frequencys moving left to right in mix position?????

[figurehead]

situation:

in 11 x 11 room with angled roof going from 6' at the back to 7' at the front

monitors are 4' of the front wall and 3' of the side walls

the monitors are 58" apart and so i am also 58" away, which unfortunatly puts me about a foot away from the rear wall.

problem:

when running a sine wave test as i go up through the spectrum in the mid and high area the tone changes from the middle to the right and then back to the middle and then to the left and then all over again

worse area is the 400-800 range, so it seems like my vocal tracks keep panning around when it hits that certain freq.

assumption:

i am aware of flutter echo, and that is what im guessing im experiencing, however im not sure where from?

more details:

again i am in asmall square and the wall behind me is not treated to well,
so im sure that would help if i had rock wool.

but i wanted to know if what is causing this is in fact back to rear, and not side to side, which is what it seems like, almost like each side of my room resonates at a different tone.

also i did try to put up a reflective board, actually a dry erase board with white side out, which i put to my right at an angle to deflect the sound away.

this somewhat helped, but actually just changed the pitch at witch it shifts by about 50hz.

is thier a proper method for what i am attempting, should i look into deflection, diffusion, or absorbtion

all help is greatly appreciated, and i hope will keep me sain, in this insain situation

thanks,
figurehead.

[Ethan Winer]

FH,

> the tone changes from the middle to the right and then back to the middle and then to the left and then all over again <

Do you have any absorption at the first reflection points? If not, adding that will probably fix this problem. Rather than explain it all in a post here, see the sidebar "Creating an RFZ" in the Acoustics FAQ, second in the list on my Articles page:

www.ethanwiner.com/articles.html

--Ethan

[figurehead]

thanks for the the reassurance on the issue. i kinda thought that was the problem from your article, but i also wanted to make sure that room symetry does not play a part in that whole issue. i am going tommorow to get some 2" rock wool, so ill let you know how it goes.

thanks for the help
figurehead

[figurehead]

thanks for the the reassurance on the issue. i kinda thought that was the problem from your article, but i also wanted to make sure that room symetry does not play a part in that whole issue. i am going tommorow to get some 2" rock wool, so ill let you know how it goes.

thanks for the help
figurehead

[figurehead]

hey ethan well i went and got some wool today first of all i did get some 703 with the fsk in 2" which was 75 bucks for 6 pieces of 2 x 4, but i also got some roxul 8lb density instead of the 3 with the oc.

is there a big differenced in the two, or one better for a certain application, i did some basic sound testing and they seem to do about the same, as far as highs and mids

well most of the freq pboblems have been rectified yet still in the 600 - 620 range it is moving to the left, there are still other freq problems but this is the one that moves the vocals all around, so im not sure what to do, again i am in a small 11 x 11 room with a angled cieling of only about 7' where my speakers are, also because of the room size my speaks are only about 8" off the wall, could that be the problem?? also i am using the roxul on the two side walls and back wall and 703 on the roof

thanks for the help
figurehead

[figurehead]

hey ethan well i went and got some wool today first of all i did get some 703 with the fsk in 2" which was 75 bucks for 6 pieces of 2 x 4, but i also got some roxul 8lb density instead of the 3 with the oc.

is there a big differenced in the two, or one better for a certain application, i did some basic sound testing and they seem to do about the same, as far as highs and mids

well most of the freq pboblems have been rectified yet still in the 600 - 620 range it is moving to the left, there are still other freq problems but this is the one that moves the vocals all around, so im not sure what to do, again i am in a small 11 x 11 room with a angled cieling of only about 7' where my speakers are, also because of the room size my speaks are only about 8" off the wall, could that be the problem?? also i am using the roxul on the two side walls and back wall and 703 on the roof

thanks for the help
figurehead

[Ethan Winer]

F,

> is there a big differenced in the two, or one better for a certain application <

For treating first reflection points you want plain rigid fiberglass, not the type with a paper facing.

> yet still in the 600 - 620 range it is moving to the left <

Besides the side walls, did you also treat for first reflections off the ceiling?

--Ethan

[knightfly]

If your speakers are 3 feet from the side walls, in your square room they should be only 22 inches from the front wall (behind the speakers) - here's a diagram/explanation -

http://www.cardas.com/cgi-bin/main_cont ... om+Setup+8

If you place them that close to the front wall, be sure and use some of your absorbent on that wall behind the speakers, preferably spaced out several inches - since your speakers will likely take up about 12 of the 22 inches, you can just place the absorbent touching the rear of the speaker boxes.

