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38 percent rule
Old 7th January 2009
  #1
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dpianomn's Avatar
 

38 percent rule

hey all-
my room is roughly 14' x 24'...it's used for mixing as well as tracking. that puts my mix position aprox. 9' from the front wall...yikes! i'd in the middle of the room. i'm just beginning to set the room up, so it has not been fully treated yet...currently my mix pos. is set up at 5' from the front wall and the space seems to work/flow nicely. can i get away with this?

thanks for any and all help.
Old 7th January 2009
  #2
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Glenn Kuras's Avatar
First the 38% is not a rule but only a starting point. I would recommend testing the room with the following program (it is free) to see what kind of response you are getting. You can then determine what location is best.
Room EQ Wizard Home Page
Old 7th January 2009
  #3
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Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by dpianomn View Post
My room is roughly 14' x 24' ... my mix pos. is set up at 5' from the front wall and the space seems to work/flow nicely. can i get away with this?
As Glenn said, 38 percent is a starting point. It's also less important in larger rooms. My one-room studio is 34 feet long, and I have the mix position at one end with the speakers firing down the length.

More to the point, you'll want to add as much bass trapping as possible anyway, and that goes a long way toward reducing peaks and nulls.

--Ethan
Old 7th January 2009
  #4
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thank you glenn and ethan!
i'll shoot the room later today. i've got a lot of glenn's traps already and will be ordering more as soon as i can raise the capital.
Old 7th January 2009
  #5
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Weasel9992's Avatar
 

Quote:
Originally Posted by dpianomn View Post
hey all-
my room is roughly 14' x 24'...it's used for mixing as well as tracking. that puts my mix position aprox. 9' from the front wall...yikes! i'd in the middle of the room. i'm just beginning to set the room up, so it has not been fully treated yet...currently my mix pos. is set up at 5' from the front wall and the space seems to work/flow nicely. can i get away with this?

thanks for any and all help.
...and remember that the 38% rule puts your *ears* at 9', which is well off-center of the room. I know you're not wild about losing the front 9' of the room, but you'd have to put the listening position somewhere, right? If you have a 5' triangle, then you'd probably be at least 6' out into the room anyhow, so you're only losing 3' more than that, really. Plus, the benefits of getting the positioning right will outweigh the loss of that 3' of space.

Frank
Old 8th January 2009
  #6
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dpianomn's Avatar
 

Quote:
Originally Posted by Weasel9992 View Post
...and remember that the 38% rule puts your *ears* at 9', which is well off-center of the room. I know you're not wild about losing the front 9' of the room, but you'd have to put the listening position somewhere, right? If you have a 5' triangle, then you'd probably be at least 6' out into the room anyhow, so you're only losing 3' more than that, really. Plus, the benefits of getting the positioning right will outweigh the loss of that 3' of space.

Frank
yeah, i moved my mix pos. to 9' and it does aesthetically kill the room...i've got a 6' foot grand and a drum set in the back half. :(

also, i bought an SPL meter to test my room tonight, but it was broken right out of the box! i suppose once i shoot the room and order the rest of my traps i'll have a much better sense of what will work.
Old 27th August 2012
  #7
I did the listening position at 38 percent of the length of the room and it greatly reduced a booming bass problem. I previously just placed the speakers 1 foot away from the front wall. It's a small untreated room and it only required me to move the speakers 6 inches from the previous placement (room dimensions 10X12 feet, speakers 2.5 feet apart).
Old 27th August 2012
  #8
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Rod Gervais's Avatar
 

In smaller home studios - when there are combination tracking/mixing rooms - a lot of people mix close to the wall with nearfields - and then slide back into the sweet spot to listen to the mix with midfields - that way they can have their cake and eat it too........

Rod
Old 27th August 2012
  #9
Gear Maniac
 

hey Rod,
nice tip with moving further back just to check mix!
in my room i can only get low frequencies right when sitting very close to the front wall. but in that position i have always problems with low mids. i can control mid frequencies better when i sit around 38% but in that position it sound too shy in low frequencies. i will try moving further from the front wall just to check mids.
thanks
Old 27th August 2012
  #10
As a follow up on my previous reply, I hit me that I overlooked the mimum 4 feet apart rule. I could potentially get 4.5 feet before getting too close to the front wall but wouldn't I risk reintroducing the booming bass? Maybe I should stick to 4 feet? Just thinking out loud....

