DIY diffuser/absorber panel for listening room

I am nearing completion of the building phase of a dedicated listening room. I have gone to a great deal of effort and fair amount of expense in soundproofing, room dimensions, etc. and now it’s time to start treating the inside. Of course, between the construction and new audio toys I’m buying, I’ve almost totally blown my budget, so I am going to test my handyman skills (ha!) and build some of my own treatment panels. The biggest challenge I’m going to face is that the room is small - 11 x 14 - so lows will be my primary foes. I’ll build some big thick absorbers for the corners. But I’ve heard two theories about what to do at 1st reflection points - some say diffuse (to make the room sound bigger to your ears) and some say absorption is the only way to go. I am intrigued at the idea of doing BOTH - building a diffuser that also absorbs. I’ve seen the ones with a slotted front over absorbing material, but that doesn’t seem it will do much in the way of diffusion. Comments? I just saw a YouTube video of a guy who made a “skyline” diffuser out of used wine corks. Like me, you’ll probably first think it’s funny, but cork is somewhat absorbing, so it seems like it might fit my needs. It’s not scientifically structured, but I think it will work for me. Any thoughts? Suggestions?

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That’s inspired - I like it :slight_smile:
Labour intensive though.
Nice cat in the video too.

I hope this works for you too, I’m tempted…

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I don’t know whether you have heard your system in your unfinished room but I would not assume areas to treat without listening first. A smaller room does not necessarily require bass traps. Short of a spectrum analysis with mic and software, your ear can tell you if you’re bass sounds too fat or thin, or your highs are dull or piercing. Getting rid of room nodes and controlling reflections can be a challenge but trying temporary solutions such as rigid insulation panels for absorption and multi surface reflectors like books for reflections can get you a long way in determining what and where it is needed. My room is about the same size as yours. Over time, I have reduced absorption and have increased diffusion. Whatever the outcome, enjoy the process, but do note that You Tube videos look much easier than in reality. A 3D skyline diffuser is a great choice but takes time. An 18” square one with 1 1/2” blocks is 144 blocks.
They work great and look great, but be prepared.

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Thanks for the reply. And no, I will not install anything before hearing the room first. I deliberately created all walls and ceiling so they are a few degrees out of parallel with the opposite surface (my builder joked that I should have just told him to make the walls straight and he would have made them unparallel anyway), so that should help with too much direct reflection. Without looking into fancy room treatments, I would have at least put down an area rug and some absorbing things, so I’ll likely start there and experiment. And as for the amount of work, I’ve shifted from the wine cork diffuser to a Binary Amplitude Diffuser idea. Still researching though.

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The bass absorber work better away from wall so the energy of the wave creates heat through initial pass through then have air gap to wall so wall reflection is absorbed again. . Thick scatter plate diffuser is a better option than a skyline absorber for high and mids if your system has LF problems.

Don’t under estimate rock wool in bags in space under sofa, or chair cushions. Along with thinner scatter plates at first reflection or on front wall.

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I’ll help by drinking wine . . . .

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That’s so funny because I used to be quite the wine aficionado, until I realized one day that wine was no longer quite a Jon aficionado. I contacted yesterday an old wine slurping companion to ask if she had a huge collection of corks she might be willing to part with. “But you don’t drink anymore…” she said. “I just wanted to remind myself of what a good weekend used to look like,” I replied.

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You have a small room so that will present challenges. As to the effectiveness of the slotted diffusion/absorber designs - don’t underestimate their effectiveness. In my 14’ x 19’ x 11’ tall room 2" thick GIK Alpha Pro absorber/diffusers at first reflection points proved preferable to pure absorber traps. The speakers are located about 40" from the side walls in my room. I went down the rabbit hole of building DIY acoustic controls many years ago and in the end I felt that building large DIY corner bass traps was worthwhile as to cost/benefit but it was impossible to compete with GIK’s price/benefit ratio when it came to the smaller acoustic/diffusion panel products. The main problems with GIK are their slow build/ship times due to Covid supply chain issues and reports of some quality control issues. I’ve ordered three times from GIK (pre Covid) and appearance was acceptable if not up to the standards of much more expensive products.

