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Help Needed With Room Null
Old 15th June 2019
  #31
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[QUOTE=akebrake;14037976]Yes, I've already been plotting and tweaking your latest mdats in a number of different ways.



Me too...

[QUOTE]... I tried dinococcus' idea of putting a speaker on the floor to measure...
Quote:

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.



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)
akebrake - The 8341's are my main speakers. They were about 4" away from the wall but for these measurements they are 2" away. The new .mdat file only has measurements from today in this new position. The nulls did change shape. The file was too large to include both yesterday and today's measurements.

I included measurements of both subs individually. The 8341's are exactly 42" away (measured to the tweeter) from the side walls.

Thanks for taking a look at these
Attached Files
File Type: mdat 6-14-19 Room Measurements II.mdat (14.72 MB, 15 views)
Old 16th June 2019
  #32
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Couple of questions

Quote:
Originally Posted by EastNashRocker View Post
...
akebrake - The 8341's are my main speakers. They were about 4" away from the wall but for these measurements they are 2" away. The new .mdat file only has measurements from today in this new position. The nulls did change shape. The file was too large to include both yesterday and today's measurements.

I included measurements of both subs individually. The 8341's are exactly 42" away (measured to the tweeter) from the side walls...

In your latest ”BetterView of Room” pic it looks like there’s a fire place to the right?
(A photo from the left loudspeaker position toward the right rear of the room would be interesting...)

I guess there is quite a large (rigid) surface that will bounce sound back to the LP? (sketch below)

Also your 8341’s are close to (0.2.0) width mode null. Try move NS 10’s away temporarily and run a test to see what happens with the Genelecs a little closer together.

I’m have no practical experience of what the SAM system can and can’t do.
Like can the subs be operated individually? With diff EQ?

Can you drive mains full range and just add (low passed) sub for the lowest freq band? As I understand it in the tips from DeeDeeYeah:
Quote:
"- 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...?"
or our moderator Northward:

Jason Foi Studio Design - Tuning
Attached Thumbnails
Help Needed With Room Null-fire-place-1.jpg  
Old 16th June 2019
  #33
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Quote:
Originally Posted by akebrake View Post
In your latest ”BetterView of Room” pic it looks like there’s a fire place to the right?
(A photo from the left loudspeaker position toward the right rear of the room would be interesting...)

I guess there is quite a large (rigid) surface that will bounce sound back to the LP? (sketch below)

Also your 8341’s are close to (0.2.0) width mode null. Try move NS 10’s away temporarily and run a test to see what happens with the Genelecs a little closer together.

I’m have no practical experience of what the SAM system can and can’t do.
Like can the subs be operated individually? With diff EQ?

Can you drive mains full range and just add (low passed) sub for the lowest freq band? As I understand it in the tips from DeeDeeYeah:


or our moderator Northward:

Jason Foi Studio Design - Tuning
Got some free time today and did a ton of testing. AKebrake you were right to have me put the speakers closer to the wall.. that improved the nulls from 150-200Hz. Putting 703 near the back left wall of the room improved the 100Hz null the most! This was surprising since having that same 703 in front of the fireplace definitely helped a little but not as much as the back left corner.

I moved the NS-10 speaker stands and moved the genelecs (tested one at a time) into several positions flat across the back wall. My triangle to the listening position is not equilateral any more. The speakers are 62" apart and the listening position is 70" from both speakers. I wonder if the increased sense of mono will make much difference? Your thoughts? The frequency response is certainly better this way.

I enjoyed the link to Northward's post.. it helped me re-approach how I was measuring. The SAM software with the genelecs basically just does some reduction of any low end build up. I might be explaining this incorrectly but it just cuts and does not boost any frequencies. It also appears to only do any real work (for my room at least) up to 300Hz. I can see the original and adjusted eq curves. I only use it to make small changes after i get everything I can out of the room naturally.

