Timn8ter said:
Huh??? Tim... set the bong down and step back
Non-parallel walls do work, an irregular triangle is a good shape... recently a series of GM's Jordan JX-92 ML-TLs were built -- by all reports the triangular cross-section one was clearly better.... this jives with my own experience.
dave
It doesn't, a cab acts just like a well sealed room, or if vented, then like a door or corridor opening into a really large space, so non-parallel walls reduce the intensity of each eigenmode (standing wave) which reduces their ability to reflect back through (modulate) the driver(s) since they lose some energy at every reflection like a billiard ball, ergo sound improvement is due to both having no direct reflections off the walls and having them rapidly decay to below the noise 'floor' of the driver's output.
There will be one strong set though if a true triangular cross section is used and the driver is ~directly opposite a corner, so if the cab is large enough then the driver should be offset, which is a good idea anyway since it will smooth out the baffle's radiation response. Regardless, some fairly dense stuffing should be used to fill the 'V' corners and experiment with various densities on the top plate.
Of course if the cab's dimensions are small compared to the speaker's intended BW as is often the case with a sub/LF/midbass speaker, then shape has no effect on performance since the driver is coupled to a ~uniform particle density mass of air on the inside and the space it's in dominates on the outside.
GM
That's a good explanation, thanks GM. It just seemed to me that any air column/space which contains a wave generator is going to have some sort of standing wave or eigenmode regardless of shape. The key word in my previous statement being "eliminate". I was hoping to stimulate some discussion to help me better understand the phenom.
googler said:
If you're going to mess with a triangular cross-section, try making the rear corner a 90 degree angle, because then you have one right angle to put together - much easier with readily available tools. That'll be quite helpful when putting the thing together, no to mention also being able to do some B&W style internal bracing between the two back sides.
Good luck,
Francois.
one material I found that had low resonance high mass and very cheep and easy to form is concrete ! I have used it it works great , but heavy, I used 1.5" wall thickness mixed with #8 stone and a plasterizer to get it to flow while pouring. driver shapes and resess were molded in front encloser
I agree that non-paralell walls doesn`t eliminate standing waves, but it lowers the Q of the standing wave(s), and gives it a wider BW.
If you got two non-paralell walls 10cm in one end and 30cm in the other end, you can exite standing waves corresponding to the 10cm dimension and 30cm dimension and all in between...
Regards,
Peter
If you got two non-paralell walls 10cm in one end and 30cm in the other end, you can exite standing waves corresponding to the 10cm dimension and 30cm dimension and all in between...
Regards,
Peter
Once upon a time concrete was used for hifi driver enclosures quite a lot. I'm thinking about when mono ruled; they were actually quite common -most hifi was DIY based in some form or another during the 1940s - 1950s.
I remain unconvinced about non-parallel sides in cabinets, at least in BR designs; from what I can make out they don't eliminate or minimise standing waves at all, they just make them harder to mathematically plot. Not good. Same with rooms; golden ratios are well and good; if I had the money to build a listening room I'd use it as a starting point, but none take any account of the furnishings etc, which have a far greater measureable effect.
On the original point, my favourite metallic cabinet was / is the Celestion SL6000 with it's aerolam construction. Right from the aircraft industry, a honeycombed aluminium structure. They sound like electrostatics. I love them, and am still seeking out another decent pair; not easy as that cabinet is easily damaged and Celestion don't have any spares left (mine were stolen a couple of years back by some little baboon I would dearly like to meet with a cricket bat, a block, a rope and a drum of nitric acid.)
Best
Scott
I remain unconvinced about non-parallel sides in cabinets, at least in BR designs; from what I can make out they don't eliminate or minimise standing waves at all, they just make them harder to mathematically plot. Not good. Same with rooms; golden ratios are well and good; if I had the money to build a listening room I'd use it as a starting point, but none take any account of the furnishings etc, which have a far greater measureable effect.
On the original point, my favourite metallic cabinet was / is the Celestion SL6000 with it's aerolam construction. Right from the aircraft industry, a honeycombed aluminium structure. They sound like electrostatics. I love them, and am still seeking out another decent pair; not easy as that cabinet is easily damaged and Celestion don't have any spares left (mine were stolen a couple of years back by some little baboon I would dearly like to meet with a cricket bat, a block, a rope and a drum of nitric acid.)
Best
Scott
.....lets mount a driver in a safe
I wonder how much internal bracing can reduce standing waves. Or at least keep the waves away from the back of the cone.
I have been debating using MDF or Birch Ply for my project. I even found some 3/4 MDF core Birch ply (for $50.00 a sheet). For $50.00 I could get a sheet of 3/4 MDF, a sheet of 1/8 Luan and a quart of fiberglass resin and cloth and have change left over.
