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Does my room need diffuser?
Old 1st October 2010
  #1
Gear Nut
 
Rairun's Avatar
 
🎧 10 years
Does my room need diffuser?

Hi,
My room's dimensions are: 437 L x 306 W x 270 H cm (I'm approximately 260-270 cm away from the back wall). Do you think i should use diffuser on the back wall instead of absorption?(I definitely don't want a too dead room) If yes, what type of diffuser you suggest me to build? And time is not a concern for me these days, so you don't need to consider ease of building when suggesting.
Thanks.

(Btw, i built corner bass traps and broadband absorbers for the FR zones.)

*I forgot the mention that there is a door on the right and a large column on the left of the back wall. So the area needs be treated is 115 cm wide.
Old 1st October 2010
  #2
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
wow big room. Yes diffusion would be great in there. A QRD would be fine I would think.
Old 1st October 2010 | Show parent
  #3
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Rairun's Avatar
 
🎧 10 years
Quote:
Originally Posted by Glenn Kuras ➑️
wow big room. Yes diffusion would be great in there. A QRD would be fine I would think.
Really? I thought my room was not big enough for a home studio heh.

Speaking of QRD diffuser, i'm planning to build four of this one for back wall:
PME Records QRD Diffusor Construction
The problem is that there is only 115 cm available on the back. Two adjacent QRD panels are 120 cm wide. I wonder if diffuser will loose its effectiveness if i build some of them as one array missing. I mean:
Old 1st October 2010 | Show parent
  #4
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Glenn Kuras's Avatar
 
🎧 15 years
Hold on. I thought it was in inches.
Yes a small room. You can use diffusion on the back wall but I still would put some absorption for the low end nulls and peaks.

Sorry about that.
Old 1st October 2010 | Show parent
  #5
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Rairun's Avatar
 
🎧 10 years
Quote:
Originally Posted by Glenn Kuras ➑️
Hold on. I thought it was in inches.
Yes a small room. You can use diffusion on the back wall but I still would put some absorption for the low end nulls and peaks.

Sorry about that.
I knew something was wrong, you broke my heart, he he .
I have absorption panels, i'm just curious that if it is worth building diffusers instead of absorption panels for back wall. If my room won't benefit much from diffusion then i don't want to waste time and money.
Old 2nd October 2010 | Show parent
  #6
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Ethan Winer's Avatar
 
🎧 15 years
Lightbulb

Quote:
Originally Posted by Rairun ➑️
I have absorption panels, i'm just curious that if it is worth building diffusers instead of absorption panels for back wall. If my room won't benefit much from diffusion then i don't want to waste time and money.
Your room is definitely not too small for diffusors. If you're up for the time and effort needed to make real QRD diffusors, I'm sure that will be a nice touch in the rear of your room. The room used for my company's video Hearing is Believing is only a little larger than yours, and it sounded fabulous when loaded up with diffusion. So you can take that as validation that diffusion would be good in your room too.

--Ethan

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Old 3rd October 2010 | Show parent
  #7
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Rairun's Avatar
 
🎧 10 years
Thank you very much Ethan. Do you have any idea about:

Quote:
Originally Posted by Rairun ➑️
The problem is that there is only 115 cm available on the back. Two adjacent QRD panels are 120 cm wide. I wonder if diffuser will loose its effectiveness if i build some of them as one array missing. I mean:
Old 3rd October 2010 | Show parent
  #8
Lives for gear
 
1 Review written
🎧 10 years
QRDude can calculate a patern with specified well sizes so you can adjust your design to 115 cm without losing a row of wells.
Old 3rd October 2010 | Show parent
  #9
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Rairun's Avatar
 
🎧 10 years
Ok, thanks everybody.
Old 3rd October 2010 | Show parent
  #10
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Glenn Kuras's Avatar
 
🎧 15 years
see the following how I would lay out diffusion in your room.
GIK Acoustics: Room Setup
Old 3rd October 2010 | Show parent
  #11
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Jens Eklund's Avatar
 
🎧 10 years
Confusion regarding diffusion

There seems to be some confusion regarding diffusion.

