Unusual room resonance frequency

[bachatero]

A few months ago, I was playing around with a sine generator in my desktop audio setup and found that my bedroom has a huge resonance at almost exactly 129 Hz. I then applied the appropriate PEQ filter to bring it in line with nearby frequencies and that was that.

For Christmas I got a UMIK-1 and found the same exact thing again in my room, a huge resonance at 129 Hz. However, that got me thinking about this more seriously. The dimensions of my bedroom are 11.75 x 8.2 x 11.75 feet or 3.58 x 2.5 x 3.58 meters. By dividing them by 340m and getting the inverse, it looks like my bedroom SHOULD resonate at 95 Hz or maybe 136 Hz. That's not anywhere close to 129. How is this possible?

 

[fpitas]

Maybe a multiple of a lower frequency mode? My 41Hz mode reappears as 162Hz, for example.

 

[bachatero]

129 / 2 is about 64 and 129 / 4 is 32. The horizontal diagonal of my room is sqrt(3.58^2 * 2) = 5.06m, which equals 67Hz. 67 * 2 = 134, so still not quite 129. Even getting that diagonal plus the vertical is just 60Hz or 120Hz. I'm not sure if diagonals can even create resonances. In other words, there's no obvious way for this to happen unless the wave is actually going through the plaster wall and resonating in a different space. Anybody else have any other ideas?

 

[Balle Clorin]

But still it does… many reflections , front Black, side, ceiling , floor, …. Try some of the online simulators or the REW simulator. Also room walls/windowns Are fleksible and theoretical values can deviate by 10% or more, my main bass mode does that..

 

[Duke]

I recall reading in @Floyd Toole 's book about a listening room built for research that was extremely solid, with the door being an extra-rigid studio-quality door. When they measured the low frequency modes of the room, the lowest mode in the dimension that included the door was lower than expected, as if the room's length in that dimension was several feet longer than it actually was. Despite all the efforts they had gone to, that door was in effect a "soft spot", such that the effective acoustic dimension of the room at very low frequencies was different from the actual physical dimension of the room.

I came away from this story with the impression that the physical room dimensions are not necessarily reliable predictors of modal behavior at low frequencies because of the inevitable "soft spots" in the room's boundaries. Whether this phenomenon or something like it is behind to your 129 Hz resonance, I don't know.

 

[bachatero]

I came away from this story with the impression that the physical room dimensions are not necessarily reliable predictors of modal behavior at low frequencies because of the inevitable "soft spots" in the room's boundaries. Whether this phenomenon or something like it is behind to your 129 Hz resonance, I don't know.

This is in fact is the perfect explanation for my 129 Hz resonance. My room has two doors facing opposite to each other at the corners, and my speakers are only a couple feet away from each door. Therefore, it makes perfect sense that these doors would create a soft spot meanwhile the speakers' placement accentuates their output in this area.

 

[olieb]

If your room is not a cuboid because of the doors a lot of things can happen.
But this can be a cuboid room mode nevertheless, a so-called "oblique mode". That is a mode that has nodes in all three dimensions.
Actually there are two different modes (1,2,1 and 2,1,1) with the same frequency (127 Hz) in your room.

Calculate Room Modes

www.mh-audio.nl

Simulated in REW.

 

[neRok]

A few months ago, I was playing around with a sine generator in my desktop audio setup and found that my bedroom has a huge resonance at almost exactly 129 Hz. I then applied the appropriate PEQ filter to bring it in line with nearby frequencies and that was that.

For Christmas I got a UMIK-1 and found the same exact thing again in my room, a huge resonance at 129 Hz. However, that got me thinking about this more seriously. The dimensions of my bedroom are 11.75 x 8.2 x 11.75 feet or 3.58 x 2.5 x 3.58 meters. By dividing them by 340m and getting the inverse, it looks like my bedroom SHOULD resonate at 95 Hz or maybe 136 Hz. That's not anywhere close to 129. How is this possible?

Plug your dimensions in to SBIR Calculator and see what it says.

 

[Flaesh]

You can [try] to look for the cause of the resonance. For example, the peak of the SBIR effect will move in frequency according to the movement of the speaker, and for modal resonance the frequency will not change, but the amplitude will change [more or less] in accordance with the theory.