the 38% rule

[macleod]

hello,

i have just started moving all my stuff into a new room. I see that on RealTraps - How To Set Up a Room it talks about setting up either 38% from the front wall or 38% into the room.

Is their any sonic difference between the two ? if i am 38% from the front wall ( 4.5 meters in my case ) are the speakers too close to the wall ?


many thanks

K

[Jade]

Originally Posted by macleod

if i am 38% from the front wall ( 4.5 meters in my case ) are the speakers too close to the wall ?

That depends where you put them.

[Rick Sutton]

I did some quick calcs. Is your room really 39 feet deep? (12 meters)

[mds]

Mix position should be 38% into the room, i.e. where you're sitting. Speaker location can be varied somewhat. Getting them a bit off the front wall is good. Just find the 38% spot and make an equilateral triangle between that spot and the two monitors in front of you.

[Glenn Kuras]

Originally Posted by mds

Mix position should be 38% into the room, i.e. where you're sitting. Speaker location can be varied somewhat. Getting them a bit off the front wall is good. Just find the 38% spot and make an equilateral triangle between that spot and the two monitors in front of you.

Right on the money.. Note that the 38% rule is a starting point, so you might find that moving forward or back will improve the low end responce.

Glenn

[mmcfarlane]

To give you an idea beyond the 38% rule, here's the caclulated response of my badly rectangular control room. The graphs on the edge show where particular frequencies are the strongest and the weakest. The idea is to place both your monitors AND your ears in areas that don't have holes or peaks in the frequency spectra. I used the chart to place my couch also.

My head is the purple circle. The little grey lines are the monitors.

[macleod]

hi, my room is 7 meters long so its 434cm in from the rear wall or 266 from the front.

if i go to the front it seams like my speakers are just too close to the front wall, so i guess i will have to start by going 38% from the rear wall.

What is a good starting point for the width of my speakers.

Thanks

K

[fooman]

I moved from 55% or so to 38%... my bass response is much better. But that's my experience =)

[numrologst]

it depends much on the room dimensions and if the room is square or rectangular. It is a good rule to get going, and for most people it will help.

[jwl]

All else being equal, 38% back from the front wall is better than 38% from the rear wall, only because you are then further from the rear wall, which means rear reflections will have less energy when they reach your ears (since they have to travel a bit further). So the smearing that comes from first reflections will be a bit less intense.

Generally, 38% is a good starting point, as Glenn says, because there are likely to be few/no nulls or peaks in that area. This is a good theoretical starting point; your ears should always be the judge.

As far as speaker placement, the speakers should make an equilateral triangle with your head, ideally with the tweeters at the same height as your ears. As far as how widely they are spaced, it really depends on what else is going on in the room. I don't know if this is intentional, but in many rooms I've noticed that the speakers are approximately the same distance from the center line of the room (ie, a line from the front to the rear, going through the mix position) as they are from the front wall. In other words, if the speakers are 6' apart (3' each from the center line, have them be 3' from the front wall. These numbers are round; by far I think it is more important to make the equilateral triangle between the speakers and your head, such that the speakers fit comfortably into your space.

I'm sure there is a theoretical optimum, but if you keep things symmetrical, make the equilateral triangle, and add bass traps and absorbers for a RFZ you should be doing just fine.

[pfo]

Originally Posted by mmcfarlane

To give you an idea beyond the 38% rule, here's the caclulated response of my badly rectangular control room. The graphs on the edge show where particular frequencies are the strongest and the weakest. The idea is to place both your monitors AND your ears in areas that don't have holes or peaks in the frequency spectra. I used the chart to place my couch also.

My head is the purple circle. The little grey lines are the monitors.

That's a pretty neat chart -- what did you use to create it?

[Glenn Kuras]

Originally Posted by macleod

hi, my room is 7 meters long so its 434cm in from the rear wall or 266 from the front.

if i go to the front it seams like my speakers are just too close to the front wall, so i guess i will have to start by going 38% from the rear wall.

What is a good starting point for the width of my speakers.

Thanks

K

If you are going to be in the back of the room then put the thickest panels on the back wall you can (6" if you can). You will want to also space them off the wall the same thickness as the panel.

Glenn

[mmcfarlane]

Originally Posted by pfo

That's a pretty neat chart -- what did you use to create it?

I used the Harmon Room Mode Calculator (Excel Spreadsheet) to get the graphs you see for the rooms length and width.

Then I did a little copy and paste in MS Paintbrush and drew the floor plan and lines myself. Took about an hour but I'm a visual kind of guy.

The Harmon spreadsheet has another graph that is nice to show you the trouble areas in your rectangular room.

The real solution is, don't build a rectangular room !

[dnaflr2]

Originally Posted by Glenn Kuras

If you are going to be in the back of the room then put the thickest panels on the back wall you can (6" if you can). You will want to also space them off the wall the same thickness as the panel.

