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Author Topic: Unwanted resonance  (Read 1802 times)

ruffrecords

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Unwanted resonance
« on: December 18, 2007, 12:01:54 pm »

I have recently moved house and fitted out a top floor room as a studio/monitor room. It is quite small; 12ft 3in wide, 11ft 9in long and 7ft 5in high although, as it is an attic room, the ceiling slopes down on either side to just 3ft 6in at the sides.

I have fitted bass traps wherever I can and the walls and ceilings have plenty of foam attached but I have this annoying resonance that is particularly noticeable at the mix position - about one third the length back from the wall. I can easily hum the note and checking on my keyboard I find it is close to D# below middle C. From the web this appears to correspond to a frequency of about 155Hz and a wavelength of 222cm which is 7ft 3in i.e pretty close to the room height but also not far from a half wavelength of the distance from the mix position to the rear wall.

The resonance is fairly localised to the mix position - if I move my head a foot left or right  or back it is gone although it seems to last a bit further as I approach the wall nearest the mix position. It does NOT occur at the same postiion at the other end of the room.

Any suggestions as to how to fix it are welcome.

Cheers

ian
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Ethan Winer

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Re: Unwanted resonance
« Reply #1 on: December 18, 2007, 03:36:44 pm »

ruffrecords wrote on Tue, 18 December 2007 12:01

Any suggestions as to how to fix it are welcome.

More bass traps. Really, that's your only recourse. That, or move the mix position. If you can post a photo of your space we'll be glad to take a look and give an opinion.

--Ethan

gullfo

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Re: Unwanted resonance
« Reply #2 on: December 18, 2007, 10:12:42 pm »

it may be simpler to move yourself back a foot or so in the room. based on calcs you do have something around 151hz so with the wall-ceiling angle you're probably on the money for 155hz. since it disappears when moving or from the other end, its something to do with the location you've chosen. if you're situated about 38% (~4' 5")of the room depth from the wall (where this is occurring) does it still happen? being almost square it doesn't help to have the modes so few and spaced so far... so as Ethan pointed out, bass trapping is a good idea. the short wall is also a good space to build out some trapping since its usually not convenient for placing desks, monitors, etc.

From Measurements                     
      ratio   size   m   sqrt(2)   bolt   ebu   iec   > 5%h   1.00   7.42   2.26   0.17   TRUE   TRUE   FALSE   FALSEw   1.58   11.75   3.58   0.12            l   1.65   12.25   3.73   0.26                                       ax 1st   ~note   ax 2nd   ~note   ax 3rd   ~note   ax 4th   ~noteh   75.91   D2   151.82   D3   227.73   A3   303.64   D4w   47.91   F#1/Gb1   95.83   F#2/Gb2   143.74   C#3/Db3   191.66   F#3/Gb3l   45.96   F1   91.92   F2   137.88   C3   183.84   F3                           tot vol   tot surf edge   area   raw rt60 rate (ms)   Dc   mfpft   1068   644   126   144   1.07   341.68   4.46   6.63m   30.23   59.82   38.30   13.37                                       T(ms)   eyring   millington   Fcut   ~note   Fc   ~note   5.89   0.93   0.82      45.96   F1   254.68   B3                           ratios   diatonic stdev   modes   df      Fs   ~noteh-w   1.58   +V   0.02   125   1.18      375.88   F#4/Gb4w-d   1.04   +I   0.41               
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Glenn Stanton

www.runnel.com/

ruffrecords

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Re: Unwanted resonance
« Reply #3 on: December 19, 2007, 01:16:41 pm »

Ethan Winer wrote on Tue, 18 December 2007 20:36

[
More bass traps. Really, that's your only recourse. That, or move the mix position. If you can post a photo of your space we'll be glad to take a look and give an opinion.

--Ethan


Here are some pics

http://i103.photobucket.com/albums/m124/ruffrecords/newstudi o/newstudioNE.jpg
http://i103.photobucket.com/albums/m124/ruffrecords/newstudi o/newstudioE.jpg
http://i103.photobucket.com/albums/m124/ruffrecords/newstudi o/newstudioSE.jpg
http://i103.photobucket.com/albums/m124/ruffrecords/newstudi o/newstudioS.jpg
http://i103.photobucket.com/albums/m124/ruffrecords/newstudi o/newstudioSW.jpg
http://i103.photobucket.com/albums/m124/ruffrecords/newstudi o/newstudioW.jpg
http://i103.photobucket.com/albums/m124/ruffrecords/newstudi o/newstudioNW.jpg
http://i103.photobucket.com/albums/m124/ruffrecords/newstudi o/newstudioN.jpg


Cheers

Ian
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gullfo

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Re: Unwanted resonance
« Reply #4 on: December 19, 2007, 04:51:58 pm »

i think i would take advantage of the low walls and the low wall in the window alcove to put in low frequency absorption. you also have the option of putting some absorption on the wall/ceiling corners since that space looks like it would not interfere with the room space. putting an absorber between the windows will help also.

http://img530.imageshack.us/img530/2020/ruffrecords2wi2.th.jpg
http://img187.imageshack.us/img187/3603/ruffrecords1fm2.th.jpg
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Glenn Stanton

www.runnel.com/

Ethan Winer

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Re: Unwanted resonance
« Reply #5 on: December 20, 2007, 04:29:08 pm »

ruffrecords wrote on Wed, 19 December 2007 13:16

Here are some pics


Ian, I see only a few small foam triangles. To tame bass resonances you need real bass traps, and a fair number of them.

BTW, what brand of foam is that? Is it at least Auralex?

--Ethan

brett

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Re: Unwanted resonance
« Reply #6 on: December 22, 2007, 03:45:34 pm »

Glen and Ethan as always you guys are awesome! I might add a suggestion of shooting the room with an RTA to really pinpoint all the non tonal stuff your ears can't hear. I suggest shooting any room for professional work anyway. Wave lab, room eq wizard etc are good tools. Spectrafoo can be helpful as well. room optomizer...So buy or borrow a nice omni test mic and run some tones and see exactly where your issue are. then you can know if tuned solutions will be required to suppliment the great broad band solutions noted above.

And Gien, how do you do those CAD mock-ups so fast? what application?  
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gullfo

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Re: Unwanted resonance
« Reply #7 on: December 26, 2007, 03:56:50 pm »

i agree - measuring the room is your best bet because estimates only get you so far. ETF, REQ, and a number of other products are within reach for most people. as far as drawing - Sketchup Pro (+ many years CAD experience) and Kerkythea 2007
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Glenn Stanton

www.runnel.com/
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