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 Post subject: Re: Acoustic hangers
PostPosted: Mon Jan 12, 2015 12:37 pm 
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Anton - hangers take up a lot of space - they typically are either in the ceiling above a false ceiling or in a rear wall behind a cloth wall.

I'm now using a new design - take a look at the rear wall in this corner control room:

Attachment:
rear_slot.JPG


It's a vertical slot resonator where the depth is great, the slots are deep 6" - 8" (150 - 200mm) and the gap between slats is 1/4" - 1/2" (5mm and 10mm)
It is tuned to 30 - 100hz range.

In this control room it solved the typical bass buildup problem at the couch.

http://www.johnlsayers.com/Pages/Rose_Lane.html

I'm now using them in the rear corners with hangers above.

Attachment:
Rear_Slots.jpg


They are very heavy so I doubt you'd wheel them around. :)


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 Post subject: Re: Acoustic hangers
PostPosted: Mon Feb 02, 2015 5:17 pm 
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Quote:
As far as i understand the gap in the back wall is fitted with resonators (these are helmholz, right?)
As John said in the post, they are slot resonators, tuned to the range 30 to 100 Hz.


Quote:
But generally though, i meant something diferent when asked you about the hangers
I think John's point was that, whereas he used to use hangers almost exclusively in rooms he designed, he has now come up with something that is even better (even though hangers are really good already), and that he now uses a combination of this vertical slot wall design as well as hangers, as he shows in the second image.


Quote:
I had homosote glued with 705 or 703 in my mind, not panel resonators..
Those are hangers, yes. Just like the ones John shows in the top section of his second image. Hangers are not panel resonators (although they might perhaps act like them, under the right circumstances, that isn't how they work principally).

Quote:
I was thinking to put a triangle frame with a cloth finish around it and instead of making it a superchunk filled with 703 do a hanger style rolling trap in the corner,
You could do that, yes. and it would like the top section of John-s second image, without the bottom section, and on wheels. It would still be fairly heavy, though. A superchunk on wheels would likely be lighter in weight.

Quote:
And studying the forum i got confused weather it was a good idea or not..
Hangers in room corners work, and they are a good idea. Superchunks also work. I'm not aware of any studies on which one is more effective, though. But that sure would be an interesting subject for research!


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 Post subject: Re: Acoustic hangers
PostPosted: Wed Apr 15, 2015 12:48 am 
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hello i find some information on the bbc work who may be can explane a part of the way who work acoustique anger
https://ia600709.us.archive.org/14/item ... 987_15.pdf
page 19
it may be a part of the combination

all the best
sam


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 Post subject: Re: Acoustic hangers
PostPosted: Wed Apr 15, 2015 1:38 am 
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That's very interesting, Sam! Thanks for posting that.

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 Post subject: Re: Acoustic hangers
PostPosted: Wed Apr 15, 2015 4:54 am 
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I am the audio Director for a new performing arts center located in an old church. The stage is approximately 35 feet long, 16 feet deep and about 3 feet high. It is well constructed with quite rigid framing but only has one layer of 3/4 inch plywood with a thin veneer on top of that. It is open underneath with access doors. The room sounds pretty good having added some curtains and pew cushions to tame a 2 second reverb time with a heavy mid range focus. The only issues I'm having now are in the 250HZ range. I suspect the stage is not helping and am wondering if installing hangers underneath will be helpful? What do you think?

Thanks

Gary


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 Post subject: Re: Acoustic hangers
PostPosted: Wed Apr 29, 2015 11:28 am 
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garysjo wrote:
I am the audio Director for a new performing arts center located in an old church. The stage is approximately 35 feet long, 16 feet deep and about 3 feet high. It is well constructed with quite rigid framing but only has one layer of 3/4 inch plywood with a thin veneer on top of that. It is open underneath with access doors. The room sounds pretty good having added some curtains and pew cushions to tame a 2 second reverb time with a heavy mid range focus. The only issues I'm having now are in the 250HZ range. I suspect the stage is not helping and am wondering if installing hangers underneath will be helpful? What do you think?

Thanks

Gary


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 Post subject: Re: Acoustic hangers
PostPosted: Wed May 13, 2015 2:43 pm 
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Hi "garysjo". Please read the forum rules for posting (click here). You seem to be missing a couple of things! :)

That said, it sounds like you have the typical mid-range reverberations issues that can be expected from a medium sized room like that. It might be the stage, but is more likely to be a general RT issue in the low mids. Fortunately, that can probably be fixed with suitably designed and placed absorption panels.

I'd suggest starting your own thread and providing more details about the room, including a basic analysis with REW, a diagram with dimensions, and some photos.

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 Post subject: Re: Acoustic hangers
PostPosted: Fri Oct 09, 2015 1:12 am 
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Make sense this placement?
Thanks


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 Post subject: Re: Acoustic hangers
PostPosted: Tue Jul 26, 2016 6:13 am 
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It's always good to update a thread based on empirical results, with actual theory and laboratory testing!

It turns out that in 2009 a group of acousticians actually did analyze how hangers work, and confirmed exactly what John (and I) have always said: they act mostly like waveguides, as well as like impedance tubes, but there is also some resonant stuff going on between the panels. The panels themselves do not resonate much, so that is not the method by which sound is absorbed.

