General Asylum

General audio topics that don't fit into specific categories.

Return to General Asylum

Message Sort: Post Order or Asylum Reverse Threaded

Diffusion over the listening position

75.66.101.2
Posted on July 13, 2015 at 20:10:12
Bigby
Audiophile

Posts: 85
Location: Southern US
Joined: May 28, 2010
 I have 6 RPG Omniffusors over the listing position. I recently made some changes to my room and I have 6 extra ones. I was thinking of adding them to the ones overhead to make a solid array of diffusion over the listening position. I listen to a lot of classical music. Will the added diffusion give me a more spacious feel of a concert hall and what are the advantages and disadvantages?

I've included a link to pictures my listening room. The room has been acoustically treated and measured. It sounds pretty good now. I wanted to get some opinions before making the next round of changes.

 

Hide full thread outline!
    ...
RE: Diffusion over the listening position, posted on July 14, 2015 at 00:21:37
bwaslo
Manufacturer

Posts: 245
Location: Portland, OR USA
Joined: September 10, 2006
 If I were you, I'd put them on the back wall, behind you. If they can be 5ft or more behind you and catch enough of the speaker sound that goes past you (returning it to you diffused 10msec or so later, called a 'kicker'), that can make a large difference in apparent room size and particularly image depth. I'd even take some off the ceiling to put more behind you.
_

Make easy high performance diffusors:-->http://www.libinst.com/diffusers/Depot_Diffuser.html

Horn Design Spreadsheet:--> http://libinst.com/SynergyCalc/

SmallSyns:-->http://www.diyaudio.com/forums/multi-way/292379-s

 

RE: Diffusion over the listening position, posted on July 14, 2015 at 00:40:21
bwaslo
Manufacturer

Posts: 245
Location: Portland, OR USA
Joined: September 10, 2006
 Though I see that what you have are 2d diffusers. What I described above works best with 1d (horizontal spread) diffusers. With 2d, scattered energy goes in all directions, much of it only to be absorbed in furniture, rugs, or other treatments. I.e., it may as well (and more easily) could just have been absorbed in the first place rather than diffused. 1d is more controlled, able to return enough to be perceived as ambience.
_

Make easy high performance diffusors:-->http://www.libinst.com/diffusers/Depot_Diffuser.html

Horn Design Spreadsheet:--> http://libinst.com/SynergyCalc/

SmallSyns:-->http://www.diyaudio.com/forums/multi-way/292379-s

 

RE: Diffusion over the listening position, posted on July 14, 2015 at 07:04:26
genungo
 Those 2D diffusors would probably do the most good up on the ceiling. I would expect better diffusion and a more spacious sound with additional panels up there. You can try spreading them around the room but I'm guessing that you would be hesitant to mar your ceilings and walls with too many *experimental* mounting holes. If you're not in the mood to experiment, I'd put them all up on the ceiling and be done with it. I really don't think you can guess how things will sound, though - you've got to try things out.

I've never heard of anyone complain about having too much diffusion overhead.

 

Diffusion on the ceiling FIRST-REFLECTION REGION is better than over the listening position, posted on July 14, 2015 at 07:51:52
John Marks
Manufacturer

Posts: 7806
Location: Peoples' Democratic Republic of R.I.
Joined: April 23, 2000
 So, assuming that the ceiling first-reflection region is not covered at present (hard to judge from the photos, as helpful as they are), I'd put the extra diffusors there, especially because your back wall is already treated.

I attach a link to a Stereophile column of mine on how to determine reflection points using only a tape measure, string, and a helper.

Best of luck,

John Marks

 

RE: Diffusion over the listening position, posted on July 16, 2015 at 05:39:29
Dave_K
 First of all, kudos for putting serious effort into room acoustics. I've put a lot of effort into it as well and I'm kind of disappointed that more audiophiles don't bother to measure and treat their rooms.

I'm a little confused by the pictures because in one shot it looks like you have absorbers on the ceiling and in the other it looks like there are diffusors. For this post, I'm going to assume you have absorbers on the ceiling in the front half of the room covering the first reflection points and diffusors on the ceiling in the rear half above the listening position. If I'm interpreting it wrong, please correct me.

Assuming the above, I don't think adding 6 more 2x2' diffusors to the 6 you already have up there will make a significant difference. If it were me, I would start by relocating the existing 6 diffusors so they are all together above the listening position in a tight grouping, and only then consider adding more.