Would lining a MDF cabinet with a layer of fiberglass improve it's sound ?
I wonder how much internal bracing can reduce standing waves. Or at least keep the waves away from the back of the cone.
I have been debating using MDF or Birch Ply for my project. I even found some 3/4 MDF core Birch ply (for $50.00 a sheet). For $50.00 I could get a sheet of 3/4 MDF, a sheet of 1/8 Luan and a quart of fiberglass resin and cloth and have change left over.
Would lining a MDF cabinet with a layer of fiberglass improve it's sound ?
Scottmoose said:
At frequencies on the order of the lengths involved it does help, sometimes quite a bit. And why would a bass-reflex be any different? At the frequecies involved the bass loading is usually inconsequential.
The rooms dimensions & the effect of furniture on how a room sounds are at completely different frequency bands. At the frequencies where room shape plays a role, furniture is all but invisible.
dave
Some old ideas are the best. My 1970's 3-way Castle Conway 2 speakers are still going strong, just a bit of rewiring and rubber on the woofer's disintegrated foam surrounds, but those 24"x14"x14"cabinets are really non-resonant.
Apart from the usual bitumen pads and foam, they incorporated a shelf at the top going the whole depth of the cabinet apart from a 1" gap at the back filled with foam to act as a Helmholtz resonator to absorb the main vertical resonance plus give some extra bracing. The mid-range unit has it's own internal enclosure formed from a very thick cardboard tube 5" diameter running from front to back. This also acts as a damping brace, and seems to be much more efffective than stiff wooden braces are at helping a cabinet pass the knuckle rap test. There's a few ordinary braces, plus I've added one that forces itself against the woofer magnet when the cast aluminium chassised woofer is bolted down, this gives bracing front to back where it's most needed for the bass end.
Apart from the usual bitumen pads and foam, they incorporated a shelf at the top going the whole depth of the cabinet apart from a 1" gap at the back filled with foam to act as a Helmholtz resonator to absorb the main vertical resonance plus give some extra bracing. The mid-range unit has it's own internal enclosure formed from a very thick cardboard tube 5" diameter running from front to back. This also acts as a damping brace, and seems to be much more efffective than stiff wooden braces are at helping a cabinet pass the knuckle rap test. There's a few ordinary braces, plus I've added one that forces itself against the woofer magnet when the cast aluminium chassised woofer is bolted down, this gives bracing front to back where it's most needed for the bass end.
A couple of years ago when I was developing my Wilson Watt Puppy clones I did a lot of thinking and studying about enclosure design.
In later years Rockport actually made a speaker like I was thinking.
There are ways to built enclosures as good or better than the Wilsons, Rockports and Thiels. OF course the upper line thiels use a thick cement baffle and a heavily braced MDF cabinet.
Here are some facts which most of you will know but for those who are new I post.
For the bass cabinet rigidity is the most important thing to resist high internal air pressures and low frequency excitment. It is very important to have as much internal bracing as possible regardless of the material to raise the resonant frequency of each panel. It is easier to dampen or reduce the amplitude of a high frequency resonance so all the bracing makes any internal damping methods more effective.
As you go up in frequency high mass and internal damping of the material become more important to resisting panel resonances. This implies that mid and tweeter cabinets need higher wall thickness and even tighter bracing.
One interesting thing about metal is that even though it is rigid it has poorer internal damping that many other products. Steel is not really a good material for cabinets unless it is highly damped in some way. Aluminum is better but there are other things that are better yet.
When Wilson audio was testing materials they use to have a test panel and speaker mounted on a wire in free air with an accelerometer on it. Each material test panel was the same size and thickness and used the same speaker and test tone at the same SPL. They measured how well the materials own internal damping reduced the resonances.
Because certain materials like steel had high mass they resisted excitation but once they were made to resonant they would ring for a long time.
THe best materials turned out to be mineral filled acyrilics and phenolic composite panels. The phenolic composite panels are made from compressing linen or paper or fiberglass or carbon fiber at high pressure with phenolic resins. The resulting panels are lighter than aluminum and stronger and more rigid than steel of equivalent thickness. This material is so tough that it is used to make high strength gears in applications where no oil or lubricant is allowed. They panels are also used as ultra high voltage insulators in power stations and high voltage substation panels.
