Measuring Acoustic Diffusers

[Richard Dale]

I posted about this article on another forum, but didn't get much of a response. Maybe measuring acoustic diffusers has a bit of a limited appeal. The article discusses measuring acoustic diffusers:

 

http://www.enjoythemusic.com/magazine/viewpoint/0420/Understanding_Diffusion_Acoustics_First_Corporation.htm
 

I’m a fan of diffusers and I use Vicoustic Multifuser DC2s and GIK Gotham quadratic diffusers in both the listening rooms I’ve treated. When I was first starting to try out acoustic treatments I had never heard diffusers before and was surprised how much difference even a single DC2 on the back wall could make. Without any absorbers in place they increased the attack of instruments like acoustic guitars at the expense of sounding a bit too bright. I think you need to listen in order to get the right balance between absorption and diffusion - it doesn't seem possible to be objective about that

 

REW is a great program for measuring rooms but as far as I know it can’t tell you much about the effect of diffusers, which is why I found the article the first one I’ve found on the subject.

 

Although this is the 'objective' part of Audiophile Style, and the article is about measurements, I would think it would be great if people with the experience of listening to different sorts of diffusers could describe the differences and where it makes sense to use one sort of diffuser over another, and where best to site them when treating a room

[Archimago]

Hi Richard, thanks for the link.

 

Certainly room treatments like diffusers and absorbers make a huge amount of sense and audible difference. Unfortunately, they're not "sexy" devices and have little visual appeal for the most part 🙂.  Even though they make so much more difference than say... cables 🤨. Furthermore, it might be hard to generalize the "sound" since it very much will depend on the room characteristics.

 

Alas, I'm one of those guys who has a few shelves of LPs behind the listening spot to act as "diffusers" so can't say I have any experience with this but would also be curious about other's experiences...

[Richard Dale]

8 hours ago, Archimago said:

Hi Richard, thanks for the link.

 

Certainly room treatments like diffusers and absorbers make a huge amount of sense and audible difference. Unfortunately, they're not "sexy" devices and have little visual appeal for the most part 🙂.  Even though they make so much more difference than say... cables 🤨. Furthermore, it might be hard to generalize the "sound" since it very much will depend on the room characteristics.

 

Alas, I'm one of those guys who has a few shelves of LPs behind the listening spot to act as "diffusers" so can't say I have any experience with this but would also be curious about other's experiences...

I tend to be a bit of a 'one trick pony' in that whenever someone says they've got a problem with their system, my first thought is to make the room sound better, with acoustic treatment. But when I do the reply is often 'I would end up getting divorced if I put up some acoustic panels in my listening room'. One guy said that, and later he posted a picture of his room - it had bare white walls with no decoration of any sort, and the HiFi system was surrounded by cables all over the place. A few attractive panels would have made all the difference to the dull appearance of the room as well as improving the sound.

 

I think acoustic panels can be actually visually 'sexy', and improve the appearance of a room. Particularly a make like Artnovion whose panels are quite expensive but look like works of art. I've got a couple of black Vicoustic DC2 diffusers either side of a picture (part of the homage to the square series by Josef Albers), and people who don't know what a diffuser is tend to think they are some kind of sculpture. My niece who is an expert on the history of art thought they diffusers looked like examples of mid 20th century British Constructivist sculpture.

 

I like LPs, but I don't think they are a particular good acoustic treatment for either absorption or diffusion. The measurement technique described in the article would be able to give a nice visual picture of whatever effect they had though.

[Solstice380]

21 minutes ago, Richard Dale said:

The measurement technique described in the article would be able to give a nice visual picture of whatever effect they had though.

 

I've worked on the acoustics in my listening space and it is well worth the effort.  I'm "stuck" in a man-cave mostly concrete wall basement "area".  It's 1/4 of the whole basement - half the width on one end with a room next to it, and open to the rest.  I've played with a few different diffusers and absorbers so I am really interested in getting a good topic / discussion going on this.  I agree it's as important as which cables and probably even most DACs!

