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Bass trap

Tim Link

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Most bass traps are velocity absorbers, not pressure absorbers.

While the terms pressure absorber and velocity absorber get used, in reality something has to move or there is no absorption, so all absorbers are velocity absorbers. At ASC we consider our TubeTraps to be pressure zone absorbers, meaning they do their work when placed in a high pressure zone, like a corner, by converting the pressure to velocity as the pressure outside the trap causes flow across the fibrous membrane to try to equalize to pressure inside the trap. The flow creates heat, which absorbs some of the sound energy. The bigger the volume inside the trap relative to the surface area of the membrane, the lower the absorption can go, which is why bigger diameter TubeTraps can work down to lower frequencies.

There are traps that can work in velocity zones, where sound pressure levels are low but air movement is relatively high. These would inevitably create some pressure in that zone as they slow the air movement through friction, converting sound energy to heat. These would need to be larger and less resistive than a trap working in the pressure zone.

It's conceivable that a real pressure device could be made without moving parts. One I could imagine would be some method of rapidly heating and cooling the air in the corner of a room in a manner out of sync with the pressure swings. If you could cool the air rapidly as it's trying to compress in the corner, and then heat it rapidly as it's trying to expand you could reduce reflection out of the corner. Maybe a dense grid of very thin heating wires hooked up to an AC current working against an air column of cooled air created by a interweaved grid of tiny cooling tubes.... Nah. If something like that could work it could also be used a subwoofer to generate sound.
 

MRC01

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A chonker is just a big thing, sorry. I have tons of pretty dense insulation that works very well for absorbing sound, and as I mentioned I can go pretty thick. Is this not a good approach?
Bass frequencies have long wavelengths. In feet, wavelength = 1100 / frequency, so 50 Hz has a wavelength of about 22 feet. So a simple layer of insulation is invisible to a bass wave; it passes through it like it's not even there. The key to bass treatments is to use the geometry of the treatment to affect longer wavelengths than the insulation alone would affect. That's what bass traps and tube traps do.

Do you have any photos of these traps? I see some steps but no photos so hard to grasp.
It's simple: curve a sheet of fiberglass into a cylinder and seal (using liquid nails or similar glue) the ends to each other. Attach round plates to the top & bottom and seal them to the fiberglass. Now you've got an airtight hollow cylinder whose walls are made of fiberglass. The endcaps can be wood, plastic or whatever.

That sheet of insulation (even several inches thick) does pretty much nothing to bass, as a flat panel. But when formed into this hollow airtight cylinder, it does. A 75" sheet curves into a cylinder of about 2' diameter, which is plenty big enough to affect the lowest octave. The diameter of the cylinder determines the frequency range, the length (and thus total volume) determines how much effect it has. Google "DIY tube trap" and you'll see plenty of videos & photos.
 

Snoochers

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Bass frequencies have long wavelengths. In feet, wavelength = 1100 / frequency, so 50 Hz has a wavelength of about 22 feet. So a simple layer of insulation is invisible to a bass wave; it passes through it like it's not even there. The key to bass treatments is to use the geometry of the treatment to affect longer wavelengths than the insulation alone would affect. That's what bass traps and tube traps do.


It's simple: curve a sheet of fiberglass into a cylinder and seal (using liquid nails or similar glue) the ends to each other. Attach round plates to the top & bottom and seal them to the fiberglass. Now you've got an airtight hollow cylinder whose walls are made of fiberglass. The endcaps can be wood, plastic or whatever.

That sheet of insulation (even several inches thick) does pretty much nothing to bass, as a flat panel. But when formed into this hollow airtight cylinder, it does. A 75" sheet curves into a cylinder of about 2' diameter, which is plenty big enough to affect the lowest octave. The diameter of the cylinder determines the frequency range, the length (and thus total volume) determines how much effect it has. Google "DIY tube trap" and you'll see plenty of videos & photos.

That sounds pretty cool, though a lot more work than just throwing insulation in a corner!! Perhaps something for down the road. I have too many projects on the go!
 

caught gesture

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That sounds pretty cool, though a lot more work than just throwing insulation in a corner!! Perhaps something for down the road. I have too many projects on the go!
Stack insulation in the corners and have a listen. From the dimensions of the bass traps you gave earlier, I think that you’ll be pleasantly surprised by the tightening up of the low end.
 

Bjorn

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If you only have one corner to add bass absorption and you not aiming for a specific frequency, the better solution to simply add loose porous material and make it as big and thick as possible. Don't build as a tube though. Either as a square or triangle. As long as it's sufficiently big, it generally works much better than most commercial bass traps. The commercial acoustic market consist of a lot of poor products with very low efficiency and generally cannot be trusted.
 

Bjorn

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Perfect choice for room acoustic treatment in Europe on:
https://ssteu.com/acoustic-tube-bass-trap-copy-2E_AUvgHRMDR4S77zrTGl

They ship their product by Eurosender due to all EU and surrounding countries.
Price, quality, and aboundounce of final decorative TUBE TRAP surface is the benefit.
Can you explain to us how a device with such small dimensions can work well for frequencies below 100 Hz? And especially as low as 20 Hz. Where are valid measurements confirming this?

And why are they placed at non pressure points in the pictures?
 

Wes

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I can only make a couple of background, elementary additions, which might be what the OP or others need.

Rooms have standing waves, which are spatial - they don't change in time if the driving force (music freq.) is present. Imagine a chart of pressure that is spread along your floor as the axis. There might be a wiki with a drawing of a rope fixed at one end and moved up & down by somebody. That's the visualization.

2nd, use 2 or more subs before using bass traps of any type.
 
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