The fiberglass and carbon fiber panels are extremely expensive. Maybe 4000 - 5000 USD for a 1 inch thick 4 x 8 foot panel. The linen and paper varieties which are most likely the ones Wilson uses are about 1000 - 1200 a 4 x 8 foot sheet in small quantities. This is for .75 to 1 inch thickness. The panels are available in up to 4 inch thickness and are really high priced in those thicknesses. Wilson propably gets a discount for volume buying. His ads claim M material is 14 times what MDF is. That about 350 USD a sheet which is really cheap so he must use enough of the stuff to get a big discount. Also in some photos of his manufacturing process it looks like he is using .5 inch material. So this may save him some money.
I thick the best construction method available for a upper range unit would be to use the Rockport method or something similar.
The kinds of materials that have the best of both characteristics are composite panels which have a very rigid skin on both sides and and a internal either high mass center or a rigid center with high damping.
THis is work intensive but will yield the best possible cabinet and though not cheap is reasonable for the DIY'r.
Ok, construct a cabinet mockup out of cheap rigid building foam and hand lay up both the inner and outer walls with fibergalss and epoxy resin. The thicker the better. The mold needs to be made so that it can seperate and then the foam removed. The internal braces which can be MDF or Aluminum are skinned with the fiberglass or carbon fiber if you can afford it, to be part of the internal shell.
After the shell layout is finished the skins are put back together and filled with a mineral filled epoxy or a pourable type of casting acrylic. You can use sand or crushed rock. Although it is better if the particles are flat instead of round shaped as they lock together better in the matrix. However, it may be that sand which is more rounded though less strong may have better damping characteristics.
The low frequency cabinets can be made in the same way or be built from MDF and skinned inside and out with the fiberglass epoxy resin skin. This skin increased the rigidity a lot.
OR if you can afford it make the lower cabinet out of the phenolic composite panels. They must be machined with CNC equipment because they are too hard to work with hand tools.
Here are some variations that should work well. Pourable marble like plastics are available and are used to cast bathroom sinks and similar things. You can add crushed rock or sand into this and pour the mixture into hand made polyethelyne molds and then cut the molds away after curing. These can then be skinned afterwards with epoxy and fiberglass if desired but would work reasonably well alone.
YOu could also mold a cabinet out of a very dense and rich cement mixture with lots of sand and small rocks. Then the cement structure can be skinned with fiberglass and epoxy resin to significantly increase the rigidity of the concrete. The resin finish can be made into a very high quality finish with polyester gel goat or a similar epoxy coating.
Pigments can be added to the resin so that it does not need to be painted. Only sanded and buffed to a high shine.
Here is my take on damping methods. It is better to absorb as much internal acoustic energy as possible and turning it into heat by using a convoluted foam bonded to a high loss thin damping material is a good way to abord internal cavity energy. Becasue the convoluted foam will move it will turn a lot of internal energy into heat without exciting the panels.
Also the drivers should be mounted firmly in a medium to stiff damping material which allows the connection to both sink some of the drivers energy into the higher mass cabinet and absorb some of the energy through the damping gasket.
Hezz
In later years Rockport actually made a speaker like I was thinking.
There are ways to built enclosures as good or better than the Wilsons, Rockports and Thiels. OF course the upper line thiels use a thick cement baffle and a heavily braced MDF cabinet.
Here are some facts which most of you will know but for those who are new I post.
For the bass cabinet rigidity is the most important thing to resist high internal air pressures and low frequency excitment. It is very important to have as much internal bracing as possible regardless of the material to raise the resonant frequency of each panel. It is easier to dampen or reduce the amplitude of a high frequency resonance so all the bracing makes any internal damping methods more effective.
As you go up in frequency high mass and internal damping of the material become more important to resisting panel resonances. This implies that mid and tweeter cabinets need higher wall thickness and even tighter bracing.
One interesting thing about metal is that even though it is rigid it has poorer internal damping that many other products. Steel is not really a good material for cabinets unless it is highly damped in some way. Aluminum is better but there are other things that are better yet.
When Wilson audio was testing materials they use to have a test panel and speaker mounted on a wire in free air with an accelerometer on it. Each material test panel was the same size and thickness and used the same speaker and test tone at the same SPL. They measured how well the materials own internal damping reduced the resonances.
Because certain materials like steel had high mass they resisted excitation but once they were made to resonant they would ring for a long time.
THe best materials turned out to be mineral filled acyrilics and phenolic composite panels. The phenolic composite panels are made from compressing linen or paper or fiberglass or carbon fiber at high pressure with phenolic resins. The resulting panels are lighter than aluminum and stronger and more rigid than steel of equivalent thickness. This material is so tough that it is used to make high strength gears in applications where no oil or lubricant is allowed. They panels are also used as ultra high voltage insulators in power stations and high voltage substation panels.