I have another, separate suggestion. It looks like you have 2" thick absorber panels on the side walls in the front of the room flanking the speakers and in the rear of the room flanking and behind the listening position. I see what looks like 3 2x4' panels and 2 4x4' panels. Given their locations, I don't think they're doing much other than taking some reverb out of the room. At the side wall first reflection points I see 1-d QRD type well diffusors. These diffusors work best at low angles of incidence (near face on) and not so well at oblique angles. So they may not be the best treatment for first reflections except in wide rooms where the speakers are far away from the side walls. I think you might be better off putting two of the 2x4' absorbers at the side wall first reflection points (preferably mounted horizontally) and moving the diffusors back.

And then I would consider taking out the 4x4' absorbers, to increase RT60 a bit and hopefully make the room sound more spacious without introducing flutter echo. If you do get some flutter echo, you could use the spare diffusors you were going to put on the ceiling.

 

RE: Diffusion over the listening position, posted on July 16, 2015 at 10:02:48
Inmate51
 Your biggest problem is the 8 foot ceiling. I suspect that isn't going to change, though.

If you want to make the room sound larger, making it more dead is not the way to go. That will make it sound smaller. And diffusion won't help, either.

Diffusion is a whole 'nuther issue. The purpose of diffusors is to scatter the sound when the surfaces of a room, or its furnishings, don't adequately do the job. Even then, "which" diffusors to use is important. The size and depth of the wells in a pre-built diffusor will affect some frequencies and not others. This is because of the different wavelengths at various frequencies. For example, a 100 Hz tone won't even see a three-inch diffusion well.

People who advocate "treating" the first reflection points are often misguided. The "first reflection points" make the soundstage wider and taller. Our ears and brain integrate sound which arrives within several milliseconds into one cohesive sound. If you want to widen your soundstage, keep the first reflections.

To sum up, diffusors and absorbers are two different things. If you want a larger sounding room, diffusion "may" be good, absorption is not good.

For folks who want to learn more, most of this is discussed in detail in Everest's "Master Handbook of Acoustics" and in Knudsen & Harris's "Acoustical Designing in Architecture".

:)

 

RE: Diffusion over the listening position, posted on July 16, 2015 at 17:10:53
Dave_K
People who advocate "treating" the first reflection points are often misguided. The "first reflection points" make the soundstage wider and taller. Our ears and brain integrate sound which arrives within several milliseconds into one cohesive sound. If you want to widen your soundstage, keep the first reflections.


A very live room with a lot of reflections produces a room full of sound, but not a bigger soundstage. A wall of sound is not a soundstage.

My experience is obviously contrary to yours.

The first things I noticed when starting to treat first reflection points is that imaging became more precise, depth of stage improved, and ambient information on acoustic recordings improved. The next thing I noticed was that recordings with spatial effects processing like QSound became much more convincing. Third, with some minimally miked recordings, the soundstage got a bit larger overall. Studio recordings with a lot of panned mono didn't really grow or shrink in width or height, but I did get a better sense of depth after treatment.

Also, in my room with 8 foot ceiling, I found that treating the first reflection points on the ceiling yielded a much bigger improvement than treating the first reflection points on the side walls.

 

RE: Diffusion over the listening position, posted on July 16, 2015 at 19:00:36
fantja
Audiophile

Posts: 15524
Location: Alabama
Joined: September 11, 2010
 Very nice room + gear, Bigby.

 

RE: Diffusion over the listening position, posted on July 30, 2015 at 07:39:44
Bigby
Audiophile

Posts: 85
Location: Southern US
Joined: May 28, 2010
 Thank you for your response.

The absorbers on the ceiling are GIK 244's. They cover the first overhead reflection points from the speakers.

The sidewall first reflect points are treated with RPG Abffusors. They are designed to give near field diffusion and broader bass absorption than flat panels at the first reflection point.

Per your suggestion I'm going to move the diffusors on the ceiling over the listening position closer together then a the extra diffusors to the ceiling.

Bigby

 

RE: Diffusion on the ceiling FIRST-REFLECTION REGION is better than over the listening position, posted on July 30, 2015 at 07:47:02
Bigby
Audiophile

Posts: 85
Location: Southern US
Joined: May 28, 2010
 John,

Thank you for your response and link. I'm going to use the string method to re-look at adding broadband absorption to the sidewall - ceiling corners. I already have broadband absorption at the front and back - ceiling corners. It made a big difference in the cleaning-up the sound.

Kind Regards,

Bigby

 

Page processed in 0.035 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]