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Not treating nulls Analog Processors (HW)
Old 28th December 2010
  #1
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Not treating nulls

I alluded a few days ago in a thread that concluded to not treat nulls, and instead attack the peaks-which has been my understanding. However I have measured to what appears to being able to treat the nulls with no effect on the peaks. Well maybe that is all I can see in a graphical measurement?

So , I thought I'd share my findings to get a better understanding and for hopes to finally make a positive treatment in my situation. As mentioned measurement trumps calculations, which I agree totally-especially when a coupled mix room is adjoining another room with no door(s).

Below is the measurements and a plot drawn out for the shape and treatments(in green) top view. At this point I am only concerned of the modal issues.
Legend of pics:
fr/etc, wf, and room for measurement for the starting point
http://i58.photobucket.com/albums/g259/ttonio/1.png
Attached Thumbnails
Not treating nulls-etc1.png   Not treating nulls-wf1.png  
Old 28th December 2010
  #3
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Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by tonio View Post
I alluded a few days ago in a thread that concluded to not treat nulls, and instead attack the peaks-which has been my understanding. However I have measured to what appears to being able to treat the nulls with no effect on the peaks.
I don't understand. Peak and nulls and ringing are all damaging and must be improved. In fact, in many rooms nulls are the biggest problem. When you can't hear the fullness in a mix, you add too much bass. This is one of the most common problems we hear about - mixes sound good in your CR but too boomy and bassy elsewhere.

--Ethan

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Old 28th December 2010
  #4
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Understand

tonio, I don't understand either. To clarify, are you talking about placing traps in peaks vs nulls? This can be confusing, it does me anyway!
Peaks generally is taken to mean areas of high Pressure modulation.
In such locations the air particles are barely moving. e.g. at a Boundary.
On the other hand Nulls are areas of High Particle Velocity/Displacement.
One might assume that fibrous absorption would interfere strongly with particles in vigorous motion. Thus it would seem that absorption should have maximum effect at nulls. Andre has said that the effect is about one third of the Peak location. I don't have the links to hand and I have no idea how or why this happens. It's on my list....!
I note that Tangentials can have a Null mid wall, pretty much where one might place an RFZ panel.
A good reason to use thick RFZ panels IMHO.
DD
Old 28th December 2010
  #5
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Ethan,
I don't understand either

From the measurements the placement of an additional panel has an effect on the nulls upwards of 10dbs ( 79 and 110hz), yet the peak(89-93hz) is not effected. Although the additional panel does appear to attentuate @ 2-3dbs across the full spectrum-and yes the mic was stationary.

So the nulls are a resonance cancellation created by the mode(s) ?
Old 28th December 2010
  #6
Gear Guru
Unclear

Sorry T, I am finding it impossible to understand. I don't know which pictures are related to what sentence and so on. Maybe you could post the pictures directly. Screenshots work.
Generally though, you may be placing panels at SBIR spots, thus diminishing a cancellation. If you play Sinewaves at the frequencies in question, it should become very clear if it is a mode or a reflection.
DD
Old 28th December 2010
  #7
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If I'm not mistaken, the initial intent of this thread was to demonstrate a room treatment's ability to affect nulls. A phenomenon suggest by some on this board was an impossibility. At least that's they way I understand it.
Old 28th December 2010
  #8
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Lightbulb

Quote:
Originally Posted by tonio View Post
the placement of an additional panel has an effect on the nulls upwards of 10dbs ( 79 and 110hz), yet the peak(89-93hz) is not effected.
Bass waves propagate in strange ways around a room, so a trap placement that affects a peak or null at 100 Hz might have no affect on a peak or null at 120 Hz. Also, nulls can be infinitely deep, whereas peaks are typically 6 dB or less. So adding traps that improve a null by 20 percent could raise the null by 10 dB. But a peak at the same frequency might be lowered only 1 or 2 dB, even if the improvement is also 20 percent.

--Ethan

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Old 28th December 2010
  #9
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Quote:
Originally Posted by DanDan View Post
tonio, I don't understand either. To clarify, are you talking about placing traps in peaks vs nulls? This can be confusing, it does me anyway!
Peaks generally is taken to mean areas of high Pressure modulation.
In such locations the air particles are barely moving. e.g. at a Boundary.
On the other hand Nulls are areas of High Particle Velocity/Displacement.
One might assume that fibrous absorption would interfere strongly with particles in vigorous motion. Thus it would seem that absorption should have maximum effect at nulls. Andre has said that the effect is about one third of the Peak location. I don't have the links to hand and I have no idea how or why this happens. It's on my list....!
I note that Tangentials can have a Null mid wall, pretty much where one might place an RFZ panel.
A good reason to use thick RFZ panels IMHO.
DD
DD,
My understanding is to use porous absorbers(velocity) in the 1/4 wavelength - off the boundary. Yet I have the usual corners, RFZ panels.

Quote:
On the other hand Nulls are areas of High Particle Velocity/Displacement.
One might assume that fibrous absorption would interfere strongly with particles in vigorous motion. Thus it would seem that absorption should have maximum effect at nulls. Andre has said that the effect is about one third of the Peak location
That makes sense with "about one third of peak location".


Picture attached- upper right hand corner has an additional panel in front of the existing corner panel.Altthough it woul dbe hard to call it a corner, as it is a opening without a door. I do also have ceiling/wall panels-which does not appear to do much.

Its difficult to find the pressure points. I did SPL /ear tests, however the pressure seems its in a mix of axial &tangential . I'm sure there are multiple modes creating the confusion. High pressure around the rear of monitors and center left wall same to right side.