The room is getting better! This discussion and ideas has been helping a lot!
Attached Thumbnails
Help Needed With Room Null-img_4818.jpg   Help Needed With Room Null-direct-view-l-speaker.jpg   Help Needed With Room Null-direct-view-l-speaker.jpg   Help Needed With Room Null-703-test-fireplace.jpg   Help Needed With Room Null-703-test-left-wall.jpg  

Attached Files
File Type: mdat Room Measurements 6-16-19 II.mdat (15.37 MB, 10 views)
Old 17th June 2019
  #34
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BTW: What's your desk -- interested. Thanks.
Old 17th June 2019
  #35
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EastNashRocker's Avatar
 

Quote:
Originally Posted by johannburkard View Post
BTW: What's your desk -- interested. Thanks.
It's called a Pneumatic Adjustible-Height Lecturn that's from Stand Up Desk Store. I bought it on Amazon. I've only had it a few months but it's worked well. I went the minimal route and I only put my keyboard, trackpad, monitor controller, and control surface on there. The tilt feature is nice.
Attached Thumbnails
Help Needed With Room Null-img_4819.jpg   Help Needed With Room Null-img_4820.jpg  
Old 17th June 2019
  #36
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Ultrasonic_UK's Avatar
 

It may be an odd camera angle, but the recent photo with the microphone looks like this was placed much higher than where your head would be?
Old 17th June 2019
  #37
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Quote:
Originally Posted by Ultrasonic_UK View Post
It may be an odd camera angle, but the recent photo with the microphone looks like this was placed much higher than where your head would be?
It does look odd.. I used the pano feature on my phone to try and show more of the room but some things look warped as a result. Thanks for pointing that out. To get the mic height I alway sit in my chair and make sure that the tip of the mic is exactly at ear level. I’ve got a spot on the floor that marks 38% of the way in from the front wall. And I use a tape measure from the mic to both speakers to make sure that everything is lined up equidistant. This should hopefully make for some decent measurements but let me know if there’s anything I’m not doing that would be good for me to include.
Old 19th June 2019
  #38
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Suggestions

Quote:
Originally Posted by EastNashRocker View Post
... Putting 703 near the back left wall of the room improved the 100Hz null the most! This was surprising since having that same 703 in front of the fireplace definitely helped a little but not as much as the back left corner...
Seems like you moved one trap from one wall to another? That means you changed two things.
1. Removed a trap from one position.
2. Added this trap in another position.

Just change one thing at a time. And measure at each stage. Before/ after

Moving the same traps around makes it very difficult to draw conclusions about the gained improvement.
(In your case it seems like more trapping is needed at the rear wall and the fireplace also...).

There are several boundaries involved in the resulting dips.
The trick is to identify which one (or pair)of the boundaries is causing each null.

We almost have the needed information already...
A. With help from the Harman mode diagram in your post no 1.
B. The (aproximate) reflection paths (arrows) I added to the pic in post 16
Plus a number of REW IR’s from different pos in the room.

A. Resonant Reflections/ Modes:
Speaker in a null will not "drive" that mode efficiently.
Listener/ mic in a null will not "hear" that mode so well.

Tip: Neither put speaker nor listener/mic in a null by accident. (Only by purpose)

B. Non Resonant Reflections/ ”SBIR” (like floor, ceiling or wall bounce)

Prediction of SBIR
Make a sketch/ drawing (to scale) and measure the Reflection Path on the drawing. (from Spkr to wall to mic/LP)
Subtract the Direct Path from that . Now you have the Path Length Difference (PLD).

When the PLD equals ½ wavelength we have the first null in a combfilter. (e.g. Direct & First reflection are in opposite phase). What frequency?
Divide Speed of sound by 2. (565 ft/s or172m/s) ; Divide that figure by PLD.

Or... measure in reality (tape measure) from the speaker to the wall to the mic.
Subtract Direct path length (spkr to mic distance).
Sometimes this null happens at the same frequency as a room mode null huh

Practice this by watching nulls and holes in the decay of the WF / Wavelet and
compare to the calculated/measured nulls in your sketch/reality.

Some effort and patience needed

Looking at the WF one can see big nulls at some frequencies. Also some deep ”holes” along the decay.
(We like modes to decay evenly at the same rate)

Help Needed With Room Null-r-no-sub-wave-jun-16-23-56-46.jpg

The Wavelet plot (my favourite btw) will show more detail of these "holes" due to frequency dependent windowing and the ability to normalize frequency peaks.
Then compare Wavelet plots using different resolution (time/ frequency trading) for best detail of the ”happening”.