The paper is called "Sound field characterisation and absorption measurement of wideband absorbers", and you can download it here, if you want to give them some information about you:

http://www.academia.edu/1223399/Sound_F ... _Absorbers

Very interesting. It even includes a predictive model that you could use to calculate the peak absorption frequencies, and probably to to even tune them, to a certain extent!

Fascinating stuff!

John has been right all these years, and his critics have been wrong... (as usual... :) ) Even his method for laying them out is confirmed by the theoretical and practical work...

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 Post subject: Re: Acoustic hangers
PostPosted: Thu Feb 16, 2017 12:59 pm 
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John Sayers wrote:
Anton - hangers take up a lot of space - they typically are either in the ceiling above a false ceiling or in a rear wall behind a cloth wall.

I'm now using a new design - take a look at the rear wall in this corner control room:

Attachment:
rear_slot.JPG


It's a vertical slot resonator where the depth is great, the slots are deep 6" - 8" (150 - 200mm) and the gap between slats is 1/4" - 1/2" (5mm and 10mm)
It is tuned to 30 - 100hz range.

In this control room it solved the typical bass buildup problem at the couch.

http://www.johnlsayers.com/Pages/Rose_Lane.html

I'm now using them in the rear corners with hangers above.

Attachment:
Rear_Slots.jpg


They are very heavy so I doubt you'd wheel them around. :)


Hey John,

Beautiful design! Is this something you are sharing or keeping secret?

What is the difference between "Hangers" and "Waveguides".

I'm trying to combat an SBIR issue in my room, it seems to be coming from the rear port on my DynAudio BM6A's. After setting my mix position to the 0.375 times the length of the room area, I began taking REW readings beginning with a single speaker at farthest position. The further I get the speaker off the wall the stronger of a 50hz Null I would get.

So now I am trying to develop my next plan.

• Go crazy on the front wall with acoustics? (Hangers, Waveguides, super thick Fluffy stuff?)

• Invest in Front Ported Speakers?

Anyway, if anyone has ANY advice please shoot it my way. Talking at wall isn't helping.

Thanks,

Keith Moore


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 Post subject: Re: Acoustic hangers
PostPosted: Thu Feb 16, 2017 1:56 pm 
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Hi Keith. Please read the forum rules for posting (click here). You seem to be missing a couple of things! :)

Quote:
Beautiful design! Is this something you are sharing or keeping secret?


John already did share! He gave you the exact dimensions that he used for that, and you even quoted them...

It's unlikely that you'll get more than that, considering that this was a paid design project for a high-end commercial studio.

Quote:
What is the difference between "Hangers" and "Waveguides".
All hangers act as waveguides, but not all waveguides are implemented as hangers. If you are looking for the theory of how they work, try googling "theory of acoustic waveguides". There's about 430,000 hits on that subject. The first few seem to be pretty good, at initial glance.

Quote:
I'm trying to combat an SBIR issue in my room, ... I began taking REW readings beginning with a single speaker at farthest position. The further I get the speaker off the wall the stronger of a 50hz Null I would get.
That's not SBIR. If it were SBIR, the frequency would change as yo moved the speaker further from the wall, and it would not be at 50 Hz. That is very likely a modal issue, and you happen to be moving the speaker closer and closer to a peak location in the room, so it is triggering it more and more strongly. What are the dimensions of your room? What treatment do you have in there? Photos?

Quote:
it seems to be coming from the rear port on my DynAudio BM6A's.
How did you determine that? Did you plug the port? If so, what did you use? Or is this just a guess that it might be the port?

Quote:
• Go crazy on the front wall with acoustics? (Hangers, Waveguides, super thick Fluffy stuff?)
For 50 Hz modal issues, that won't work. For SBIR at 50 Hz it won't work either.

Quote:
• Invest in Front Ported Speakers?
That won't change anything. The problem is not your speakers; it is your room. Either the layout geometry), or the dimensions, or the treatment. Or all three.

Quote:
Anyway, if anyone has ANY advice please shoot it my way.
First things first: set up the room correctly, test it correctly with REW, and determine what the problem actually is. Then treat it accordingly.


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 Post subject: Re: Acoustic hangers
PostPosted: Fri Feb 17, 2017 5:44 am 
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Soundman2020 wrote:
Hi Keith. Please read the forum rules for posting (click here). You seem to be missing a couple of things! :)

Quote:
Beautiful design! Is this something you are sharing or keeping secret?


John already did share! He gave you the exact dimensions that he used for that, and you even quoted them...

It's unlikely that you'll get more than that, considering that this was a paid design project for a high-end commercial studio.

Quote:
What is the difference between "Hangers" and "Waveguides".
All hangers act as waveguides, but not all waveguides are implemented as hangers. If you are looking for the theory of how they work, try googling "theory of acoustic waveguides". There's about 430,000 hits on that subject. The first few seem to be pretty good, at initial glance.

Quote:
I'm trying to combat an SBIR issue in my room, ... I began taking REW readings beginning with a single speaker at farthest position. The further I get the speaker off the wall the stronger of a 50hz Null I would get.
That's not SBIR. If it were SBIR, the frequency would change as yo moved the speaker further from the wall, and it would not be at 50 Hz. That is very likely a modal issue, and you happen to be moving the speaker closer and closer to a peak location in the room, so it is triggering it more and more strongly. What are the dimensions of your room? What treatment do you have in there? Photos?