Great reminder on making sure the panels are spaced away from the wall. But nobody seems to talk about this when it comes to corner bass traps. I realize they are a bit less space-hogs, but physically/mathematically, there are only a few places where you’re getting the benefits of the full thickness, right? So I’m thinking 18 or 24-inch square traps, open on all sides, and away from the walls in the corner, would be better.

Hey, thanks for the feedback. I’ve had good experience in discussions with GIK, so I might reconsider going with pre-made diffuser/absorber panels, but I’ve located a DIY type that requires nothing more than drilling hundreds of holes. I wish my grandson was old enough to enjoy that project. “We’re making Swiss Cheese…”

I think a lot of corner traps may not have back corrner filled completely. So wave is address twice. The long ones say eight feet on floor that lets sound waves pass trough both end s an bounce off walls spaced several feet away. I found quite effective to mitigate bass in an overloaded room.

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I don’t know what your time is worth to you… Or how important a priority you place on aesthetics, but DIY BAD (Binary Amplitude Diffuser) scatter plates made with a hand drill are apt to look pretty bad. Here is a cost-effective alternative to that portion of your proposed DIY project.

This past winter I commissioned Lukasz at Seven Audio in Poland to make me eight BAD scatter plates from 1/8" maple plywood. They were laser cut in a specific size to fit the 49.5"x25.5"x5" DIY broadband absorptive traps I had made a decade prior. As always with Lukasz, the product was made exactly to specification and packaged brilliantly.

The plywood veneer wasn’t perfect but apparently maple plywood was hard to come by in Poland. Once I had sanded stained and sealed the scatter plates, they looked fine installed.

Including parcel post economy shipping from Poland to Ontario Canada, the all-in price was about $400 CAD for the eight scatter plates. As always with Lukasz’ work, the price was amazingly good for the quality of work offered.

BTW, Lukasz custom made the N7x7 fractal QRD diffusers for the five unit modulation seen on the rear wall along with the trio of N13 2D diffusers used in my DIY rear ceiling cloud as well.

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Oh, the wine cork “diffuser” you posted a link to- A TERRIBLE IDEA acoustically. If you want a phase grating diffuser to work in a predictable and sonically worthwhile way, you must follow the math provided for such things and construction best practices. Round wine bottle corks do not offer the required smooth, hard surfaces or the perfectly identical square cross-section required to make them suitable as the stakes in a skyline diffuser.

In this case the DIY builder in question would have achieved MUCH better results with simple broadband absorptive ceiling clouds. The cork surface and the gaps formed between the stacks of round corks would have resulted in absorptive losses to such a degree that it really wouldn’t have offered any useful diffusion. And its unintended absorptive performance would not have come close to an absorptive ceiling cloud constructed from a similar depth of fiberglass, mineral wool, or other suitable porous insulation. This particular DIY build has no value other than as an upcycled piece of of art.

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Hey, sick minds think alike! It wasn’t long after first posting this question that I switched over to the “Swiss cheese” design like the one you pictured. I used to work in marketing for a company that makes engraving machines, so about an hour ago, I sent an inquiry to find out what it would cost to have it laser or rotary-cut out of wood. It also occurred to me that they could cut it out of thick plastic where I could choose a color or texture. It seems wood would be better, but have you seen the cost of a sheet of plywood recently? I’ll let you know what cost they come back with. Thanks much for the reply and pictures. By the way, what a great looking room!

Maple or birch plywood will still be considerably less expensive than making the BAD scatter plates from a similar 1/8" thickness Lexan (plexi-glass).

JLawry, do you want a room that “looks cool” or a room that sounds awesome because you have chosen a room acoustics strategy that observes best practice implementation and makes good acoustics sense??? If you don’t understand the operating principals and usage requirements for the treatments you are considering, then you are quite literally throwing sh*t at the walls and hoping for the best. That is a crappy strategy. Best to do a bunch more research or you end up wasting your time, energy, and money like the fellow making wine cork “diffusers” that knowledgeable folk laugh at!

