Wood acoustic diffusers have become a decorative item - loved the idea!

[DJBonoBobo]

I understand your frustration, dealing with room acoustics is not an easy task because one room is not the same as the other, and you can not translate the problems on a 1:1 scale from one room to another. There is no "one-fix" solution and you must get to know your particular listening room.

My approach is to take one step at a time. I use measurements of my room and try my best to recognize the most significant problems and deal with them one at a time, I don't try to solve them all in one go. It's a really cool way of doing it because you learn a lot in the process, you recognize a particular problem and you think about the best solution for that specific problem based on the specs of the absorber (or for this thread, the diffuser) and go for that. And when you re-measure the room response you see what that solution did and if you got close to what you aimed for and according to the result of that, you take the next step to get closer to the end goal you set from the beginning.

In short, don't try to solve everything in one go, take one step at a time and see where it goes.

You probably need both absorbers and diffusers to reach the goal, and the goal is to hear as much direct sound as possible from your speakers without overdoing things. By maximizing the direct sound from your speakers, the more you hear the recorded information. But(!), just to the point where the shortcomings of the somewhat simple stereo illusions are not revealed for what they really are. I hope that makes sense because we all have heard that listening to music in an anechoic chamber is not a very pleasant exercise.

I have watched a couple of highly educating videos on room acoustics on the Audioholics Youtube site with Anthony Grimani, an acoustic expert I have learned to trust. He has treated over three hundred rooms and has come to the conclusion that about 15% absorption and about 20% diffusion are the most common equation for most rooms. He likes to treat the rooms even by spreading out the absorbing material in the room to get the overall room reverberation times down, and after that, about 20% diffusion material.

It's pretty easy, just use mathematics and you know how much coverage is needed for every wall and ceiling when it comes to absorbing material and diffusion material. But just think of it as a "rule of thumb", measure, and re-measure step by step to know if you are moving in the right direction. The goal is to have an even reverberation time over the full spectrum.

The area under 100 Hz is the most problematic one and you will probably have a hard time dealing with that acoustically wise, and if that's hard to solve (because that is, in most cases, in need of some seriously big solutions), you can fall back using EQ as a last step to take care of that frequency area.

Personally, I have solved the reverberation times in my listening room to an accepted level of an average of about 350 milliseconds from around 100 Hz and up. The bass is a mess but doesn't get in the way of most music because the energy of most recordings is low under 50 Hz, and I take care of that with EQ adjustments at the moment (but I have a free corner in the room and I think about adding a serious bass trap there). My next step is most likely to add some diffusion to the room, maybe in the ceiling or to the wall behind my listening position. It's all a work in progress, but it's amazing how much better it gets with all the solutions and the "window" to the recordings gets clearer and more transparent. But at the same time, I must make sure I don't overdo anything, so a step-by-step approach is a way to do it for a non-acoustic expert like me.

@DjBonoBobo I am not an acoustician, but I do like to read. Since I lack personal experience, I will try to avoid unsupported assertions but instead provide references whenever possible. I think that your frustration comes down to both fundamental problems in how measurements are done and interpreted, as well as a failure in most discussions to simply identify individual preferences as the starting point for further exploration (e.g. https://www.audiosciencereview.com/...-of-lokki-bech-toole-et-al.27540/#post-950580). In a similar manner of different concertgoers having different preferences (clarity vs loud, reverberant sound vs timbre) and therefore arguing about what makes an optimal concert hall (or to make it a bit more complicated, whether LOC to improve the experience of more of the audience, like http://www.davidgriesinger.com/The_Physics_of_auditory_proximity_2.pptx), the discussion of what to do with reflections gets bogged down quickly without identifying or prioritizing preferences first.

Regarding measurements, at least in terms of absorption, you might be interested to read https://www.stereophile.com/content/nwaa-labs-measurement-beyond-atomic-level and http://nwaalabs.ipower.com/Files/NWAA Labs/AES PNW Old Problems, New Solutions, Architectural Acoustics in Flux2.ZIP, as well as Toole's second edition of Sound Reproduction regarding angles of incidence and fabric coverings. For diffusion, see the Stereophile artcle above and http://nwaalabs.ipower.com/Files/NWAA Labs/Diffusion, When phase and energy becomes more important than directivity in the perception of space 2017 NOLA.pdf. Compare what he says about binary amplitude diffusion devices in the latter with comments regarding localization in the former vs perception of the room opening up in the latter, for example, but also what he implies about QRD devices in the former.

