bending plywood
suggestions:
1. There is a kind of plywood called "bending plywood" in which all the layers are laid up with grain in the same direction, instead of rotating 90 degrees from one layer to the next. This is easy to bend in quite tight radius, e.g. less than a foot. In the states you can get it in 4 foot by 8 foot sheets and it can be bought to bend in either the lond direction or the short direction.
2. You can also buy impregnated cardboard honeycomb in 2' by 4' panels in half, 3/4 and 1" thickness. This is used to make very stiff and lightweight structures. It is used for airplane interiors for example. If you used a elastomeric roofing cement which can be applied cold, to join two sheets of bending plywood with honeycomb between them, you should have a structure which is about as lightweight, rigid, and dead as physics allows. Especially if you then coat the inside of the box with impregnated felt, black hole, loaded vinyl, or similar.
navin said:
suggestions:
1. There is a kind of plywood called "bending plywood" in which all the layers are laid up with grain in the same direction, instead of rotating 90 degrees from one layer to the next. This is easy to bend in quite tight radius, e.g. less than a foot. In the states you can get it in 4 foot by 8 foot sheets and it can be bought to bend in either the lond direction or the short direction.
2. You can also buy impregnated cardboard honeycomb in 2' by 4' panels in half, 3/4 and 1" thickness. This is used to make very stiff and lightweight structures. It is used for airplane interiors for example. If you used a elastomeric roofing cement which can be applied cold, to join two sheets of bending plywood with honeycomb between them, you should have a structure which is about as lightweight, rigid, and dead as physics allows. Especially if you then coat the inside of the box with impregnated felt, black hole, loaded vinyl, or similar.
Re: Do you want to die?!
There's another problem with wood. It involves what is called a "cross grain gluing situation". This happens when you have one piece of wood glued to another and the grain of the two run perpendicular with eachother. Not a problem if the junction is small, say less than six inches, but at a foot or more it's asking for trouble. That's because when humidity changes (from a heated winter space to a humid summer) the wood swells and shrinks a lot across the grain but almost not at all with the direction of the grain. Furniture makers use all sorts of tricks to avoid this, e.g. the elongage holes for screws, use sliding (not-glued) dovetails, and other tricks to let wood in a cross grain configuration move past eachother. I have seen wooden chests literally break apart from their own expansion if this is not taken into a account.
The main place in speaker building where this could occur is gluing the baffle and the rear to the top and bottom. Usually the grain on the top and bottom runs side to side, so it's continuous around all four sides, where the grain on the front and back runs up and down. Hence the connection between between front and top is a cross grain configuration.
Not a problem with plywood and mdf because these don't shrink much with humidity, and they do so uniformly without bias as to direction. If you want to build a speaker box out of pure hardwood, and you live in a situation where there is any significant humidity variation you should rely on bolts or screws, elongated holes, and putty or caulk to make it airtight, and not glue for these particular joints.
Rarkov said:
There's another problem with wood. It involves what is called a "cross grain gluing situation". This happens when you have one piece of wood glued to another and the grain of the two run perpendicular with eachother. Not a problem if the junction is small, say less than six inches, but at a foot or more it's asking for trouble. That's because when humidity changes (from a heated winter space to a humid summer) the wood swells and shrinks a lot across the grain but almost not at all with the direction of the grain. Furniture makers use all sorts of tricks to avoid this, e.g. the elongage holes for screws, use sliding (not-glued) dovetails, and other tricks to let wood in a cross grain configuration move past eachother. I have seen wooden chests literally break apart from their own expansion if this is not taken into a account.
The main place in speaker building where this could occur is gluing the baffle and the rear to the top and bottom. Usually the grain on the top and bottom runs side to side, so it's continuous around all four sides, where the grain on the front and back runs up and down. Hence the connection between between front and top is a cross grain configuration.
Not a problem with plywood and mdf because these don't shrink much with humidity, and they do so uniformly without bias as to direction. If you want to build a speaker box out of pure hardwood, and you live in a situation where there is any significant humidity variation you should rely on bolts or screws, elongated holes, and putty or caulk to make it airtight, and not glue for these particular joints.
Navin,
Working with granite-filled epoxy is not difficult at all, just a little smelly. This is accomplished by making a slurry of granite dust with marine-grade epoxy. The slurry is then poured into the box (for increasing effective panel thickness) or slots cut into the panels and allowed to cure. Its best to use long-cure epoxy to counteract the effects of expansion and contraction associated with short-cure epoxies in large batches.
I've used this material to make an external housing for mounting my tweeters to the main cabinets. I have found this material to be very strong, easy to machine, and have very good damping characteristics.
