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Author Topic: 38% rule  (Read 5412 times)

jimmyjazz

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38% rule
« on: October 07, 2007, 11:10:19 pm »

I'm working on a new mix room, and don't have any of my reference materials handy right at the moment.  I'm intrigued with the "38% rule" which says that the best compromise for a listening position is 38% from the front (or back?) wall.

Not being a fan of hard and fast "rules" with no understanding of where they came from, I'm curious . . . where did this rule come from?  Is there a good statistical or analytical reason that shows 38% distance from one wall minimizes modal or boundary issues?
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gullfo

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Re: 38% rule
« Reply #1 on: October 08, 2007, 10:46:45 am »

the fast answer? 100/38. its an irrational number (like pi or a golden ratio 1.618...) which promotes balance to the room. that said, like any rule for acoustics, it has to be moderated by looking at a number of other "rules" and determining how to make the trade offs (which always have to be made). what if you have a room size that has a mode hit @ 38%? so you move it to 36% or 42% (apparently 42 is the answer to life, the universe, and everything). what if you're building a 5.1 mix room? chances are you're likely to be around 50% which typically has the mother of all modes.

one simple check for monitor placement ratios (besides golden) is: monitors - 70% of room width apart, l-r monitors and mix position form an equilateral triangle on 60 degree legs.

its a starting point, not necessarily the finish line. and it typically assumes free standing (edit: or more correctly stated by Wes below - wall mounted) monitors. when you look at this diagram you see the 38% spot is where you would sit - inside the triangle - this becomes the core of the "sweet spot".

index.php/fa/6403/0/

(this diagram loosely derived from Jeff Cooper's great book Building a Recording Studio)
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Glenn Stanton

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jimmyjazz

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Re: 38% rule
« Reply #2 on: October 08, 2007, 02:05:16 pm »

Thanks, Glenn.  Right now the mix position is sitting a bit too close to the center of the room (46% from the front wall), but the free-standing monitors are in a nice spot, spanning 61% of the front wall, with the mix position at a perfect equilateral triangle.  I'm going to try to push the mix position forward a bit, but that will probably force the monitors a bit closer to the front wall, and I don't know how that will sound.  (I can't bring the monitors closer to each other, so just moving the mix position forward will likely create a "hole" in the image.  I'll check it out, though.)
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Ethan Winer

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Re: 38% rule
« Reply #3 on: October 08, 2007, 02:54:59 pm »

Jimmy,

jimmyjazz wrote on Sun, 07 October 2007 23:10

where did this rule come from?


I believe it originated from studio designer Wes Lachot. He explains his reasoning in a sidebar in this article:

http://www.realtraps.com/art_room-setup.htm

Wes is a regular here so hopefully he'll chime in and elaborate.

--Ethan

Greg Reierson

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Re: 38% rule
« Reply #4 on: October 08, 2007, 02:57:53 pm »

It looks good on paper but I don't think I've ever seen a hi-end studio set up like that.

Anyone?


Greg Reierson
Rare Form Mastering
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jimmyjazz

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Re: 38% rule
« Reply #5 on: October 08, 2007, 03:03:03 pm »

Thanks, Ethan.  That's exactly what I was looking for.  I'll dig into Wes' articles and see if what he is proposing makes sense to me.
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Wes Lachot

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Re: 38% rule
« Reply #6 on: October 08, 2007, 07:50:29 pm »

Hey guys. Yes, I think it was I who started the whole 38% thing as a starting point for the listener position. But I never called it a "rule" - that just sort of happened as it spread around the internet.

The main point is to get safely outside of the midpoint (50%) of the room, and 38% often works out to be about right, particularly when using wall-mount speakers in a typical mid-sized (20 ft. deep) control room. For a mastering room, approx. 38% from the back wall might actually be better, if the room is deep enough that 38% is 10 ft. or so.

For an all-in-one room like the one in the EQ article, there are many considerations other than just the straight up question of where to place the listener in an empty room. You've got to have room to accomodate performers, room for a couch, and so on. So it usually makes sense in that type of scenario to place the console and listening position forward of the 50% location. And again, 38% is recommended as a starting point, not a "rule".

I often use RPG's Room Optimizer program to check the interaction of the modal and boundary effects, and combine that with knowledge gained from experience of past room designs. Then there's the size of the sweet spot, and the interaction of the speaker focus point with the room modes to consider. All of these things go into the equation when deciding on the listening position. But all things considered, 38% is not a bad place to start.

--Wes
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Wes Lachot Design
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franman

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Re: 38% rule
« Reply #7 on: October 11, 2007, 08:34:41 pm »

The rule of 'thirds' has long been observed in the hi-fi community... the setup being speakers one third of the way into the depth and listening position being 2/3 the way in... in a rectangular room  (as Wes says) this is often a good starting point. We also you room sizer and room optimizer all the time.
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Francis Manzella - President, FM Design Ltd.
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C.Cash

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Re: 38% rule
« Reply #8 on: October 24, 2007, 04:33:13 pm »

Silly question;

When setting up this position,do I aim the monitors at me or straight ahead?
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gullfo

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Re: 38% rule
« Reply #9 on: October 24, 2007, 07:08:21 pm »

depends on the monitors, how far apart they are, and does it sound correct? by correct meaning the center image level (the phantom image in stereo) so that the audio "stage" or "plane" feels balanced.

if the monitors are close together, then generally they'll be pointing straight at you. if they're far apart, you'll turn them. this is because the mid-high frequency drivers are mostly directional and this is what gives you the sense of direction. low frequencies are mostly omnidirectional and you depend on the rooms balance to provide you with correct information.

there are numerous electronic, computer, laser, metering devices to try to get this right. room optimizer is a good place to start with getting the speakers positioned but from there its all about the room and you and experience to use it...
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Glenn Stanton

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Greg Reierson

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Re: 38% rule
« Reply #10 on: October 24, 2007, 10:00:40 pm »

gullfo wrote on Wed, 24 October 2007 18:08

depends on the monitors


Definitely! Some monitors are built for the near field (generally fairly narrow dispersion) while others are designed for the free or far field. Most of the really great sounding monitors I've heard have a very wide dispersion. That makes room influences even more important and can dictate how the monitors are placed with regard to stereo angle, height and distance.


Greg Reierson
Rare Form Mastering
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