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2D Quadradic Diffusor

Flint

"Do you know who I am?"
Superstar
#1
I've been contemplating building a lightweight 2D quadradic diffusor I can easily and consistently move in front of my TV in my listening room for critical listening, then remove when doing TV viewing. Based on the calculators I've demoed, I can make one which is about 10 inches deep with 1 inch wide channels and get a unit which is effective from about 750Hz to 6,000Hz. That would be excellent and a huge improvement over the flat reflective surface of a TV.

If I take my time and make an effort a precision, I should be able to make it fairly light weight which might allow me to hang it with pullies so I can raise it out of the way for TV viewing and lower it for music listening.

With a 2D diffusor it would be easy to have a cavity behind the reflective surface of each channel, thus makin it lighter. However, with a 3D diffusor I cannot think of a method to get a light solution.
 

TKoP

Well-Known Member
#2
Ok, i'll bite -- what's the difference between a 2d and 3d diffusor? My quick google searching yielded a lot of false leads, but nothing that really explained one or the other.
 

Flint

"Do you know who I am?"
Superstar
#3
Ok, i'll bite -- what's the difference between a 2d and 3d diffusor? My quick google searching yielded a lot of false leads, but nothing that really explained one or the other.
It is literally in the name. 2D diffusers diffuse reflections on one plane, usually a horizontal plane. A 3D diffuser does similar but in two planes.

2D diffusers tend to operate more effectively over a broader frequency range but 3D diffusers are less impacted by placement.
 

TKoP

Well-Known Member
#4
Sorry, that part i kind of got... it was more the "what does it look like" kind of thing. What I thought would have been a 3d diffusor (i.e., the random block wall) turned out to be a 2d diffusor, Again, my internet skillz may have misled me...
 

Flint

"Do you know who I am?"
Superstar
#5
Here's the most common style of 2D diffusor installed:




Here's the most common style of 3D diffusor installed:
 

Flint

"Do you know who I am?"
Superstar
#6
In a stereo listening room with perfect symmetry, 2D diffusers like the Quadradic panels from RPG are more ideal as they are more impactful over wider frequencies. But, in rooms where placement can change or the room is far from ideal in terms of symmetry for stereo listening, 3D panels like the Skyline style might be better suited though they are individually less effective for their size.
 

Flint

"Do you know who I am?"
Superstar
#9
Auralex, makes a lightweight plastic 3D diffusor called a T-Fusor. Some some guy named Flint sold them to me, just repainted them black the other day.

Flint, what do you think about these diffractal diffusors vs QRD's. As in less absorption vs ORD's and being more effective in the high frequencies?
http://arqen.com/wp-content/gallery/diy-diffuser-builds/diffuser-build-pablo-crespo-5-w800.jpg
The diffusor you linked to may be better for higher frequencies than the QRD because of the little quadradic pattern on each larger section, but they will not perform as well for middle frequencies because they are not separated by walls - there needs to be a slot cavity for each reflective area. The general shape of this diffuser when it comes to lower frequencies is that of a half round dispersing reflector like I built for my HT.

I've seen traditional cavity QRD style diffusers which also have the small quadradic pattern on each reflective portion of the cavity, which would be better.

But, that said, diffusion isn't that important above about 7kHz because even reflective flat walls disperse a little bit, as does everything in the room. Not to mention that higher frequencies are absorbs by the air itself, so high frequency energy tends to not bounce around for very long in a typical room with rugs, fabric chairs, people, knobs on equipment, and so on. The critical range is from about 7khz down to the first low frequency where there appears a standing wave null or mode. If there is still some high frequency problems, a few absorbers properly placed can address the issue pretty easily.
 

Flint

"Do you know who I am?"
Superstar
#10
Auralex, makes a lightweight plastic 3D diffusor called a T-Fusor. Some some guy named Flint sold them to me, just repainted them black the other day.

Flint, what do you think about these diffractal diffusors vs QRD's. As in less absorption vs ORD's and being more effective in the high frequencies?
http://arqen.com/wp-content/gallery/diy-diffuser-builds/diffuser-build-pablo-crespo-5-w800.jpg
The more I look at the diffusor in the photo you linked to, the less I think it was worth the effort which went into making it. It is too symmetrical, no effort was made to make it "quadradic" - it isn't quadradic at all, really - and it probably weighs a ton. Yet, it clearly would take quite a bit of work to build it. Sure, it is likely much better than doing nothing, but why not just put the same effort into a proper QRD?
 

TitaniumTroy

Well-Known Member
#12
Flint, just curious what should be the depth of a ORD diffusor in a room that is 5' behind the speaker and and about 14' from the listener? I know the original QRD's from RPG were 9" deep.
 

Flint

"Do you know who I am?"
Superstar
#13
Flint, just curious what should be the depth of a ORD diffusor in a room that is 5' behind the speaker and and about 14' from the listener? I know the original QRD's from RPG were 9" deep.
I don't think there's a simple answer. What are the overall dimensions of the room so that we can consider at what frequency the sound shifts from "ray" dispersion characteristics to "pressure" dispersion characteristics? The depth determines the lowest effective frequency and the width of each "trench" determines the highest effective frequency. It also matters what other acoustics control devices are in the room. If you are aggressively absorbing in the lower midrange or upper bass, then dispersion in that range may not be necessary and a simple angled reflector to send reflections away from your ears would be better.
 

Deerhunter

Well-Known Member
#15
After seeing this build, with that material. I want to get some fabric like this. Its a digital print 44"x 33"

My wife will also like it. I just need to do it..more like time home to get it done. Screenshot_20181009-174225_Chrome.jpg
 

Flint

"Do you know who I am?"
Superstar
#16
HA!

I assume you are referring to my acoustic absorption panels I wrote about in the other thread. But, yeah, while picking fabric from the bedding section of Walmart I did see some patterned sheets I almost went for. I am quite glad I didn't go that route.

I love the wolves, though. What would be better than two wolves on the panel? Three wolves on the panel:

 
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