I need some help taming spikes in my rooms response

Hi all, I posted here a while ago looking for advice for acoustic treatment for a bedroom studio (two, actually, one for summer and one for the school year here at Purdue U.) and I got some really helpful info. I ended up coming across a great deal on some auralex products so I coudn't pass it up (a friend of mine was getting rid of his stand mounted lenrds and max wall out of his studio). I have it all installed now, and the room's sound is VASTLY improved, which is to be expected. The only problems I am having now are two big spikes at 114hz and 146 hertz (about 30 db from average). I have removed the mirrored closet door from the room and was thinking that maybe turning this closet into a bass trap would help, but I don't know HOW MUCH it would help. The room is your typical 10' x 13' x 8' bedroom converted to temporary project studio. I don't know very much about what causes these problems, other than the fact that every room has its own specific set of modes, etc. It's just funny that these two frequences in particular are problematic, and this makes me think that something in the room is resonating at these frequences. One of the side walls has two windows on it, so that might be the issue, or perhaps it's the desk I am using. Another thing to note is that the ceiling begins at an angle and then flattens out at both the front and the back of the room. It's like the ceiling starts to angle up to create a pyramid shape, and then is cut off by the flat ceiling. The angled parts are about 3.5 ft. I understand that this might not be enough info, but it's all I can think of for now. Please don't hesitate to reply if you have any ideas! Thanks for your time, - Nick

I'm not seeing any modal reasons for your peaks - can you post a drawing showing EXACT dimensions between walls, floor, ceiling and your head and speakers? Speakers, - how far from each wall, measured from center of woofer - ditto floor and ceiling. Head - same measurements. You have one axial mode at 113 (2nd harmonic of the 10' dimension), slightly supported by a tangential at 112 - not enough by itself to cause your problem. Other than that, a slight hole in modal density at around 55 hZ is all the dimensions show. However, positioning in the room can cause you or your speakers to be located in an antinode of one of your modes, and that WILL cause particular frequencies to be exaggerated. If you can post a plan showing all the above distances, I can probably point you toward a fix... Steve

Thanks for replying, Steve. I also forgot something important from my last post: There is a radiator in the corner of the room, in the corner opposite the closet (diagonal from the door). For this reason, I am unable to get my fourth bass trap all the way in the corner. Instead, I have it standing against the wall and the radiator (which isn't hooked up, so there is no danger of it burning the bass trap). I am unable to remove the radiator because this is rented space. Could this be the problem? Here is the drawing from my original post: My desk, which is 46x24x41 in. is placed 30 in. from the back wall, with an Auralex max wall between the wall and the desk. My head and speakers are both 42 in. from the ceiling, and 51 in. from the floor. My head is 59 in. from the side walls, 68 in. from the front wall, and 79 in. from the back wall. The speakers are about 53 in. from the side walls and 35 in. from the front wall. The speakers are 33 in. from one another, and the same distance from my head. I have attempted to roughly modify the drawing (which a friend did for me originally) to show the placement of myself and the desk. I hope this is enough info, and thanks for your time! - Nick

Your drawing was a bit rough - I resized the important part and scaled locations of your head and speakers (the circles) - I also superimposed the axial mode plots for length and width, and drew red lines for no-no's and green ones for good placement - so wherever horizontal and vertical green lines meet (and it's still symmetrical) is a good location - in some cases, just a few inches will make a noticeable difference. Your two problem frequencies are the second harmonics of height and width - for symmetry, you need to be centered left to right so there's not much that can be done about that one - if you could get your head/speaker height a bit further from centered vertically it might help the higher of the two frequencies. Your speakers and head are shown where they are now(the yellow circles) - you could try moving the speakers away from you and outward to the next green intersection (the green circles); this would put them at 44" from sidewalls and 32-33" from the front wall. Your head would move back about 2" mainly to keep close to an equilateral triangle. Does the irritating radiator go floor to ceiling, or could you possibly put some rigid fiberglass insulation across the corner ABOVE the radiator for a broadband trap effect (which would be duplicated in the other front corner)? I don't think this is the problem, it would just help if you could get symmetry side to side. Can't think of anything to add right now, maybe something else will come to me later... Steve

Hi Steve, Firstly, thanks so much for going to the trouble to make that nice diagram of my space and make these suggestions. Sorry about the roughness of my picture. I tried both lowering and raising my speakers in an attempt to break up the vertical symmetry, but I am still getting those two spikes. It is probably that stupid radiator vibrating or something, but I don't know much about this stuff so I could be way off. Let me know if you have any ideas about what else I could do. I will check back here as much as possible. Thanks again! - Nick