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Author Topic: Trapping these bass peaks...tubes or panels?  (Read 4030 times)

scoring4films

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Trapping these bass peaks...tubes or panels?
« on: June 25, 2010, 03:12:03 pm »

The peaks shown in these plots resonate quite noticeably when a bassline in a mix happens to pass through them.  My guess is that the ~103Hz peak is the room width and length resonating (136" and 132") and the ~118Hz peak is the floor to ceiling dimension (111").  Looks like the peaks are echoed up the octave at ~204Hz and 237Hz.

After much trial/error with monitor placement and mixing position, this seems to be as good as it's going to get.  

The room is already packed with four bales worth of large SSCs (Roxul corner traps).  

So now what?  Would you go with tuned/open-ended sonotubes or panels?  Maybe both?

If tubes are the way to go, should their lengths be chosen according to the room dimensions or these REQ plots?

Will it take a half dozen or more tubes to make an impact on these peaks?

Should I skip the bass trapping for now and make a cloud first?

What about the big null centered at ~88Hz?  Will taming the peaks flatten it out also?


Any suggestions greatly appreciated!


thanks,
t
p.s. this question is also posted in the acoustics forum at GS

http://www.ftylershaw.com/30-300%20june25%20spectrum.jpg

http://www.ftylershaw.com/30-200%20june25%20waterfall.jpg
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Ethan Winer

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Re: Trapping these bass peaks...tubes or panels?
« Reply #1 on: June 26, 2010, 12:32:32 pm »

Your room is almost square, and very small, but with only four corners fitted with bass traps that's only 1/3 of the available corners. So I'd look at bass traps in the wall-ceiling and even wall-floor corners where possible. Very thick traps flat on the front and rear walls will help further. I would not use tuned absorption in a room like that. Broadband is the ticket, with traps as thick and as many as possible.

--Ethan

scoring4films

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Re: Trapping these bass peaks...tubes or panels?
« Reply #2 on: June 26, 2010, 04:00:37 pm »

Thanks as always Ethan.  After getting one of the main room modes going with a sine wave (~103Hz) and walking around in the resultant "forest" of peaks/nulls, I noticed the highest volumes were at the back wall.  I thought about hanging some roxul batts there, but read somewhere that you can't trap low bass with a device that is physically smaller that the 1/4 wavelength of the low bass in question.  Guess that's not really true (?)

So how thick is "very thick"?  Will 6" do it (two layers of Roxul SnS)?

cheers,
t    
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Constantin

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Re: Trapping these bass peaks...tubes or panels?
« Reply #3 on: June 27, 2010, 06:22:30 am »

porous absorbers should be placed in the point of maximum flow, not in the region of maximum pressure.
search the corner with minimum soundpressure at 193hz for best performance at 103hz
cheers

bruno putzeys

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Re: Trapping these bass peaks...tubes or panels?
« Reply #4 on: June 27, 2010, 09:00:09 am »

By definition a hard surface has a velocity of zero. A corner doubly so...
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Constantin

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Re: Trapping these bass peaks...tubes or panels?
« Reply #5 on: June 27, 2010, 09:06:18 am »

@ bruno

the world is 3D  Razz
when you place a pannel in the middle over a wall/celling corner, it is in the middle of the Wall/wall dimension.
when you look at a 3d model pressure plot, you will clearly see what i mean

have a look at this tool:

http://www.trikustik.at/rechner/rechner-raummoden.html


cheers

Ethan Winer

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Re: Trapping these bass peaks...tubes or panels?
« Reply #6 on: June 27, 2010, 02:02:12 pm »

scoring4films wrote on Sat, 26 June 2010 16:00

read somewhere that you can't trap low bass with a device that is physically smaller that the 1/4 wavelength of the low bass in question.  Guess that's not really true (?)


Yes, that's not true. Further, you don't need to absorb 100 percent to improve the LF response significantly. If a reflection is reduced from 100 percent reflecting to 6 dB down (50 percent absorption), a null that was infinitely deep is now only 6 dB deep. This is a huge improvement! Even 25 percent absorption reduces an infinite null to only 11 dB deep.

Quote:

So how thick is "very thick"?  Will 6" do it (two layers of Roxul SnS)?


The thicker the better, but 6 inches is good.

--Ethan

Thomas Jouanjean

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Re: Trapping these bass peaks...tubes or panels?
« Reply #7 on: June 27, 2010, 06:17:45 pm »

Constantin wrote on Sun, 27 June 2010 08:06

@ bruno

the world is 3D  Razz
when you place a pannel in the middle over a wall/celling corner, it is in the middle of the Wall/wall dimension.
when you look at a 3d model pressure plot, you will clearly see what i mean

have a look at this tool:

http://www.trikustik.at/rechner/rechner-raummoden.html


cheers


Nice little app!
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Thomas Jouanjean
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Thomas Jouanjean

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Re: Trapping these bass peaks...tubes or panels?
« Reply #8 on: June 29, 2010, 09:46:40 am »

I would suggest you put your commercial or rockwool panels at a healthy distance from the walls too. It will make a difference in their efficiency (re: what Constantin said).
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Thomas Jouanjean
Northward Acoustics - Engineering and Designs
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franman

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Re: Trapping these bass peaks...tubes or panels?
« Reply #9 on: July 05, 2010, 09:43:46 am »

Yes.. I like this app as well. It reminds me of the 'acoustics' software that Pilchner Shoustal used to sell a few years ago.. AcoustiX... showed the pressure distribution of the modal response... It was a great learning tool.
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