Glenn

While we are at it- in regards to covering the rear of the room w/bass traps- What would yeild the best results?

1) Lining all of the rear flat walls w/ traps -OR-
2) Making sure all of the rear corners (ceiling to wall, and wall to wall) ar covered with traps?

[Ethan Winer]

Originally Posted by dnaflr2

1) Lining all of the rear flat walls w/ traps -OR-
2) Making sure all of the rear corners (ceiling to wall, and wall to wall) ar covered with traps?

Both.

--Ethan

[Ethan Winer]

Originally Posted by macleod

Is their any sonic difference between the two ? if i am 38% from the front wall ( 4.5 meters in my case ) are the speakers too close to the wall ?

The only way to know the best speaker and listener placements is to measure the LF response at high resolution as you try different positions.

--Ethan

[numrologst]

ethan you dirty dog...or cat... I didn't know you were such a kick ass musician. I just watched your videos... Amazing shit man

[Blue Bongo]

Holy Smokes! That's an amazing piece of work Ethan! I cannot tell you how much I enjoyed that video. I was smiling the whole way through!
You made my day!

Merry Christmas, sorry I don't know anything about the 38 percent rule.

Blue Bongo

[vespiz]

Maybe this has been covered somewhere, but I want to clarify things a bit.
We're planning to build a control room inside an existing room (concrete walls, ceiling and floor) and we'll be making a front wall filled with glass/mineral wool. (I'll probably have to make a whole new thread about the plans, there are some tricky bits in the room...)
Anyways, does the 38% rule apply to the "outer" concrete wall or the "new" wall? From what I've read it's the concrete wall, but I'd like to be sure because it might affect our plans.

Thanks!

[mmcfarlane]

Originally Posted by vespiz

Maybe this has been covered somewhere, but I want to clarify things a bit.
We're planning to build a control room inside an existing room (concrete walls, ceiling and floor) and we'll be making a front wall filled with glass/mineral wool. (I'll probably have to make a whole new thread about the plans, there are some tricky bits in the room...)
Anyways, does the 38% rule apply to the "outer" concrete wall or the "new" wall? From what I've read it's the concrete wall, but I'd like to be sure because it might affect our plans.

Thanks!

Use the inner walls if they are 'hard' surfaces like drywall, the outer wall if the inner wall is absorptive.

Don't build a rectangular control room if you can avoid it, build a symetrical room around the mix position but with angled walls, preferably more than 4 walls. (You need a fair large angle to break up the standing waves, a few degrees wont help). Proper room geometry will help the sound of the room better than trying to fix the problems with traps. Don't have any dimensionsmultiples of the other dimensions, including the ceiling height, e.g. 8 * 8 * 16 is horrible. Planned properly, you could end up with some storage space for mic stands, a computer equipment room etc, in the new 'dead space' that you will be creating by angling the inner walls.

Do yourself a huge favor and check out a studio design forum like MarkTaw.com and get some guidance on your specific plans before you start to build.

[Ethan Winer]

Originally Posted by numrologst

ethan you dirty dog...or cat... I didn't know you were such a kick ass musician. I just watched your videos... Amazing shit man

Originally Posted by Blue Bongo

Holy Smokes! That's an amazing piece of work Ethan! I cannot tell you how much I enjoyed that video. I was smiling the whole way through! You made my day!

Thanks guys!

--Ethan

[willerichey]

Not to high jack this thread.....

I moved my studio into a bigger room in my house (the home office). The right wall (looking forward in the mix position) is covered with cherry wood cabinets that extend out about 2 feet from the wall. The 1st reflection point is not obstructed by cabinets and the actual wall is visible (it is a cut out section for a desk).

My question is, should I center my mixing position with this wall or the cabinets? This would mean the mix position would shift from left to right. My desk is currently centered in reference with the cabinets.

[Glenn Kuras]

Originally Posted by willerichey

Not to high jack this thread.....

I moved my studio into a bigger room in my house (the home office). The right wall (looking forward in the mix position) is covered with cherry wood cabinets that extend out about 2 feet from the wall. The 1st reflection point is not obstructed by cabinets and the actual wall is visible (it is a cut out section for a desk).

My question is, should I center my mixing position with this wall or the cabinets? This would mean the mix position would shift from left to right. My desk is currently centered in reference with the cabinets.

If I understand the set up then the wall. I would though move the cabinet out of the front of the room.

Glenn

[jwl]

I think the answer to these questions (which is REALLY the center of the room) depends on acoustics. In other words, we have to think with our "ears" not our "eyes."

The visual center of the room and the acoustic center of the room may not be the same thing.