The fiberglass and carbon fiber panels are extremely expensive. Maybe 4000 - 5000 USD for a 1 inch thick 4 x 8 foot panel. The linen and paper varieties which are most likely the ones Wilson uses are about 1000 - 1200 a 4 x 8 foot sheet in small quantities. This is for .75 to 1 inch thickness. The panels are available in up to 4 inch thickness and are really high priced in those thicknesses. Wilson propably gets a discount for volume buying. His ads claim M material is 14 times what MDF is. That about 350 USD a sheet which is really cheap so he must use enough of the stuff to get a big discount. Also in some photos of his manufacturing process it looks like he is using .5 inch material. So this may save him some money.
I thick the best construction method available for a upper range unit would be to use the Rockport method or something similar.
The kinds of materials that have the best of both characteristics are composite panels which have a very rigid skin on both sides and and a internal either high mass center or a rigid center with high damping.
THis is work intensive but will yield the best possible cabinet and though not cheap is reasonable for the DIY'r.
Ok, construct a cabinet mockup out of cheap rigid building foam and hand lay up both the inner and outer walls with fibergalss and epoxy resin. The thicker the better. The mold needs to be made so that it can seperate and then the foam removed. The internal braces which can be MDF or Aluminum are skinned with the fiberglass or carbon fiber if you can afford it, to be part of the internal shell.
After the shell layout is finished the skins are put back together and filled with a mineral filled epoxy or a pourable type of casting acrylic. You can use sand or crushed rock. Although it is better if the particles are flat instead of round shaped as they lock together better in the matrix. However, it may be that sand which is more rounded though less strong may have better damping characteristics.
The low frequency cabinets can be made in the same way or be built from MDF and skinned inside and out with the fiberglass epoxy resin skin. This skin increased the rigidity a lot.
OR if you can afford it make the lower cabinet out of the phenolic composite panels. They must be machined with CNC equipment because they are too hard to work with hand tools.
Here are some variations that should work well. Pourable marble like plastics are available and are used to cast bathroom sinks and similar things. You can add crushed rock or sand into this and pour the mixture into hand made polyethelyne molds and then cut the molds away after curing. These can then be skinned afterwards with epoxy and fiberglass if desired but would work reasonably well alone.
YOu could also mold a cabinet out of a very dense and rich cement mixture with lots of sand and small rocks. Then the cement structure can be skinned with fiberglass and epoxy resin to significantly increase the rigidity of the concrete. The resin finish can be made into a very high quality finish with polyester gel goat or a similar epoxy coating.
Pigments can be added to the resin so that it does not need to be painted. Only sanded and buffed to a high shine.
Here is my take on damping methods. It is better to absorb as much internal acoustic energy as possible and turning it into heat by using a convoluted foam bonded to a high loss thin damping material is a good way to abord internal cavity energy. Becasue the convoluted foam will move it will turn a lot of internal energy into heat without exciting the panels.
Also the drivers should be mounted firmly in a medium to stiff damping material which allows the connection to both sink some of the drivers energy into the higher mass cabinet and absorb some of the energy through the damping gasket.
Hezz
Is it the strengh of the of the materials or the denisty of it / look at this way if you were pounding a nail in a springy board the board springs, but if you back it up with a sledge hammer it dont move, say its the mass of the material. concrete is cheep and it can be rubed out like a tumestone.
Well it depends on the frequency. For high frequency energy high mass is more important because if it massive enough it can completely stop the vibrations. At lower freqencies rigidity and strength is more important than mass. But even so if the mass is sufficient it will work at the lower frequencies also. IT depends how close to cost weight optimization you are working.
If you were making a two part cabinet. Cement would be a good choice for the mid/tweeter cabinet because the cabinet is smaller. But using cement in the bass cabinet can make the speaker too heavy to move around and increases the wall thickness too much to where it may take up too much needed internal volume that the drivers can use for better Q bass.
I think the fiberglass skinned MDF is the best compromise approach for the bass and the skinned cement or skinned molded mineral filled plastic is best compromise for the smaller mid/tweeter cabinet. If the speaker is only one cabinet then a good compromise is to make the front baffle only of thick cement or mineral filled plastic. The rest of the cabinet can be skinned MDF.
Hezz
If you were making a two part cabinet. Cement would be a good choice for the mid/tweeter cabinet because the cabinet is smaller. But using cement in the bass cabinet can make the speaker too heavy to move around and increases the wall thickness too much to where it may take up too much needed internal volume that the drivers can use for better Q bass.
