ceiling treatment without losing too much height

Hi everybody! For 2 months I`m already planning our new basement studio and I`ve learned a lot in this amazing forum!! Thanks alot, guys! Our control room (12,9 x 13 x 6.8ft) will be constructed on the basis of an RFZ design. (Multiple) Splayed walls, absorption on the back wall, no early reflections, etc. The room is very small and almost square (arrgggh), but we are doing our best to fight normal modes problems. We will use tuned Helmholtz-, panel- and slot-absorbers to deal with that. My question: While the horizontal design is almost perfect, we have problems concerning the design of the ceiling-treatment. The standard advice for treating such low ceilings is to make it as absorbtive as possible, mostly with 2"-4" 703. But we would lose too much height when applying so much 703 (my partner is quite tall ;-) . An idea was to use a thin layer of 703 (1/2"-1") in combination with a well calculated area of slot-absorbers with mininum depth (should be as effective towards "lower" frequencies as a thicker layer of 703, shouldn`t it?) to deal with the mids (low to high). I think this should be fine, because the main problem (concerning reflections between parallels) between ceiling and floor are the mids, because the high frequencing usually don`t reach the ceiling with so much intensity, `cause they are radiating from the speaker almost horizontally and only the lower frequencies, such as low mids, radiate more directly towards the ceiling. Am I right? Please help me with my basement ceiling! Everythings perfect until now, so I don`t want to lose so much sound quality because of poor or wrong ceiling treatment. Please help, thank you very much! Best wishes, Schroeder :P

I`ve forgotten a detail in my description: The floor is covered with laminate. Please help! :-] Thank you!

Schroeder, welcome to the board; I think that, under your circumstances you are on the right track - here's about as good as I can do for sizes, this would lower your ceiling a total of 2", or 50mm, and should be run so that the slats go sideways (left to right as you face your speakers) - you should do a complete (but not STUFFED) fill of insulation - if you can spare the height, 2" insulation and 2" furring strips would be better, then you could widen the slots a bit (easler construction) HTH... Steve

Thank you, Steve! It`s good to hear that my idea isn`t completely weired... :-) That`s fine! You propose using 273 Hz as centre frequency. That`s between two axial modes and will probably be one of the typical "muddy frequency", reflecting from the ceiling... What do think about additionally using other slot widths to deal with the modes directly? I`ve calculated 168 and 336. Or does the complete fill with insulation make the absorber so broadband, that different slot widths doesn`t make so much difference? Have a nice day! Schroeder

The insulation fill will broaden response somewhat, probably effectively around 3 octaves total; but I'm not getting the same modes you posted; are those dimensions using commas to replace decimal points, as in "12,9" means 12 feet nine inches, or is that 12 9/10 FEET? Steve

Hi Steve! Oh, I`ve made a mistake.... I`m not really common with your measuring system... ;-( Our room is 3,87m x 3,90m x 2,04m (lowest, 2,10 maximum). To convert it into feet I just divided the centimetres by 30, then you get the 12,9 x 13 x 6,8 (12 9/10 feet....) Calculation of the modes: f Dimension 1, length (m) 3,94 43,5 Dimension 2, width (m) 3,88 44,2 Dimension 3, height (m) 2,04 84,1 modes (unsorted) D1 43,5 87,1 174,1 348,2 696,4 1392,9 2785,8 D2 44,2 88,4 176,8 353,6 707,2 1414,4 D3 84,1 168,1 336,3 672,5 1345,1 2690,2 The modes under D3 are the one I asked about. The 84,1 Hz can`t be treated with a slat-absorber with a low depth. The 168,1 and 336,3 are lower or near 300Hz and could cause modal problems. What do you think?

OK, first you can convert meters to feet by multiplying meters by 3.28 - that puts your dimensions in feet at 12.8 feet, 12.7 feet, 6.79 feet (using average height) - this puts lower axial modes at 44.1 44.5 83.2 88.3 89.0 132.4 133.5 166.4 176.6 178.0 220.7 222.4 249.6 264.8 266.9 309.0 However, when you factor in tangential and oblique modes the only area where your room has modal balance problems would be a LACK of modes around the 40-60 hZ region - for that, normally just broadband corner trapping (including wall-ceiling corners) makes more sense... Steve

Thank you Steve! I think we got different values for the modes because of calculating with different sound speeds. You assumed a temperature of 21,5 °C (70.7F) and have got 1129.96 ft/s, I assumed 19°C (66.2F). I have to admit that the 70.7F are much more realistic in a control room with lots of hot beats... :-) Now lets go to the main issue... My idea was to deal with the modes individually because they are likely very strong (doubled in intensity because of two similar dimensions, and even tripled in the "80s"Hz). 2 Helmholtz absorbers (with filling, moderate q) to deal with the 44Hz in two corners, another 2 Helmholtz absorbers (with filling, moderate q), and 2 panel absorber on the side wall near the ceiling for the "80s" Hz (also not too high q). Everything above the "80s" I wanted to treat with some broadband absorption (backwall) and the slat absorbers on the ceiling/sidewalls (splayed). By building tuned absorbers for the modes which are "doubled" and two more for those who are "tripled", I thought I could get a quite linear response in the control room. Don`t the absorbers (40s / 80s) reduce the room response at these frequencies so that the lack at 60Hz is evened out?? When you think this concept is going to work - tell me. Thank you very much for your time! :-] Best wishes, Schroeder

Yes, that approach sound to me like it will work out; but before you go to all the work of building slats, etc, you may want to try just stacking thick batts of insulation in both rear corners of the room, and see what that does for you... Steve

Sounds good. I`ve already planned to do some measuring when the outer walls are finished. I`ll give the corner bass traps with insulation a try. I`ll see what they`ll do for the room response. Thanx a lot Steve!! 8)