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[dnafe]

Hi All

Been a while

Today I ran the Real Trap test tone CD (10-300hz in 1 hz increments and measured with an RS SPL Meter at the listening position) in my CR room and the numbers came back looking quite good.

The odd thing was there were a couple of groups of frequencies that made the audio appear to be coming from just the right side of the room and some made the audio appear to be on the left side of the room.

Almost like light to heavy panning and then back to center.

I've included a JPG of the layout of the room.

Any explanation and possible solutions would be appreciated

thanks

Don

[dnafe]

a bit more info for you

The corner panels are 2 Roxul RX40 3" thick 2'X4' batts stacked floor to ceiling with empty space behind them.

The wall panels are single Roxul RX40 3' thick batts hung 35.5" from floor and ceiling and mounted 3" off the wall

The ceiling clouds are the same as the wall panels but hung 3" from the ceiling

DOn

[jimmyjazz]

I'm puzzled, but it looks like the main thing that might throw your room out-of-whack from a symmetry point of view is the bookshelves & keyboard.  Can you pull those from the room, close the door, and see if you're still getting the weirdness?

[dnafe]

That was my plan for today...unfortunately they will have to go in the room somewhere

Don

[jimmyjazz]

You can't remove them just for the test?  Or are you saying that eventually they have to reside in the control room?

If the latter is true, and removing them eliminates the weirdness you're hearing, could you put them between your monitors and behind your console?  Or at the back of the room somehow?  Maintaining physical symmetry may be critical in your room.  (It's somewhat critical in most rooms, although I don't think I've ever heard of the kind of extreme effects you are talking about.  I think there might be something else at play, too.)

[dnafe]

Keeping the room symetric is going to be a bit of a PITA. That being said it isn't impossible...only annoying.

And in answer to your question they can be removed for the test but will eventually have to be put back into the room.

Don

[jimmyjazz]

Well, it's almost hard to believe that the cause of what you're hearing is anything but an acoustic issue, but I suppose you might have an amplifier crapping out or something.  If in fact it is caused by the shelves on one side of the room, then finding a way to move them to a symmetrical location will (of course) be worth the effort.

Do you HAVE to have the desk in the back?  That would be a perfect location for bookshelves, if indeed you have them loaded with random books.  It's a poor-man's diffusor.

[dnafe]

The amp has been checked out as has the wiring too and from the amp and speakers.

There are four large shelves (60" width) above the desk filled with varying sized and density items from Books to CD's to Tapes to open spots...vary randomly placed

there are also four shelves (3' width)above the 3'w X 2'h X 18"d file cabinet with mostly small nicnack sized items on them.

As for the rest of the room behind the file cabinet it is symmetrical with the exception of the windows behind the acoustic panels.

Amazing what a small piece of furniture can do to skew the room assuming that's the problem

D

[dnafe]

I pulled all the non essential gear out of the front 2/3rds of the room and the change is only minor...tomorrow I'll go after the rest of the room and listen again...also could the windows be causing some of this problem?

DOn

[jetbase]

the wall on one side looks like an outer wall & the other looks like an inner wall. could different contruction on those walls be causing assymetry of lower frequencies?

[jfrigo]

The solution may be as simple as pulling the file cabinet & bookshelves off the wall a bit. Often the low end in a room is skewed by having a big equipment rack pushed up against a wall. When you pull it a foot or two off the wall, the problem largely (but not necessarily completely) disappears. You may be experiencing a similar problem, though not knowing more about the cabinet and shelves limits the value of prediction. Give it a try. Also, is your front desk open on the bottom? Completely enclosed consoles/desks can cause trouble too.

[jfrigo]

dnafe wrote on Thu, 14 September 2006 14:49

also could the windows be causing some of this problem?

Possibly.  I just noticed the windows on that far wall. Those certainly can change how one side of the room responds with bass. Photos could also aid in understanding the space and being able to make suggestions. I assume the construction is standard residential GWB on studs? What are the windows like? How are those panels affixed in relation to the windows that appear to be behind them? Do they cover them entirely?

