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 Post subject: DIY Diffusers
PostPosted: Thu Nov 10, 2016 8:33 am 
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Joined: Mon Dec 13, 2010 12:55 pm
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Location: Niagara Region, ON, CA
There are plenty of on-line tutorials for the skyline-type wooden diffusers, however I'm interested in some sort of lightweight diffuser that can be made from foam panel board or the like (balsam might work, but I suspect it would be very expensive). The reason is that I have a 60" TV directly behind my speakers that I would like to be able to easily cover with with a good looking difuser. GIK has some pricey products and Arqen has free DIY designs. Does anyone have photos of their diffisers? Anyone experimented with fabbing these from a high density blue or pick foamboard. GIK has foam ones, but most are wood, which would be very heavy. Suggestions? I already have quite a bit of absorption in the corners and first reflections.


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 Post subject: Re: DIY Diffusers
PostPosted: Thu Nov 10, 2016 12:32 pm 
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Location: Charlottetown, PE, CA
I have built a few using foam and a hot wire foam cutter. Formular works well for the Arqen A1-LF design. I built a huge N23 diffuser as well using foam. Over 6' wide in one piece. What kind of info are you looking for?


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 Post subject: Re: DIY Diffusers
PostPosted: Thu Nov 10, 2016 2:35 pm 
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Location: Niagara Region, ON, CA
Serenity_now wrote:
I have built a few using foam and a hot wire foam cutter. Formular works well for the Arqen A1-LF design. I built a huge N23 diffuser as well using foam. Over 6' wide in one piece. What kind of info are you looking for?


Thanks for the response. I guess, any pointers or tips, as well as any pics or places for info to build. The hot wire cutter is a great tip for example. Did you cover them in fabric or paint them or otherwise dress them up? Whats the N23 diffuser? Where did you get the plans etc. Thanks a bunch


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 Post subject: Re: DIY Diffusers
PostPosted: Fri Nov 11, 2016 3:53 am 
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Location: Charlottetown, PE, CA
Sure, ok deep breath, long post.

First, you must decide on what type of diffuser you want to build. There are 3 basic types that are easy to DIY. These are Polycylindrical, QRD and Fractal designs. The info provided here is from my own DIY builds. I have hands on experience building, testing and measuring the effect of each of the options. I would not recommend building a 2D skyline diffuser simply because they are very time consuming and labor intensive when compared to other options to get the same area of coverage in the final install. They are also super heavy if constructed out of wood.

Using foam for construction saves weight, time and cost. My advice is to get a large T-Square, a heavy blade Olfa knife and a couple bar clamps to set up a cutting station on a work table. Work slowly and make sure your cuts are square through the depth of your material. Building a hot wire foam cutter is very useful, but not required to build a great product in the end. Be sure to use water based paint to finish your foam diffuser. Spray paint in a can contains chemicals that eat foam. Test on a small area of scrap foam before you start covering your project in paint. PL premium is all that is required for gluing if you go with a deep QRD design. If you go with a stacked fractal design I recommend 3M Super 77 instead. Wear a mask, gloves and safely glasses when using Super 77. 8)

Here is my room so you get a general idea of where the upcoming diffuser pics live in my space.

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Polycylindrical Diffusers (Sidewall location recommended - near listener ok)
For a simple Polycylindrical how-to go here.
https://www.gearslutz.com/board/attachm ... panels.pdf

Poly diffusers are considered a mild form of diffusion when compared to the other options. They are effective at mitigating parallel room reflections and reducing flutter echo problems when the room dimensions are relatively small. They are not recommended to be used in a repeating fashion in small rooms, as they will create a lobing effect at certain frequencies. I used them in my room to reduce the lateral ring without eliminating acoustic energy from my center channel. Their effect is subtle, but can easily be verified by creating a loud impulse between their opposing locations in the room. The pitched after ring was eliminated in my space.

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Quadratic Residue Diffusers (Front or rear wall recommended- distance to listener must be considered)
For a QRD diffuser design I suggest downloading the free QRDude software here. http://www.subwoofer-builder.com/qrdude.exe It is free software based on the work of Dr. Trevor Cox (an authority in diffusion and diffraction research.)

QRD diffusion is aggressive when compared to other designs. Their design is based on prime number formulas and a "period" reflects the number of wells in a given design. So, a QRD having a period width of 23 wells is referred to as an N23 QRD diffuser. Each QRD is based on a single period design and multiple periods may be ganged together to increase lateral area of coverage. Multiple period installs should include inverse designs to mitigate lobing effects. This is most practical in large rooms where an entire wall (the rear wall in a performance hall typically) is covered in QRD diffusers. Since QRDs work by "phase grating" (simply put, shifting the relationship between incoming vs outgoing phase at a given frequency) their effects are best appreciated when the distance to the listener allows the phase shift to be less apparent. The rule of thumb is for every inch of well depth the listener should be placed 1 foot away from the QRD. In my experience you can actually sit closer than the rule of thumb suggests. Sitting very close to the QRD can be subjectively described as listening through a seashell.