Too much (or strange) information? Feel free to ask!
I tried hard to make it short
Attached Thumbnails
Help Needed With Room Null-r-no-sub-wf-jun-16-23-56-46.jpg   Help Needed With Room Null-r-no-sub-wave-jun-16-23-56-46.jpg  
Old 20th June 2019
  #39
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EastNashRocker's Avatar
 

Quote:
Originally Posted by akebrake View Post
Seems like you moved one trap from one wall to another? That means you changed two things.
1. Removed a trap from one position.
2. Added this trap in another position.

Just change one thing at a time. And measure at each stage. Before/ after

Moving the same traps around makes it very difficult to draw conclusions about the gained improvement.
(In your case it seems like more trapping is needed at the rear wall and the fireplace also...).

There are several boundaries involved in the resulting dips.
The trick is to identify which one (or pair)of the boundaries is causing each null.

We almost have the needed information already...
A. With help from the Harman mode diagram in your post no 1.
B. The (aproximate) reflection paths (arrows) I added to the pic in post 16
Plus a number of REW IR’s from different pos in the room.

A. Resonant Reflections/ Modes:
Speaker in a null will not "drive" that mode efficiently.
Listener/ mic in a null will not "hear" that mode so well.

Tip: Neither put speaker nor listener/mic in a null by accident. (Only by purpose)

B. Non Resonant Reflections/ ”SBIR” (like floor, ceiling or wall bounce)

Prediction of SBIR
Make a sketch/ drawing (to scale) and measure the Reflection Path on the drawing. (from Spkr to wall to mic/LP)
Subtract the Direct Path from that . Now you have the Path Length Difference (PLD).

When the PLD equals ½ wavelength we have the first null in a combfilter. (e.g. Direct & First reflection are in opposite phase). What frequency?
Divide Speed of sound by 2. (565 ft/s or172m/s) ; Divide that figure by PLD.

Or... measure in reality (tape measure) from the speaker to the wall to the mic.
Subtract Direct path length (spkr to mic distance).
Sometimes this null happens at the same frequency as a room mode null huh

Practice this by watching nulls and holes in the decay of the WF / Wavelet and
compare to the calculated/measured nulls in your sketch/reality.

Some effort and patience needed

Looking at the WF one can see big nulls at some frequencies. Also some deep ”holes” along the decay.
(We like modes to decay evenly at the same rate)



The Wavelet plot (my favourite btw) will show more detail of these "holes" due to frequency dependent windowing and the ability to normalize frequency peaks.
Then compare Wavelet plots using different resolution (time/ frequency trading) for best detail of the ”happening”.

Too much (or strange) information? Feel free to ask!
I tried hard to make it short
akebrake - Thank you so much for putting the information together! I'm still working on deciphering some of it but I can tell that I'm learning more of what I need to know about my room. That Wavelet plot is awesome.. somehow I've never used that graph before but interpreting seems somewhat intuitive.

I measured the distance from my speaker to the wall to the mic (minus) the distance from the mic to the speaker. That works out to 141-70= 71" Does this help me understand if my listening position is in a null?

My speakers are closer together than when I started, which was a 70x70x70" equilateral triangle with the listening position. Now the speakers are in the best position for frequency response and the two speakers are 63" apart from each other and both are still 70" from the listening position. I know this breaks the general rule of having an equilateral triangle but I'm curious if the setup now is still in the "range" of what is acceptable? I still want the mono/stereo balance to be as even as possible. What are your thoughts on this?

The tests I did with the 703 was using extra insulation that was stored in my basement. I had added new absorption to what was already in the room because I agree with you.. if I had just rearranged my existing treatment then the results wouldn't tell me much. The tests I did were:
1. The room with its normal treatment
2. The room with its normal treatment with the extra 703 treatment by the fireplace.
3. The room with its normal treatment with the extra 703 treatment on the left wall near the back of the room.
I anticipated that the absorption by the fireplace would make the biggest difference but it was #3 that had the most impact. In both places the 703 improved the null at roughly 110Hz but for some reason the back left wall really worked better.. which is a mystery to me.

In my impulse response I see a big spike that I can't figure out. From what I can tell it is too far away to be a first reflection but I could be mistaken.

