Holy bleeping standing waves!!!!

R

Razor

New member
I don't believe it. I just figured out exactly what is wrong with my control room. I am suprised that anything I've ever done in here has been even listenable.

This afternoon I finally had enough free time to do a simple test: create some pure sine waves at various frequencies and see just where the strengths and weaknesses in my little room are. I had a sneaking feeling that there was a problem around 60 - 100 hz as I always have to really carefull there to have mixes translate.

I couldn't beleive my ears, There is almost NO 80hz at the mix position......Help!!! It was actually rather unsetteling. An 80 hz tone is almost inaudible untill I roll back a foot. Two feet back it is at full volume. It dissapears again near the back wall and then disappears completely behind that.

O.K.....I guess my plan to tear this place apart and start again from scratch is no longer something I can put off. I am going to re-orient the whole room and build out the corners. SOON

Any thoughts on the best way to avoid future mode problems would be greatly appreciated. I know that my room dimensions are the problem. Will tuned traps do it? What sort of corners can I build?.......Help

Thanks in advance,

Charles Rieser
Southwind Studio
Austin, Tx.
 
Welcome to the world of room tuning :) Your sine-wave test is pretty much what the pro's do, except instead of their ears, they have some fancy test equipment to monitor the reflection level.

Anyway, before you gut and pillage your walls, may I recommend instead you take a piece of plywood, stand it on its side, between two cinderblocks. Repeat your test and move it around the room at slightly different angles from perpendicular to the studio monitor/speakers. This will adjust the shape and reflections drastically, especially if its a small room, and you can hear the difference easily.

You didn't mention if the room was small, large, or what have you, but its very possible that the distance between the monitors and the back wall is either a full wave or 1/2 wave length of an 80 hz waveform :) There are several ways to fix this. You could kill the liveness of the room by attaching deflectors/absorbsion materials, but it will take you a while to get it to where you are satisfied. Oh, a little known trick is that sound absorption material is almost four times more effective if its scattered all around, rather than just pasted end to end on the back wall, or ceiling.

Another thing you can do, as my plywood suggestion above will suggest in practice, is to alter the back wall, by making it not perpendicular to the speakers. A slight triangle (pointed in the center) with about 5-10 degrees of angle would be enough to cause a lot of scattered reflections. In a small room this typically moves the "dead bass" problem to a different area of the room, which is okay if its not immediately near where you sit, and where the speakers are.

Hope that helps, and is not terribly confusing. I tend to write off the cuff. Feel free to email me at midiguy732@hotmail.com. Just put "Studio" in the subject line so I know its not "Spam" :)

Frederic
 
frederic ,

Thanks!! Your suggestions speak to exactly what I was considering. Yes, I've got 'dem small parallel-walled room blues.

My 3-bedroom house is now a 3-room studio and the master bedroom here is the control room. At 14x11x8, I have always known that there are mode problems , I just never realized how bad they were. I do have a contiguous (sp?) wall behind me and have been experimenting with varous forms of diffusion and absorbtion, now I know that a more drastic approach is neccessary.

How would three rounded, convex sections along the back wall work? Should they be filled?.....How about tuned traps or building the corners in?....

Thanks much!!

Charles
 
Thanks!! Your suggestions speak to exactly what I was considering. Yes, I've got 'dem small parallel-walled room blues.
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You are more than welcome, happy to help.

My 3-bedroom house is now a 3-room studio and the master bedroom here is the control room. At 14x11x8, I have always known that there are mode problems , I just never realized how bad they were. I do have a contiguous (sp?) wall behind me and have been experimenting with varous forms of diffusion and absorbtion, now I know that a more drastic approach is neccessary.
Click to expand...

Well, its not necessary as drastic as you may initially think. I've built several studios for myself as well as larger studios for friends, with their assistance. Most, if not all, had more concrete, flat walls, and other undesirable traits in them. The most important thing to decide before you do anything, anything at all, is whether you want a dead room, a live room, a listening room, or something in the middle somewhere. From there, you can decide whether treatments, rebuilding the wall with different, denser materials, or moving the wall to a new angle is your ticket. Sometimes, the solution is a mix. Your ears know best.

How would three rounded, convex sections along the back wall work? Should they be filled?.....How about tuned traps or building the corners in?....
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Tuned traps for a home studio are overkill, in my opinion. Auralex and other companies have foam blocks that are 1'x1'x1' that fill the corners and absorb nicely. Duct taping two down pillows in each of the back four corners actually do very well. Yes, I said down pillows :)

Rounded deflectors tend to spread the sound out evenly. Triangular, or angled deflectors, tend to create dead spots elsewhere, which might be okay if you sit in approximately the same spot. You will notice most deflectors are a combination of bumps, angles, circular domes across the 2'x2' surface. This dispurses the sound the most.

A friend of mine (being as cheap as they come) purchased one such deflector tile, and plastered the wall. After plastering, while the plaster was wet, pushed the tile against the wall repeatedly. Sorta like a mosaic imprint. It worked well until he discovered that 3" thick wet plaster tends to become extremely brittle when it dries. Anyway, I'm just speaking aloud here. It popped into my head. Try the plywood thing, and see if angling the wall helps. If it does, thats probably the cheapest solution. A few 2x4's and a few pieces of sheet rock won't amount to much compared to some of the better quality, fire retardent wall treatments.

Hope that helps.
 
digido.com talks about this phenomenon. It happens when you are sitting in an antinode.

I think I read that repositioning the speakers could also help
 
In a room with the dimensions provided, I would suggest that treatment of the rear wall alone will not be sufficient to create a level of accuracy. Your comments re low frequency 'disappearing' at certain positions indicates this.