EDIT:Took a look at Genelec setup guide. "Avoid listening position closer than 1 m from any wall." (side and back wall colored red). That would make my max 3.2 feet apart. EDIT2: That goes for the front wall as well according to Genelec! I'm screwed....Maybe I should aim for the 3ft apart ghetto minimum I've seen mentioned?
Old 28th August 2012
  #11
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38 percent rule only applies when the monitors are flush with the wall, or close as possible. Also, it usually doesn't apply to the side walls, rather height and length. So, if you plan on a speaker layout with the 38 percent rule in mind, speakers against the front wall.

But that also entails messing the stereo angle, which could end up narrow or wide for the best response. Symmetrically adjusting the monitor distance from the side wall is the best option if you don't mind the angle change. The monitor height also matters.
Old 28th August 2012
  #12
Quote:
Originally Posted by OpusOfTrolls View Post
38 percent rule only applies when the monitors are flush with the wall, or close as possible.
Interesting. I guess that would theoretically put some restrictions on the max room size as well, if the 38 percent rule is to be followed while keeping a nearfield listening triangle.
Old 28th August 2012
  #13
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Jens Eklund's Avatar
The “38% rule” has to be the one rule of thumb that has created the biggest confusion of all time.

The best way to find a good listening position is to try different practical positions and confirm with measurements which one results in the best combined response in terms of imaging (lack of early reflections) and low frequency behavior (modal and SBIR related).

In general (observe: yet another dangerous rule of thumb!), it´s usually best to position the speakers centered against a short wall (or preferably in it if possible) and then find a listening position that results in an adequate listening triangle (equilateral or at least close to it) but if you have options, you can experiment with different sizes of it that will affect the LF response due to different positions (listener) along the length axis of the room. Once you´ve found the position that results in the best LF response (and still practically acceptable); treat surfaces related to different issues (early reflections, modal or SBIR related problems) to enhance the situation further.

Again; rules of thumb are dangerous as they do not apply to every given situation. The above might apply to a number of situations but if for example the walls are lossy (resulting in complex acoustic impedance at low frequencies), it might not.
Old 28th August 2012
  #14
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BriHar's Avatar
 

Guideline not rule or law.
Old 28th August 2012
  #15
Quote:
Originally Posted by Jens Eklund View Post
In general (observe: yet another dangerous rule of thumb!), it´s usually best to position the speakers centered against a short wall (or preferably in it if possible) and then find a listening position that results in an adequate listening triangle but if you have options, you can experiment with different sizes of it that will affect the LF response due to different position along the length axis of the room. Once you´ve found the position that results in the best LF response (and still practically acceptable); treat surfaces related to different issues (early reflections, modal or SBIR related problems) to enhance the situation further.
I think I got most of what you said but please see if these drawings and annotations I made corresponds to what you are suggesting:


Measure at each position, pick the best one, optionally move on to step 2.
OR?
Measure at each position, pick the best one, DONE.
Old 28th August 2012
  #16
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Jens Eklund's Avatar
I would start with "step 1" assuming the speakers are up against the front wall as close as practically possible but again; there’s no "rules" so any position might turn out to be the "best" one depending on a lot of factors.
Old 28th August 2012
  #17
Ok, so 'step 2' was just me reading too much into what you said? The left-side 'step 2' was what I had originally planned before you chimed in. Anyway, I'm just trying to find a reasonable method that allows me to chart some of the more likely "best" positions, taking measurements over a weekend. I understand there's no hard rules and every room is different but it can't all be a shot in the dark, right?
Old 28th August 2012
  #18
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jim1961's Avatar
 

In my ongoing room drama I made yet more changes. Finally took peoples advice and moved my listening position forward some. Guess what? 38.8% from the rear wall

25.75 length. 10 ft from back.
Old 28th August 2012
  #19
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Rod Gervais's Avatar
 

BTW- just as an aside here - I would not simply measure once at each spot - I would take multiple measurements of the working area in a carefully controlled grid so I could make an informed decision on the "best location" - your head will never be held in a vise - and even small movements can translate to huge differences - what you are really looking for is the best working location, this would be include averages of the sound field that your head is going to exist within while working.......

Multiple measurements will also give you data you'll need to rule out anomalies that might otherwise taint your decision.
Old 29th August 2012
  #20
Quote:
Originally Posted by jim1961 View Post
In my ongoing room drama I made yet more changes. Finally took peoples advice and moved my listening position forward some. Guess what? 38.8% from the rear wall

25.75 length. 10 ft from back.
So you moved the listening position to the 38 percent point and liked it? No measurements?


