from an old copy of the audio critic comes this excerpt (regarding getting more bass from smaller boxes, this time with the explanation of how and why stuffing works)
arrgh, can't copy and paste from the pdf....http://www.theaudiocritic.com/back_issues/The_Audio_Critic_17_r.pdf
he talks about the stuffing absorbing heat upon compression and releasing it later, and again upon rarefraction the opposite, the net result being that the woofer moves more freely. (pdf page twenty in the section of acoustic suspension boxes of s/one can copy and paste for me)
That is for me a good description, well one I can understand, of why stuffing a box makes it seem larger to the woofer.
It makes me think of a regenerator in a stirling motor, and led me to wonder what the results may be if we used a metal, say steel wool of sufficient thinness instead of fibreglass.
It will more readily heat and cool than fibreglass no?, therefore would we see a 'bigger box' for the woofer?
Leaving aside any electrical contact and shortciruits (not hard to overcome) or any magnetic induction (surely not a real world problem or hard to overcome) but purely based on the ability to store heat and release it quickly, would not fine steel wool work better than equivalently sized fibreglass?
arrgh, can't copy and paste from the pdf....http://www.theaudiocritic.com/back_issues/The_Audio_Critic_17_r.pdf
he talks about the stuffing absorbing heat upon compression and releasing it later, and again upon rarefraction the opposite, the net result being that the woofer moves more freely. (pdf page twenty in the section of acoustic suspension boxes of s/one can copy and paste for me)
That is for me a good description, well one I can understand, of why stuffing a box makes it seem larger to the woofer.
It makes me think of a regenerator in a stirling motor, and led me to wonder what the results may be if we used a metal, say steel wool of sufficient thinness instead of fibreglass.
It will more readily heat and cool than fibreglass no?, therefore would we see a 'bigger box' for the woofer?
Leaving aside any electrical contact and shortciruits (not hard to overcome) or any magnetic induction (surely not a real world problem or hard to overcome) but purely based on the ability to store heat and release it quickly, would not fine steel wool work better than equivalently sized fibreglass?
not thinking of trying it, just curious about the aspects outlined, the better (presumably) ability to store and release heat, which seems to be the reason for stuffing.
for the sake of a 'mind experiment', lets say any practical problems can be overcome, which surely would not be hard to do. Not hard to keep any steel wool away from unwanted areas. let's say a manufacturer could easily overcome those problems, if they could would there be any 'market' advantages in terms of better performance?
for the sake of a 'mind experiment', lets say any practical problems can be overcome, which surely would not be hard to do. Not hard to keep any steel wool away from unwanted areas. let's say a manufacturer could easily overcome those problems, if they could would there be any 'market' advantages in terms of better performance?
Aperiodic by using better damping material
Recently I have been thinking about this question. The purpose of searching better damping materials is to avoid building acoustic labyrinths inside the speaker enclosure. If damping material is good enough, the speaker becomes aperiodic by simply filling the speaker cavity.
I would probably try this way:
Recently I have been thinking about this question. The purpose of searching better damping materials is to avoid building acoustic labyrinths inside the speaker enclosure. If damping material is good enough, the speaker becomes aperiodic by simply filling the speaker cavity.
I would probably try this way:
- The speaker cabinet is a simple box or a sealed enclosure of some other shape.
- Cover backside of the driver with some plastic mesh or fabric that is acoustically transparent but keeps damping materials away from moving parts of the driver.
- Surround back side the driver with polyfill or other light damping material. Only immediate vicinity. This is cheap and low-density material.
- Surround the light damping material with angel hair. This damping material is also electrical insulator. Density is greater than density of polyfill.
- Below angel hair and other light damping material would be a thick layer of copper wool. It is more expensive than steel wool, but also it is not ferromagnetic, which is desirable because this layer would be quite close to the speaker magnet. Density is essentially bigger than density of angel hair.
- Most of the inside volume of the cabinet below the layer of copper wool would be filled with steel wool. Because this is ferromagnetic, I would not place any of it near the magnet. Density is approximately equal to the density of copper wool.
I was thinking along similar lines a few months back ( you might be able to find the short thread ), I managed to find the thermal conductivity, density and thermal " density " of different materials and there didn't seem much benefit from metal as far as I can remember, I was thinking more about copper - perhaps the shielding from tv coaxial cable. Didn't Philips use ceramic for the regenerater? I think Andy Ross used stainless steel shim, with dimples to keep it spaced apart.
Typical steel wool, as pointed out is bad. When working on guitars, the magnets attract fine bits so easily. Right away it sounds bad to put anything like steel wool into a speaker IMO.
As for non-magnetic materials, anything that is conductive sounds like a bad idea. While a particle isn't enough to cause a short, over time I would think it possible that a layer of dust like particulate could maybe become conductive enough to cause a short. NASA won't even allow unleaded solder because of tin whiskers. Just because it's okay now doesn't mean it's going to have a long service life.
Recently when reading about guitar maintenance, it was pointed out that there is a poly wool that acts very similar to steel wool in its abrasive properties... I am not too sure how it would function as a stuffing material, but it sounds much safer an experiment, tho it may not do what you want it to.
As for non-magnetic materials, anything that is conductive sounds like a bad idea. While a particle isn't enough to cause a short, over time I would think it possible that a layer of dust like particulate could maybe become conductive enough to cause a short. NASA won't even allow unleaded solder because of tin whiskers. Just because it's okay now doesn't mean it's going to have a long service life.
Recently when reading about guitar maintenance, it was pointed out that there is a poly wool that acts very similar to steel wool in its abrasive properties... I am not too sure how it would function as a stuffing material, but it sounds much safer an experiment, tho it may not do what you want it to.
For steel wool, in addition to the concern of being attracted to magnets, it also is prone to corrosion, at which point (depending on the fineness of the steel wool and the rate of corrosion) you have somewhere between a little and a lot of fine iron oxide dust, which is also attracted to magnets.
There's bronze wool, and there is (or was) some Pferd product that looked and acted a lot like steel wool but that is totally nonmetallic
This discussion does raise my curiosity about whether something like Scotchbrite pads might have interesting characteristics, maybe as an alternative material for an aperiodic vent.
There's bronze wool, and there is (or was) some Pferd product that looked and acted a lot like steel wool but that is totally nonmetallic
This discussion does raise my curiosity about whether something like Scotchbrite pads might have interesting characteristics, maybe as an alternative material for an aperiodic vent.
When I used to go camping I would bring a back-up all weather fire starter with me. A tuft of steel wool in a plastic baggie and a 9V battery in a different pocket. Be aware that if the steel wool were to contact the speaker terminals inside a wooden vented enclosure there could be a problem. 
Not saying that I would use it as dampening, far from it not least for the reason you stated.
I merely said that some stainless steels like 18/10 (304) are naturally non-magnetic.