I cannot use calculations for my coupled room, as they manifest big differences vs what is measured.
Attached Images
File Type: bmp ROOM2.bmp (615.9 KB, 196 views)
Old 28th December 2010
  #10
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Quote:
Originally Posted by johndykstra View Post
If I'm not mistaken, the initial intent of this thread was to demonstrate a room treatment's ability to affect nulls. A phenomenon suggest by some on this board was an impossibility. At least that's they way I understand it.

True that John. Although my underlying movtive is to kill these bastard modes the best I can heh
Old 29th December 2010
  #11
Gear Guru
Puzzling

Quote:
My understanding is to use porous absorbers(velocity) in the 1/4 wavelength - off the boundary. Yet I have the usual corners, RFZ panels.
Kind of a classic conundrum there eh? See Q4Avare.

I will ask Andre where he got that third thing from.

I find a good Sine Generator is invaluable for isolating the modes. They can be very close and very confusing. Most Gennies in software have little jumps in frequency which seem erratic. Personally I have an old Analogue beauty, but Signalsuite is excellent, as is the 'Frequency follows Cursor' in the REW generator.

From what you say the usual answer seems to apply. i.e. More or bigger traps in the front area.

Where is this ' don't treat nulls' thread or post?

DD
Old 29th December 2010
  #12
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This thread:

Calculating room modes for an irregular shape

starting at post #31
Old 29th December 2010
  #13
Gear Guru
Nonsense

Quote:
thread that concluded to not treat nulls
I don't think it possible to extract that conclusion, from a brief scan of the thread.

Many of our treatment efforts are by nature limited and we expect a limited result. C'est la vie.

If we diminish a mode by absorbing the peaks at the boundaries, of course the depth of the null will be diminished.

Only communists would expect the null to be fully fixed.

DD
Old 29th December 2010
  #14
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avare's Avatar
 

Quote:
Originally Posted by DanDan View Post
Kind of a classic conundrum there eh? See Q4Avare.

I will ask Andre where he got that third thing from.
My first thought when I read this thread and some one remembering my remark about the effectiveness of porous absorbers not at points of high particle velocity was "I barely remember making the remark, and I think it was in passing." Well a bit research showed my initial thoughts to be accurate. Also, this tangent reminds me of the importance of always trying to be technically correct in threads. What ever we write, will be brought back to life at some point in the future.

The original post was #17 in this thread. The BBC RD reports that are relevant are 1983-04 and 1985-11. The latter shows experimental results, and the formers lays down some of the theoretical groundwork. The former also has some interesting insights in its first appendix relating to another thread.

Andre
Old 29th December 2010
  #15
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Quote:
Originally Posted by DanDan View Post
Kind of a classic conundrum there eh? See Q4Avare.

I will ask Andre where he got that third thing from.

I find a good Sine Generator is invaluable for isolating the modes. They can be very close and very confusing. Most Gennies in software have little jumps in frequency which seem erratic. Personally I have an old Analogue beauty, but Signalsuite is excellent, as is the 'Frequency follows Cursor' in the REW generator.

From what you say the usual answer seems to apply. i.e. More or bigger traps in the front area.

Where is this ' don't treat nulls' thread or post?

DD
DD,
Your suggestion of Signalsuite was when I got closer to finding the modal pressure, and realized the typically suggested corner traps, cloud and RFZ panels just don't cut it anymore. I suppose thats old news for most here.

From the thread John linked to, I started to make drastic moves and measurements to see the best approach as using math didn't get me close to what modes I was dealing with. It did not force much effort, just prompted to get more knowledge.
Yes, I will keep in mind of treatment limitations. Just want to get a better understanding for improving my strategy without wasting effort and budget.

Andre, thank you for the links .
Old 29th December 2010
  #16
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avare's Avatar
 

Quote:
Originally Posted by tonio View Post
Andre, thank you for the links from the beasty Q4Avare thread.
You are welcome. Sorry, the links are not from that thread. But they could have been considering the content.

Andre
Old 29th December 2010
  #17
Gear Guru
Links

Thanks for that Andre, yes I am watching you.....
Those papers are fairly heavy going and from a (not too) brief scan seem to require what I call a conversational fluency in engineering maths.
If I may be so crude, can we draw any practical guide from these papers? Would it be fair to conclude, lots of slack allowed, that absorption at regions of high particle velocity has approximately one third the effect of at pressure zones? Plse, further detail if needed, e.g. is this trend true at boundaries or away from them or both?
Furthermore, if it is broadly speaking, as simple as that, doesn't that go a long to toward explaining why absorbers DO work at boundaries, despite the low particle velocity? Probably should be in Q4Avare, but that thread is too long now.



DD
Old 30th December 2010
  #18
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DrFrankencopter's Avatar
What is the root cause of the null?

If you're just talking about a 'hole' in the frequency response this could be from a number of different reasons. For example:
1) A problem with you transducer (speaker/mic)
2) You are located on or near a node point of a standing wave
3) Your room has no modal support near that frequency.

To better explain (3), imagine a room that has modes at 20, 25, 30, and 50, 55 Hz. There's a mode 'hole' around 40 Hz and no amount of trapping @ 40Hz is going to help fix it....the room is just not actively supporting that frequency.

Bass trapping can help if (2) is the cause (though moving the listening position might work even better). Switching speakers will help if (1) is the cause. Damping adjacent peaks might help mask a problem if (3) is the cause. Changing the room geometry will help with (2) and (3).

Cheers

Kris
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