[dnafe]

jfrigo wrote on Thu, 14 September 2006 22:43

The solution may be as simple as pulling the file cabinet & bookshelves off the wall a bit. Often the low end in a room is skewed by having a big equipment rack pushed up against a wall. When you pull it a foot or two off the wall, the problem largely (but not necessarily completely) disappears. You may be experiencing a similar problem, though not knowing more about the cabinet and shelves limits the value of prediction. Give it a try. Also, is your front desk open on the bottom? Completely enclosed consoles/desks can cause trouble too.

I moved the File cabinet out of the room and removed the bookshelves (wall mounted open shelves) off the wall and there's no real difference....now the desk does have a solid front...and I'll look at that this weekend

The panels (2'x4') are presently mounted on stands that hold them centered between the floor and ceiling and approximately 4" from the wall and they do not completely cover the windows...3/4 would be a good estimate with 5" between the back of the panel and the window

The windows are wood - single pane casement windows with an exteior aluminum sliding window/screen

The walls are standard 2x4 with plywood/brick on the exterior walls (top and right end) and drywall on the interior walls (bottom and left end)

Hope this helps

edit - For the record I don't hear this phnomenon at all when mixing or when listening to instruments in solo...only the test tones and especially 120 - 129 hz

DOn

[dnafe]

Here's front left...

note these pics were taken back in april when the room was full of junk...it has since been cleaned up but these pictures will give you a basic idea of the room layout as it is today

[dnafe]

Front right

[dnafe]

left rear

[dnafe]

Right rear

[dnafe]

window wall

[dnafe]

front ceiling

[dnafe]

rear ceiling

[L_Tofastrud]

It is possible, and likely, that the difference in wall construction can cause this.
Are you sending your signals to both speakers at the same time?
It is not uncommon for rooms to have varying bass response for left and right side.  Do you hear it while playing music?

Regards
Lars Tofastrud

[dnafe]

L_Tofastrud wrote on Fri, 15 September 2006 16:11

It is possible, and likely, that the difference in wall construction can cause this.

That and the windows are probably the culprit

Quote:

Are you sending your signals to both speakers at the same time?

yes

Quote:

It is not uncommon for rooms to have varying bass response for left and right side.  Do you hear it while playing music?

Nothing that I've been able to detect

Quote:

Regards Lars Tofastrud

thanks for the comments

DOn

[dnafe]

well today I cleared out absolutely everything that was nonessential and lo and behold the phenomenon is still there albeit less pronounced...I can only assume it is a function of the difference in wall construction and the windows because with the exception of my DAW, the desk it's on and the panels the room was empty.

Moving the panels altered things a tad but less than removing the misc stuff in the room...interesting

Bottom line is I don't hear it when I'm mixing so it's of no great importance but it was interesting to see how removing the stuff in the room effected this phenomenon.

Anyway next step is to ETF the room and see what the results are.

DOn

[slicraider]

It occurs to me that your door could be diaphramatic at certain frequencies which would explain the shift of certain frequencies to the left.

Rick Slater

NYC

[dnafe]

In fact there are two doors side by side on that wall (I forgot to put the second door in on the diqagram) and I agree there is a real probability that the two doors, in conjuction with the different wall construction and the windows on the exterior wall are creating this phenomenon.

That being said I will carry on merrily with my mixing / room analysis / tweaking / mixing / room analysis / tweaking etc. until I get the room as good (acoustically) as I can.

Don

[jfrigo]

I think you've tracked it down. Windows, differing walls, and doors are all possible influences. A few things I saw from the pictures: since the bookshelves are open on the sides (not a bookcase) and sparsely spaced they aren't really going to be greatly affecting the bass. The filing cabinet against the wall may have, but you've removed that. Also, the size and configuration of the panels over the windows maintains the windows as a factor for your bass issue. So yes, less than a revolutionary post here, I know, but my vote says you've got a working idea of the problem. The good news is that problems like this, if minor, can sometimes be pretty benign in your everyday work. You may not notice it in context (I believe you've said as much) and your ability to work may not be significantly impaired. Good luck and good listening!

[dnafe]

Thanks for the comments Jay.

I realise I've made a huge assumption here as to the cause of this panning phenomenon (as I call it) but it seems to make sense and unless one of the more knowledgeable members of the various forums I've posted to chimes in with a different explanation I'll just carry on in my ignorance.



Don