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1D diffusor - vertical or horizontal?
Old 24th September 2012
  #1
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🎧 10 years
1D diffusor - vertical or horizontal?

Couldn't find info on that...

When looking at studio/treated room pics mostly diffusors (1D, not the Skylines...) are installed vertically. If there's lots of diffusors vertical and horizontal ones are combined.

When would you choose to hang such a diffusor horizontally over vertically?
Old 25th September 2012
  #2
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Ethan Winer's Avatar
 
🎧 15 years
Lightbulb

The orientating determines which direction reflected waves are sent. In most (control) rooms it's better to spread them out horizontally around the room, rather then up toward the ceiling or down toward the floor.

--Ethan

The Acoustic Treatment Experts
Old 25th September 2012 | Show parent
  #3
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Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Ethan Winer ➡️
The orientating determines which direction reflected waves are sent. In most (control) rooms it's better to spread them out horizontally around the room, rather then up toward the ceiling or down toward the floor.
+1


Some general considerations regarding control room treatment and placement of diffusers:


First of all, “RTxx” (RT60/45/30 etc; Reverberation Time) does not exist in small acoustic spaces (“SAS”). “Decay time” might be a valid term sometimes but in general, all we are really interested in is the shape of the ETC (and perhaps the slope of the linear fit (after sparse reflections) of the Schroeder integral, in order to evaluate the “decay times” at higher frequency bands.

Since all design concepts share the same (more or less) criteria’s for the lower frequency range (below about Schroeder); = good modal control and as low decay time as the rest of the frequency range (or preferably even lower) and naturally; an as even frequency response as possible; we´ll focus the rest of this discussion on the range above the modal range from now on since this is where the various design philosophies differ.

In order to advise on placement of acoustic treatment and diffusers in particular, one first needs to decide what acoustic response (speaker-listener response primarily, but environment response might also be important) we are trying to accomplish in the room. Assuming a studio control room; the more common options are: LEDE/RFZ (or possibly CID), NE (or any of the variants of it) or perhaps “Ambechoic” if surround formats are important (or at least something similar to it; like a LEDE/RFZ but no termination of the “ISD-gap” but still featuring a “decay time” of about 0,3 seconds by a highly diffused sound fled).

If hi-fi listening room (not critical listening), there are no rights or wrongs, but I would still personally try to at least avoid early strong reflections and try to create some kind of diffuse return to the listening position in order to keep some life in the room instead of ending up with a “dead” sounding space (unless this is what is requested naturally). The criteria’s of LEDE/RFZ would be my first choice, or perhaps something in-between LEDE/RFZ and Ambechoic (a proper termination, no termination, or limited termination of the ISD-gap assuming highly diffuse decaying sound field). Also, since we´re talking about placement of diffusers, NE design is probably not of much interest, especially for normal listening rooms since this approach tries to achieve an anechoic speaker-room response although one can use diffusers even if NE in order to keep the general room response somewhat alive (but without scattering too much speaker energy to the sweet spot thus deteriorating the anechoic speaker-listener response).

Assuming we strive for a LEDE/RFZ (or possibly CID) response, we first need to select an ISD-gap and this is either done by simply measuring the room and identifying the first order reflection from the rear wall, or calculating the time difference between the direct sound and the reflection from the rear wall based on the geometry, and then deciding if this is an appropriate ISD-gap (between about 12-25 ms). If the control room is connected to a large recording room, the live room usually dictates the ISD-gap needed in the control room. Preferably, the ISD-gap in the control room needs to be at least about 3-5 ms longer than the recording rooms generic ISD-gap). If the distance to the rear wall in the control room is too short to provide a sufficient ISD-gap, treatment and/or geometry can be used to extend the natural ISD-gap of the room (by using absorption and/or splayed walls on the first reflection point on the rear wall and using rotated 1D diffusers on side walls for instance).

If a less strict treatment is requested, then at least try to avoid placing diffusing elements in such a way that they scatter early energy back to the listening position within about 10-12 ms or earlier compared to the direct sound. I would personally try to extend this period to at least about 15-17 ms, 20-25 ms if possible (a longer ISD-gap allows you to hear the acoustical footprint of the recording easier, especially of larger recording rooms). Use geometry and/or absorption to redirect/absorb early energy (away) from the listening position that would otherwise arrive too soon (within the desired ISD-gap).

If absorption is used, make sure to use thick panels so that you don´t simply “EQ” the reflections, only removing the high midrange and highs from it, leaving the low mids and bass frequency range unaffected. Use at least 120 mm, preferably 200-300 mm or deeper (and make sure to use a wool with appropriate flow resistivity for the given depth). Only use broadband absorption where needed, or you´ll struggle to keep the energy needed to keep the room “alive” (in order to reach the desired gain of the ISD-gap termination).

Use the ETC to track down your early reflections and figure out what areas needs attention. Also, remember that diffusers also absorb energy more or less. One cannot “add” energy to a room by adding diffusers unless replacing treatment that absorbs more than the diffuser replacing it. Just adding diffusers to a room does not automatically make it sound “more spacious”, it´s the combination of all treatment in a well thought out design that achieves this.

The energy return (the termination of the ISD-gap) should arrive primarily from the rear sides in a LEDE/RFZ/CID room and this is the reason why you normally see 1D diffusers on the rear wall in such rooms. As stated above, if your room is too short to provide a sufficient ISD-gap using the rear wall, one can extend this gap by various treatment options but assuming the room is not too short (or too long); the rear wall is the most efficient place to put 1D diffusers, since they will scatter the sound to the sides and then back to the listener via the rear side walls.