In terms of small rooms, Cox and d'Antonio (founder of RPG) write in their book "Acoustic Absorbers and Diffusers," "How far away should a listener be positioned from the diffusers? The distance from listener to diffuser can be determined by considering the scattered and total field. First consider the scattered field, i.e. just the reflections from the diffuser. A diffuser requires a certain time or distance to form a wavefront. There is an analogy to loudspeakers that can be made here. A listener would not consider sitting 30 cm from a multi-way loudspeaker, because the listener would be in the near field of one of the drivers. At some distance from the loudspeaker, all individual high, mid- and low frequency waves from the individual drivers will combine to form a coherent wavefront. The same holds true for scattering surfaces. They also can be thought of in terms of near and far field, although the situation is a bit more complex than for loudspeakers...Consequently, listeners should be positioned as far from scattering surfaces as possible. Precedence has shown that it is best if the listener is at least three wavelengths away from diffusers. Since diffusers used in listening room applications have a lower frequency limit of roughly 300–500 Hz, this means a minimum distance of 3m is recommended."

Also with "Acoustics of Small Rooms," Kleiner and Tichy distinguish between small rooms used for music reproduction and small rooms used for voice and music practice with interesting distinctions in discussion. They discuss the use of diffusion more in the latter than the former.

Anyway, just my thoughts reading your post. I think it may be a bit more complicated than what I'm interpreting from @sarumbear.

Young-Ho

Thank you for your answers. Sadly, i do not have the time to respond properly, because it is a complicated topic (for me). I actually tried pretty hard to take step by step in the last years and also tried to document what i was experiening in my threads i mentioned in my earlier post.

Just one more thing at the moment: The quote @youngho posted "a minimum distance of 3m is recommended" is a good example for the conflicting information i meant: In my small room (3x5 m), only the back wall is further away than 3 meters from listening position. So if I follow this quote, it would mean from my understanding that it would only make sense there.
But @sarumbear wrote:

In most small rooms absorption often creates more issues than it solves. Diffusion is a better solution. (...)
They are a much better choice than foam panels to stop a reflection from a wall -- much, much better.

Isn't that a contradiction? Or what am I misunderstanding?

Apologies if this question has been answered in this thread before, i have to catch up yet...

 

[sarumbear]

Isn't that a contradiction? Or what am I misunderstanding?

There’s no contradiction. You are reading bits and pieces without fully grasping their meaning. Remember, acoustic treatment is bespoke. No room is the same and there is no panacea, no template, no samples. Only principles.

If you post your layout I can try to guide you.

 

[DJBonoBobo]

You are reading bits and pieces without fully grasping their meaning.

Indeed. Probably in the past I overestimated what i can reasonably do myself at home without hiring someone. After all, I did not build my kitchen myself
Thank you for your offer! I don´t want to derail this thread and still have to think about what i want at this point, but perhaps i come back to you at some point.

 

[youngho]

Thank you for your answers. Sadly, i do not have the time to respond properly, because it is a complicated topic (for me). I actually tried pretty hard to take step by step in the last years and also tried to document what i was experiening in my threads i mentioned in my earlier post.

Just one more thing at the moment: The quote @youngho posted "a minimum distance of 3m is recommended" is a good example for the conflicting information i meant: In my small room (3x5 m), only the back wall is further away than 3 meters from listening position. So if I follow this quote, it would mean from my understanding that it would only make sense there.
But @sarumbear wrote:

Isn't that a contradiction? Or what am I misunderstanding?

Apologies if this question has been answered in this thread before, i have to catch up yet...