To properly apply diffusers in a design you must first of all decide how long the ISD-gap should be. If the control room is connected to a recording room then the ISD of the recording room determines the length of the gap in the control room. Once an ISD-gap is decided, diffusers should be placed so that the scattered energy arrives to the listening position after the ISD-gap. If areas are too close to achieve this, one can use 1D diffusers but angled 90 degrees so that the scattered energy is not directed back to the sweet spot but instead reflected to other areas where it might be further diffused by other diffusers. If one wants to be extra picky, diffusers should not be used on areas that creates a specular reflection even after the ISD-gap unless the diffuser is effective above approx. 10-15 kHz.


/Jens
Old 3rd October 2010 | Show parent
  #12
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Rairun's Avatar
 
🎧 10 years
Jeans, i don't know what ISD means. Mine is a home studio. I mostly use vst instruments and sometimes record live guitar or vocal. My priority is mixing, not recording audio. Anyway, here is a drawing of my room. I'm planning to put diffusers to the space between the door and the column (115cm width). And I'm approximately 260-270 cm away from the back wall. I can also make diffusers for back side walls.
Old 3rd October 2010 | Show parent
  #13
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Jens Eklund's Avatar
 
🎧 10 years
ISD = Initial Signal Delay:

Sound system engineering - Google Books

/Jens
Old 3rd October 2010 | Show parent
  #14
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Rairun's Avatar
 
🎧 10 years
Ok, i have been reading for hours and i am still confused.
First i don't know if i should prefer QRD (1D) or Skyline (2D).

Secondly, on his article Ethan says: "Note that for diffusion to be effective, you need to treat more than just a few small areas." The back wall on my room has 115cm width available for diffusing. Is 115 cm small or large enough?

For example, i've exported this design using QRDude:
Quote:
Standard N41+0,0 Panel

Design frequency 600 hz

Number of wells: 41

Deepest well in mm: 280

Fin width in mm: 3

Width of wells in mm: 25

Ratios 0 1 4 9 16 25 36 8 23 40 18 39 21 5 32 20 10 2 37 33 31 31 33 37 2 10 20 32 5 21 39 18 40 23 8 36 25 16 9 4 1

Well depths in mm: 0 7 28 63 112 175 252 56 161 280 126 273 147 35 224 140 70 14 259 231 217 217 231 259 14 70 140 224 35 147 273 126 280 161 56 252 175 112 63 28 7

Block heights in mm: 280 273 252 217 168 105 28 224 119 0 154 7 133 245 56 140 210 266 21 49 63 63 49 21 266 210 140 56 245 133 7 154 0 119 224 28 105 168 217 252 273

Phase shift in degrees 0 8 35 79 140 219 316 70 201 351 158 342 184 43 280 175 87 17 324 289 272 272 289 324 17 87 175 280 43 184 342 158 351 201 70 316 219 140 79 35 8

Scatter 300 Hz Diffuse 600 Hz HF cutoff 6880 Hz

Period width 1148 mm

Minimum distance to seating position 1.72m (3 times wavelength of lowest diffusion frequency)

Good result: Period width of 1148mm is is not less than the design wavelength of 574 mm

Good result: The well width is large enough to avoid viscous losses

Good result: Plate frequency of 24600 hz is higher than HF cutoff of 6880 hz, so it has no effect

Good result: The HF cutoff frequency of 6880 hz is 11.4 times the design frequency of 600 hz

True diffusion frequencies: 600 1200 1800 2400 3000 3600 4200 4800 5400 6000 6600 hz

Current auto-well strategy: Auto-adjust well width so that wells are at least 25mm wide to minimise viscous losses
I can't be sure if this will work with my room.
Old 4th October 2010 | Show parent
  #15
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Ethan Winer's Avatar
 
🎧 15 years
Lightbulb

It depends on where that 115 cm is located. If it's centered behind your head then it's a good place for diffusion.

--Ethan

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Old 4th October 2010 | Show parent
  #16
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Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Ethan Winer ➑️
It depends on where that 115 cm is located. If it's centered behind your head then it's a good place for diffusion.
... unless this area gives reflections arriving within the ISD-gap.

