# what to do with 31Hz and 38Hz room modes?



## tpaxadpom (Jul 15, 2006)

I have 31Hz and 38Hz room modes. The room has been treated with multiple bass traps (Auralex foam and rigid fiberglass based bass traps) that for obvious reasons have no effect on such low frequencies. I've heard of panel membrane and Helmholtz resonator types that can be tuned to lower frequencies. What is the common treatment for room modes in this frequency range?


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## atledreier (Mar 2, 2007)

Helmholtz or EQ.


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## tpaxadpom (Jul 15, 2006)

Panel membrane type seemed very attractive to me but I wasn't able to find calculation formulas to calculate the Q of the panel. I only saw formula to calculate frequency range given membrane density and depth of the box.
I don't use PC as the main source and have no plans on adding the EQ.


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## cinema mad (Jan 28, 2007)

I would & am going with Helmholtz resonator to treat the very low modes 

My design so far has A band width of 73.80Hz/ center frequency of (f res) 68.66Hz/ Q .93 / f low 31.7Hz / f high 105.56Hz/ port length 2cm / port diameter is 70cm/ & the volume is 421.88 Lt..

Note that with Helmholtz resonators they work best positioned in high pressure zone's..


Cheers....


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## cinema mad (Jan 28, 2007)

tpaxadpom said:


> Panel membrane type seemed very attractive to me but I wasn't able to find calculation formulas to calculate the Q of the panel. I only saw formula to calculate frequency range given membrane density and depth of the box.
> I don't use PC as the main source and have no plans on adding the EQ.


Hi tpaxadpom I have A calc that I got from this forum (Brian I think), that gives you the Q for Helmholtz and also does alot of other types of acoustic panels if you want it PM me or I will post A link...

Cheers....


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## tpaxadpom (Jul 15, 2006)

cinema mad, thanks for sharing the info. I have a closet in my 2 channel dedicated room. The house was built by the subcontractor company that didn't want me to do any changes. I don't mind the closet and thought I could build membrane bass trap inside the closet tuned to 30-40Hz range. The closet is likely too deep for panel resonator. I always keep one door open as I get more even frequency response in the sweet spot. If I can build something that I can stick inside the closet assuming the door stays open that would've been the ideal case. The only caveat is that the closet is on the opposite side of the room where the main speakers are. With the room emphasis they measure down to 16Hz at -3dB. I also have couple of SVS PB13-Ultras in my room that help me out to even out the frequency response and they are located next to the futon I sit on.

I will PM you for calculator.


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## Chriswil (Jun 14, 2010)

Hi Jason

I came across your old message, but I didn't see any further message about whether it was succesful. Did your resonator work? My Calcualtor actually puts the resonant frequency slightly lower than yours at 65.9Hz. If you can still remember how much effect did it have (any before and after measurements?) and what was the actual resonant frequency in the end?

regards

Chris


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