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Which of these corner trap orientations is best? Effects Pedals, Units & Accessories
Old 16th September 2011
  #1
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Which of these corner trap orientations is best?

Which of the three orientations of a floor-to-ceiling panel of rockwool would be best to trap bass?
Thanks!
Jeff
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Which of these corner trap orientations is best?-trap-placement.jpg  
Old 16th September 2011
  #2
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SörenHjalmarsson's Avatar
 

A generall question can never get more than a generall answer, but the generall answer is: C (straddling) is the most efficient position for velocity based absorbtion.


MVH
Old 16th September 2011
  #3
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Glenn Kuras's Avatar
C would be, but if you put another panel with B (closing the space) I would think that would be better over C but cost twice as much to do. If you want C to work the best then straddle the corner so it is 48" across and 24" high. Note though you would only do this if you have the budget as you really want to cover as much corner area as possible. Bit more info then you where asking for but thought I would point it out.
Old 16th September 2011
  #4
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avare's Avatar
 

A big +1 (or is it 3?) for c.

Numerically,
Andre
Old 16th September 2011
  #5
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Interesting. I must be wrong in visualizing how sound travels. I saw it bouncing all around in every direction, so I figured to suppress it you need to have the panel where the greatest number of angles will strike it. That's why I figured 'A' would catch more than 'C', because it sticks out further into the room. But from what you're saying, I suppose the key is to have as much of the material as far away from the corner as possible, because the material isn't useful if deep into and touching the corner?
Old 16th September 2011
  #6
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aackthpt's Avatar
 

Quote:
Originally Posted by MusicManic View Post
I saw it bouncing all around in every direction, so I figured to suppress it you need to have the panel where the greatest number of angles will strike it. That's why I figured 'A' would catch more than 'C', because it sticks out further into the room. But from what you're saying, I suppose the key is to have as much of the material as far away from the corner as possible, because the material isn't useful if deep into and touching the corner?
In some rooms higher frequencies could be said to "bounce all around in every direction", though not in a typical small room (certainly not in an untreated and unfurnished one). However you asked about low frequencies (bass "trap") which do not really ever do that in a small room. The strongest of the modes that you want to mitigate run straight along the main dimensions of the room in a rectangular room. Further, you are right that material directly in the corner is technically not contributing. So 'A' is out due to that. 'B' is out because it doesn't act on every direction. 'C' catches every direction, places all of the material somewhere advantageous, and also takes advantage of a "trampolining" seen when placing panels across the corners that way.
Old 16th September 2011
  #7
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SörenHjalmarsson's Avatar
 

Quote:
Originally Posted by MusicManic View Post
Interesting. I must be wrong in visualizing how sound travels. I saw it bouncing all around in every direction, so I figured to suppress it you need to have the panel where the greatest number of angles will strike it. That's why I figured 'A' would catch more than 'C', because it sticks out further into the room.
Mr Brandt explained it like this at one point (might help you to vizualize):

"Sound waves (wave region) are reflected at boundaries. (all frequencies are reflected at boundaries of a highly reflective surface) Multiple boundaries, like corners, will focus these waves. Therefore the corners are a good place to catch them - like fish. So, bass traps work best in corners."

And this is from Wikipedia:

"Since low frequency resonances in a room have their points of maximum pressure in the corners of the room bass traps mounted in these positions will be the most efficient. There are three main places where a bass trap can be positioned: a tri-corner, a wall-wall corner and on the wall or ceiling. There are bass traps designed for explicitly for placement in each location. Bass traps are typically used to attenuate modal resonances and so exact placement depends on which room mode one is trying to target. Bass traps typically combine structural mechanisms that can work at both positions of high particle velocity/low pressure (thick fiberglass) and high pressure/low particle velocity (membranes)."

Quote:
But from what you're saying, I suppose the key is to have as much of the material as far away from the corner as possible, because the material isn't useful if deep into and touching the corner?
The SSC (or superchunk) is actually a slightly better performer than the straddle. Read the part on bass traps in the following article: Acoustic Treatment and Design for Recording Studios and Listening Rooms


MVH
Sören
Old 16th September 2011
  #8
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Glenn Kuras's Avatar
Fill up your sink full of water and drop something in the middle. That is how the low end will more or less react. heh Not totally right but you notice the waves don't run like a ray
Old 16th September 2011
  #9
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SörenHjalmarsson's Avatar
 

Preferably a sink with 90 degree corners...