Quote:
Originally Posted by Rod Gervais View Post
BTW- just as an aside here - I would not simply measure once at each spot - I would take multiple measurements of the working area in a carefully controlled grid so I could make an informed decision on the "best location" - your head will never be held in a vise - and even small movements can translate to huge differences - what you are really looking for is the best working location, this would be include averages of the sound field that your head is going to exist within while working.......

Multiple measurements will also give you data you'll need to rule out anomalies that might otherwise taint your decision.
Good point.
Old 29th August 2012
  #21
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jim1961's Avatar
 

Quote:
Originally Posted by RoadToNever View Post
So you moved the listening position to the 38 percent point and liked it? No measurements?
I moved the listening position yes. But I moved it for other reasons other than the 38% rule. Still, the FR response did smooth a bit.

There are ETC and one partial FR measurement in this thread:

LEDE / RFZ ideas applied to a critical listening room
Old 29th August 2012
  #22
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Quote:
Originally Posted by Rod Gervais View Post
BTW- just as an aside here - I would not simply measure once at each spot - I would take multiple measurements of the working area in a carefully controlled grid so I could make an informed decision on the "best location" - your head will never be held in a vise - and even small movements can translate to huge differences - what you are really looking for is the best working location, this would be include averages of the sound field that your head is going to exist within while working.......

Multiple measurements will also give you data you'll need to rule out anomalies that might otherwise taint your decision.
The statisticians in the audience love this kind of data-rich approach. I'm no stats freak, but in research projects I design, I'm always accused of taking too much data. Until the work is done and the customer realizes that there is a means to the madness.
Old 29th August 2012
  #23
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Rod Gervais's Avatar
 

Quote:
Originally Posted by Syncamorea View Post
The statisticians in the audience love this kind of data-rich approach. I'm no stats freak, but in research projects I design, I'm always accused of taking too much data. Until the work is done and the customer realizes that there is a means to the madness.


Understood - I've been accused of the same sort of things - but when you take this approach you don't have to worry (when all is said and done) about someone finding fault with your data.

Measure twice cut once comes to mind in this regard.

I will even take a series of multiple readings in exactly the same spot to make sure there were no anomalies that affected the readings......

Sometimes the strangest things jump out at you when doing this - and you realize that a particular reading has nothing to do with the room itself.

You might have 5 shots in one location - and 4 of them are near identical - while one is drastically different in some regard......

When you have them to compare to one another it is easy to see which one you can ignore - however - if the one with the anomaly happened to be the first one - and you never gathered enough data to rule that out - then you're making decisions based on faulty data.

Perhaps what appeared to be the worst set up in the room was actually the best.......

Rod
Old 30th August 2012
  #24
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gullfo's Avatar
 

Quote:
Originally Posted by jim1961 View Post
Guess what? 38.8% from the rear wall
or what i like to call the "62%" position in the room heh
Old 30th August 2012
  #25
So, anyone have comments on post #15?
Old 30th August 2012
  #26
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jim1961's Avatar
 

Quote:
Originally Posted by gullfo View Post
or what i like to call the "62%" position in the room heh

Quite true
Old 30th August 2012
  #27
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by RoadToNever View Post
So, anyone have comments on post #15?
Yes, measure at each position as you experiment, then pick the best one. That's exactly the method I recommend in my article How to set up a room.

--Ethan
Old 31st August 2012
  #28
Quote:
Originally Posted by Ethan Winer View Post
Yes, measure at each position as you experiment, then pick the best one. That's exactly the method I recommend in my article How to set up a room.

--Ethan
Thanks but are they all worth going through? If so in which order?
Old 31st August 2012
  #29
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Ethan Winer's Avatar
 

Lightbulb

Just start at "38 percent" and slide the speakers along the axes, as explained in the article.

Also, no matter what you measure, placement can only get you so far. You also need plenty of bass traps.

--Ethan
Old 10th September 2012
  #30
Quote:
Originally Posted by Ethan Winer View Post
Just start at "38 percent" and slide the speakers along the axes, as explained in the article.

Also, no matter what you measure, placement can only get you so far. You also need plenty of bass traps.


--Ethan
Emphasis mine
Maybe I'm being thick, but which drawing/s in post #15 does this recommendation correspond to?
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