Also, you didn't include any diagrams or pix - can you either do that (best) or describe what you've done; speakrs horizontal or vertical, resting on pads or wood or steel, sitting behind the console or on the bridge, etc - and, does this "auto-pan" feature happen with your head "clamped in a vise" between the speakers, or is your head moving a bit when it happens?

The more info you can provide, the better suggestions you'll get... Steve

[figurehead]

well the speakers are vertical and resting on three small squares of heavy wieght pad thats about an 1'8 of an inch which is resting on wood.

as far as absorbant material behind the speaks i have 4 sheets of 705 frk leaning at angle up against wall with a minimum gap of 4" to a max of about 12" to the ground, i didnot think highs or mids would be a problem, i thought it was more of the lows that were the problem so i put the foil face into the room should i turn the two panels behind the speaks, also it is a large glass surface behind them if that helps, and the wall is slightly angled from left to right about 2" if that helps any

asfar asmy console it is a 51"high rack mount angled on bottom that is between my speakers, which i try to keep behind the speakers

since the lastpost i have slightly changed the speak position soknow ther in at about 4', i did this so i am not right in the middle of the room while in the listening position, but a little closer to the front wall instead, is this wise?

and as far as the freq shiftsi have been able to stableize it somewhat, but still happens here and there somewhere in the 700 range but yes i keep my head very still and the tone will just completely jump to different sides on me

a new problem im noticing is that my vbery low end like 40 - 70 is really thin in the mix and thick right behind the mix. is this freq re4ally that important and if so what would be the best idea a panel trap or will corner traps be good enough for such a small room. and i also have a raised floor of about 8" but not sealed is this any help with the low end?

i will be doing more test today and ill try to give you some more details on the issues, i appreciate all the help.

thanks
figurehead

[knightfly]

What monitors are you using, and are they active or passive? It's almost sounding like they are wired out of phase. Have you tried changing the polarity on just one of the speakers to see if the bottom comes back? What about swapping speaker leads (left to right, right to left) to see if the problem reverses itself? (As in, instead of "swooping to the right", it now "swoops to the left", or whatever way you want to describe the frequency shift)

Can you measure from the centers of your woofers exactly to ceiling, floor, side, front and rear walls and post that info? Preferably with a rudimentary drawing (not necessarily to scale, just for easy reference, with distances noted on the drawing)

BTW, you're not doing these tests with a flanger in the signal path, are you?

Seriously though, can you also describe your exact signal chain - make and model of each thing the signal is going through, from the sine wave generator to the speakers, and everything in between? Sounds like any less depth will be a waste of time here... Steve

[lovecow]

figurehead,

Humor me for a second (I'm joining a little late):

Do you have any HVAC (supply or return) vents on the ceiling in the general vicinity of the mix area? Any radiators, open windows, etc.? Any amps setting between the speakers? Ceiling fans? Box fans? Farting flies? (OK, that last one was a joke.)

I'm looking for possible heat or cool/hot airflow sources.

Again, humor me... :D

Best regards,

Jeff D. Szymanski
Chief Acoustical Engineer
Auralex Acoustics, Inc.

[figurehead]

i think your dead right. as far as the room it is just a shed so... i have installed a small ac on the left side of my mix. the problem is the building has a metal roof and is hard to keep cool. the temp fluctuates quickly when the ac is off its hot when its on its cool and really cold on on the right side to which the vents are pointing. could this be the tempral problem you were looking for.

thanks for all the help

[lovecow]

figurehead,

Thought that could be the case when the treatments didn't seem to address all the problems. Check these quotes from "Myth 7" from a Russ Berger Design Group white paper:

Temperature gradients and air movement between a speaker and listener can drastically affect the sound field. In particular, they are likely to cause perceived shifts in the acoustical stereo image, much like heat rising from hot pavement can distort an optical image...

This same phenomena is often observed where air diffusers for the heating, ventilating, and air conditioning (HVAC) systems have been located incorrectly in a room.

I've also heard Russ tell the story of where he first ran into this problem. He spent hours with a colleague trying to figure out what was happening to the imaging in a studio they were tuning. They were thinking electrical or acoustical - only after noticing the cycling a/c did they figure out it was "atmospheric," so to speak.

Anyway, something to investigate, to be sure! Glad I could help.

Best regards,

Jeff D. Szymanski
Chief Acoustical Engineer
Auralex Acoustics, Inc.