Acoustic suspension speakers actually require an incomplete seal to function properly.
If you believe the info for BL, it's not just the material, but the arrangement of the fibers that really makes a difference in BOTH thermal and acoustic properties. Just cramming cotton balls inside will do something, but most likely not be as effective.
Here's another little empirical stuffing study. Author, unknown. Box was about 3/4 cut. ft. To me, results were as expected. Foam was somewhat of a surprise though. However, at 1 lb of foam in that 0.74 cu. ft. box must have been VERY tightly packed since foam's inherent density is much lower than FG.
http://www.pitt.edu/~szekeres/resonant.txt
http://www.pitt.edu/~szekeres/resonant.txt
Thanks. Another good little study. I was going to look that one up next.
Nousaine's final recommendation is for 1.5 lbs/cu.ft. polyfil. Because of the basic differences in material specific gravity, this would approximately equate to 1 lb/cu. ft. fiberglass, which is my general rule of thumb for stuffing closed boxes.
Did your measurements go higher up? If so, any difference?
I'm curious if your test speaks at all the relative ability of each material to damp the backwave, and thus keep reflections away from the cone.
Pallas,
I would have similar questions about the filler materials. The information that tvrgeek presented seems to only address lowering the fs point of a box. Higher frequency attenuation is not included in this information and the reduction of the reflected backwave is not as simple as hanging or attaching stuffing internally.
I would have similar questions about the filler materials. The information that tvrgeek presented seems to only address lowering the fs point of a box. Higher frequency attenuation is not included in this information and the reduction of the reflected backwave is not as simple as hanging or attaching stuffing internally.
Michael Wright (Dayton-Wright) showed that it indeed works both with his ESLs and his dynamic speakers.
dave
thankfully, the slightly teased out cotton wool balls, when contained and mixed with the diced BAF, a la Raymond blanc, provide a variable stuffing density. This i imagine would help to diffuse and absorb, and help to a small extent with reflections. A composite is probably the best way, as is the case in many engineering applications
Capel, in his book, talks of Cu wires 'spun' into absorbent, to increase the heat diffusion through the enclosure. Its got to be a safer bet than steel wool!
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Correct in that this test was only dealing with the shift in Fs. Casual observation suggested the wool to maybe, and I say maybe, have a slight advantage over the cotton. To make that test more valid, I would want to build a very large baffle so I could separate box internal issues from edge issues. The box does have a boded FG lining.
Back-wave is a much more complicated issue. In my last set, I used a square section brace behind the woofer twisted 45 degrees. It seemed to help a tiny bit. Everything in the back-wave question is a tiny bit. These were small regular sided boxes, so not the best. I did not do any modifications to the driver to deal with the edge issues in the frame and magnet. All that said, back wave suppression should be a simple matter of comparing the NRC, or now SAA ratings.
Need to go read the above studies.
S.D. Sealed boxes want to be sealed work work the best, but that does give a problem with changes in temp and pressure. Too good a seal and drive it hard, the cone will get offset. The trick is a pinhole that is large enough to leak, but small enough not to whistle. Effectively sealed.
Back-wave is a much more complicated issue. In my last set, I used a square section brace behind the woofer twisted 45 degrees. It seemed to help a tiny bit. Everything in the back-wave question is a tiny bit. These were small regular sided boxes, so not the best. I did not do any modifications to the driver to deal with the edge issues in the frame and magnet. All that said, back wave suppression should be a simple matter of comparing the NRC, or now SAA ratings.
Need to go read the above studies.
S.D. Sealed boxes want to be sealed work work the best, but that does give a problem with changes in temp and pressure. Too good a seal and drive it hard, the cone will get offset. The trick is a pinhole that is large enough to leak, but small enough not to whistle. Effectively sealed.
Reading up. If one dismissed the backwave portion, then I should go back and do impedance plots and find a way to measure by weight my stuffing. Testing my crossover shows I have just a tad of a hump before I roll off so getting a bit more shift would be advantageous to make the crossover to the syb easier. If I was leaving these as stand alone, than that hump is helpful to provide an overall shift in weight to balance the highs.
So, after my current project, I'll build a more suitable test box (easier to open) and get a tad more scientific. The claims of 40% effective size shift I have a hard time with, as I have never seen mention or achieved above 20%. Fish scale, yea that should work.
