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U6astik
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Room mode distribution plots

Hello,

Could tell if there is any possibility to fix my room acoustics depending on the room mode distribution plot?

There are big gapes between some frequencies, while others seem to be too close to each other. Alton Everest in his Handbook of Acoustics suggests that gapes should be in region 5-20Hz.

If they are not, how can I understand what measures (diffusion, absorption, reflection) should I take and in which regions (floor, ceiling, front-, back-, side- wall)?

Thank you

Axiom05
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Bass Traps

Don't get too hung up on what the calculations are telling you, low frequency behavior in real rooms is much more complicated than that. Most (many) low frequency problems can be "fixed" by using low frequency absorption, i.e., bass traps. How much absorption will depend upon the frequency range of the problems as well as the intensity. Go to the RealTraps web site (link below) and read all of the articles and watch the videos. There is a ton of useful information on this site to educate yourself on low frequency room problems. Invest the time and effort to fully understand what you are dealing with. Warning: fixing low frequency problems can get very expensive if you are trying to deal with frequencies below 60Hz or so. The products really work (as do products from other makers). Once you experience tight, controlled bass in your room, you will never want to be without it. Personally, I use RealTraps in my room and can fully recommend their products and support.

http://www.realtraps.com

Additional information can be found at

http://gikacoustics.com

U6astik
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To Axiom05

Thank you for the info.

I've heard about RealTraps, I am now researching this area.smiley

tmsorosk
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Plots

The Op didn't say what audible problem he/she had if any, just that the distribution plots were not right. 

geoffkait
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Low frequency response

Ironically the 5 - 20 Hz region has oft been described as in audible.  Besides, there are precious few systems capable of reproducing frequencies below 30 Hz much less below 20 Hz.  Perhaps even more serious, room aberrations extend through the upper bass, midrange, all the way up through the highest frequencies.  In terms of spoiling the sound, I suggest that the upper bass, midrange and high frequencies are the worst offenders.  An ordinary man has no means of deliverance.

 

Geoff Kait

Machina Dynamica

U6astik
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True

tmsorosk is right.

Lets suggest that I have a mode distribution plot like this:

http://www.pixhost.org/show/1638/14135785_axial-mode-distribution-plot.png

I would like to know - how will the sectors like "A" (modes are too close to each other) and "B" (modes are too far apart) affect the frequency responce of my room.

As I understand (or may be misunderstand), too close modes ("A") will emphasize certain frequency range (about 175 Hz, as seen from picture), while the "hole" where the modes are separated too much ("B"), will result in absence or significant degradation of those frequencies (180 - 220 Hz) in my room.

Is it right?

Thank you.

U6astik
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To geoffkait

Sorry, but you didn't get it.

...the gapes (!) between room mode frequencies should be in region of 5-20Hz.

That means: "Frequencies that are closer to each other than 5 Hz or frequencies further apart from each other than 20 Hz result in poor in-room acoustics."

geoffkait
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Gapes

Thanks for the correction, now I see what you meant.  My bad.

 

GK

MD

U6astik
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Update

I would appreciate if somebody could answer the post #5.

Axiom05
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Yes, your understanding of

Yes, your understanding of the theory is correct: too close of a spacing between modes will empasize certain frequency ranges while large gaps between modes will result in a lack of modal support. e.g., nulls, at other frequencies. However, reality is much more complicated than that. There are also tangential and oblique modes and it is very difficult to predict the effects on the room response. There is also constructive and destructive interference due to the build up of sound waves in the room at low frequencies. In a nutshell, trying to predict and manage low frequencies in a listening room can be a nightmare! In my own listening room the axial modes seem to have no effect whatsoever. For example, I should have a mode at 35Hz, yet this frequency seems to be totally absent from the room. If you are truly interested in room mode calculations, try the calculator that I have linked below.

http://www.bobgolds.com/Mode/RoomModes.htm

U6astik
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To Axiom05

Thank you for your explanations about the plots.

I have used the online calculator from bobgolds.com, but to be honest, I prefer the .xls room mode plot from http://www.studiotips.com/tools/MODESv2p.zip and online tool from http://amroc.andymel.eu/. They offer more readable plots (and they do offer axial, tangential and oblique modes).

But I have to agree that the calculator on bobgolds.com is however, sometimes more useful, as it shows the weighting of sertain room modes (%)

Axiom05
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That % value is actually the

That % value is actually the spacing percent. It is the percent difference between one mode and the one lower in frequency to it.

U6astik
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That %

Ow.

OK, I got it. Then, unfortunately, there is not so much help in that calc.sad

IMHO

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