Assuming one understands that diffusers also absorbs energy (more or less) and that we are now probably striving away from LEDE/RFZ and moving towards the Ambechoic response; one can add diffusers to other surfaces as well as long as they don’t (partially) scatter energy back to the sweet spot within the ISD-gap (with or without termination).

A note on low frequency treatment (modes and SBIR related issues): I recommend pressure based absorbers for the bass region for two reasons: First, they don´t need to be ridiculously deep in order to be effective at low frequencies and secondly, they don´t absorb the upper range that one usually struggle to preserve in order to achieve a proper termination of the ISD-gap and the semi diffuse field that should follow it (assuming LEDE/RFZ/CID design or Ambechoic with decent “decay times”).

For proper use of any acoustic treatment; measure and analyse your room and decide on a response model to use as a guide when deciding on different treatment options. I know this might sound daunting, but the alternative is usually a less than perfect outcome but if you´re happy with that: build/buy some panels and fire away!


More on topic here:
eigenmodes calculator
ISD gap for my room help pls!
My diffusor design - is it ok?
Help: Studio is too loud
Old 27th September 2012
  #4
Lives for gear
 
🎧 10 years
Thx for your replies!

Wow, Jens, I guess that's gonna be one of your reference posts that you'll hand a link to every once in a while!
I'm gonna have to look up some of those abbreviations and read that again...!

While my question was out of general interest, in my case right now I was thinking about where to hang these diffusors I've got around now.
Since it is a small room at home for rough songwriting and listening/mixing purposes I guess I wouldn't have to hang them anywhere.

I've attached a Google Sketchup to this post where you can see the situation.
There is bass trapping and I like the diffusors in the back side walls but my main question is about the ones that are cut in half (not yet) and hung above the bass traps.

In this horizontal position they would scatter some sound back to my listening position but I felt it was still better than blank wall.

I had all 4 hanging in that sloped ceiling part but didn't like it.
I didn't have any flutter to begin with...

Where would you hang them? Would you use them at all in that kind of room?
Attached Images
File Type: jpg Music room Sketchup shot 2.jpg (57.2 KB, 2511 views) File Type: jpg Music room Sketchup shot 3.jpg (64.1 KB, 1517 views) File Type: jpg Music room Sketchup shot 1.jpg (44.1 KB, 1394 views)
Old 27th September 2012 | Show parent
  #5
Gear Guru
 
Ethan Winer's Avatar
 
🎧 15 years
Lightbulb

Diffusers work best when they're in the "line of fire" of sound from the speakers. You show them out of the way of direct sound, so I don't see a lot of benefit there. In fact, ceiling corners are better for bass traps.

--Ethan
Old 27th September 2012 | Show parent
  #6
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Ethan Winer ➡️
Diffusers work best when they're in the "line of fire" of sound from the speakers. You show them out of the way of direct sound, so I don't see a lot of benefit there. In fact, ceiling corners are better for bass traps.

--Ethan
Hi Ethan,

the problem is, there's not really any space in the line of fire left.
It's me, then 2 6'' bass traps in front of the window...

For the moment, I can't add more bass trapping as I just recently installed as many as I could afford, which was a huge improvement on the sound.
Old 28th September 2012
  #7
Lives for gear
 
🎧 10 years
Sry for double post.

Would the diffusor setup in the attached pic make sense (in front of the bass traps) or are they just too close to the listening spot?
Attached Images
File Type: jpg Music room Sketchup shot 4.jpg (51.4 KB, 1387 views)
Old 28th September 2012
  #8
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kasmira's Avatar
 
🎧 10 years
Holy cow Jens. Bookmarked for future reference. Killer post! Is that all new content you just wrote? I sense you linking to it often in the future...
Old 28th September 2012 | Show parent
  #9
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kasmira's Avatar
 
🎧 10 years
Quote:
Originally Posted by Ciaccona ➡️
Sry for double post.

Would the diffusor setup in the attached pic make sense (in front of the bass traps) or are they just too close to the listening spot?
Much better placement, though I'm not quite certain whether you're too close or not. How far of a distance will your head be from the front face of the diffusers?

Edit: Another possible idea would be to have angled reflectors on the back wall that could send the sounds direct from the monitors, off the angled reflection panels, to the side walls where they could be diffused. Just an idea, not sure on practicality.
Old 28th September 2012
  #10
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gullfo's Avatar
 
🎧 10 years
maybe use 1/2 that number and space them out so the level returned is lower but still providing some information back to the seat position.
Old 28th September 2012 | Show parent
  #11
Lives for gear
 
Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Ciaccona ➡️
While my question was out of general interest, in my case right now I was thinking about where to hang these diffusors I've got around now.
Since it is a small room at home for rough songwriting and listening/mixing purposes I guess I wouldn't have to hang them anywhere.

I've attached a Google Sketchup to this post where you can see the situation.
There is bass trapping and I like the diffusors in the back side walls but my main question is about the ones that are cut in half (not yet) and hung above the bass traps.

In this horizontal position they would scatter some sound back to my listening position but I felt it was still better than blank wall.

I had all 4 hanging in that sloped ceiling part but didn't like it.
I didn't have any flutter to begin with...

Where would you hang them? Would you use them at all in that kind of room?
https://gearspace.com/board/8020723-post4.html
https://gearspace.com/board/7972534-post8.html



Quote:
Originally Posted by Jens Eklund ➡️
For proper use of any acoustic treatment; measure and analyse your room and decide on a response model to use as a guide when deciding on different treatment options. I know this might sound daunting, but the alternative is usually a less than perfect outcome but if you´re happy with that: build/buy some panels and fire away!


More on topic here:
eigenmodes calculator
ISD gap for my room help pls!
My diffusor design - is it ok?
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