What about - don't laugh! - papier mache? there are at least a thousand different ways of preparing & using it. You can laminate sheets under compression, apply strips, pulp & mould, or any combination of these to form composites.
Properties will vary from loose & light "egg-carton" consistency to approaching metallic degrees of hardness & mass largely dependant on the adhesive phase utilised - wall paper paste/PVA/virtually any kind of resin!
Mixes can be loaded with anything you like; fibres, lead shot, rubber etc. Surely it's worth a dabble?
Properties will vary from loose & light "egg-carton" consistency to approaching metallic degrees of hardness & mass largely dependant on the adhesive phase utilised - wall paper paste/PVA/virtually any kind of resin!
Mixes can be loaded with anything you like; fibres, lead shot, rubber etc. Surely it's worth a dabble?
HI Noah.
curved shape, ok. Did not get that.
Fibreglass: ok, the damping might be not bad, but with the resin you spoil it all together, since you will almost only have the properties of the resin and not the fibreglass. What core are we talking about anyway? I thought we were talking about wooden cabinets. If you talk about sand filled cabinets, then its a good option of course.
Just wanted to make this clear...
You say fibreglass has basically double the density of wood (i.e. double the weight for same thickness). I am not that familiar with the densities but I always thougth fibreglass is very light??? MDF is quite heavy really. Do you know details??
Hi Fez,
I am not laughing. Any idea is worth a thougth or test. Some of thebest speaker cones are made of paper and some of this is made quite similar to paper mache. However I am not sure how you can achieve the stiffness that you would certainly need. Maybe if you use a lot of resin again...
There was an article in the audio engineering society magazine reporting about a company that uses MDF dust to mould all sorts of shapes...
curved shape, ok. Did not get that.
Fibreglass: ok, the damping might be not bad, but with the resin you spoil it all together, since you will almost only have the properties of the resin and not the fibreglass. What core are we talking about anyway? I thought we were talking about wooden cabinets. If you talk about sand filled cabinets, then its a good option of course.
Just wanted to make this clear...
You say fibreglass has basically double the density of wood (i.e. double the weight for same thickness). I am not that familiar with the densities but I always thougth fibreglass is very light??? MDF is quite heavy really. Do you know details??
Hi Fez,
I am not laughing. Any idea is worth a thougth or test. Some of thebest speaker cones are made of paper and some of this is made quite similar to paper mache. However I am not sure how you can achieve the stiffness that you would certainly need. Maybe if you use a lot of resin again...
There was an article in the audio engineering society magazine reporting about a company that uses MDF dust to mould all sorts of shapes...
"but with the resin you spoil it all together, since you will almost only have the properties of the resin and not the fibreglass."
The fibers greatly increase the stiffness and strength compared to the resin alone.
I haven't read back, but I think I started off talking about foam core, like surfboards.
The specific gravity (density compared to water) of fiberglass is about 1.6, MDF about .6 IIRC, aluminum and glass are 2.7
The fibers greatly increase the stiffness and strength compared to the resin alone.
I haven't read back, but I think I started off talking about foam core, like surfboards.
The specific gravity (density compared to water) of fiberglass is about 1.6, MDF about .6 IIRC, aluminum and glass are 2.7
The idea of firbeglass & carbon fibre being "light" is a bit of a red-herring; they are both quite heavy substances, it's just that they are incredibly strong out of all proportion to their weight: if you're careful in getting an inherently stiff shape like a dome or an egg, or if you use in composite materials, you're onto a winner. Don't expect a flat sheet of carbon or glass fibre to be overwhelmingly stiffer than a comparable sheet of MDF.
ahh, foam. That might be interesting, very light but might work.
Yes of course fibreglass gives you more stiffness, I thought you wanted to use it for more dampening. Sorry got that all wrong then.
Density: so you are saying that fibreglass is almost 3 times the density of MDF, interesting, thanks for that.
Yes of course fibreglass gives you more stiffness, I thought you wanted to use it for more dampening. Sorry got that all wrong then.
Density: so you are saying that fibreglass is almost 3 times the density of MDF, interesting, thanks for that.
The formula for the coincidence frequency of a panel is:
fg= c *c / 2 / pi * sqrt (m''/B) in Hertz
with m'' = kg/ squaremetre (mass per area)
and c = 340m/s (speed of sound)
pi= 3,141
and B= stiffness of the material (found in tables)
You see that the heavier the panel the lower the frequency but also the thicker the lower the frequency. Please do not forget the square root in the equation.
What this means is that below this frequency the panels do not emmit much sound but at this frequency a lot of sound and above this frequency the emmision declines again.
So what you have to try to do is get this frequency as high as possible.
On the other hand you want the panel to be stiff and have a reasonable dampening factor over all. That means usually stiff and heavy materials because the transmission damping factor R is calculated as:
R= (20*lg{pi*f*m''/p/c} - 3) in dB
with p = density of air, c = speed of sound, f = frequency and m'' = weight per area.
R should be as big as possible and therefor m'' should be rather large. You can also see that the factor is increasing with increasing frequency. That means that the lower frequencies are most problematic. Keep in mind though that the ear is most sensitive between 500 and 5000Hz, especially for resonances.
