helmholtz resonator question

ok so Ifigure it out what to do with my basement http://www.johnlsayers.com/phpBB2/viewt ... t=basement ,and I am planning to make holes on plasterboard on the celling, to use it like Helmholtz resonator. here are the room modes Room Length : 4.7 meter Room Width : 2.9 meter Room Height : 2.10 meter === Axial === Axial Length 36,20Hz Hz 72,40Hz Hz 108,61Hz Hz 144,81Hz Hz 181,01Hz Hz 217,21Hz Hz 253,41Hz Hz 289,62Hz Hz 325,82Hz Hz Axial Width 58,67Hz Hz 117,34Hz Hz 176,02Hz Hz 234,69Hz Hz 293,36Hz Hz 352,03Hz Hz 410,71Hz Hz 469,38Hz Hz 528,05Hz Hz Axial Height 81,02Hz Hz 162,05Hz Hz 243,07Hz Hz 324,10Hz Hz 405,12Hz Hz 486,14Hz Hz 567,17Hz Hz 648,19Hz Hz 729,21Hz Hz === Tangential === Tangential Length & Width 68,94Hz Hz 122,80Hz Hz 179,70Hz Hz 237,47Hz Hz 93,19Hz Hz 137,88Hz Hz 190,33Hz Hz 245,60Hz Hz 123,44Hz Hz 159,89Hz Hz 206,83Hz Hz 258,60Hz Hz 156,24Hz Hz 186,38Hz Hz 227,93Hz Hz 275,77Hz Hz Tangential Length & Height 88,74Hz Hz 166,04Hz Hz 245,75Hz Hz 326,11Hz Hz 108,66Hz Hz 177,49Hz Hz 253,63Hz Hz 332,08Hz Hz 135,50Hz Hz 195,08Hz Hz 266,23Hz Hz 341,81Hz Hz 165,93Hz Hz 217,32Hz Hz 282,94Hz Hz 354,97Hz Hz Tangential Width & Height 100,04Hz Hz 172,34Hz Hz 250,05Hz Hz 329,36Hz Hz 142,60Hz Hz 200,07Hz Hz 269,91Hz Hz 344,68Hz Hz 193,77Hz Hz 239,25Hz Hz 300,11Hz Hz 368,81Hz Hz 248,28Hz Hz 285,20Hz Hz 337,88Hz Hz 400,15Hz Hz === Oblique === 106,39Hz Hz 176,10Hz Hz 147,12Hz Hz 123,49Hz Hz 159,93Hz Hz 186,93Hz Hz 203,32Hz Hz 212,77Hz Hz so above the plasterboard is metal grid but and above the grid is 20 cm (7,87'') of mineralwool. between the plasterboard and mineralwooi is 2cm (0,78'') air gap. so my question is can I and where make hole to for best performance. Helmholtz Resonator, 14. listopad 2008 - 15:10:16 ------------------------------------------------------ Height : 100 cm Width : 45 cm Depth : 2 cm Port length : 1,25 cm Port diameter : 6 cm Port area : 28,27 cm2 f res : 124,76 Hz Volumen : 9,00 Liter Q : 1,25 Bandwidth : 99,55 Hz f-low : 74,99 Hz f-high : 174,53 Hz ---------------------------------------------- IF you has any idea it would be nice thanks

Forget room mode prediction tables because they're rarely accurate once the room is built. The proper way to assess modes in a room is to measure with software: ETF, Windows, $150 FuzzMeasure, Mac, $150 Room EQ Wizard, Windows and Mac and Linux, Freeware This article explains how I use ETF, but the principles apply to all such programs. Also, a room that size will probably do better with simple bass traps made from rigid fiberglass rather than tuned Helmholtz traps. That way you absorb all frequencies in all corners. Versus trying to build 75 different trap types. :) --Ethan

thanks for reply know that predictions are not good, I just wanted to know can it be done that simple, and if "stop" firs freq with the helmholtz res. I didn't understand ETF $ is without mic and preamp? think I'll use REQ but still have to buy mic

Yes, ETF is $150 for just the software. If you have REW that's at least as good if not better. More on suitable microphones: Comparison of Ten Measuring Microphones --Ethan