/Jens
Old 4th October 2010 | Show parent
  #17
SAC
Registered User
 
🎧 10 years
Quote:
Originally Posted by Jens Eklund ➑️
... unless this area gives reflections arriving within the ISD-gap.
If it does, a rather simple option is to used angled reflection on the back wall to redirect the energy to rear side wall mounted 1D QRDs and with the additional time offset due to the additional travel distance, redirect said energy back to the ISD in the form of a laterally arriving diffuse field that can serve to terminate the ISD.

And thus all of the bases are covered. heh
Old 4th October 2010 | Show parent
  #18
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🎧 10 years
Quote:
Originally Posted by SAC ➑️
If it does, a rather simple option is to used angled reflection on the back wall to redirect the energy to rear side wall mounted 1D QRDs and with the additional time offset due to the additional travel distance, redirect said energy back to the ISD in the form of a laterally arriving diffuse field that can serve to terminate the ISD.

And thus all of the bases are covered. heh
exactly.
Old 4th October 2010 | Show parent
  #19
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Ethan Winer's Avatar
 
🎧 15 years
Lightbulb

Quote:
Originally Posted by Jens Eklund ➑️
unless this area gives reflections arriving within the ISD-gap.
After doing many experiments I've concluded that diffusion nearby is not as bad as I often see stated. It's still vastly better than a bare wall, and in some cases better than absorption. Of course this is my subjective opinion. But I've done the work to come to this conclusion.

--Ethan

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Old 4th October 2010 | Show parent
  #20
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Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Ethan Winer ➑️
After doing many experiments I've concluded that diffusion nearby is not as bad as I often see stated. It's still vastly better than a bare wall, ...
On this point, I totally agree!


Sincerely Jens Eklund
Old 4th October 2010 | Show parent
  #21
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Rairun's Avatar
 
🎧 10 years
Quote:
Originally Posted by Jens Eklund ➑️
... unless this area gives reflections arriving within the ISD-gap.

/Jens
How will i find out that? I looked at the link you gave but it's hard to understand for me. ( thanks to my poor English and math )
Old 4th October 2010 | Show parent
  #22
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Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Rairun ➑️
How will i find out that? I looked at the link you gave but it's hard to understand for me. ( thanks to my poor English and math )
First, you need to decide on an ISD-gap. Once this is done, you need to calculate the reflection path lengths and compare with measurements. This will tell you which areas are far enough away to give reflections after the ISD-gap.


Sincerely Jens Eklund
Old 4th October 2010 | Show parent
  #23
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Rairun's Avatar
 
🎧 10 years
Quote:
Originally Posted by Jens Eklund ➑️
First, you need to decide on an ISD-gap. Once this is done, you need to calculate the reflection path lengths and compare with measurements. This will tell you witch areas are far enough away to give reflections after the ISD-gap.


Sincerely Jens Eklund
Is this really necessary or can be ignored?
Old 4th October 2010 | Show parent
  #24
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Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Rairun ➑️
Is this really necessary or can be ignored?
Nothing is necessary but if you want to approach this in an "easier" way, you could use the old ”mirror trick” meaning ask a friend to hold a mirror against the walls (and ceiling) and while sitting in sweet spot, looking at the mirror and if you see a speaker in it, use broadband absorption on this surface. The exception being the rear wall; if the distance from you to the rear wall (while sitting in sweet spot) is bigger than approx 3,5 meters, then diffusion is generally recommended.

On all other surfaces, you can use diffusers but it’s not generally wanted to scatter energy back to the sweet spot if it arrives within the ISD-gap. Clever use of 1Ds (rotated in different ways) can solve these problems.


Sincerely Jens Eklund
Old 4th October 2010 | Show parent
  #25
SAC
Registered User
 
🎧 10 years
In the effort to make this easier, you are actually making it MUCH harder than need be!

Calculating distances and times and ....

Why spend your time trying to redesign what a tool already directly provides????

The ETC will 'tell' you ALL of this.

First you select a target response for the room. Do you desire to have a later arriving diffuse soundfield, or not. Maybe you don't know. So perhaps you have two options, a room with a defined and terminated ISD, or a room with a defined and terminated ISD and a later arriving integrated diffuse soundfield (an LEDE),

Thus the ETC will provide you will ALL of the information necessary to see what you are actually dealing with. What you actually have to start with, and it will show you when you have achieved the response as the acoustical response is displayed in terms of the ETC gain and arrival times and spatial/temporal quality f each energy arrival (whether it is focused or diffuse).

