.

So I feel like we've largely ruled out the floor as the culprit. I've tried all the tests and speaker placement methods that I know.. hoping that others smarter than me and with more experience have other insights or suggestions. Thanks!
Old 1 week ago
  #26
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Quote:
Originally Posted by johannburkard View Post
Can your post your .mdat? Nice symmetrical setup otherwise so you should be able to get good results.

One thing that I'm thinking: The pros in here talk about how some materials become reflective at certain depths.... Maybe that's what's happening here? Too much absorption turns the absorbers into reflectors and the null is a regular interference?
johannburkard - I put a more comprehensive .mdat in post #17 . If you get a chance to look at it I'd greatly appreciate any thoughts/suggestions you have for identifying/fixing the issue I have between 100-200Hz
Old 1 week ago
  #27
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i fear i cannot help any further: i'm neither an acoustician nor an expert with rew - i'm a very experienced mixing engineer and do a lot of system alignment, both live and in the studio, but i'm using smaart to analyze...
Old 1 week ago
  #28
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Quote:
Originally Posted by EastNashRocker View Post
johannburkard - I put a more comprehensive .mdat in post #17 .
Tried to open that file, got an error message that the file is not in .mdat format.
Old 1 week ago
  #29
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akebrake's Avatar
 

Quote:
Originally Posted by EastNashRocker View Post
akebrake - What up! I did the measurements (and REW update) you recommended and posted the .mdat. I wanted to see if you'd be willing to take a look at it?
Yes, I've already been plotting and tweaking your latest mdats in a number of different ways.

Quote:
I'm having trouble diagnosing the issue in the 100-200Hz region.[
Me too...

Quote:
... I tried dinococcus' idea of putting a speaker on the floor to measure...
I noticed that, and I compared that (floor) position with the others. A lot of comparisons to do (and I'm not ready yet).

First reflections (and possibly second) will combine with modes and create strange interference nulls and peaks. Visible more or less depending on our chosen frequency resolution.

Quote:
...and I tried putting 4" of 703 on the floor in the area when there'd be a 'floor bounce' but neither test had an effect one way or the other on the nulls between 100-200Hz.
EDIT: IMHO a lot larger and thicker trap is needed to have an effect on a 100Hz bounce.

Some questions:
I guess the 8341's are your "main" speakers. Are they as close to the front wall as possible.(2"?)
How far from the side walls?

Would you mind measure & upload L / R Subs only (separately of course )

Best

PS Your mdats works fine for me (I'm on mac OSX 10.10.5)

Last edited by akebrake; 5 days ago at 05:08 PM.. Reason: Added info
Old 1 week ago
  #30
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Quote:
Originally Posted by johannburkard View Post
Tried to open that file, got an error message that the file is not in .mdat format.
It opens OK for me, in REW 5.20 beta 9 on a laptop running Windows 10.
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