-Joe
Working with granite-filled epoxy is not difficult at all, just a little smelly. This is accomplished by making a slurry of granite dust with marine-grade epoxy. The slurry is then poured into the box (for increasing effective panel thickness) or slots cut into the panels and allowed to cure. Its best to use long-cure epoxy to counteract the effects of expansion and contraction associated with short-cure epoxies in large batches.
I've used this material to make an external housing for mounting my tweeters to the main cabinets. I have found this material to be very strong, easy to machine, and have very good damping characteristics.
-Joe
i managed to make a 6 layer cabinet using 3 layers of 3mm MDF and 3 layers of 4mm ply. I dont know how this will last over time. I live in Bombay, India and at times the temps get to 40deg C and humidity up to 95%. If it survives this then i guess it will do so anywhere else. We also have occasional days of dry weather so that should tst the wood out in dry conditions too.
redrumjoe666, I would love to find out more about the granite filled epoxy. I dream of using this to make tweeter "heads" a la B&W Nautillus.
David B, any idea what this "impregnated cardboard honeycomb" looks like? a pic (low res) would be helpful.
redrumjoe666, I would love to find out more about the granite filled epoxy. I dream of using this to make tweeter "heads" a la B&W Nautillus.
David B, any idea what this "impregnated cardboard honeycomb" looks like? a pic (low res) would be helpful.
navin said:
Here's a link with a photo, description and pricing.
http://www.vacupress.com/accessories.htm#honeycomb
Good luck!
For more, try a google search under "resin impregnated honeycomb". You can also get the same stuff made out of aluminum intead of impregnated cardboard - much more expensive but incredibly strong and light.
There have been a number of research projects run by various people about different cabinet construction solutions. I don't have the URL's handy but I can share a couple of tips that I gleaned from this work of others. I can't claim any original insights here.
Also, get vance dickason's loudspeaker design cookbook. That has a good discussion of box design, rigidity, damping material etc. His main point is that there are two good solutions -- either make it really rigid (e.g double layer of 3/4 mdf and/or a lot of internal bracing) - or - make it really dead using a constrained layer approach. Doing both would probably be overkill.
- "Constrained layer damping" really only requires three layers - two rigid layers of dissimilar material and an accoustically dead layer that's bonded to the two. Sounds cause the two rigid materials to try to vibrate at their respective (but different) resonant frequencies, and the dead stuff in between kills the vibes and turns them into heat. Whether for a loudspeaker or a 777 Jet, the same approach works. So one layer of mdf, one layer of masonite or cement backer board, and asphalt impregnated felt (aka tar paper for making roofs) can work. According to the theory, it works best if the stuff in the middle is glued to both other layers, I have seen people use contact cement, spray on scotch adhesive, or roofing elastomeric cement (apply with a notched trowel). ANy of these should work and are probably available in your area.
- I saw a study where someone just took two layers of MDF and sandwiched 4 sheets of 30 lb roofing felt (tar paper) between them -- and just bolted them at the edges, he didn't even bother with any glue. This guy tested this structure against several other wall structures with a pretty scientific set up and it outperformed several much more exotic and expensive solutions.
- There are actually different problems to solve and you don't want to overkill one at the expense of neglecting the other. One problem is you don't want the walls to resonate and xmit sound outside. The other is you dont want standing waves inside. So after building some sort of three piece of wall or highly braced one piece wall, you still have to line the inside iwth something to kill the vibrations. Particularly if you with the "rigid" rather than the "dead" school of box construction as described above. Wayne Jaschke of Speakerbuilder.net has said that an excellent and not exotic solution is to first apply something heavy and inert thin layer, e.g. 1/8" mass-laden vinyl (available from industrial supply catalogs as sound absorbing cover or curtain) and then overlay on that 1/4 " thick real wool felt (same source; felt is used for vibration control in a lot of industrial applications). These two materials together kill the low and mid range reflections almost as well as black hole and other costly exotic solutions, but of course are more labor intensive to apply.
Finally, if you happen to be in a high end audio store, take the time to rap with your knuckles the sides of a bunch of good quality speakers. THat way you can "calibrate" yourself as to what a well braced and well designed cabinet sounds like.
Hope that helps -- and that you'll publish the results of your experiments here.
Also, get vance dickason's loudspeaker design cookbook. That has a good discussion of box design, rigidity, damping material etc. His main point is that there are two good solutions -- either make it really rigid (e.g double layer of 3/4 mdf and/or a lot of internal bracing) - or - make it really dead using a constrained layer approach. Doing both would probably be overkill.