Edit: And then imagine it happening in 3D!
Old 16th September 2011
  #10
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Quote:
Originally Posted by aackthpt View Post
..The strongest of the modes that you want to mitigate run straight along the main dimensions of the room in a rectangular room..
I'm trying to wrap my mind around this. So, if the source, say a bass amp, is placed in the center of a rectangular room, and the strongest room modes run straight along the main dimensions(which I'm visualizing as back and forth from wall to wall or ceiling to floor) wouldn't bass traps in corners miss most of the back and forth reflections?

Even if the corners focus the energy (I'm imagining like a whisperdish: WHISPER DISHES - YouTube) wouldn't it take a long while of parallel bouncing before the perpendicular wall to wall, ceiling to floor reflections finally gravitate towards the corners?
Old 16th September 2011
  #11
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aackthpt's Avatar
 

Quote:
Originally Posted by MusicManic View Post
I'm trying to wrap my mind around this. So, if the source, say a bass amp, is placed in the center of a rectangular room, and the strongest room modes run straight along the main dimensions(which I'm visualizing as back and forth from wall to wall or ceiling to floor) wouldn't bass traps in corners miss most of the back and forth reflections?

Even if the corners focus the energy (I'm imagining like a whisperdish: WHISPER DISHES - YouTube) wouldn't it take a long while of parallel bouncing before the perpendicular wall to wall, ceiling to floor reflections finally gravitate towards the corners?
I was trying to speak simply. Here's a better explanation:
A sound wave is not one-dimensional. It's more like the surface of a sphere (and it repeats, but that's another show). At very low frequencies the sphere is really large so the surface is nearly flat. So imagine a flat sheet of material moving perpendicular to itself (so, say, you and some friends using a sheet as a parachute while running down the street, except the sheet is literally made of air and it moves itself). The waves bouncing off the walls forming the modes, then, are like flat sheets bouncing between two walls (and parallel to them). The reflections don't need to gravitate to the corners, these waves are so big they are already there.

Since the corners are common to the walls, you can cover several directions at a time there which is one big reason it is a good place to put LF control devices.

It does take a few cycles after a sound is started for the standing wave ("mode") to develop, because it has to reflect a few times to set up the interference pattern. But consider that the sound waves travel at 1236 kph (768 mph). In a room with a typical length, let's say 3m, there are about 114 reflections per second across that distance, or one every 9 msec, so the build-up doesn't take all that long by ordinary measures.

The Whisper dish is a better analogy for what happens at mid and high frequencies, but not at LF. I don't suppose I've ever played an LF source into one though. That could be fun, though I imagine security would look at me strangely as I lugged a subwoofer into the museum (and tried to figure out where to plug it in near the whisper dish...).
Old 17th September 2011
  #12
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Thanks for the explanation. It makes more sense to me now, though it brings up another thought...
This massive spherical emanation seems beastly and ominous, yet just before the bass player plucks his first note it doesn't exist, or can be thought of as infinitely small. But, just after the first pluck, it grows quickly into this earthshaking beast. Is there any way to divert or tame it while it's still small? Perhaps focussing it, like the whisper dish, and redirecting it into a ghostbuster trap to be stored miles below the earth beside our nuclear waste?
Old 17th September 2011
  #13
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aackthpt's Avatar
 

Quote:
Originally Posted by MusicManic View Post
Is there any way to divert or tame it while it's still small? Perhaps focussing it, like the whisper dish, and redirecting it into a ghostbuster trap to be stored miles below the earth beside our nuclear waste?
There's no real way to "tame it" while it's still small except by enclosing it in an airtight passage, which is exactly what horn subwoofers do. Once it is out in the 'open' it immediately bends itself all the way around the cabinet of whatever is producing it and now it is going everywhere in the new space. You can, of course, take the room out of the equation by monitoring on headphones. Otherwise there's no escaping that the "sound system" literally is a system of speaker, room, and listener.

You might be well served with Bob's "bass guitar trap" though. Schematic diagram here.
Old 17th September 2011
  #14
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lol and thanks!
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