Corner Trap Nonsense

[Keith_W]

I was wondering what ASR thinks of this video.

TLDR:
- Bass modes are formed by reflections from walls. Not the corners.
- What % of the wall is treated by the corners? Answer: a very small surface area.
- Corner traps are a marketing con designed to sell traps to people to put in corners, where there is usually nothing anyway

Sadly, no measurements.

 

[NTK]

I don't have measurements either, but here are my simulations.

For simplicity and expediency, I simulate only a 2-D rectangular room of 5.0 m X 3.5 m. (A 2-D simulation would represent floor to ceiling line sources in a rectangular room with perfectly reflective floor and ceiling.) Here are the first 22 room modes. For rectangular rooms, every mode will have pressure peaks at the corners, and therefore the reasoning behind "corner" trap (efficient locations to absorb/dissipate the pressure of every room mode).

I simulated in-room response for mode 9 (103.8 Hz). I had 2 speakers, both located 1/3 m from the left wall, one is 2/3 m from the bottom wall, and the other is 2/3 m from the top wall (you can notice the sources in the 2 bottom plots).

The top plot simulates all 4 walls with an absorption coefficient of 0.1 and no corner bass trap. The second from top plot simulates a bass trap (increase absorption coefficient to 0.8) that extends 1/2 m both horizontally and vertically from the lower left corner. The third plot adds another bass trap to the top left corner. The fourth plot adds a third bass trap to the lower right corner, and the fifth plot have bass traps in all 4 corners.

The simulations do show the trap(s) had some effects. Since these are only my highly simplified simulations, I'll let you make your own conclusion.

 

[olieb]

The simulations do show the trap(s) had some effects.

Sure, but you just simulated a surface absorption increase of 0.1 to 0.8. If you cover the wall with some texture that will hardly do anything to bass.
Typical bass traps are fibrous material that absorb movement of air through an area. They dissipate movement not pressure, but in the corners there is no movement. The traps become more effective the further they are from the wall.
A better place for a fibrous trap to reduce the mode would probably be at the yellow ellipse where the air moves most.

The video is right about the walls (not the corners) being the problem. There are room modes in cylinders and spheres too. (So it is not about parallel walls either.)
An he is right about the psychology and the advantage of selling for the corners. Who wants a big trap at the marked place in the middle of the wall?
If you have corners you could place (tuned) Helmholtz resonators there for absorption, these work in the pressure maximum.

 

[NTK]

Typical bass traps are fibrous material that absorb movement of air through an area. They dissipate movement not pressure, but in the corners there is no movement. The traps become more effective the further they are from the wall.

I am referring to membrane traps that respond to pressure, such as:

RPG Modex Corner - Acoustic Products

Modex Corner Products Products

www.rpgeurope.com

 

[Blockader]

The placement of porous absorbers in your room is not critical for absorbing low frequencies. Low frequencies have long wavelengths and are less affected by the specific location of the absorbers. Only where you put the membrane traps matter. Porous absorbers don't.

 

[Justdafactsmaam]

I was wondering what ASR thinks of this video.

TLDR:
- Bass modes are formed by reflections from walls. Not the corners.
- What % of the wall is treated by the corners? Answer: a very small surface area.
- Corner traps are a marketing con designed to sell traps to people to put in corners, where there is usually nothing anyway

Sadly, no measurements.

This guy is full of crap. Ethan Winer said it best. He knows just enough to be dangerous

 

[olieb]

I am referring to membrane traps that respond to pressure, such as:

Yep, membrane (oscillator) absorbers will work too (like the Helmholtz') on walls and in corners. These are tuned to 60-70 Hz but still rather broadband. The lowest and probably strongest mode in the modeled room is the first length mode at 34 Hz, the Modex absorbers will not do too much to this mode.

And these do not come cheap. You modeled 1m x room height as absorbing area per corner. These Modex absorbers have 0.36 sqm each for 200+£. Stacked to the ceiling (2.5m?) this is about 1000$/€ per corner for about 60% of the modeled area.
But that is how it is, bass absorption is delicate.

 

[NTK]

Yep, membrane (oscillator) absorbers will work too (like the Helmholtz') on walls and in corners. These are tuned to 60-70 Hz but still rather broadband. The lowest and probably strongest mode in the modeled room is the first length mode at 34 Hz, the Modex absorbers will not do too much to this mode.

And these do not come cheap. You modeled 1m x room height as absorbing area per corner. These Modex absorbers have 0.36 sqm each for 200+£. Stacked to the ceiling (2.5m?) this is about 1000$/€ per corner for about 60% of the modeled area.
But that is how it is, bass absorption is delicate.

The products offered by the company that made the video aren't cheap either. For example, their subwoofer stands (with the completely dubious claims that subwoofers must be elevated from the floor to justify the need, and nonsensical placement advice):

Subwoofer Carbon Platform SWCP - Acoustic Treatment

Sub woofers generate a lot of low frequency energy that fills our rooms. Most of that energy will simply not fit into our small rooms. A 12" driver produces 2 dB more energy than a 10". All of this energy must be managed and the best location to manage unwanted low frequency pressure is as close...

www.acousticfields.com

 

[Axo1989]

This guy is full of crap. Ethan Winer said it best. He knows just enough to be dangerous

Yes, he's the "activated carbon" guy ...