- "Constrained layer damping" really only requires three layers - two rigid layers of dissimilar material and an accoustically dead layer that's bonded to the two. Sounds cause the two rigid materials to try to vibrate at their respective (but different) resonant frequencies, and the dead stuff in between kills the vibes and turns them into heat. Whether for a loudspeaker or a 777 Jet, the same approach works. So one layer of mdf, one layer of masonite or cement backer board, and asphalt impregnated felt (aka tar paper for making roofs) can work. According to the theory, it works best if the stuff in the middle is glued to both other layers, I have seen people use contact cement, spray on scotch adhesive, or roofing elastomeric cement (apply with a notched trowel). ANy of these should work and are probably available in your area.
- I saw a study where someone just took two layers of MDF and sandwiched 4 sheets of 30 lb roofing felt (tar paper) between them -- and just bolted them at the edges, he didn't even bother with any glue. This guy tested this structure against several other wall structures with a pretty scientific set up and it outperformed several much more exotic and expensive solutions.
- There are actually different problems to solve and you don't want to overkill one at the expense of neglecting the other. One problem is you don't want the walls to resonate and xmit sound outside. The other is you dont want standing waves inside. So after building some sort of three piece of wall or highly braced one piece wall, you still have to line the inside iwth something to kill the vibrations. Particularly if you with the "rigid" rather than the "dead" school of box construction as described above. Wayne Jaschke of Speakerbuilder.net has said that an excellent and not exotic solution is to first apply something heavy and inert thin layer, e.g. 1/8" mass-laden vinyl (available from industrial supply catalogs as sound absorbing cover or curtain) and then overlay on that 1/4 " thick real wool felt (same source; felt is used for vibration control in a lot of industrial applications). These two materials together kill the low and mid range reflections almost as well as black hole and other costly exotic solutions, but of course are more labor intensive to apply.
Finally, if you happen to be in a high end audio store, take the time to rap with your knuckles the sides of a bunch of good quality speakers. THat way you can "calibrate" yourself as to what a well braced and well designed cabinet sounds like.
Hope that helps -- and that you'll publish the results of your experiments here.
thanks.
gotta print this out.
i think the felt idea is nice
"e.g. 1/8" mass-laden vinyl (available from industrial supply catalogs as sound absorbing cover or curtain) and then overlay on that 1/4 " thick real wool felt (same source; felt is used for vibration control in a lot of industrial applications). These two materials together kill the low and mid range reflections almost as well as black hole and other costly exotic solutions, but of course are more labor intensive to apply"
thanks again.
gotta print this out.
i think the felt idea is nice
"e.g. 1/8" mass-laden vinyl (available from industrial supply catalogs as sound absorbing cover or curtain) and then overlay on that 1/4 " thick real wool felt (same source; felt is used for vibration control in a lot of industrial applications). These two materials together kill the low and mid range reflections almost as well as black hole and other costly exotic solutions, but of course are more labor intensive to apply"
thanks again.
I have an old copy of a Speaker builder magazine where the guy makes pretty strong claims that speaker cabinet material that is too dense and strong can be detrimental to the speakers performance. He proceeded to make his own material out of tire rubber, sand, and I think glass. He said it had the best performance of any of the materials he tested. I can post more info from the article if anyone is interested.
What about water? If you could somehow make your box sit inside another and then fill the gap inbetween with water, how would this dampen? Same could be said for other liquids, maybe thick oil?
I am sure I heard my uncle say his friend has a pair of speakers that you filled with water but this was quite some time ago so I could be wrong.
I am sure I heard my uncle say his friend has a pair of speakers that you filled with water but this was quite some time ago so I could be wrong.
Here is the article on constrained layer damping
I have enclosed a link to the aforementioned article on constrained layer damping. It includes some very intriging test results.
Constrained layer damping
I have enclosed a link to the aforementioned article on constrained layer damping. It includes some very intriging test results.
Constrained layer damping
Opposite Moduli Speaker Cabinet
Ok, here is the information from the "Speaker Builder" issue.
Apparently he performed multiple experiments and found that extremely rigid enclosures (i.e. marble, concrete) perform very well in the bass region, but poorly in the mids and highs. On the other hand, softer enclosures such as cardboard perform well with highs and mids but suffer in the bass region.
I will quote the next part directly from the magazine-
"One day it occured to me to try joining two contrasting materials with modern grouting compound. I consulted "Physics for Scientinsts and Engineers" by Raymond A. Serway, and a British science data book to learn more about density, expansivity, tensile strength, Young's modulus, the speed of sound, and other information having to do with solids.
I found out that diamond on one side and rubber on the other side could be the right partners. Since I could not afford diamonds, I chose quartz sand as a substitute because it has a very high Young's modulus and a high rate of sound transmission. I contrast, rubber shows a low Young's modulus as well as a low speed of sound in a thin specimen.