PM me if you’d like to arrange a facetime or zoom call to discuss…

Hi MTB_Vince, I could honestly care less about how my room looks. As for throwing sh*t at the walls, I’ll do plenty enough of that with the music I listen to. Seriously, I’m going with as much of an acoustics strategy as I can afford. One guy I talked to said there is no way my room will ever sound decent, unless of course I cover the walls with HIS panels that cost $950 each. My plan is to set up my system, do the best I can to achieve the best sound (speaker placement, listening position, etc.) before any room treatments at all, Then I’ll begin with wall treatments - 1st reflections, trap bass in the corners, ceiling, and an area rug. I’ll experiment with different things, but the budget does have limits. As for the “operating principals” of the diffuser, I have found very little that discusses which size panel, which size holes, or hole patterns for a particular size room or to address specific problems. There seem to be lots of specialized calculators for skyline diffusers, but I haven’t found anything for BAD systems. Did you provide specs for the guy in Poland? Did you find some kind of calculator or theories to arrive at that?

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Again, I’m happy to set up a facetime or zoom conversation to cover the “acoustic treatments 101” best practice basics with you. Like you I’m an enthusiast but I became fascinated with the impact small room acoustics and acoustic treatments have on sound reproduction more than 30 years ago. I’ve been accumulating theoretical and practical knowledge ever since.

The folks at RPG Acoustics invented the BAD (Binary Amplitude Diffuser) panel. The pseudo random hole pattern of the 2 dimensional BAD panel is typically derived from a mathematic sequence. I believe Lukasz simply “went to school” on the RPG design when making my custom sized panels and so they will offer comparable performance. Up to 1kHz the scatter plate behaves as though it was not there. So the behavior is purely absorptive to the degree that the performance of the porous fiber absorptive panel behind dictates. Over the 2+ octaves between 1kHz and 5Khz the panel gradually transitions between mostly absorptive and mostly diffusive behavior. Above 5kHz the BAD panel is mostly a diffuser but with about 30% absorptive losses.

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Thanks much for the advice. I might likely take you up on your offer to connect, but I’m wanting to do as much research on my own first. Do you have any familiarity with the 2D QRD diffusers - the ones that look like a bento box after I’m done with it?


I would imagine there are specific formulae for creating these too?

Yes, I’m VERY familiar with both one and two dimensional QRD and primitive root phase grating diffusers. I’ve even DIYed a few way back when. Here is a link to a DIY Skyline style diffuser I built years ago. And yes there is a mathematical formula based upon prime numbers behind their creation. You can find links to QRD calculators on line (there should be a link to one in my old build thread).

Well width and maximum well depth dictate the diffuser’s operational bandwidth. The low frequency cut off dictated by the deepest well depth also dictates the minimum distance the diffuser should be placed from the MLP (Main Listening Position). Minimum listener distance is 3x the wavelength of the diffuser’s low frequency cut off. So for a 5-6" deep diffuser you want the listeners ears to be a minimum of 5 feet away from the diffuser.

If you are looking for an easy to DIY diffuser, stick with Poly Cylindrical diffusers. These are very easy to implement, not difficult to make look good, and are architecturally interesting. Large ones can act as bass traps if you lightly stuff the rear cavity with fiberglass or other porous insulation.

Phase grating diffusors are a lot trickier. After building several myself I decided that they were so much effort to DIY well that moving forward I’d pay for properly implemented commercial designs. Buyer beware though. there are a bunch of really poor designs being sold commercially. If the maximum well depth is much less than 4" I would not even bother.

Below is a few pics of the custom N13 Hoffa style 2D diffusers that Lukasz at Seven Audio made for my recent compound ceiling cloud project. These are 29.5" square and almost 5" deep. These three diffusers cost about $500 CAD each all-in by the time they arrived from Poland.

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@MTB_Vince is giving you good guidance. Polyfusers are probably the most realistic diy project. Best bang for your DIY time and probably the better looking result with equal or better acoustic results.

I spent $150 a piece for these from GIK. My guess is a handy person could make a bunch of these for less.Evolution PolyFusor © - Sound Diffuser / Absorber Combination

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