@DjBonoBobo

That recommendation was in the context of relatively deep QRD diffusers effective down to several hundred hertz. These sorts of "mathematical" diffusers scatter sound in both direction and phase, so since the speed of sound is ~343 m/s, the wavelength of 300 Hz is ~1.14 meters, and the authors suggested that the listener should be positioned at least three wavelengths away. For shallower diffusers, the relative distance would be accordingly less, and hybrid diffusers/absorbers like RPG BAD or Kinetics TAD or RealAcoustix FAST or GIK Alpha panels really only scatter at much higher frequencies, so the listener can be much closer still (@anotherhobby, the NWAA paper I linked above suggests one possible explanation for what you observed: http://nwaalabs.ipower.com/Files/NWAA Labs/Diffusion, When phase and energy becomes more important than directivity in the perception of space 2017 NOLA.pdf)

There are also geometric diffusers (think of shapes like half-cylinders, half-spheres, etc) that scatter in direction but not phase, though repeating them in arrays can increasingly reduce their effectiveness with lower frequencies (see Toole's second edition of Sound Reproduction, also Cox and d'Antonio's book).

Hope that helps.

 

[youngho]

If it can be done, the first reflection points are the obvious starting points for the chosen room treatment. And as I've learned, covering everything is not always the best solution because the edges of the absorbing panels are also effective areas, and leaving some space between the panels can even be more effective than not. If the same rules are true when it comes to diffusion panels I do not know.

Yes, that was what I understood from the NWAA white paper: "The ratio of perimeter length to the area and spacing between units are the controlling factors [for absorption]." I believe that for diffusion, larger panels or arrays (not comprised of identical and/or identically oriented units) are more effective due to wavelength size for diffusion effect (for the QRD effective down to 300 Hz, for example, 300 Hz is 3.76 ft wavelength, so how well would a 1.5-2 ft wide diffuser be expected to work?

 

[kemmler3D]

Just finished reading this: https://www.nature.com/articles/s41598-017-05710-5#Tab1

The upshot is that you can get good diffusion with thin panels, in the paper they go down to 250hz with a 3cm thick panel. The tradeoff is there is some uneven absorption, but in the paper they say this can be mitigated by making the panel thicker. I think we could go to 5 or even 10cm, what say you?

(another downside: I don't think they look as cool as 'traditional' QRDs, but that's a matter of taste.)

However, I lack the math skills to know how to generalize their result and generate new designs of similar panels. It looks like they give a decent description of everything, but I am no engineer or scientist... Where is the QRDude for this style of panel?

This could be really interesting, since the profile of panel they show in the paper would be even more trivial to 3D print than a normal "thick" QRD panel. But I will need to read a lot more closely to figure out how to customize one.

 

[Ciobi69]

Just finished reading this: https://www.nature.com/articles/s41598-017-05710-5#Tab1

The upshot is that you can get good diffusion with thin panels, in the paper they go down to 250hz with a 3cm thick panel. The tradeoff is there is some uneven absorption, but in the paper they say this can be mitigated by making the panel thicker. I think we could go to 5 or even 10cm, what say you?

(another downside: I don't think they look as cool as 'traditional' QRDs, but that's a matter of taste.)

However, I lack the math skills to know how to generalize their result and generate new designs of similar panels. It looks like they give a decent description of everything, but I am no engineer or scientist... Where is the QRDude for this style of panel?

This could be really interesting, since the profile of panel they show in the paper would be even more trivial to 3D print than a normal "thick" QRD panel. But I will need to read a lot more closely to figure out how to customize one.

Wow very cool i hope somebody could make a 3d printing file for this ahahah

 

[fpitas]

So, it seems the Shakti Hallograph was before its time as a wooden diffuser:

The Hallograph - Shakti Innovations

The Hallograph Soundfield Optimizer The Hallograph breakthrough technology is the result of over 10 years of research that studied the effects of the speaker/room interface. We learned how to reduce the audibility of the chaotic reflections from the walls of the listening room so they wont...

www.shakti-innovations.com

Cheap, too!

/

 

[restorer-john]

So, it seems the Shakti Hallograph was before its time as a wooden diffuser:

The Hallograph - Shakti Innovations

The Hallograph Soundfield Optimizer The Hallograph breakthrough technology is the result of over 10 years of research that studied the effects of the speaker/room interface. We learned how to reduce the audibility of the chaotic reflections from the walls of the listening room so they wont...

www.shakti-innovations.com

Cheap, too!

/

What about a Shitak stone?

 

[fpitas]

What about a Shitak stone?

View attachment 246706

Works in your car, too. These guys are geniuses!