My design was calculated with QRDude accordingly. The design depth was based upon the stock foam material dimensions I had to work with.

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Here it is pre-painting. The fins are 1/4" wall panelling from Home depot ripped to the max well depth. It was assembled in pieces first and then glued to back rails for wall mounting. The well depths of "0" were a logical place to break up the design for modular construction. I finished the "0" wells with a piece of the same stock used to build the fins cut to the well width.

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Fractal Geometry Diffuser (May be placed closer to the listener than a true QRD design)
Fractal designs are becoming more popular because they offer high diffusion in a shallower footprint. They are extremely light because they can be built entirely of foam (no well dividers required.) Good designs have been made free at Arqen by Tim Perry. I built a modified version of the A1-LF design. Here, I used 1/2" Foamular insulation and diced it up with a hot wire foam cutter. This made the cuts very precise and repeatable, plus I got to build something else in the process. :wink: Here is where the 3M super 77 really cut assembly time down and made gluing time short. It gets tacky quickly so things stay put where you want them. A water based paint sprayer is best to finish them off if you use foam.

Assembled before paint.

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Spraying

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Of all the designs I made the deep QRD in stalled on the front wall was by far the most obvious and pleasant contributor of diffusion in my room. If you want more info feel free to shoot me a PM.


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 Post subject: Re: DIY Diffusers
PostPosted: Fri Nov 11, 2016 4:47 am 
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Location: Niagara Region, ON, CA
Amazing. You're a very talented builder. This is precisely what I was looking for. So many good ideas. In fact I think I'm calling in sick today to take measurements, do research and plan a trip to Home Depot. Thank you so much for taking the time to post this.


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 Post subject: Re: DIY Diffusers
PostPosted: Fri Nov 11, 2016 4:57 am 
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Joined: Sun Mar 20, 2016 8:58 am
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Location: Charlottetown, PE, CA
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 Post subject: Re: DIY Diffusers
PostPosted: Fri Nov 11, 2016 5:09 am 
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Location: Ardrosssan, AB, CA
Serenity-now, thanks so much for sharing all that great information.

Do you have more pictures of the completed diffusers mounted in your room?

Did you consider or experiment with any ceiling mounted panels?


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 Post subject: Re: DIY Diffusers
PostPosted: Fri Nov 11, 2016 11:03 am 
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Location: Charlottetown, PE, CA
I did consider a ceiling cloud at one point. The further I got along in my space I realized I was out of absorption headroom. My decay times were more or less right around 300ms per octave. Going below this threshold is generally not recommended in living spaces. It becomes oppressive and unnatural.

Ceiling panels along with lateral reflection control is common in close mic recording spaces and mixing rooms. It is my opinion that ceiling reflections are the least detrimental ones to consider when working within the bounds of acoustic decay headroom in listening spaces. Horizontal energy and floor bounce is where I focus my efforts in room consultations. With a carpeted floor, ceiling reflected energy is largely attenuated in short order anyway. 8)

I'll get some pics up later when I'm home.


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 Post subject: Re: DIY Diffusers
PostPosted: Fri Nov 11, 2016 5:24 pm 
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Location: Charlottetown, PE, CA
Some pics. The overhead image in the other post is an accurate scale render of the space. Hope this helps you decide to build some and share your results.

N23 QRD Diffuser behind acoustically transparent screen wall. Sorry, its dark back there.

Image

I built a stand for it and pinned it to the wall with screws as well. It weighs about 70lbs. I put furniture felt pad between the runners and the wall to prevent rattling during heavy bass passages. The drywall is mounted on resilient channel.

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QRD diffuser being tested temporarily in 2ch setup.

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Impression of screen wall setup during construction.

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Rear wall fractal diffusers. They weigh about 3lbs each. I mounted them with 3M command strips.

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Old almost complete room shot. (Are they ever really done?)

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 Post subject: Re: DIY Diffusers
PostPosted: Sat Nov 12, 2016 3:52 am 
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Joined: Tue Dec 07, 2004 4:18 pm
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Location: GTA, ON, CA
Nicely done and thanks for sharing!


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 Post subject: Re: DIY Diffusers
PostPosted: Tue Sep 19, 2017 10:16 am 
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Joined: Tue Aug 29, 2017 3:04 pm
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Location: Sherwood Park, AB, CA
Isn't that against code using polystyrene as it is combustible?


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