 

Proper diffusers are based designed on a mathematical formula.  Not exactly sure that all of the "cubist architecture" ones are, but the slotted and linear types are.  I have a Dayton mic so I was able to do measurements - but at the time the software was poor so couldn't save them.  I started with the cheap essentially styrofoam type of linear on the front wall.  It definitely improved the soundstage and reduced what I thought was too much "directivity" from the front concrete wall.  The waterfall decay plots smoothed out but still had a lot of energy in the higher frequencies.  I balanced the diffusers with some of the 2" acoustic foam panels and that improved things.  But, I ended up taking out the diffusers and using 2 4" RealTraps panels with the foam.  I think it was in Jim Smith's book "Get Better Sound" that said diffusers shouldn't be used on the front wall.  (More on that later)  This really tightened up the imaging so I was convinced that absorption panels "on my front wall" was the way to go, maybe because it is concrete.  I also used the foam corner pieces to knock down the bass buildup and that helped clear up things.  The "rear wall" is open to the rest of the basement with half-height record racks so I don't have issues from that to deal with.  Pic attached of the way it ended up sounding best and measuring decently.

 

Through the mis-fortune of a flood in the basement, I was able to replace everything up to 18" high with current generation (thanks replacement cost insurance!) so I decided to investigate other available products.  Man there are a lot of ways to skin this cat!  There is a ton of info - and some of it technical - on the manufacturers' websites like GIK and RPG Acosutic, etc.  I had heard good thing about GIK and found the good info on their site supported their products.  I gave them my room layout and construction and they made recommendations.  So I got some 2' x 4' x 4" panels - both diffusers and absorbers, and some custom height corner bass traps.  Wow, everything was significantly better from the start with these panels compared to the foam crap!!!  They recommended using the diffusers on the front wall and absorbers on the side walls, at the reflection points.  I first set the room up this way but didn't like the sound - imaging was fuzzy with elements of the sound too blended together.  I didn't do measurements, which I should have, but knowing the "sound" of my room I felt good winging it and I swapped the absorber and diffuser panels.  Voila!  Great individual performer focus, properly placed in a full soundstage that is outside the speakers.  Does the psychedelic part of Led Zep's "Whole Lotta' Love" spin around your head?  If so, your setup is good. 😎  The addition of the hanging quilt my wife made for me ehlps achieve the recommended "30%" front wall coverage I found recommended on a couple of those web sites.  Pic of current arrangement attached.

 

Have you guys observed the same differences?  Imaging improvements, any overdamping (bad), too diffuse, long decay, slap echo?  Bass modes are tough for box rooms so I think I'm lucky having the open space behind.  Can't load up the room but I can turn it up way too loud before any disturbing issues pop like a bass mode or shrill treble.

 

[Richard Dale]

7 hours ago, Solstice380 said:

 

I've worked on the acoustics in my listening space and it is well worth the effort.  I'm "stuck" in a man-cave mostly concrete wall basement "area".  It's 1/4 of the whole basement - half the width on one end with a room next to it, and open to the rest.  I've played with a few different diffusers and absorbers so I am really interested in getting a good topic / discussion going on this.  I agree it's as important as which cables and probably even most DACs!

 

Proper diffusers are based designed on a mathematical formula.  Not exactly sure that all of the "cubist architecture" ones are, but the slotted and linear types are.  I have a Dayton mic so I was able to do measurements - but at the time the software was poor so couldn't save them.  I started with the cheap essentially styrofoam type of linear on the front wall.  It definitely improved the soundstage and reduced what I thought was too much "directivity" from the front concrete wall.  The waterfall decay plots smoothed out but still had a lot of energy in the higher frequencies.  I balanced the diffusers with some of the 2" acoustic foam panels and that improved things.  But, I ended up taking out the diffusers and using 2 4" RealTraps panels with the foam.  I think it was in Jim Smith's book "Get Better Sound" that said diffusers shouldn't be used on the front wall.  (More on that later)  This really tightened up the imaging so I was convinced that absorption panels "on my front wall" was the way to go, maybe because it is concrete.  I also used the foam corner pieces to knock down the bass buildup and that helped clear up things.  The "rear wall" is open to the rest of the basement with half-height record racks so I don't have issues from that to deal with.  Pic attached of the way it ended up sounding best and measuring decently.