So, after my current project, I'll build a more suitable test box (easier to open) and get a tad more scientific. The claims of 40% effective size shift I have a hard time with, as I have never seen mention or achieved above 20%. Fish scale, yea that should work.
Darn right. You wouldn't want a strand of steel wool to get across the speaker terminals.
(For anyone who hasn't tried it: Take a small piece of steel wool, such as a scouring pad slightly teased out. Touch it across the terminals of a fresh alkaline type 9 volt battery, or a battery from a cordless electric drill. Be prepared to drop the steel wool on a non-flammable surface once it ignites. Or, just search Youtube for "steel wool".))
I believe that that only has to do with professionally made loudspeakers that will be used at higher and lower altitudes than the altitude of manufacture. Diy is typically used at one altitude only(Unless you move a lot). Barometric pressure is a non issue. One or two hz at the most.
Sulfur Hexaflouride increases the virtual volume of the enclosure by a factor of 27! It is so heavy, that it can actually be poured into the box like water before sealing..
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REMLAB,
Where are you getting this information on the increase in affective volume being 27 times that of air? I would like to read that article or paper on this subject. Changing the density to that extent would seem like it would increase the speed of sound through the gas almost as if it had become a solid. Tell me more or send me in the right direction.
Steven
Where are you getting this information on the increase in affective volume being 27 times that of air? I would like to read that article or paper on this subject. Changing the density to that extent would seem like it would increase the speed of sound through the gas almost as if it had become a solid. Tell me more or send me in the right direction.
Steven
Sulfur Hexaflouride is legal and you can get it from Concorde Gas
You'd have to contact them directly to buy it, and they may ask what you want it for, but it's not a controlled substance. From their site:
Founded in 1995, Concorde Specialty Gases is a leading independent producer and distributor of specialty gases utilized in a variety of industrial, commercial and consumer applications.
Concorde is your sole source for Super SF6. Made via a proprietary chemistry and manufacturing process, Super SF6 is a unique formula of sulfur hexafluoride that sets a higher standard for purity, quality and low moisture content.
All SF6 gases are not created equal. Utilizing proprietary chemistries and refining technologies, Concorde has created Super SF6 gas. It is a superior quality Sulfur Hexafluoride which features the lowest moisture content and least amount of impurities of any SF6 gas in its class.
Super SF6 (Sulfur Hexafluoride) is an inert, non-toxic gas with excellent physical properties, including dielectric, cooling, insulating and arc quenching capabilities. With its unique physical properties, Concorde Super SF6 is ideal for applications such as: electric utilities, magnesium casting, sound insulation, semiconductor etching, nuclear accelerators, scientific and medical instrumentation and more.
We certify that this gas complies with the requirements of ASTM D2472-00, IEC 376, and GB12022-89. Water content, maximum dew point, -62° C
Sources: http://www.concordegas.com/sf6.html
Sign in to report abuse or send a compliment EddieNygma 68 months ago
You'd have to contact them directly to buy it, and they may ask what you want it for, but it's not a controlled substance. From their site:
Founded in 1995, Concorde Specialty Gases is a leading independent producer and distributor of specialty gases utilized in a variety of industrial, commercial and consumer applications.
Concorde is your sole source for Super SF6. Made via a proprietary chemistry and manufacturing process, Super SF6 is a unique formula of sulfur hexafluoride that sets a higher standard for purity, quality and low moisture content.
All SF6 gases are not created equal. Utilizing proprietary chemistries and refining technologies, Concorde has created Super SF6 gas. It is a superior quality Sulfur Hexafluoride which features the lowest moisture content and least amount of impurities of any SF6 gas in its class.
Super SF6 (Sulfur Hexafluoride) is an inert, non-toxic gas with excellent physical properties, including dielectric, cooling, insulating and arc quenching capabilities. With its unique physical properties, Concorde Super SF6 is ideal for applications such as: electric utilities, magnesium casting, sound insulation, semiconductor etching, nuclear accelerators, scientific and medical instrumentation and more.
We certify that this gas complies with the requirements of ASTM D2472-00, IEC 376, and GB12022-89. Water content, maximum dew point, -62° C
Sources: http://www.concordegas.com/sf6.html
Sign in to report abuse or send a compliment EddieNygma 68 months ago
It would appear special woofer designs are necessary to operate with the gas system. Where can we DIY'rs get them?
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