It would be helpful if you could post a drawing indicating the position of your monitors relevant to the walls, as well as detail the current surfaces in your control room (including ceiling).
 
You're right. Absolutely right.

I made the assumption that he wouldn't want to move his monitors. I wouldn't move mine. :) The reason being is ergonomically, they are in the right place for where I sit in my "special" chair, in front of the console table. For some reason, maybe incorrectly, I'm more picky as to how my workspace is set up as compared to rebuilding/slanting a wall.

Go figure.

CyanJaguar said:
digido.com talks about this phenomenon. It happens when you are sitting in an antinode.

I think I read that repositioning the speakers could also help
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It would be helpful if you could post a drawing indicating the position of your monitors relevant to the walls, as well as detail the current surfaces in your control room (including ceiling). [/B]
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Razor - Sjoko2 is right, is there any way you could make a diagram like the one I attached? (Its a 91K .bmp file).
 

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Thanks guys,

I really appreciate all your help. Sjoko2, Fred I would love to post a floor plan, but I am sorta graphically challanged. I just have never learned anything about creating .bmps or any others.

I'll try to paint it in less than (a pix is worth a...) 1000 words. All descriptions will be from the perspective of the mix position.

Comp monitor and monitor speakers are close (6" to a foot) from one of the shorter walls (11') about 4" off the ground. I sit in my "special chair" 5-6 feet out into the room. The front wall is heavily foamed and there is more over head for direct reflection management. There are Leonards (2) in each of the front corners and spot treatment on the sides.
I have racks on either sides of me there is a window with curtains on my right side just behind the mix position. The entrance door is on the wall on my left all the way back. The back wall is uninterupted and, for now, untreated. I breifly tried experimenting with some plywood as suggested and didn't get any great results....will try more.

Obviously the back wall is the question. Also I know I need to address monitor placement. Untill now they have been on a shelf against the wall that also hold bears the comp monitor, so I have had my hands tied as to placement. I am looking for some stands.

That will have to do. Any suggestions would be so greatly appreciated. I start an indi CD project soon (just got a Dstressor and some nice mics, WOW!!!!) I don't event want to get to used to them until I get the room happening.


Charles Rieser
Southwind Studio
Austin, Tx
 
Just another quick thought: I see many designs that have the room oriented towards a corner. This has also been against my instincts, but it seams to work for people. I guess that way speakers would not be right in a line between two parallel walls.
Is this maybe the answer?

Thanks again,

Charles
 
All good suggestions guys !,
The only question is time?-money?-and the balance between the two. I would try - 1) repositioning your rig first, try moving yourself back about a foot ( you mentioned you had audible differences there) then - 2) Adjust your monitors in and out accordingly, THEN - 3) If needed, as a last resort, try some simple acoustic treatments.

Good luck, Every room has it's own unique characteristics and quirks to be worked out - even if it was constructed from scratch with the best acousticians and materials available!
 
I really appreciate all your help. Sjoko2, Fred I would love to post a floor plan, but I am sorta graphically challanged. I just have never learned anything about creating .bmps or any others.
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You're welcome, happy to help if I can. If you want to do a picture, you can use pbrush.exe or even Microsoft Office's powerpoint. Just think in "feet" while drawing "inches". Anyway, from what you typed, I don't think a drawing is necessary.

From what you described, you need a little more than back wall treatments. I would suggested that you put Lenards in all four corners, and 4' along the ceiling seam to the wall, at the back wall. You can use cubes in the corners. This should round out the bass a little bit.

The rear wall can use reflectors (diffusers) or absorption material. Whats majorly (if thats a word) hurting your bass is the racks on the sides. How wide are they? 19-25 inches or so (one rack wide), or do you have several racks wide of space? I ask, because you might considering making a panel to go over the front with foam on the front surface, and just lean it on the racks. A nice handle for easy removal and positioning. Can the racks be moved to the front corners, or is that not really feasible?

Also, you might try angling the monitors slightly to face where you sit if they are blasting straight back. As you know the sound coming out of the woofers tend to disperse in a cone pattern, spreading out as the waves travel. If you angle them towards each other slightly, you have less bass energy flowing down the wall, and sometimes that reduces standing wave issues. Though, sometimes it creates a cancellation right by your ears in the center - its one of those "adjust and see" type of things. Whats neat is rotating your speakers don't cost anything :)

You have absorption material spread out along the sides - thats very good. Typically, I've found that 2x2' tiles, with 3" of space between them, exposing the wall surface, offers the flattest response in rectangular rooms. Of course your mileage might vary. Covering the entire wall end to end often makes tuning bass issues and high issues very difficult. Moving 2x2' tiles around is much easier than changing layers :)

Hope that helps.

Frederic
 
I've read this whole thing and I pretty much understand it, and I assume I have room problems because I have no room solutions whatsoever. I saw the part about how you can test your room, but can someone kinda describe in detail how to test my room? (without buying lots of $$ equipment)
 
Sure, my method wasn't very scientific, but it told me what I needed to know.
All I did was generate sine waves (pure tones) at different frequencies and walk around the room while they were playing. I did this with Cool Edit Pro though I imagine there are lots of ways to generate pure sine waves. Try tones at 60, 80. 110, 140, 180, 240, 300, 380, 460 hz.....(you get the idea) and move around for each one. For certain frequencies you may notice drastic volume differences in different parts of the room. These differences are the result of standing waves.
I had a pretty good idea of where my troubles were because I have sat here so many hours listening.

Good Luck,
Charles
 
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