Hope this clears up a few things...
fg= c *c / 2 / pi * sqrt (m''/B) in Hertz
with m'' = kg/ squaremetre (mass per area)
and c = 340m/s (speed of sound)
pi= 3,141
and B= stiffness of the material (found in tables)
You see that the heavier the panel the lower the frequency but also the thicker the lower the frequency. Please do not forget the square root in the equation.
What this means is that below this frequency the panels do not emmit much sound but at this frequency a lot of sound and above this frequency the emmision declines again.
So what you have to try to do is get this frequency as high as possible.
On the other hand you want the panel to be stiff and have a reasonable dampening factor over all. That means usually stiff and heavy materials because the transmission damping factor R is calculated as:
R= (20*lg{pi*f*m''/p/c} - 3) in dB
with p = density of air, c = speed of sound, f = frequency and m'' = weight per area.
R should be as big as possible and therefor m'' should be rather large. You can also see that the factor is increasing with increasing frequency. That means that the lower frequencies are most problematic. Keep in mind though that the ear is most sensitive between 500 and 5000Hz, especially for resonances.
Hope this clears up a few things...
did you prepair any comparative tables that could easily be accessed? I, for one never considered the potential virtues of mixing materials for different driver enclosures...
noah katz said:
Everything I know agrees with using fiberglass and carbon fiber. Fiberglass is generally fine for speakers and with it's lower cost would generally be preferred. If you really like the look of carbon fiber, you could still use fiberglass and just make the outside layer carbon. Kevlar and nomex fabrics would be good to use for some layers too, as they are better damped materials than carbon or glass fiber. The main advantage of fiberglass is making complex shapes, though.
There are even damping epoxies that can be used to even better effect. That's what Rockport uses in their cabinets. That kind of epoxy isn't very common though, as far as I know.
General question: Does anyone know how common natural fiber cloths, like paper and cotton, are to composite construction? It seem like they are used in making phenolic, but are not really mentioned otherwise that I've seen.
el`Ol said:
Granite is actually a pretty nice material, not because of it's density, but because it is naturally a heavily damped material. It seems like I found reference where granite has been used as base material for machines that are used to make microprocessors, where the tiniest amount of vibration can be terrible. The main material in granite is quartz. Quartz can be used in modern composite construction to create panels that are even more well damped than granite: http://www.zanite.com/ .
I have found that making a 'sandwich' of 3/4" MDF and 1/4" hardboard, where the hardboard is cut into a jigsaw puzzle of odd sized pieces that all fit together. The pieces are then glued with a non-plyable glue to the MDF with the pieces seperated by a saw blade width. Like tile and grout are laid out. This makes a panel that has no primary resonance, just lots of smaller amplitude, much higher freq ones. These higher freq resonances are harder to excite and spread over a larger range to distribute the energy.
I also have glued rings of sonotube of all diameters to the insides of cabinets with hard glue. This increase the rigidity of the panel without much volume or weight. Try 4 graduated diameter rings, 2" rings nested non-concentrically on each side. It really works well!
Finally, I've used two sonotubes, one inside the other (12" and 10" dia) and filled the spce between them with fine sand. Talk about dead! Route out a base board with grooves for the two tubes to make keeping them the right distance apart easy. Vibrate the tube as you fill it to settle the sand. Try it for a unique sub that the wife can put fabric or some such on!
I also have glued rings of sonotube of all diameters to the insides of cabinets with hard glue. This increase the rigidity of the panel without much volume or weight. Try 4 graduated diameter rings, 2" rings nested non-concentrically on each side. It really works well!
Finally, I've used two sonotubes, one inside the other (12" and 10" dia) and filled the spce between them with fine sand. Talk about dead! Route out a base board with grooves for the two tubes to make keeping them the right distance apart easy. Vibrate the tube as you fill it to settle the sand. Try it for a unique sub that the wife can put fabric or some such on!
I'm about to start my next speaker project so this is all very interesting to me.
Q.
Does anyone (probably Aus only) have any experience with 'Brimsboard' ?
Sposed to be '7 layer mdf'.
I'm (at this stage) going to be using 25mm.
One sheet (2440x1220) is just enough to do both cabinets.
Each finished cabinet should weigh around 20kg without drivers.
Q.
Does anyone (probably Aus only) have any experience with 'Brimsboard' ?
Sposed to be '7 layer mdf'.
I'm (at this stage) going to be using 25mm.
One sheet (2440x1220) is just enough to do both cabinets.
Each finished cabinet should weigh around 20kg without drivers.
I'm planing on building a new set of speakers soon. Has any one seen a high qaulity cutting board, (like one you would see in your grandmas kitchen?) I was thinking of using this for my cabinents.
I would think it would be very stable considering the mixed grain.
I'm planing on building a set of desktops for my computer, I was also planing on using this material.
would this be a good Idea?
I would think it would be very stable considering the mixed grain.
I'm planing on building a set of desktops for my computer, I was also planing on using this material.
would this be a good Idea?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.