DTB,
What you did to your ceiling is just standard sound absorbancy. 5.5 inches of cotton batting agains a solid surface is about as effective as 2.5 inches with a 3 inch gap to the solid surface.
I never said it was 5.5 inches against a solid surface.....
My joist space is about 9" total from floor to drop ceiling. So "technically" I have about 3" behind the cotton to the ridgid suface of the floor above as the cotton sits right against the ceiling tiles. While 5.5 inches is not really what one needs (probably more in the area of 12"-16" is required) but something is better than nothing.
The absorption ratings of the cotton is very close to that of the very common rigid fiberglass and mineral wool, but without the iching and scratching you get from the fibers. Ratings are out there to view.
And according to the frequency response testing I did, the cotton did some improvements - not GRAND mind you, but a slight improvement - and every little bit helps.
a Bass trap on the other hand is made from material similar to peg board. basically a sheet of wood with holes in it, with something absorbant behind (fibreglass is best for turning the sound energy into heat) (which is what happens when you absorb sound).
The resonance tuned traps you speak of are used by some people out there. Some use FRK, some use a type of covering or membrane to assist with reflection of the mids and highs and to also help with the returning wave, then there are the resonance tuned traps you speak of which can be tuned for a more specific frequency if you wish.
The theory goes something like this: Bass sound waves are HUGE, 20 or 30 feet long in some cases, while hi frequencies are very, very short. so what happens with bass and 5.5 inches of any material is very little, the big wave goes straight through, bounces off the wall and comes back unchanged. but, if they hit a hard surface with holes, some of the energized air goes through the holes, reflects off whatever is behind then only by chance can it get back through the holes and into the listening space.
Thanks for the basics of sound waves instruction....
Going through and back does not happen unchanged, there is some absorption happening, how much is not as great as a thicker or denser product, or ones like the resonance tuned traps you keep referring to. But there is some absorption occuring with the changing of energy into heat as you noted.
Again, this resonance trap you are refering to, is usually used with a solid piece of wood with a space between it and then the absoption material. These can be "tuned" based on the materials used on the front of the panel.
a thick rubber membrane against the wall is also very good at reducing bass energy, it has some "give" in it and moves slightly, turning some of the bass energy into movement. sp,e people incorporate the peg board thing with the rubber thing for increased bass absorbtion.
This short paragraph is vastly simplified, by the way.
Just thick rubber by itself really does not acomplish much, but with something else used with or in layers (wood, metal, etc has been used), as used in some studios or testing facilities can accomplish a great amount of absoption.
But us poor audiophiles in small room, without the ability to build brand new walls with the proper abosoprtion and design are limited to the bass trapping with product like rigid fiberglass, mineral wool, and acoutical cotton. We need to use it in many places to gain the same improvments in our rooms due to the inability to have walls or the entire room designed properly for this.
We also do not have the ability to take up 12-16" sticking out taking up valuable living space around the room, or even the extra sizes with the tuned traps. And unfortunately most of us have our setup in living areas and not dedicated rooms. With a dedicated rooms, better acoustic treatments and room construction can occur giving better results.
But the results in my room with the GIK products, first reflection point treatment, and the addition of the acoustical cotton above the ceiling is more than a slight improvement in sound and it was also measurable to show the differences.
So while there is always better, what some of us have used from either GIK or Real Traps, works for our applications and room limitations. And if you REALLY do not think their products have any benefit at all, I suggest you get in contact with Ethan or Glenn to dispute the products as false advertising.
in my partial basement, any additional broadband absorption I could add would be a benefit.