 

[Todd k]

sarumbear. Would this room benefit with some

diffusion on first glance? Room sounds pretty good, cathedral ceiling, pickets on bridge above, 8 x 11 thick wool rug on large wall, 12 x 15 rug on floor.

 

[Bjorn]

Hi

As an acoustician I am tired to tell people not to think room treatment only as absorption. In most small rooms absorption often creates more issues than it solves. Diffusion is a better solution. However, all I hear: they are expensive, ugly and difficult to place in a room. I am hence pleasantly surprised when I stumbled upon these on Etsy!

Wood Sound Diffuser - Etsy UK

Check out our wood sound diffuser selection for the very best in unique or custom, handmade pieces from our wall decor shops.

www.etsy.com

Not all are done correctly but nevertheless any similarly constructed panel will diffuse the sound in a room. They are a much better choice than foam panels to stop a reflection from a wall -- much, much better. Taste is personal but there are so many to choose from that finding one to your taste shouldn't be a problem. They are not unaffordable either.

Absorbers work on reducing the reverberations. Reverberations increase sound in a room and makes the sound bright. Due to the limitations of the materials absorbers are ineffective at low frequencies. This makes the rooms to sound bass heavy, dull sounding, and not a nice place to listen music to. Diffusers on the other hand stops reflections by scattering the sound so that reflections occur at very high frequencies and hence at less amplitude. This makes the room to disappear (figurately speaking). Here is a good article about diffusers and DIY options. Here is another more technical one.

I hope you will try a diffuser on your room when you need acoustic treatment. If you are already using one I love to hear from you. If I can be of any help do please ask.

All the best

As one who sells acoustic products and make more money on diffusers than absorbers I would love to agree. But there are a lot of simplification in what you share and conclusions that that are IMO wrong.
The better treatment very much depends.

Simply stating that diffusion is better is IMO quite misleading. Besides, much of what you are linking to are not proper diffusers but simple scattering units with a high level of lobing, focusing certain frequencies in certain directions, and very bandlimited that with alter the frequency spectrum. If the goal is accuracy (which it doesn't have to be of course), this type of treatment would be what one should avoid.

 

[sarumbear]

As one who sells acoustic products and make more money on diffusers than absorbers I would love to agree. But there are a lot of simplification in what you share and conclusions that that are IMO wrong.

Simply stating that diffusion is better is IMO quite misleading.

I didn't said that. On my first post I said "In most small rooms absorption often creates more issues than it solves. Diffusion is a better solution...Not all are done correctly but nevertheless any similarly constructed panel will diffuse the sound in a room. They are a much better choice than foam panels to stop a reflection from a wall -- much, much better."

Besides, much of what you are linking to are not proper diffusers but simple scattering units with a high level of lobing, focusing certain frequencies in certain directions, and very bandlimited that with alter the frequency spectrum. If the goal is accuracy (which it doesn't have to be of course), this type of treatment would be what one should avoid.

I disagree simply because I have not seen any data of what you suggest will happen. If you have please show.

From my experience devices like below will not cause any loping that will affect the FR as you suggested.

Genuine Wood Sound Diffusers 45 X 12 2 Pack FREE SHIPPING in USA - Etsy UK

This Musical Instruments item by DiffuserDude has 266 favorites from Etsy shoppers. Ships from United States. Listed on 27 Mar, 2024

www.etsy.com

 

[Yannick Willox]

@DjBonoBobo

That recommendation was in the context of relatively deep QRD diffusers effective down to several hundred hertz. These sorts of "mathematical" diffusers scatter sound in both direction and phase, so since the speed of sound is ~343 m/s, the wavelength of 300 Hz is ~1.14 meters, and the authors suggested that the listener should be positioned at least three wavelengths away. For shallower diffusers, the relative distance would be accordingly less, and hybrid diffusers/absorbers like RPG BAD or Kinetics TAD or RealAcoustix FAST or GIK Alpha panels really only scatter at much higher frequencies, so the listener can be much closer still (@anotherhobby, the NWAA paper I linked above suggests one possible explanation for what you observed: http://nwaalabs.ipower.com/Files/NWAA Labs/Diffusion, When phase and energy becomes more important than directivity in the perception of space 2017 NOLA.pdf)

There are also geometric diffusers (think of shapes like half-cylinders, half-spheres, etc) that scatter in direction but not phase, though repeating them in arrays can increasingly reduce their effectiveness with lower frequencies (see Toole's second edition of Sound Reproduction, also Cox and d'Antonio's book).