With my subs engaged the null at 85Hz appears to go away. I'm used to dealing with issues below 100Hz but not most of my issues are between 100-400Hz. My sub region looks really good to me. I'd like to know your thoughts about improving the 100-400Hz range and how far away am I from having a decent monitoring environment? I feel like I'm getting close on the frequency range side (peaks and nulls are mostly within a 10db range) but I know my decay times need work. It'd be nice to have a general sense of what is left and when I can feel good about the balance I'm hearing in the room
Old 23rd June 2019
  #40
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akebrake's Avatar
 

More nulls

Quote:
Originally Posted by EastNashRocker View Post
akebrake - Thank you so much for putting the information together!
My pleasure

Quote:
It'd be nice to have a general sense of what is left...
Sorry, I not quite follow...
(but I'll try to answer some of your questions here).

Quote:
...when I measured the distance from my speaker to the wall to the mic (minus) the distance from the mic to the speaker. That works out to 141-70= 71" Does this help me understand if my listening position is in a null?
Yes, that's how it works but there's more to it.
(I appreciate what’s been missing in my "tutorial"... )

Example. R spkr: Direct sound path= 70 ”/ 1.78 m;
Dist spkr > R wall> Mic 141” (3.58m)
Half spead of sound (565ft/s / 172m/s) divided by PLD: 70” /5.83ft/1.8m
Gives: 96Hz. The first "null" (in a combfilter) created on a frequency plot with just one reflection.
Fairly close to 100 Hz! But we have many more reflections and also modal nulls.

Note: There are two kind of "nulls"! Non resonant (first reflection)"nulls" and resonant (modal) "nulls". The latter shown in the diagram post 1.
Some times occuring in the same frequency range

Quote:
I know this breaks the general rule of having an equilateral triangle but I'm curious if the setup now is still in the "range" of what is acceptable?
Have you tried moving the mic a bit forward?

BTW Forget about "rules" spreading on internet. Every room and listening situation is unique and generic rules are no solution to specific situations.
It can be a starting point and then we go from there measure, listen and adjust for a reasonable compromise (effort, esthetics, time scedule, budget etc)
Same reply for "Acceptable" (Depends how picky you are)

Quote:
I still want the mono/stereo balance to be as even as possible. What are your thoughts on this?
If L/R FR response are very similar, reflections are controlled and L& R decay at the same rate your stereo balance would be exceptional. Especially with these coaxial 8341 speakers.

Quote:
In my impulse response I see a big spike that I can't figure out.
Can you show a diagram?

Quote:
I'd like to know your thoughts about improving the 100-400Hz range and how far away am I from having a decent monitoring environment?
Difficult to say. Your room have good dimensions but needs a lot more bass trapping. Then focus on the mains. Make them as good as possible an then just add the subs for the lowest octave. (Nortward advice).

Best
Old 25th June 2019
  #41
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Quote:
Originally Posted by akebrake View Post
My pleasure

Can you show a diagram?

Best
Take a look at the attached impulse response. There's a spike at 4ms, is this probably from a floor bounce? I've read that spikes above -20 are an issue. I've gotten better at taken measurements.. but it's still hard to decipher that information into what I should do about it.
Attached Thumbnails
Help Needed With Room Null-screen-shot-2019-06-24-6.24.06-pm.jpg  
Old 25th June 2019
  #42
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Quote:
Originally Posted by akebrake View Post
My pleasure

Difficult to say. Your room have good dimensions but needs a lot more bass trapping. Then focus on the mains. Make them as good as possible an then just add the subs for the lowest octave. (Nortward advice).

Best
All the treatment in my room is at least 4" of 703 but if it's thicker than 6" it has R-19 behind it.

My rear wall is 100% treated
My front wall is 90% treated
Left and right walls are 40% treated
The ceiling is 30% treated and my floor is just a rug on a hardwood floor
All eight corners are trapped.

It's getting to the point where it would be hard to have a lot more bass traps but anything is possible.

I used to have big issues below 100Hz but those are largely improved via treatment. Now my issues are mostly between 100-200Hz. I've read where the axial modes cause ugly peaks in the sub region but once those are improved that the tangential modes are generally what cause nulls above 100Hz. Is this consistent with what you've found? My goal in saying this is just to identify what next steps are.. you mention more bass traps.. but where they should go is still a mystery.

Since my speakers are closer to each other now (more ideal for frequency response) than to me my fear would be that everything sounds more mono and that I'll be tempted to pan out further as a result. But my 70x70x63 setup isn't too far off an equilateral triangle.. so a few trips to a buddy's studio should tell me if my mixes are compensating too much for my current setup.
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