Quote:
it seems to be coming from the rear port on my DynAudio BM6A's.
How did you determine that? Did you plug the port? If so, what did you use? Or is this just a guess that it might be the port?

Quote:
• Go crazy on the front wall with acoustics? (Hangers, Waveguides, super thick Fluffy stuff?)
For 50 Hz modal issues, that won't work. For SBIR at 50 Hz it won't work either.

Quote:
• Invest in Front Ported Speakers?
That won't change anything. The problem is not your speakers; it is your room. Either the layout geometry), or the dimensions, or the treatment. Or all three.

Quote:
Anyway, if anyone has ANY advice please shoot it my way.
First things first: set up the room correctly, test it correctly with REW, and determine what the problem actually is. Then treat it accordingly.


- Stuart -


Hello Stuart,

Thanks for your quick reply and I apologize if I went rogue on the rules. I looked them over more thoroughly and will do my best in this post to stay on track.

I've been researching and accepting guidance from a few regulars on the GS's forum. SBIR is a direction I was guided in from a few fellow GS'ers as I originally suspected my issue was modal but then questioned it upon their recommendations.

I am attaching a few pictures (adjusted in compliance to the rules). These are taken from far rear wall, far front wall and mid point. I also provided a few pictures of the rear corner SuperChunk bass traps (which I'll go into more detail).

Control Room Dimensions:

Length - 28' 7"

Width - 11' 9"

Height Left - 6' 4"

Height Right - 8' 1 1/2"

Side Door (to live room) - 10' 9" (from front of room on right side) 3' 1" width x 7' height

Rear Door (to outside) - 4' 3" (from Left wall) 3' 1 1/2" width x 6' 10" height

The current treatment in the room:

Front corners 34" Wide SuperChunks using Knauf R30

Rear corners 40" Wide Face (please see pics) SuperChunks using Knauf R30

Front wall 4' x 6' x 2" Knauf Insulation Board PCF 3.0 (2" air gap)

Side walls (Mix position) 4' x 8' x 2" Knauf Insulation Board PCF 3.0 (2" air gap)

Side walls (Mid Room) 6' x 2' x 4" Knauf Insulation Board PCF 3.0 (4" air gap)

Side walls (Rear Room) 4' x 8' x 2" OC703 (2" air gap)

Rear Door 4' x 2' x 4" OC703 (4" air gap)

Cloud (Mix Position) 4' x 6' x 4" Knauf Insulation Board PCF 3.0

Ceiling 5.5" Ultratouch Cotton Insulation

Hope all that translates well.

I later discovered that Knauf does not provide G.F.R. details on their products. I mistakenly assumed any fluffy insulation would provide desired results. This has left me wondering if I should simply rebuild my corner traps.

So far I have set up my mix position at around 9' from the front wall, the golden cuboid setup listed on the Cardas site as well as the 0.375 times the length of the room. All of these have displayed Null's in the lower frequencies. 63hz was the culprit in the golden cuboid position if I recall correctly. Moving the speakers and mix position rather close to the front wall brought the low end loss back.

Hope this reply helps and I look forward to any replies/suggestions. I'm more than happy to take REW measurements and post them.

Also, feel free to move this post if it is not appropriate in the "Acoustic Hangers" thread.

Thanks again,

Keith Moore


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 Post subject: Re: Acoustic hangers
PostPosted: Fri Feb 17, 2017 9:03 am 
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Quote:
I apologize if I went rogue on the rules. I looked them over more thoroughly and will do my best in this post to stay on track.
:thu: You fixed it! Location in profile is The Big One! :)

Quote:
I've been researching and accepting guidance from a few regulars on the GS's forum. SBIR is a direction I was guided in from a few fellow GS'ers as I originally suspected my issue was modal but then questioned it upon their recommendations
It's fairly easy to tell the difference in most cases. Modes are standing waves related to room dimensions, and therefore occur at fixed frequencies and fixed locations in the room. The frequency of each mode is fixed, rigidly, because it is directly related to that specific wavelength fitting perfectly into a path between 2 walls (or 4 walls, or all six walls). If a mode is triggered, the frequency will be very stable (unless your walls are wobbly!), but the intensity will be different at different locations in the room, as you move to different parts of the "standing" wave. That's why it is called a "standing wave": it appears to be stationary in the room, not moving (it does, in fact, move, but it appears to be stationary becuase the pressure peaks and nulls always occur at the same spot in the room).

So the sure sign of a mode is that the frequency does not change at different points in the room, but the intensity does, and it also "rings": it carries on going for a short time after then cause has disappeared. That "short time" can be a few milliseconds, or it can also be several seconds in extreme cases, in large rooms.

The other issue, which is very different, is SBIR. As the name implies, it is all about the relationship between the speaker and the room boundary. It is purely a phase cancellation / summing issue. It is caused when the wave laving a speaker hits a wall and bounces back the same way it came. So now you have two identical waves (the original, and the "bounce"). The only difference is that the "bounce" is delayed, since it went out and came back, which requires time. That time delay is exactly the same as a change in the phase between the original source wave, and the "copy". There will be some points where the wave is in phase with its copy, so it will be louder, and some points where it is out of phase, so it will be quieter. In extreme cases, the "quite spots" can be pretty much total nulls.