 

Through the mis-fortune of a flood in the basement, I was able to replace everything up to 18" high with current generation (thanks replacement cost insurance!) so I decided to investigate other available products.  Man there are a lot of ways to skin this cat!  There is a ton of info - and some of it technical - on the manufacturers' websites like GIK and RPG Acosutic, etc.  I had heard good thing about GIK and found the good info on their site supported their products.  I gave them my room layout and construction and they made recommendations.  So I got some 2' x 4' x 4" panels - both diffusers and absorbers, and some custom height corner bass traps.  Wow, everything was significantly better from the start with these panels compared to the foam crap!!!  They recommended using the diffusers on the front wall and absorbers on the side walls, at the reflection points.  I first set the room up this way but didn't like the sound - imaging was fuzzy with elements of the sound too blended together.  I didn't do measurements, which I should have, but knowing the "sound" of my room I felt good winging it and I swapped the absorber and diffuser panels.  Voila!  Great individual performer focus, properly placed in a full soundstage that is outside the speakers.  Does the psychedelic part of Led Zep's "Whole Lotta' Love" spin around your head?  If so, your setup is good. 😎  The addition of the hanging quilt my wife made for me ehlps achieve the recommended "30%" front wall coverage I found recommended on a couple of those web sites.  Pic of current arrangement attached.

 

Have you guys observed the same differences?  Imaging improvements, any overdamping (bad), too diffuse, long decay, slap echo?  Bass modes are tough for box rooms so I think I'm lucky having the open space behind.  Can't load up the room but I can turn it up way too loud before any disturbing issues pop like a bass mode or shrill treble.

 

 

 

 

The 'cubist sculptures' that look like diffusers probably wouldn't work very well as actual diffusers, but they do look similar.

 

I hadn't heard about the 'Get Better Sound' book recommending not to put diffusers on the front wall. Putting them in the center front seems to be the most common position that is used with HiFi systems. In the two rooms I've treated I've put them on the front and rear walls and never tried the side walls. I use GIK panels with scatter panels at the sides, rather than pure absorbers though - I don't know how much difference scatter panels make.

 

Here are my diffusers - 2 Vicoustic DC2 Multifusers and a GIK Gotham 2d quadratic diffuser each side. I can't put them in the middle as there is a window in the way.

 

 

I my other smaller room I've got the same diffusers but in the center:

 

 

I'd like to try GIK GridFusers next as they are a 1d diffuser, and I can compare them with the Vicoustic skyline ones and see if they sound any different.

 

[Solstice380]

14 hours ago, Richard Dale said:

I use GIK panels with scatter panels at the sides

 

Nice setups!

 

You can see the GIK (2d he calls it, I think?) panels on my front wall there where I first put them.  The soundstage was too... well, diffuse!  I think it is because of the massive concrete wall behind that I got better imaging and instrument location with the 4" absorber panels.  I put those on the side wall reflection points.  

 

Have tried with / without coverings on the window?  Windows and big screen panels between speakers often cause directivity of the reflections.

[Richard Dale]

13 minutes ago, Solstice380 said:

 

Nice setups!

 

You can see the GIK (2d he calls it, I think?) panels on my front wall there where I first put them.  The soundstage was too... well, diffuse!  I think it is because of the massive concrete wall behind that I got better imaging and instrument location with the 4" absorber panels.  I put those on the side wall reflection points.  

 

Have tried with / without coverings on the window?  Windows and big screen panels between speakers often cause directivity of the reflections.

I think you need to combine diffusion with absorption even at the first reflection points. The panels with the 2d pattern that looks like a punched card would do that, and they’re not pure diffusion. I’ve got GIK A series panels at the sides with the same pattern as your black bass traps at the sides and they are supposed to be 1d diffusers I believe.

 

I’ve looked at acoustic curtains to go over the window in the center made by a German company called HOFA. But first there is a room mode with a big peak at 87 Hz that I want to try and treat with a couple of half width Tri-Traps above the diffusers and maybe a couple of Scopus traps tuned to 87 hz below the diffusers. I’ll see what the imaging is like after that, before getting any curtains as I don’t want to over damp the room.

[Solstice380]

3 minutes ago, Richard Dale said:

I think you need to combine diffusion with absorption even at the first reflection points.