By knowing exactly what is happening, you can then select the type of treatment and the precise placement of the sufficient to strategically modify the response in the manner you desire.

And you do this based upon the identification of what REAL 'reflections' are in play! Not possible reflections; not imaginary reflections; but REAL issues, their gain, arrival time, and spatial character - be they specular, diffuse, somewhere in between... So you need NOT run amuck applying absorption where it is not needed and simply deaden the room.

It is easy to identify the effect that each treatment type has upon the gain and spatial character of the signals. So you choose the one, or combination that best achieve that response modification.

It will then guide you through EACH step in the process and provide 'real time' feedback in order to verify exactly what effect the chosen treatment has and if what you are doing is accurately advancing the room response toward the acoustical model that you set out to achieve (and you DID select an acoustical model FIRST that acts as your goal, didn't you??? As if not, they you are simply wandering around in the dark.)

And from this display (and no other source!!) you determine the minimum length of the ISD!

No more abstract how many panels and where do I place them questions. Can/should I use diffusion? How do I know if it worked? No more questions like this at all!

As you strategically and surgically simply treat real issues and manage and redirect energy in a manner to make it correspond to the acoustical response desired.

The process is actually very simple.
Old 5th October 2010 | Show parent
  #26
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Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Jens Eklund ➑️
First, you need to decide on an ISD-gap. Once this is done, you need to calculate the reflection path lengths and compare with measurements. This will tell you witch areas are far enough away to give reflections after the ISD-gap.
If calculations agrees with measurements (which they usually do), it can speed up the process of finding good working solutions, for me at least. Maybe this isn’t as easy for a total beginner (as the OP) so perhaps my advice is confusing at best.


Sincerely Jens Eklund


EDIT: Also, perhaps you missed the quotation marks on “easier” in my earlier post. I meant to be a bit ironic since I personally don’t find this approach to be "easier", but just as you probably think, rather tedious.
Old 5th October 2010 | Show parent
  #27
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Glenn Kuras's Avatar
 
🎧 15 years
Quote:
Originally Posted by Ethan Winer ➑️
After doing many experiments I've concluded that diffusion nearby is not as bad as I often see stated. It's still vastly better than a bare wall, and in some cases better than absorption. Of course this is my subjective opinion. But I've done the work to come to this conclusion.

--Ethan

[/url]
I completely agree. As I would not say it is "bad" to be close to a deeper diffusor, but a matter of getting the full effect with distance. But yes much better then a bare wall.
Old 5th October 2010 | Show parent
  #28
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Ethan Winer's Avatar
 
🎧 15 years
Lightbulb

Quote:
Originally Posted by Rairun ➑️
Is this really necessary or can be ignored?
Forget the math and use this simple guideline which, again, I don't necessarily agree with:

For every inch of diffusor depth, your ears (or a microphone or acoustic instrument) should be at least one foot away from the diffusor. So for a QRD diffusor with wells six inches deep on the rear wall, you should be six feet from that surface.

See, simple, no propeller beanie or pocket protector needed. heh

--Ethan

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Old 5th October 2010 | Show parent
  #29
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Rairun's Avatar
 
🎧 10 years
Got it. Thank you all .

Edit:
According to QRDude (i posted it above) ,with a diffuser 28cm deep, minimum distance to seating position is 1.72m. According to Ethan's guideline, the same diffuser must be 335cm away to the listener:
(28cm=11 inch, 11 x 30.48= 335). Am i wrong?
Old 5th October 2010 | Show parent
  #30
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Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Rairun ➑️
Got it. Thank you all .

Edit:
According to QRDude (i posted it above) ,with a diffuser 28cm deep, minimum distance to seating position is 1.72m. According to Ethan's guideline, the same diffuser must be 335cm away to the listener:
(28cm=11 inch, 11 x 30.48= 335). Am i wrong?

I would trust QRDude on this one (sorry Ethan ).

I would also once again like to point out that the ISD is often the factor that determines the proper distance to a diffuser.

/Jens
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