SBIR also occurs at very specific frequencies, but with a difference: That frequency is related to the distance that the "bounce" wave travels. In other words, it is related to the distance between the speaker and the wall that the wave is bouncing off. If the distance is small, the frequency will be relatively high, because the time delay is short. If the distance is large, then the frequency will be lower, because the time delay between source and copy is longer.

So that's the key; you moved your speaker away from the wall, but the frequency of the problem you are experiencing, did not change. It stayed at 50 Hz. If it was SBIR, the frequency would have gone lower as you moved the speaker away from the wall. Since the frequency did not change, the problem you are seeing is not SBIR. Or at least, it is not SBIR from the front or back wall. It might still be related to the side walls, floor, or ceiling, since those distances did not change. However, the total distance traveled by the wave even to the side walls, did still vary a bit, as you moved the speaker, so you should have seen some variation.

There's a couple of other interesting issues that can help identify SBIR. Firstly, it does not "ring". A mode rings, becuase it is a resonant phenomena: the mode "stores" energy, then releases it again slowly. SBIR is not resonant: there is no stored energy, just phase addition/cancellation, so as soon as the signal changes, it stops, instantly. And secondly, because it is a phase issue, it shows up as comb filtering in the frequency response. If you have SBIR at 50 Hz, then it will also be there at 100Hz, 150Hz, 200 Hz, 250 Hz, 300 Hz, etc. all the way up the entire spectrum. So you will see that as a "comb" shaped pattern of intensity peaks and troughs in the frequency response plots, if you look carefully.

I'm surprised the guys at GS didn't point all of this out for your: There's some good guys over there.


Quote:
I am attaching a few pictures (adjusted in compliance to the rules).
:thu: Great! That certainly helps to understand your room better, and immediately there's several issues that are apparent, but I'll get to those later.


First: . . .

Quote:
Length - 28' 7"
Width - 11' 9"
Height Left - 6' 4"
Height Right - 8' 1 1/2"
Ouch! That's a long narrow room, with a low ceiling. That's a really tough acoustic environment to deal with. Not only that, but the ceiling slopes in the wrong way! It slopes left to right, but should slope front to back. On the other hand, if you set up your room rotated 90°, that would be even worse, as the speakers would be firing along the short axis, not the long axis, and your head would be too close to the rear wall....

In addition, it is just too long for the width and height. Most of the good ratios have the length less than 2 times the width or height, but in your case it is about FOUR times the lowest height, three times the other height, and still more than twice the width. Not a happy situation at all.


Hmmmm....


But anyway, I plugged those numbers into a room mode calculator, and what is the very first thing I notice? At 48.1 Hz, is your primary width mode! Yup. Your 0,1,0 axial mode is pegged at 48.1 Hz. I'm betting that is your problem. And at 52.0 Hz, you have your 1,1,0 tangential mode, also a primary mode, related to both width and length. That would be my second bet. They are both right there, very close to 50 Hz, where you say your problem is happening.

I would need to see the actual REW data file to be certain, but that's where my money is right now.

Quote:
The current treatment in the room:
. . . is overdone! There's too much raw absorption in there: I have not yet seen the data, but I'm betting that room is dead, muddy, lifeless, unpleasant. I'm betting the decay times are around 100 ms, or less. I'm betting it is difficult to mix in there, and fatiguing....

Most of your treatment is actually correct, but there's too much of it that is killing the room. You need to do things to add some life back again.

Quote:
I later discovered that Knauf does not provide G.F.R. details on their products
That's OK. There's a reasonably reliable relationship between the density of each type of insulation, and the GFR. If you know the density, you can roughly figure out the GFR.

Quote:
I mistakenly assumed any fluffy insulation would provide desired results.
A common mistake!

Quote:
This has left me wondering if I should simply rebuild my corner traps.
Perhaps, perhaps not. What is the density of the insualtion you used for your superchunks? What type is it? (fiberglass, mineral wool, something else). Is it fluffy, semi-rigid, rigid?

Quote:
the golden cuboid setup listed on the Cardas site
:ahh: Well, there's your problem! There is no such thing as a "golden cuboid", outside of the realm of one person who invented it, and a bunch of his followers. If you don't believe me, Google it, and try to find some actual mathematical research paper published in a respectable journal, that presents the theory behind this concept. Try to find something that does not trace back to that one single original source... (Good luck! :) )

In reality, there are many good ratios for a room, and several possible speaker/mix position layouts that work well. There is no such thing as a "perfect" room ratio, or a "perfect" setup in a small room. There just isn't, because the laws of physics prevent it! There cannot be. THe room has to be large (very large) before you can get close to that ideal, but for pretty much all normal studios (both home and pro), there simply is no possibility of having a "perfect" situation, where there is true statistical reverberant behavior across the entire audible spectrum. In practically any studio, there will always be an uneven spread of modes in low frequencies, and therefore uneven frequency response across the low end of the spectrum, regardless of the dimensions, ratios, speakers, locations of the speakers, location of the mix position, or anything else. It simply is not possible.