 

[ernestcarl]

The products offered by the company that made the video aren't cheap either. For example, their subwoofer stands (with the completely dubious claims that subwoofers must be elevated from the floor to justify the need, and nonsensical placement advice):

Subwoofer Carbon Platform SWCP - Acoustic Treatment

Sub woofers generate a lot of low frequency energy that fills our rooms. Most of that energy will simply not fit into our small rooms. A 12" driver produces 2 dB more energy than a 10". All of this energy must be managed and the best location to manage unwanted low frequency pressure is as close...

www.acousticfields.com

He’s a con artist… with a gazillion “acoustics” videos and counting.

 

[alex-z]

The 4" foam 'bass traps' that you see on Amazon are nonsense. Actual bass traps with appropriate thickness and density provide real improvement to the tangential and oblique room modes.

You don't need an acoustics degree to shove an unopened bag of mineral wool in a corner and measure the frequency response from 80-200Hz with any microphone. It will be ugly and the density is not optimal, but you can see and hear the improvement.

 

[Chrispy]

I was wondering what ASR thinks of this video.

TLDR:
- Bass modes are formed by reflections from walls. Not the corners.
- What % of the wall is treated by the corners? Answer: a very small surface area.
- Corner traps are a marketing con designed to sell traps to people to put in corners, where there is usually nothing anyway

Sadly, no measurements.

I think I won't bother watching it.

 

[Chromatischism]

The 4" foam 'bass traps' that you see on Amazon are nonsense. Actual bass traps with appropriate thickness and density provide real improvement to the tangential and oblique room modes.

You don't need an acoustics degree to shove an unopened bag of mineral wool in a corner and measure the frequency response from 80-200Hz with any microphone. It will be ugly and the density is not optimal, but you can see and hear the improvement.

Yeah, don't buy bass traps without measurements. GIK provides them for the traps I have.

 

[Justdafactsmaam]

Yes, he's the "activated carbon" guy ...

Activated carbon does work. As Ethan said, he knows just enough to be dangerous

 

[Axo1989]

Activated carbon does work. As Ethan said, he knows just enough to be dangerous

I was making fun of his communication style, and their semi-incoherent promotional collateral, more than the acoustic material. But do tell?

 

[Justdafactsmaam]

I was making fun of his communication style, and their semi-incoherent promotional collateral, more than the acoustic material. But do tell?

I was shocked

https://www.sciencedirect.com/science/article/abs/pii/S0003682X22005540#:~:text=Activated%20carbon%20performs%20much%20better%20than%20an%20equivalent%20fiberglass%20infill.&text=Low%2Dfrequency%20sound%20absorption%20is,the%20use%20of%20activated%20carbon.&text=Experimental%20results%20are%20in%20good%20agreement%20with%20theoretical%20predictions.

 

[ozzy9832001]

I was wondering what ASR thinks of this video.

TLDR:
- Bass modes are formed by reflections from walls. Not the corners.
- What % of the wall is treated by the corners? Answer: a very small surface area.
- Corner traps are a marketing con designed to sell traps to people to put in corners, where there is usually nothing anyway

Sadly, no measurements.

Corners are typically free space for most people, so I think that's where people started to get the idea from. I'm a fan of placing large baffle traps where the walls and ceiling meet. Again, it's free space that most people don't use. Looks good and serves a function. To me, tri corner traps, or whatever you wanna call them, are too thin to make any noticeable difference.

I always felt the largest traps should be placed centered along the 4 walls, but I've yet to have a room that I could actually test this theory in.

 

[Axo1989]

I was shocked

https://www.sciencedirect.com/science/article/abs/pii/S0003682X22005540#:~:text=Activated%20carbon%20performs%20much%20better%20than%20an%20equivalent%20fiberglass%20infill.&text=Low%2Dfrequency%20sound%20absorption%20is,the%20use%20of%20activated%20carbon.&text=Experimental%20results%20are%20in%20good%20agreement%20with%20theoretical%20predictions.

Ok, me also. Like a metamaterial basically.

 

[Justdafactsmaam]

Corners are typically free space for most people, so I think that's where people started to get the idea from. I'm a fan of placing large baffle traps where the walls and ceiling meet. Again, it's free space that most people don't use. Looks good and serves a function. To me, tri corner traps, or whatever you wanna call them, are too thin to make any noticeable difference.

I always felt the largest traps should be placed centered along the 4 walls, but I've yet to have a room that I could actually test this theory in.

The idea is actually founded in basic physics. Bass traps that are pressure traps not velocity traps are most effective where the pressure is at its maximum. Pressure is at its maximum where air velocity is at its minimum. Air velocity is at zero directly on the room boundaries. Corners are generally where three major room boundaries converge. That’s usually where the maximum pressure will be.

 

[ozzy9832001]

The idea is actually founded in basic physics. Bass traps that are pressure traps not velocity traps are most effective where the pressure is at its maximum. Pressure is at its maximum where air velocity is at its minimum. Air velocity is at zero directly on the room boundaries. Corners are generally where three major room boundaries converge. That’s usually where the maximum pressure will be.

Right, I get that. But most people are putting standard rockwool in the corner, not a trap that will actually work correctly for the application.