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

voodooless

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Define what you call a 1D and 2D diffuser, please.
1D
1668201485116.jpeg

2D
1668201505900.jpeg


Obviously both are 3D ;)
 
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sarumbear

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goat76

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I can only see the possibility of a 2D or a 3D diffuser. A 1D diffuser is just a plain wall! Or am I diffused by things at the moment? ;)
 

youngho

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I have no technical expertise myself and get irritated quickly. On the one hand, I've been dealing with the optimization of my room for a long time (two examples of my "quest" for better room acoustics: 1 and 2), but I'm increasingly frustrated that I can't find any consistent guides.

As far as I know, there are no reliable measurements or tests anywhere on room acoustic measures, and if you buy something yourself, you actually have to decide beforehand and only know at the very end - after you have spent hundreds or thousands and assembled everything, whether the effect has occurred as desired.

Even if you hire a professional, you don't know what you're going to get - at least I've heard various rather dissatisfied testimonials. You certainly can't generalize all that, but it seems to me to be very difficult to really get a good picture yourself of what measures are really useful and which are not.

The discussion of what to do with reflections from the side walls alone is already completely opaque, since there are renowned experts for all variants who argue convincingly in favor of one or the other measure (diffuse, absorb, reflect).

My state of knowledge so far was that especially in small rooms absorbers should be preferred (as broadband as possible) and diffusers do not work or are even harmful. You now write the opposite.

As I said, I know nothing better but certainly much worse than you. But you make it sound as if the use of diffusers in small rooms is relatively clear and unambiguous - is that so?
@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
 

anotherhobby

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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.

IMG_1805.jpeg
 
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sarumbear

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I really have to thank you @sarumbear for opening this thread!
You are very welcome. I’m happy that I made a small difference in your music enjoyment.

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.
Diffusers need distance between them and the source or the listener. Possibly that’s why they didn’t work for you as the distance is very small.
 

youngho

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Well, OK then, based on what the physics profs have taught me about wave propagation, the angle of reflection is equal to the angle of incidence, wrt a normal line perpendicular to the reflective surface. If the object is to break up the wavefront into smaller bits and send them off in different directions in order to reduce their perceivability (did I just make up a word?) at the listener’s ear, then perhaps what I wrote previously would hold. Or perhaps not. I hear you saying not necessarily,, read the papers, so I suppose the answer is in there.
I think you're describing something along the lines of difference between an RPG Skyline diffuser (https://www.rpgacoustic.com/skyline/) and a Vicoustic Multifuser DC3 (https://vicoustic.com/product/multifuser-dc3?multifuser-dc2-finishes=Black). From what I understand from Cox and d'Antonio, as well as Toole, the relative depths of the diffusers should determine the lower range of the effective frequency of diffusion. Angling likely helps with very small wavelengths, but when you look at the difference of depth related to the angle, as well as the size of the individual units, the wavelengths involved are likely above 10 kHz. Consider, by contrast, the effects of hearing damage related to age and concert attendance.
 

Berwhale

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Interesting...

 

youngho

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I can only see the possibility of a 2D or a 3D diffuser. A 1D diffuser is just a plain wall! Or am I diffused by things at the moment? ;)
Perhaps consider diffusers as acting directionally in terms of amplitude and phase, otherwise as scattering in different planes. If an appropriate sound wave hits a vertically oriented so-called 1D diffuser, it gets scattered in the horizontal plane (side-to-side, instead of just bouncing off like a beam of light hitting a mirror in a specular fashion). The horizontal plane is one dimension. If an appropriate sound waves hits a so-called 2D diffuser, it gets scattered in both the horizontal and vertical planes, which represents two dimensions. A 3D diffuser would have to scatter both in front and behind it, i.e. depth.

A plain wall does not really intrinsically scatter, so it could be called a 0D diffuser, but I believe it gets more complicated, since lower frequencies seem to reflect in an increasingly hemispheric manner until they approach modal frequencies as the reflections become planar, leading to standing wave issues.
 
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youngho

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Can you explain what you meant by "I could hear them". What was it that you are hearing compared to the bare wall?
I can't speak for @Hipper, but a few possibilities could include comb filter effects related to phase, as well as localization depending on placement of the diffusers:

From Cox and d'Antonio in Acoustic Absorbers and Diffusers: "A listener positioned near a multi-way loudspeaker with their ear close to the midrange driver hears sonic anomalies, and the same is true when the listener gets too close to a diffuser. Many of the phasing anomalies reported by room designers are due to the fact that they are listening too close to the diffuser and they are hearing near field comb filtering effects. Some listeners have even put their heads in the wells of large low frequency diffusers, and then claim something is wrong because it sounds odd! Furthermore, getting too close to a diffuser means that the temporal response is overly dominated by the surface close to the ear, which means the temporal dispersion generated by the diffuser is not heard. The direct and reflected sounds are then rather similar and comb filtering gets worse. This naturally leads us to a consideration of the total field."