 

Agreed.  That's why I moved those from the front to the side walls.  They seem to have a good combo of absorption and diffusion.  I hear no ill effects from the side walls.  I also have the absorber panels on the side walls directly even with the speakers.  I sent my mic out to get an individual calibration and it's back so I will start doing some measurements again.  Like you said, sometimes you can't see the impact of diffusion in decay or FR plots you just hear it.

[semente]

Some people like the widened soundstage and more immersive effect which early reflections produce, and it also helps to make the speakers disapear as sound sources which can be an advantage with lesser systems.

Others like myself do not because the phantom images become fuzzier and the tonal balance can also be affected depending on the dispersion characteristics of one's speakers.

 

Absorption in the early reflection zones is generally viewed as harmful because it may make the sound too dead and doesn't attenuate all frequencies evenly.

Peter D'Antonio created a layout he called the Reflection-Free Zone where the goal is to avoid early reflections in and around the listening spot by deflecting reflectied sound towards the back of the room and then diffusing it, thus delaying the arrival of the "room" sound and attenuating its amplitude:

 

 

By doing so the listener can hear a clear distinction between direct sound and reflected sound, and attain a better perception of the recorded ambience and location cues, as explained in this webpage:

 

http://arqen.com/acoustics-101/reflection-free-zone/

 

This figure compares the impulse response of an untreated room with that of an RFZ design:

 

 

 

 

[PYP]

Interesting topic and great information.  Since there seemed to be a bit of congestion in my room, I tried two GIK Gotham quadratic diffusers to start.  Because of other wall hangings, shape of room, aesthetics, etc., there wasn't a lot of choice for placement.  Hung the two diffusers between the speakers.  That got the sound closer to what I had hoped for so I added two more.  To match the decor and an accent wall, I spray painted the diffusers.  I've always thought the sound of the room benefited by the architecture:  you can't see it from this photo, but the wall behind the speakers is open (that is, the wall doesn't reach the ceiling), the right side of the room opens to other rooms and the ceilings slope upwards to about 15' with the center of the slope being right of the right speaker.  The floors are cork.  It worked out well, even if I didn't go about it in an objective way, which might have been a better route (and I would know more about the resulting measurements).  

[Richard Dale]

1 hour ago, PYP said:

Interesting topic and great information.  Since there seemed to be a bit of congestion in my room, I tried two GIK Gotham quadratic diffusers to start.  Because of other wall hangings, shape of room, aesthetics, etc., there wasn't a lot of choice for placement.  Hung the two diffusers between the speakers.  That got the sound closer to what I had hoped for so I added two more.  To match the decor and an accent wall, I spray painted the diffusers.  I've always thought the sound of the room benefited by the architecture:  you can't see it from this photo, but the wall behind the speakers is open (that is, the wall doesn't reach the ceiling), the right side of the room opens to other rooms and the ceilings slope upwards to about 15' with the center of the slope being right of the right speaker.  The floors are cork.  It worked out well, even if I didn't go about it in an objective way, which might have been a better route (and I would know more about the resulting measurements).  

The Gothams look good. The colour isn’t obvious - it looks like natural varnish to me. I spray painted the Gothams black in my larger room. I started off using a brush, but it was going to take forever with all the nooks and crannies. Spray painting worked better, but it was still a lot of effort. Although it’s great you can paint them, it would be nice if GIK offered some already finished options, particularly black. Your location at center front seems the most popular for HiFi systems, but it would be nice if we could measure what was going on as per the original article from Enjoy the Music.

[PYP]

7 hours ago, Richard Dale said:

The Gothams look good. The colour isn’t obvious - it looks like natural varnish to me. I spray painted the Gothams black in my larger room. I started off using a brush, but it was going to take forever with all the nooks and crannies. Spray painting worked better, but it was still a lot of effort. Although it’s great you can paint them, it would be nice if GIK offered some already finished options, particularly black. Your location at center front seems the most popular for HiFi systems, but it would be nice if we could measure what was going on as per the original article from Enjoy the Music.

 

Thank you.  Agree that offering finished options would be an improvement.  I started with a brush too.  My "measurement" was my wife's ears.  After the four were installed, but still unpainted, she loved the sound so much that she told me not to paint them if it changed the acoustics!  A before and after measurement would have been very interesting...