That said, a lot of real scientists and acousticians have done a lot of real research on the math and science behind this subject, and come up with a set of rooms ratios and layouts that are pretty good. Not perfect, but plenty good. People with names like Louden, Sepmeyer, Bolt, and others have published papers and equations that they derived, with experiment and math to back them up. Those are the room ratios you should be looking at, not some mythical "cuboid" that nobody every heard of.

Unfortunately, the dimensions of your room put you way, way outside the scope of all of the "best" ratios, and all of the "good" ratios. There might be a couple of "mediocre to poor" ones in that region, but I doubt it. I'd have to check, but I don't think it is worth it. Even if there is one, it won't be "good".

Quote:
All of these have displayed Null's in the lower frequencies.
Yup. Because it is a small room that is very long and thin, with a very low ceiling! No matter where you go in that room, there will always be modal issues.

Quote:
63hz was the culprit in the golden cuboid position
... Yup. That would be your 2,1,0 tangential mode, at 62.3 Hz. Also related to width and length...

Quote:
Moving the speakers and mix position rather close to the front wall brought the low end loss back.
I could give you my suggestion for that room, but I'm not sure that it is worth your while even trying to do it. It won't be a huge difference.

The big issue here is that you are fighting the room itself, not the treatment, layout, or speaker ports.

What I woulds suggest is two things, and they both involve a lot of work.

1) Make the room shorter. Build a wall across the back at a point that would give you a good ratio, or at least a much better ratio than what you have now.

2) Make the ceiling symmetrical, such that it is the same on the left and right. Yes, that would imply making it lower on the right to match the left, reducing room volume, etc, but the difference at present is just too great. Symmetry is critical for a control room: your left ear must hear the same acoustic "signature" as your right ear hears from the room, and the way you have it right now, there's a huge difference. Even though you would lose height, you could minimize the loss by having a gabled ceiling, with each side sloping down the same form a central peak. This is not the issue that you are dealing with right now, but it will be. After you solve the low-end mulchy mess from the room length, that would be your next problem. You might as well deal with both issues at once.

Yep. Probably not what you were hoping for! Nobody likes it when they hear "Your room is terrible. There's no hope. Rip it apart and build it again." That's NOT something that any studio owner wants! But in your case it is the only realistic solution I see.

I'm not sure if you are prepared / willing / able to do that, but its the realistic solution. If you can't do that, then is there another room in your house where it might be possible to set up your studio? Even if it is small, it would probably still be better than this.

Sorry to be the bearer of bad tidings,....

Quote:
I'm more than happy to take REW measurements and post them.
Let's see the one where you had the mix position at 37.5% of the room length. Upload that one to a file sharing service, and post the link here. (MDAT files are too big to upload onto the forum.)

I'll take a look at that file for you, but I can pretty much predict what it will show. I could tell you how to improve some of it, but there's no treatment or tuning that can fix a low ceiling and a drastically long thin room. In medical terms: I can show you how to put a band-aid on your scraped knee, and put your sprained arm in a cast, and take a pain killer for the headache, but there's nothing I can do for the real problem: That gaping hole in your chest where you just got shot with a bazooka! (Sorry to be a bit dramatic....)


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 Post subject: Re: Acoustic hangers
PostPosted: Thu Feb 23, 2017 9:58 am 
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Soundman2020 wrote:
Quote:
I apologize if I went rogue on the rules. I looked them over more thoroughly and will do my best in this post to stay on track.
:thu: You fixed it! Location in profile is The Big One! :)

Quote:
I've been researching and accepting guidance from a few regulars on the GS's forum. SBIR is a direction I was guided in from a few fellow GS'ers as I originally suspected my issue was modal but then questioned it upon their recommendations
It's fairly easy to tell the difference in most cases. Modes are standing waves related to room dimensions, and therefore occur at fixed frequencies and fixed locations in the room. The frequency of each mode is fixed, rigidly, because it is directly related to that specific wavelength fitting perfectly into a path between 2 walls (or 4 walls, or all six walls). If a mode is triggered, the frequency will be very stable (unless your walls are wobbly!), but the intensity will be different at different locations in the room, as you move to different parts of the "standing" wave. That's why it is called a "standing wave": it appears to be stationary in the room, not moving (it does, in fact, move, but it appears to be stationary becuase the pressure peaks and nulls always occur at the same spot in the room).

So the sure sign of a mode is that the frequency does not change at different points in the room, but the intensity does, and it also "rings": it carries on going for a short time after then cause has disappeared. That "short time" can be a few milliseconds, or it can also be several seconds in extreme cases, in large rooms.

The other issue, which is very different, is SBIR. As the name implies, it is all about the relationship between the speaker and the room boundary. It is purely a phase cancellation / summing issue. It is caused when the wave laving a speaker hits a wall and bounces back the same way it came. So now you have two identical waves (the original, and the "bounce"). The only difference is that the "bounce" is delayed, since it went out and came back, which requires time. That time delay is exactly the same as a change in the phase between the original source wave, and the "copy". There will be some points where the wave is in phase with its copy, so it will be louder, and some points where it is out of phase, so it will be quieter. In extreme cases, the "quite spots" can be pretty much total nulls.