For instance, the cabinets mentioned a few posts above. What happens when sound hits those cabinets? The answer will depend on how massive they are; most of the audible spectrum is likely to reflect back off the cabinets. The question is, to how low of a frequency does reflection occur? Eventually, you will hit a certain frequency at which the sound doesn't reflect anymore, but rather begins to travel through or around the cabinets. This is likely to be in the bass region, again depending on how massive the cabinets are.

One of the reasons to be in center of the room (left to right) is to control the effect of room modes, which are almost always in the bass range. So from that perspective, it makes sense to be in the center of the "acoustic" room, ie, centered between the walls as if the cabinets were never there.

On the other hand, another reason to be in the center of the room is to produce the most accurate stereo image, and this will be more depending on the higher frequencies. So from that perspective, it makes sense to be in the center of the "visual" room, ie, between the wall and the cabinets.

I suppose what I'm saying is (in my usually long-winded way...LOL), try it both ways and see which setup sounds best!

[vespiz]

Originally Posted by mmcfarlane

Use the inner walls if they are 'hard' surfaces like drywall, the outer wall if the inner wall is absorptive.

Do yourself a huge favor and check out a studio design forum like MarkTaw.com and get some guidance on your specific plans before you start to build.

Cool, thanks!

Yes, I've been reading for the past year or so like the John L. Sayers forum and, of course, all the acoustic threads here
I'm trying to find everything I can, so I can avoid any possible errors (the worst of which is a very low budget!)

This is a great forum! Gotta say it again

[willerichey]

Thanks Glenn and jwl.

The cabinets are to my right (when facing mix position) and are attached permanently to the wall (think law office style). the are two cubby/cubilcles with a counter and keyboard tray on each side and the rest are cabinets that stick out.

SO if I was sitting at the mix position and turned and faced the first reflection point on the right, I would be staring at the side wall where the first cubby/cubical is. There are no cabinets in this cutout section.

I am thinking since there is no direct reflection at this point from the cabinets, I should move my mix position to the right to put it exactly in the center of the room physical room.

I agree with jwl, the best solution in this situation would probably be to use my ears and not my eyes. I think I will go home tonight and move my monitors and controller over to the right 2 feet and see if my stereo spread improves. I did have a problem accurately judge the direct center of the mix, but I put a piece of 703 in the center behind my monitor and the image improved greatly.

One great thing about this room is that the entrance behind (to french doors) opens up into a huge front room with vaulted ceilings. When I open and close the doors you can definite hear a huge difference in the sound. I showed it to my dad and his untrained ears could even tell the difference. The sound is more open with the doors open. This also great becuase my control room subs as my tracking room as well.

[mmcfarlane]

I actually meant to send you to John Slayers, not Mark Taw. My bad, brain fart...

[Glenn Kuras]

Originally Posted by willerichey

Thanks Glenn and jwl.

The cabinets are to my right (when facing mix position) and are attached permanently to the wall (think law office style). the are two cubby/cubilcles with a counter and keyboard tray on each side and the rest are cabinets that stick out.

SO if I was sitting at the mix position and turned and faced the first reflection point on the right, I would be staring at the side wall where the first cubby/cubical is. There are no cabinets in this cutout section.

I am thinking since there is no direct reflection at this point from the cabinets, I should move my mix position to the right to put it exactly in the center of the room physical room.

I agree with jwl, the best solution in this situation would probably be to use my ears and not my eyes. I think I will go home tonight and move my monitors and controller over to the right 2 feet and see if my stereo spread improves. I did have a problem accurately judge the direct center of the mix, but I put a piece of 703 in the center behind my monitor and the image improved greatly.

One great thing about this room is that the entrance behind (to french doors) opens up into a huge front room with vaulted ceilings. When I open and close the doors you can definite hear a huge difference in the sound. I showed it to my dad and his untrained ears could even tell the difference. The sound is more open with the doors open. This also great becuase my control room subs as my tracking room as well.

My 2 channel listening room I have has sliding doors in the back of the room that lead outside. A lot of times I will just open up the doors which my girlfriend can even hear the difference.

Good luck on the room and if using your ears seem to not work then maybe you should just test the room. Sometimes we can "think it sounds right" one day and the next day "think it is wrong". If you test the room there will be no guessing.

Glenn

[willerichey]

Thanks again Glenn.


I have the JBL LSR 4328P monitors with room correction. On the software interface, it shows an EQ graph and where it dips when the RMC is on.

Is this an accurate definition of where my problems lie?

[Ethan Winer]

Originally Posted by willerichey

On the software interface, it shows an EQ graph and where it dips when the RMC is on. Is this an accurate definition of where my problems lie?

Not really because the "correction" from that sort of simplistic system is valid only for the one place the microphone was while measuring. If you move the mike three inches the response will be different.

More to the point, all rooms need bass trapping at all low frequencies. Not just those frequencies related to the room dimensions, or resulting from measuring.

--Ethan