Hope that helps.

It is my understanding these deep QRD units can “ring” at certain frequencies. Anyway, i’m quite shure I already heard it happening myself. Personally I am a big fan of polycylindrical diffusers. They are easy to make and dirt cheap. I have measurements they even clean up 50Hz - 150 Hz for free, if done correctly, while covering just a small percentage of the walls.

as you are on the topic of the “difference” in diffusion, directional and temporal, I would like to address once more my point there is no such thing as temporal diffusion. Temporal diffusers use time smearing to redirect. They are in effect directional diffusers, with severe lobing.which IMO is the second reason you should not sit too close.

I ask this every time the temporal diffusion argument pops up : how many 1 KHz waves can coexist in the same direction ?

Yes,a big QRD can spread a late reflection over a few msec, but I have never seen a filtered IR where it is proven this spread happens equally at all frequencies. I have a feeling this is more proof that what comes back is very time incoherent, as opposed to a polycylindrical, where what is diffused it largely time coherent, ie the sound does not fall apart Into white noise.

 

[kemmler3D]

I have a feeling this is more proof that what comes back is very time incoherent,

Yes, I think this is basically the point of diffusers...? If you want time coherent reflections, well, you get reflectors.

I have not seen any data of what you suggest will happen. If you have please show.

My understanding is that you can get some diffusion from many uneven shapes, but QRD diffusers (which have to be built according to Shroeder's formula, of course) are a unique case where you get even diffusion around the design frequency. Other shapes are not guaranteed to do that and will have unpredictable frequency characteristics.

 

[Somafunk]

My wood store doubles as diffusers, trouble is I keep burning the wood and changing the diffusion

 

[Trell]

My wood store doubles as diffusers, trouble is I keep burning the wood and changing the diffusion

So you got a real fireplace and don’t have a TV above it.

 

[Somafunk]

So you got a real fireplace and don’t have a TV above it.

Managed to reach 50 without ever owning a tv as music has always been my vice, and not much point to a tv when I have a 5k 27” iMac in front of my chair, hope the rumours of an 8k 32” iMac are true

 

[Juhazi]

Absorption Behind Speakers and Rear Wall Diffusion – Acoustic Fields

“Should you use absorption behind the speakers and diffusion on the rear wall?” That’s the area where you have the most low-frequency problems.

www.acousticfields.com

See above. Diffusers on the front wall between speakers have never got my appreciation. On sidewalls at first reflection "points" are OK.

 

[anotherhobby]

I really have to thank you @sarumbear for opening this thread! I have now discovered that GIK diffusors over my desk makes a dramatic improvement in sound quality in my office. It never really occurred to me to try and test them up there. I also tested the GIK diffusors on my front wall, but actually prefer the absorption that I currently have. The same goes for the large absorbtion panel behind the door in the image below. Next I was thinking how I wish it was easy to test them on the ceiling, and then I realized that I had a tool to hold them them quickly, easily, and secure enough for testing (see pic).

I had no idea how much the ceiling over my desk was interfering with my sound quality! I also tested an absorber up there and the diffusor is noticeably better. I get this nice airiness ambience over my head. The only disappointing part is that I promised these panels to my wife for her office, so now I need to order more. The second I took them down it was a bummer.

View attachment 242706

As a follow up to this post from 25 days ago, I did indeed order diffusor/absorber panels to go over my desk, but I got thicker 4" ones instead of the 2" ones that I tested with. Since I had already tested the 2" panels above me and had been using them for a couple of days, I knew what to expect from above diffusion, but I was really happy with the improvement in mid range clarity that additional absorption provided. The impact on voice is very noticeable when you swap back and forth between 2" and 4" panels.

Since I was already ordering panels, I also replaced the thinner 2" panels on my back wall with two 4" thick panels and two 6" thick panels. This is substantially more damping than I had on my back wall before and the improvements in bass quality are impressive.