SBIR also occurs at very specific frequencies, but with a difference: That frequency is related to the distance that the "bounce" wave travels. In other words, it is related to the distance between the speaker and the wall that the wave is bouncing off. If the distance is small, the frequency will be relatively high, because the time delay is short. If the distance is large, then the frequency will be lower, because the time delay between source and copy is longer.

So that's the key; you moved your speaker away from the wall, but the frequency of the problem you are experiencing, did not change. It stayed at 50 Hz. If it was SBIR, the frequency would have gone lower as you moved the speaker away from the wall. Since the frequency did not change, the problem you are seeing is not SBIR. Or at least, it is not SBIR from the front or back wall. It might still be related to the side walls, floor, or ceiling, since those distances did not change. However, the total distance traveled by the wave even to the side walls, did still vary a bit, as you moved the speaker, so you should have seen some variation.

There's a couple of other interesting issues that can help identify SBIR. Firstly, it does not "ring". A mode rings, becuase it is a resonant phenomena: the mode "stores" energy, then releases it again slowly. SBIR is not resonant: there is no stored energy, just phase addition/cancellation, so as soon as the signal changes, it stops, instantly. And secondly, because it is a phase issue, it shows up as comb filtering in the frequency response. If you have SBIR at 50 Hz, then it will also be there at 100Hz, 150Hz, 200 Hz, 250 Hz, 300 Hz, etc. all the way up the entire spectrum. So you will see that as a "comb" shaped pattern of intensity peaks and troughs in the frequency response plots, if you look carefully.

I'm surprised the guys at GS didn't point all of this out for your: There's some good guys over there.


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I am attaching a few pictures (adjusted in compliance to the rules).
:thu: Great! That certainly helps to understand your room better, and immediately there's several issues that are apparent, but I'll get to those later.


First: . . .

Quote:
Length - 28' 7"
Width - 11' 9"
Height Left - 6' 4"
Height Right - 8' 1 1/2"
Ouch! That's a long narrow room, with a low ceiling. That's a really tough acoustic environment to deal with. Not only that, but the ceiling slopes in the wrong way! It slopes left to right, but should slope front to back. On the other hand, if you set up your room rotated 90°, that would be even worse, as the speakers would be firing along the short axis, not the long axis, and your head would be too close to the rear wall....

In addition, it is just too long for the width and height. Most of the good ratios have the length less than 2 times the width or height, but in your case it is about FOUR times the lowest height, three times the other height, and still more than twice the width. Not a happy situation at all.


Hmmmm....


But anyway, I plugged those numbers into a room mode calculator, and what is the very first thing I notice? At 48.1 Hz, is your primary width mode! Yup. Your 0,1,0 axial mode is pegged at 48.1 Hz. I'm betting that is your problem. And at 52.0 Hz, you have your 1,1,0 tangential mode, also a primary mode, related to both width and length. That would be my second bet. They are both right there, very close to 50 Hz, where you say your problem is happening.

I would need to see the actual REW data file to be certain, but that's where my money is right now.

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The current treatment in the room:
. . . is overdone! There's too much raw absorption in there: I have not yet seen the data, but I'm betting that room is dead, muddy, lifeless, unpleasant. I'm betting the decay times are around 100 ms, or less. I'm betting it is difficult to mix in there, and fatiguing....

Most of your treatment is actually correct, but there's too much of it that is killing the room. You need to do things to add some life back again.

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I later discovered that Knauf does not provide G.F.R. details on their products
That's OK. There's a reasonably reliable relationship between the density of each type of insulation, and the GFR. If you know the density, you can roughly figure out the GFR.

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I mistakenly assumed any fluffy insulation would provide desired results.
A common mistake!

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This has left me wondering if I should simply rebuild my corner traps.
Perhaps, perhaps not. What is the density of the insualtion you used for your superchunks? What type is it? (fiberglass, mineral wool, something else). Is it fluffy, semi-rigid, rigid?

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the golden cuboid setup listed on the Cardas site
:ahh: Well, there's your problem! There is no such thing as a "golden cuboid", outside of the realm of one person who invented it, and a bunch of his followers. If you don't believe me, Google it, and try to find some actual mathematical research paper published in a respectable journal, that presents the theory behind this concept. Try to find something that does not trace back to that one single original source... (Good luck! :) )

In reality, there are many good ratios for a room, and several possible speaker/mix position layouts that work well. There is no such thing as a "perfect" room ratio, or a "perfect" setup in a small room. There just isn't, because the laws of physics prevent it! There cannot be. THe room has to be large (very large) before you can get close to that ideal, but for pretty much all normal studios (both home and pro), there simply is no possibility of having a "perfect" situation, where there is true statistical reverberant behavior across the entire audible spectrum. In practically any studio, there will always be an uneven spread of modes in low frequencies, and therefore uneven frequency response across the low end of the spectrum, regardless of the dimensions, ratios, speakers, locations of the speakers, location of the mix position, or anything else. It simply is not possible.

That said, a lot of real scientists and acousticians have done a lot of real research on the math and science behind this subject, and come up with a set of rooms ratios and layouts that are pretty good. Not perfect, but plenty good. People with names like Louden, Sepmeyer, Bolt, and others have published papers and equations that they derived, with experiment and math to back them up. Those are the room ratios you should be looking at, not some mythical "cuboid" that nobody every heard of.

