Remlab,
I know what you are saying but I am not sure that the bag itself wouldn't be transparent to the acoustical vibrations that we are talking about. It would not be the same as taking the volume away from the internal cavity. The contained gas would still see the wavefront and vibrate with it. There may be a transfer function through the bag, even some reflection but I am going to look deeper into this. That is why the bag idea caught my eye in the first place as that was my original thinking, but the information was contrary to that.
I know what you are saying but I am not sure that the bag itself wouldn't be transparent to the acoustical vibrations that we are talking about. It would not be the same as taking the volume away from the internal cavity. The contained gas would still see the wavefront and vibrate with it. There may be a transfer function through the bag, even some reflection but I am going to look deeper into this. That is why the bag idea caught my eye in the first place as that was my original thinking, but the information was contrary to that.
I guess that only experimentation would bear that out. But I still think that the weight of the gas working directly against the speaker diaphragm has something to do with it(Partly)..
http://www.youtube.com/watch?v=d-XbjFn3aqE
http://www.youtube.com/watch?v=d-XbjFn3aqE
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Just found this..
SF6 + 16Ov.2 = Subwoofer Experiment
Pretty much answers your question. I like the idea of putting a little paper boat in the enclosure to adjust the fill level to the exact amount..
SF6 + 16Ov.2 = Subwoofer Experiment
Pretty much answers your question. I like the idea of putting a little paper boat in the enclosure to adjust the fill level to the exact amount..
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The problem with this experiment, was that there was normal air in the space between the diaphragm and the gas. If the driver was placed on the side, fully sealed, with the full weight of the gas pressing up against the diaphragm(And no air in the cabinet), they probably would have gotten much better results, in my opinion. Who knows, maybe part of what it's doing is lowering the resonant frequency of the driver, by adding apparent mass to the diaphragm from the heavy gas pressing up against it ..
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Remlab,
That article wasn't very encouraging but it was never concluded. Perhaps the minor lowering of fs would not be worth the cost of the gas and the hassles of using it. I will look at the effects of just using a high volume of fiber filling and see how well that can work and what the upper limits are in stuffing density.
Steven
That article wasn't very encouraging but it was never concluded. Perhaps the minor lowering of fs would not be worth the cost of the gas and the hassles of using it. I will look at the effects of just using a high volume of fiber filling and see how well that can work and what the upper limits are in stuffing density.
Steven
Pulling this thread back. In the sub forum it was suggested that granulated charcoal , as advertised by Kef, can provide an effective reduction if Vb by 4 times. As I found about 15% the max from any conventional fiber, I don't believe it for a minute, but only quantitative testing will answer the question. BS or breakthrough.
I never found any of the mineral wool that is said to beat fiberglass. I think I can order it through the big box store. I will then report quantitative results rather than the slick sheet that Kef supplied. Briefly; Fiberglass, Acoustastuff, cotton, and 2 Lb foam all came out very close. Only the polyfill was a lot worse. The edge went to fiberglass, but of course, it is only suitable for a sealed box. I would never use it is a ported or TL where you could pump fibers into the air.
OK, I found a suitable driver. It is a modified RS-150 I used for breakup doping testing. Measured by my usual procedures and modeled it to Qtc of .7 in 25L empty box. My VAS test box just happens to be 9 L. Measured about .86 in that volume. I will repeat my cotton/wool/poly/fiberglass/daycron/foam fills while I scare up some granular carbon.
If anyone else has any other "magic" fill ideas, pass them on and I will see what I can do. I was thinking about layered fleece as the fiber size is very small. There are probably three parameters that help this. (or four counting the pores Kef talks about). Friction between the air and the fill, longer path through the fill for the soundwave, and friction between fibers transferring vibration to heat.
If Kef is right, I will quit picking on them for their muddy sounding Q1's I have.
I never found any of the mineral wool that is said to beat fiberglass. I think I can order it through the big box store. I will then report quantitative results rather than the slick sheet that Kef supplied. Briefly; Fiberglass, Acoustastuff, cotton, and 2 Lb foam all came out very close. Only the polyfill was a lot worse. The edge went to fiberglass, but of course, it is only suitable for a sealed box. I would never use it is a ported or TL where you could pump fibers into the air.
OK, I found a suitable driver. It is a modified RS-150 I used for breakup doping testing. Measured by my usual procedures and modeled it to Qtc of .7 in 25L empty box. My VAS test box just happens to be 9 L. Measured about .86 in that volume. I will repeat my cotton/wool/poly/fiberglass/daycron/foam fills while I scare up some granular carbon.