Separately, comments regarding localization: https://www.stereophile.com/content/nwaa-labs-measurement-beyond-atomic-level-page-2 and Toole on page 23 here: http://www.wghwoodworking.com/audio/LoudspeakersandRoomsPt2.pdf
 

youngho

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@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
@DjBonoBobo Actually, Cox and d'Antonio also discuss cases of music practice rooms: "The experiments verified that by utilizing limited diffsorption, hemispherical ceiling diffusion and lateral wall diffusion, along with modal absorption, a very functional and enjoyable practice room could be attained."

This ties a little into what Kleiner and Tichy wrote: "If the height of the room is less than its width or length, ceiling diffusers will be helpful to achieve good sound quality. Diffusion should not be overemphasized though as a means of improving small rehearsal and practice room acoustics...again, it must be stressed that numerical sound diffusers using wells have quite high sound absorption...polycylindrical sound diffusers such as those shown in Figure 12.5 can be advantageously designed to be both diffusive over a wide mid- and high frequency range and sound absorptive at low frequencies by means of slit absorber action as explained in Chapter 4. Different radii of curvature are recommended if several diffuser units are to be used."

Anyway, a digression...
 

Somafunk

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Interesting...

I’d take anything that shill says as very suspect, he’s a modern day door to door encyclopaedia salesman in an ill fitting suit shucking overpriced dubious products.
 

goat76

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I have no technical expertise myself and get irritated quickly. On the one hand, I've been dealing with the optimization of my room for a long time (two examples of my "quest" for better room acoustics: 1 and 2), but I'm increasingly frustrated that I can't find any consistent guides.

As far as I know, there are no reliable measurements or tests anywhere on room acoustic measures, and if you buy something yourself, you actually have to decide beforehand and only know at the very end - after you have spent hundreds or thousands and assembled everything, whether the effect has occurred as desired.

Even if you hire a professional, you don't know what you're going to get - at least I've heard various rather dissatisfied testimonials. You certainly can't generalize all that, but it seems to me to be very difficult to really get a good picture yourself of what measures are really useful and which are not.

The discussion of what to do with reflections from the side walls alone is already completely opaque, since there are renowned experts for all variants who argue convincingly in favor of one or the other measure (diffuse, absorb, reflect).

My state of knowledge so far was that especially in small rooms absorbers should be preferred (as broadband as possible) and diffusers do not work or are even harmful. You now write the opposite.

As I said, I know nothing better but certainly much worse than you. But you make it sound as if the use of diffusers in small rooms is relatively clear and unambiguous - is that so?

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. :)
 

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or to the wall behind my listening position.
I used 3' x 6' absorption panels behind my head in a 24' x 14' x 9 ' rectangular room with large archways at each end of the room and the speakers along the long wall and it sounded fantastic. Then a peep here at ASR used diffusers behind his head and said the room sucked with them there so he put them on the front wall. I think for acoustician laymen such as ourselves your approach of adding a panel or two at a time is a good approach.
 

youngho

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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.
Though placement and spacing do matter, central > peripheral, also multiple smaller pieces > single larger one, as per Toole (in Sound Reproduction) and Sauro as previously linked
 

goat76

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I used 3' x 6' absorption panels behind my head in a 24' x 14' x 9 ' rectangular room with large archways at each end of the room and the speakers along the long wall and it sounded fantastic. Then a peep here at ASR used diffusers behind his head and said the room sucked with them there so he put them on the front wall. I think for acoustician laymen such as ourselves your approach of adding a panel or two at a time is a good approach.

I think it all depends on how far from the back wall the listening positioning is. I have about 140 centimeters (4'7 feet) to the wall behind me and I'm not sure which solution is most commonly the best one in my particular case (absorption or diffusion). I'm doing my best to figure that out at the moment, but I'm not in a hurry and let the information (and counter-information) sink in before I make my next move. :)
 

goat76

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Though placement and spacing do matter, central > peripheral, also multiple smaller pieces > single larger one, as per Toole (in Sound Reproduction) and Sauro as previously linked

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.
 

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