Unfortunately, the dimensions of your room put you way, way outside the scope of all of the "best" ratios, and all of the "good" ratios. There might be a couple of "mediocre to poor" ones in that region, but I doubt it. I'd have to check, but I don't think it is worth it. Even if there is one, it won't be "good".

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All of these have displayed Null's in the lower frequencies.
Yup. Because it is a small room that is very long and thin, with a very low ceiling! No matter where you go in that room, there will always be modal issues.

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63hz was the culprit in the golden cuboid position
... Yup. That would be your 2,1,0 tangential mode, at 62.3 Hz. Also related to width and length...

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Moving the speakers and mix position rather close to the front wall brought the low end loss back.
I could give you my suggestion for that room, but I'm not sure that it is worth your while even trying to do it. It won't be a huge difference.

The big issue here is that you are fighting the room itself, not the treatment, layout, or speaker ports.

What I woulds suggest is two things, and they both involve a lot of work.

1) Make the room shorter. Build a wall across the back at a point that would give you a good ratio, or at least a much better ratio than what you have now.

2) Make the ceiling symmetrical, such that it is the same on the left and right. Yes, that would imply making it lower on the right to match the left, reducing room volume, etc, but the difference at present is just too great. Symmetry is critical for a control room: your left ear must hear the same acoustic "signature" as your right ear hears from the room, and the way you have it right now, there's a huge difference. Even though you would lose height, you could minimize the loss by having a gabled ceiling, with each side sloping down the same form a central peak. This is not the issue that you are dealing with right now, but it will be. After you solve the low-end mulchy mess from the room length, that would be your next problem. You might as well deal with both issues at once.

Yep. Probably not what you were hoping for! Nobody likes it when they hear "Your room is terrible. There's no hope. Rip it apart and build it again." That's NOT something that any studio owner wants! But in your case it is the only realistic solution I see.

I'm not sure if you are prepared / willing / able to do that, but its the realistic solution. If you can't do that, then is there another room in your house where it might be possible to set up your studio? Even if it is small, it would probably still be better than this.

Sorry to be the bearer of bad tidings,....

Quote:
I'm more than happy to take REW measurements and post them.
Let's see the one where you had the mix position at 37.5% of the room length. Upload that one to a file sharing service, and post the link here. (MDAT files are too big to upload onto the forum.)

I'll take a look at that file for you, but I can pretty much predict what it will show. I could tell you how to improve some of it, but there's no treatment or tuning that can fix a low ceiling and a drastically long thin room. In medical terms: I can show you how to put a band-aid on your scraped knee, and put your sprained arm in a cast, and take a pain killer for the headache, but there's nothing I can do for the real problem: That gaping hole in your chest where you just got shot with a bazooka! (Sorry to be a bit dramatic....)


- Stuart -


Hey Stuart,

Sorry for my delayed reply. I wasn't crying in the dark after your last message, was out of town on a job.

Although a bummer to hear, what you said was what I suspected all along. I knew this room wasn't "ideal" but I thought I could make it work for a period of time. My previous studio came to an early extinction do to a fire a few years back. I planned on converting our barn into a studio over time while still working in the previous location. Unfortunately this incident sped up the process.

The Barn consists of a "carport" which is what you saw in pictures being used as a live room and a 31'L x 19' 2.5"W x 8' 7"H room currently being used as a live room. My original "Plan" was to make the bigger room the control room, the carport into a lounge and build a new extension for the live room.

Anyway, I'll leave it at THAT for the brief history for now.

The treatment I put in was MUCH less to begin with, once I took on my first project I had been in mental "construction mode" for months leading up to then, so at first I thought maybe I just needed to adjust to the new room. It wasn't until finishing that project when I realized something definitely wasn't right. Then after testing I started implementing more and more acoustics hoping to combat my problem. Yes, I'm aware that I went over board. I think it's ofter easy to lose sight of things in frustrating times.

The insulation used for the SuperChunks was Knauf R-30 10” thick 0.44 PCF

To be honest, I feel rather lost trying to read the room mode calculator results. Is there any resource you could recommend that might break it down easier? It seems that any room dimensions you put in are going to display the modal frequencies, so how do you know which one is better than an another?

At this point, I need a plan. I spent the weekend trying to drum up new visions. Battling this room isn't something I'm feeling very passionate about. Although I've had someone rather experienced in the field offer to help me get this room setup properly. But his fee plus the build cost would be rather significant. So if I was to go that route I'd almost rather apply the time/energy/expense into a more suitable room.

One idea was to convert the live room which is 31'L x 19' 2.5"W x 8' 7"H into a control room. Maybe see if it could work as single room for both recording and mixing. Possibly use the "terrible" room as a recording booth.

Any thoughts? also, let me know if you want anymore details.