If anyone else has any other "magic" fill ideas, pass them on and I will see what I can do. I was thinking about layered fleece as the fiber size is very small. There are probably three parameters that help this. (or four counting the pores Kef talks about). Friction between the air and the fill, longer path through the fill for the soundwave, and friction between fibers transferring vibration to heat.
If Kef is right, I will quit picking on them for their muddy sounding Q1's I have.
tvrgeek,
I understand that the poly fill did not meet expectations and was wondering about that. Is that fiber a solid fiber by chance? Have you considered any of the hollow fiberfill fibers that are used in things like sleeping bags and even in some sports socks? I am wondering what the differential would be with a hollow fiber rather than a solid fiber such as fiberglass. Thanks for keeping the thread alive, I appreciate your working on the answers here. I know that the carbon granules may also be very porous but I also question if they can perform as stated.
Steven
I understand that the poly fill did not meet expectations and was wondering about that. Is that fiber a solid fiber by chance? Have you considered any of the hollow fiberfill fibers that are used in things like sleeping bags and even in some sports socks? I am wondering what the differential would be with a hollow fiber rather than a solid fiber such as fiberglass. Thanks for keeping the thread alive, I appreciate your working on the answers here. I know that the carbon granules may also be very porous but I also question if they can perform as stated.
Steven
Jute, which used to be commonly used as a carpet backing, is very effective for lining cabinets to deaden reflectivity.
1/2 inch of jute will deaden to a lower frequency than several inches of fiberglass, which is progressively more acoustically transparent below 500 Hz or so.
Although jute was common in older speaker cabinets as a liner, I have never seen it used as a fill material though, may be too dense.
Same would apply to felt.
That said, I would not think jute or felt would be any more dense than granulated charcoal...
Art
I've been there, done that. In fact, I still have the 12 lbs I bought for the work I shared here Failed stuffing experiment - Acoustic Research - The Classic Speaker Pages Discussion Forums
You can have it for the cost of postage to ship it to you.
The work was done some 5 yrs ago. The thread seems out of order. The initial post, I think, is #8. I don't see my data though.
Be aware there are two types of activated carbon. Coal based and coconut based. The coconut based stuff is very expensive. I bought the coal based stuff.
Read thru that entire thread. There are some very knowledgeable speaker guys who contributed their thoughts. Ken Kantor, Dave Smith (he worked at KEF and says he believes AC works), John O'Hanlon, Pete Basil, etc....
More recently in my stuffing testing journey I tried those powdery green blocks florists and crafters use to stick flowers into. They were tried in an AR4x cabinet which I've been using historically. There are two type of that stuff. I used the porous kind that will absorb water. I likened it to activated carbon due to its extremely fine pore structure. The bottom line, no benefit.
PM me if you want the AC.
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weltersys,
As I was just asking about the hollow fibers used in sleeping bags I would think that the jute and hemp fibers would have a similar property. These natural fibers are I think on a microscopic level hollow cellular fibers with chambers stacked one on another. Perhaps this is part of the answer to an improvement in absorption across a wider frequency band? Little mini resonance chambers built into the fibers. The hollow fill fibers would be one continuous hollow chamber though and may not work in the same manner.
Steven
As I was just asking about the hollow fibers used in sleeping bags I would think that the jute and hemp fibers would have a similar property. These natural fibers are I think on a microscopic level hollow cellular fibers with chambers stacked one on another. Perhaps this is part of the answer to an improvement in absorption across a wider frequency band? Little mini resonance chambers built into the fibers. The hollow fill fibers would be one continuous hollow chamber though and may not work in the same manner.
Steven
Careful here. This stuffing exercise is not intended to deaden reflectivity. Its purpose is for closed box systems to lower resonant frequency. No bust on you, but I see repeated threads and posts were folks get the two confused.
Vented box systems use stuffing to deaden reflectivity. Closed box systems use stuff PRIMARILY to 'increase' box volume, but also dampen rear wall reflections (that typically occurs by default due to the much higher stuffing density in closed box systems).
I thought the density was lighter that 2 lb/cu. ft. It's all gone now, so I can't run downstairs and check the packaging label.
After watching it absorb water, I thought for sure I had a winner.
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As I said in post #132:
"Although jute was common in older speaker cabinets as a liner, I have never seen it used as a fill material though, may be too dense.
Same would apply to felt."
Since the OP has volunteered to test various "stuff", thought it might be worth a try.
Seems interesting no one even suggested it before my post.
Have you already tried jute and found it ineffective in lowering the resonant frequency?
Art
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No,I haven't tried jute. Based on what I know about the basics of fiber stuffing effects in closed box systems and having studied this for over 5 yrs, I'm pretty sure it won't work. Tvrgeek is welcome to try it!
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