A nearby tire-recycling plant provided a free sack of granulated vulcanized rubber. As a grouting compound, I chose an epoxy resin that is normally used for general building repair. I mixed the epoxy concrete with quartz sand, granulated rubber, and ilmenite (FeTiO3) powder, the last ingredient serving as a weight control additive.
The basic formula for 1kg of the mix was 431g of oven dried quartz sand, 72g of the granulated rubber, 104g ilmenite, and 393g of epoxy resin (two components). You can omit the ilmenite, but you must then replace it with 98g of quartz sand."
He goes on to say that he made sheets of the material 1 inch thick, and cut them into the appropriate shapes. I must say that the final enclosure is incredible looking, a perfect black cube with natural swirls of the quarts sand everywhere. He tested the enclosure against about every other possible enclosure material you could dream up, and this one had the best results by far. The test categories included: wideband transmission loss, distortion, decay time, and resonance Q. He also noted that he obtained both US and German patents for the material, but it is free for private use.
If anybody wants more details or a copy, please email me at paulmissy@earthlink.net.
Ok, here is the information from the "Speaker Builder" issue.
Apparently he performed multiple experiments and found that extremely rigid enclosures (i.e. marble, concrete) perform very well in the bass region, but poorly in the mids and highs. On the other hand, softer enclosures such as cardboard perform well with highs and mids but suffer in the bass region.
I will quote the next part directly from the magazine-
"One day it occured to me to try joining two contrasting materials with modern grouting compound. I consulted "Physics for Scientinsts and Engineers" by Raymond A. Serway, and a British science data book to learn more about density, expansivity, tensile strength, Young's modulus, the speed of sound, and other information having to do with solids.
I found out that diamond on one side and rubber on the other side could be the right partners. Since I could not afford diamonds, I chose quartz sand as a substitute because it has a very high Young's modulus and a high rate of sound transmission. I contrast, rubber shows a low Young's modulus as well as a low speed of sound in a thin specimen.
A nearby tire-recycling plant provided a free sack of granulated vulcanized rubber. As a grouting compound, I chose an epoxy resin that is normally used for general building repair. I mixed the epoxy concrete with quartz sand, granulated rubber, and ilmenite (FeTiO3) powder, the last ingredient serving as a weight control additive.
The basic formula for 1kg of the mix was 431g of oven dried quartz sand, 72g of the granulated rubber, 104g ilmenite, and 393g of epoxy resin (two components). You can omit the ilmenite, but you must then replace it with 98g of quartz sand."
He goes on to say that he made sheets of the material 1 inch thick, and cut them into the appropriate shapes. I must say that the final enclosure is incredible looking, a perfect black cube with natural swirls of the quarts sand everywhere. He tested the enclosure against about every other possible enclosure material you could dream up, and this one had the best results by far. The test categories included: wideband transmission loss, distortion, decay time, and resonance Q. He also noted that he obtained both US and German patents for the material, but it is free for private use.
If anybody wants more details or a copy, please email me at paulmissy@earthlink.net.
I've been researching cabinet damping, and it seems to me that there are two quite different mechanisms involved, which can become confused:
Applying a damping medium between two harder sheets (eg of MDF) - if everything is adhered well, then as the panels bend in vibration, the damping medium stays on the neutral axis, and so doesn't do very much. For this to work, it seems more rational IMHO to NOT adhere the panels tightly, but instead to simply clamp them together and rely on the random lossy interaction between the panels and the damping layer (as several people have done.
Applying a damping medium to one side (the inside) of a cabinet wall puts the damping layer in compression/tension as the panel vibrates (far more strain, and consequently far more damping). In this case, you DO need very good adhesion (experiments on old BBC panel absorbers proved that they lost effectiveness when the adhesive dried out and lost some contact).
Any comments?
Applying a damping medium between two harder sheets (eg of MDF) - if everything is adhered well, then as the panels bend in vibration, the damping medium stays on the neutral axis, and so doesn't do very much. For this to work, it seems more rational IMHO to NOT adhere the panels tightly, but instead to simply clamp them together and rely on the random lossy interaction between the panels and the damping layer (as several people have done.
Applying a damping medium to one side (the inside) of a cabinet wall puts the damping layer in compression/tension as the panel vibrates (far more strain, and consequently far more damping). In this case, you DO need very good adhesion (experiments on old BBC panel absorbers proved that they lost effectiveness when the adhesive dried out and lost some contact).
Any comments?
the best material
http://www.artmaydan.org.ua/sradivarius.html[/URL]
that my solution of material issue. this is a real marble cabinet
and nice view. I can show a big picture, if anyone has interest.
http://www.artmaydan.org.ua/sradivarius.html[/URL]
that my solution of material issue. this is a real marble cabinet
and nice view. I can show a big picture, if anyone has interest.
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