Here is a link to the test you requested measures at 10.7' from the front wall (37.5%) as well as a series of tests which I believe your measured from the same position while moving the speaker closer in 12" increments. Maybe with these you can further comment if this is an SBIR vs Modal issue.

https://www.dropbox.com/sh/42qsksr0v8f8 ... jalaa?dl=0

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 Post subject: Re: Acoustic hangers
PostPosted: Thu Feb 23, 2017 3:40 pm 
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Quote:
To be honest, I feel rather lost trying to read the room mode calculator results. Is there any resource you could recommend that might break it down easier? It seems that any room dimensions you put in are going to display the modal frequencies, so how do you know which one is better than an another?
Here's how it works: Each "mode" is just a frequency where the wavelength fits in perfectly between some dimension of the room. So each time the wave completes a circuit around the room, it gets back to its starting point, going in the same direction, and in phase with the last circuit. In other words, each time around it adds more energy to itself, building up and up and up..... And when the sound that caused it ends, the mode does not end: since it has stored so much energy in that synchronized "race around the room", it carries on resonating for several more cycles while it dies away, slowly.

So, for every note on the scale where the room happens to have a "mode", the room will resonate, ring, and sing along with your music... which is probably not what you want. And for every note that does NOT happen to coincide with a mode, no such ringing happens: the note just sounds normal.

So each mode is associated with one path that a wave can take. There are only three different types of path: for "Axial" modes, the path runs straight across the room and back again, between a pair of walls, or between the floor and the ceiling. If the wavelength matches the distance between two surfaces, then you have a mode, and resonance. For example, if your front and back wall are 12 feet apart, then you will have a mode at 47.1 Hz. Why? Because the wavelength of a 47.1Hz wave is 24 feet, and the round trip between those two walls is 24 feet, so the wave fits in perfectly.

The second type is "tangential" modes, where the path involves four surfaces (instead of just two). So you could have a tangential mode that bounces of four walls, or off two walls, the floor and the ceiling.

And finally, there are "oblique" modes, where the path involves all six surfaces.

So some notes have modes, and ring, while others do not.

But what if there was a mode for every note? What if your room happened to have one mode that coincided with every single note on the scale? Well, in that case, there would be no problem! Every note would ring in the same way, and they would all sound the same! So that would be fine. The problem happens when there ISN'T a mode for every note, so only some of the ring, while the rest don't.

Even better would be the case where there are several modes for each note. But where there are several notes together and no modes around there at all, that's a problem.

As you go up the scale, there really are many modes for each note. At the top end, there can be thousands of modes for a note in the high end, many hundreds for every note in the upper mid range, dozens for every note in the lower mid range... but very few in the lows. The further you go down the scale, the fewer modes there are.

For a big room, this is not a problem, as there are many modes for every note, but in a small room, there just aren't enough modes. In fact, there's a number called the "Schroeder frequency", which is sort of the cut-off point for any give room. There's a method for calculating that, and it marks the transition point between "not enough modes", and "plenty of modes". Below there Schroeder frequency for any room, there are not enough modes to have smooth response. Above the Schroeder frequency, things are nice and rosy and happy. One way of looking at it is that you want to get your Schroeder frequency as low as possible, since the frequency response above that is smoother. This is a rather important frequency, since it defines the overall "shape" of your room's acoustic response.

A simpler way of looking at it is this: the object of playing around with dimensions and room mode calculators is simply to find a set of dimensions that causes the modes to be spread around evenly! So they are not all at the same frequency, not too close together, and not too far apart. By carefully manipulating the dimensions of a small room, you can adjust the modes to be spaced fairly evenly, or at least to avoid having two or three modes together on one note but no modes at all for the next several notes.

Fortunately, some clever scientists have already done this: They have figured out certain "ratios", or relationships between dimensions, that produce good modal spread. These guys include Bolt, Sepmeyer, Louden, Boner, etc. They already did the work for you. As long as your ratio is close to one of the good ones they found, then you should be OK.

The problem with your room is that it is long. Long narrow rooms don't have good modal response, because all of the modes are bunched up close to each other in just a few places on the spectrum, leaving large gaps between them. There are a very few ratios for long, narrow rooms, but none of them close to your dimensions.

OK, having said all that, modes are not life-and-death. You an treat the hell out of a room that has a bad ratio, and there are a few other tricks that you can do to help. Doing that can make the room usable. Maybe not fantastic, but at least decent.

Quote:
Although I've had someone rather experienced in the field offer to help me get this room setup properly. But his fee plus the build cost would be rather significant. So if I was to go that route I'd almost rather apply the time/energy/expense into a more suitable room.
I guess it all depends on how badly you need the room to work, and how good you need it to be! If it is critically important to what you do that the room have excellent acoustics response, then it's worth investing the money to get there. But if you can live with it not being perfect, and get around the big defects, then it's not worth the trouble.

You might want to try contacting a few other people, to see if somebody might be able to take you part way for a lower fee. If you want, PM me and I'll give you a list of people I trust that you could ask for a quote. I'd offer to help you myself, but I'm fully booked right now, and I can't take on any new projects until at least the end of March. But I can put you in touch with some other people, if you are interested. And number one on the list is John Sayers himself! Have you contacted John yet?

Quote:
Here is a link to the test you requested measures at 10.7' from the front wall (37.5%) as well as a series of tests which I believe your measured from the same position while moving the speaker closer in 12" increments. Maybe with these you can further comment if this is an SBIR vs Modal issue.
Cool! I'll take a look at that as soon as I have a chance, and let you know what I see. It might be a few days before I can get to that, though.

Downloading....


- Stuart -

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