I have been thinking this subject lately, because I try to remove room modes below 100 Hz inside my cellar IB. Filling my cellar with mineral wool would be my last option, because then I need to find other place for beer and potatos.
Any ideas?
First I will test some sort of leaking walls for bounding element areas for smaller areas, so that modes will be at higher freq that wont matter with sub.
Any ideas?
First I will test some sort of leaking walls for bounding element areas for smaller areas, so that modes will be at higher freq that wont matter with sub.
Store your beer and potatoes near the middle of the space, not around the walls. In my work space, I have about 150 stackable storage crates. They are normally stacked against the walls, but I tried stacking them in the middle of the space, floor to ceiling, in a "cross" shape (looked like a "+" from above.) The "arms" of the cross extended about half way from the centre of the space to the walls in each direction. With the crates stacked against the walls, the bass was "boomy" and uneven. Stacked in the centre, the bass was smooth.
Leave anechoic chamber wedges out of the argument for a moment - they work, at the macro level, like graduated density foam. Stick to homogenous absorbers so we can compare like with like.
I understand Markus's point to be that, for a given thickness and frequency, increasing the density beyond a certain point starts to deliver diminishing returns. For "absorbed" energy, increasing the density does increase the attenuation, asymptotically approaching infinity. But increasing the density also increases the amount of energy reflected at the air/absorber interface instead of absorbed, reducing the overall effectiveness. The correct density for a given thickness and frequency is one that balances the absorption and reflection to optimise the overall attenuation. (When you've stopped laughing, can you explain how badly I misunderstand it?)
I also understand your position, that polyester batting of the density used in pillows is too "porous" to provide sufficient attenuation where the thickness available is limited. It is available in higher densities, which are used in dress / costume making and craftwork where a shape has to be self-supporting and crush-proof. I used some in a pair of ported enclosures, it was easier than having to enclose fibreglass batts in fabric bags to prevent fibres being blown out the ports (I had young children playing on the floor near the speakers.) In any case, the density problem can be largely overcome by "stuffing" the batting in until the required density in Kg/m3 is achieved.
Getting back to wedges, back in the 1960s I visited the anechoic chamber of this country's Government research establishment. Funds being tight, they had come up with a "DIY" solution: They lined a large concrete bunker with coir fibre (like coarse felt, widely used in upholstery manufacture), teased so that it was thin and wispy at the surface and denser near the walls. It was about a metre deep. I don't have any performance figures, but it certainly was effective when standing in the room.
At my first company we made a chamber on the cheap based on a picture we saw in a B&K brochure. They had hung hundreds of fiberglass cubes randomly on strings. Four of us spent over a week cutting and threading hundreds, if not thousands, of chunks onto strings we hung around the perimeter of a room. I got fiberglass poisining, like a really bad case of poison Ivy.
The previous arguement was about whether absorptive materials have an operating frequency range or can be too dense. Even if theory suggests it, every measurement of every reasonable damping material that I have seen shows a turn-on frequency based on depth and then 99% absorption from that frequency up. In the case of fiberglass, every bit of data that I have seen shows it performing to a wavelength in proportion to frequency and always performing to an Octave lower every time you double its thickness. If it stops working at some thickness then the published data doesn't show it.
Furthermore, although some materials are essentially as good, I have not seen anything that works better, for a given thickness, than fiberglass.
Finally, Dacron fluff (pillow stuffing) does virtually nothing yet speaker experimenters continue to use it.
David S.
It's from the website of Faist. They've licensed the Fraunhofer "Asymmetrically Structured Absorber". It's basically a steel plate sandwiched between two layers of open cell foam. The layer facing the room is sculptured.
I wonder if Fraunhofer's Reapor glass foam's pores would perform similarly (or better) to KEF's ACE technology where they claim improved stuffing media performance over FG due to activated carbon's extremely small pore structure.
Speakerdave? thoughts?
United States - KEF Innovation - ACE
All of this depends on what the manufactor intended to do with the stuffing.
Classic case, ESS AMT3's. Filled to the brim with a white poly type damping material. 2 10" woofers in a ported enclosure. 3.3 cu ft enclosure.
In addition to dealing with some standings waves- the fill is used to tune the enclosure. I
I have experimented with different types of foams/fiberglass/rockwool/recycled cotton, etc, and none works as well as the polyfill. I always used one speaker as a constant-while changing the other.
There is no doubt the polyfill absorbs some-or breaks up standing waves present in the enclosure. Very easy to tell by simple listening. This is opposed to the tuning factor, by increasing the apparent volume with a given fill amount.
These speakers were tuned, and designed with this material in mind-as are others I imagine. At the time they were built, I doubt it was a cost cutting measure to use the polyfill-it was more that the polyfill met the characterisitcs they were looking for. And this was confimed by what I found with comparing the polyfill to the other materials.
So it might be a stretch to say it's not useful-regardless of it's damping effects vs fiberglass, or any other types of damping materials.
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I always found a bees hive to be the best material.
On a serous note - a question.
In relation to absorption material inside an enclosed box, as what point does the absorption material start affecting the volume of the enclosure.
I have a pair of Duntech Princess which I replaced the bass drivers.
(not my actual pair)
I was quite surprised to see the bass chamber was almost 2/3rds filled with some type of foam.
So lets say I wanted to make an enclosed IB bass box, With a huge amount of this fiberglass panels that have been discussed. How much do I account for the change in internal volume?
An externally hosted image should be here but it was not working when we last tested it.
On a serous note - a question.
In relation to absorption material inside an enclosed box, as what point does the absorption material start affecting the volume of the enclosure.
I have a pair of Duntech Princess which I replaced the bass drivers.
(not my actual pair)
I was quite surprised to see the bass chamber was almost 2/3rds filled with some type of foam.
So lets say I wanted to make an enclosed IB bass box, With a huge amount of this fiberglass panels that have been discussed. How much do I account for the change in internal volume?
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