I think the fiberglass skinned MDF is the best compromise approach for the bass and the skinned cement or skinned molded mineral filled plastic is best compromise for the smaller mid/tweeter cabinet. If the speaker is only one cabinet then a good compromise is to make the front baffle only of thick cement or mineral filled plastic. The rest of the cabinet can be skinned MDF.
Hezz
To Hezz; your research parallels my own
In investigating alternative cabinet materials, Wilson’s moniker of “M”, “W” and “X” materials actually cover a range of expensive supplies. I believe he first used the “M” type before he went commercial with the 80's model WATT speakers. I always believed it stood for “Micarta” a well known brand of phenolic sheet formerly manufactured by Westinghouse’s Specialty Materials Division now Norplex Micarta. The cost is about right, a 4 x 8 sheet runs around $500 in quantity. By the way Norplex has a new product “Micarta BRASS” phenolic a ballistic-resistant laminate that is superior to paper phenolic but very expensive.
Taking a tip from Thiel where the front baffle is the expensive material and the remaining cabinet is constructed from standard MDF, one could reasonably source some surplus phenolic sheet without incurring too high a cost, at least enough for some front baffles. As to the often mentioned WATT material said to be a highly mineral filled acrylic, one is left with quite an array of polymers out there. The closest probably being MMA Methyl-Methacrylate polymer, mineral filled. This resin is generally used as a polymer concrete in industrial floor systems. Sherwin Williams markets their Cor-Cote brand and EpoxySystems has their 680 MMA. As to the mineral aggregate used, one could try powdered stone such as marble dust or granite. Rottenstone as used in the furniture refinishing industry might be a potential source as well, its available from MannBrothers Specialty Paints in 50 lb. Bags.
For safety’s sake I should mention that under NO CIRCUMSTANCE WHATSOEVER mix an aggregate of any metal dust into MMA resin. The idea of a metallic hard polymer may be structurally appealing but is Highly Dangerous, no joking here folks. Any material such as iron oxide or aluminum dust incorporated into MMA resin results in a material similar to “Solid Rocket Fuel Propellant”. This is “Highly Combustible” to say the least. 
We want to keep this a SAFE hobby and a newcomer might accidentally concoct an experimental cabinet without knowing the risks of what they are working with. I just thought everyone should be cognizant of the unintended danger when working with certain resins. Picked this up from the experimental rocket hobbyists, yet another cross-reference to our own interests in Audio, you can never be too safe or too informed.
In investigating alternative cabinet materials, Wilson’s moniker of “M”, “W” and “X” materials actually cover a range of expensive supplies. I believe he first used the “M” type before he went commercial with the 80's model WATT speakers. I always believed it stood for “Micarta” a well known brand of phenolic sheet formerly manufactured by Westinghouse’s Specialty Materials Division now Norplex Micarta. The cost is about right, a 4 x 8 sheet runs around $500 in quantity. By the way Norplex has a new product “Micarta BRASS” phenolic a ballistic-resistant laminate that is superior to paper phenolic but very expensive.
Taking a tip from Thiel where the front baffle is the expensive material and the remaining cabinet is constructed from standard MDF, one could reasonably source some surplus phenolic sheet without incurring too high a cost, at least enough for some front baffles. As to the often mentioned WATT material said to be a highly mineral filled acrylic, one is left with quite an array of polymers out there. The closest probably being MMA Methyl-Methacrylate polymer, mineral filled. This resin is generally used as a polymer concrete in industrial floor systems. Sherwin Williams markets their Cor-Cote brand and EpoxySystems has their 680 MMA. As to the mineral aggregate used, one could try powdered stone such as marble dust or granite. Rottenstone as used in the furniture refinishing industry might be a potential source as well, its available from MannBrothers Specialty Paints in 50 lb. Bags.
For safety’s sake I should mention that under NO CIRCUMSTANCE WHATSOEVER mix an aggregate of any metal dust into MMA resin. The idea of a metallic hard polymer may be structurally appealing but is Highly Dangerous, no joking here folks. Any material such as iron oxide or aluminum dust incorporated into MMA resin results in a material similar to “Solid Rocket Fuel Propellant”. This is “Highly Combustible” to say the least. We want to keep this a SAFE hobby and a newcomer might accidentally concoct an experimental cabinet without knowing the risks of what they are working with. I just thought everyone should be cognizant of the unintended danger when working with certain resins. Picked this up from the experimental rocket hobbyists, yet another cross-reference to our own interests in Audio, you can never be too safe or too informed.
CFB,
Thanks for your exellent and informative follow up. In particular the safety information is very useful.
Please be aware anyone working with epoxy resins also that they can be a ventilation hazard and take necessery steps to be safe. Polyester resins can also be used as a substitute for epoxy and are a bit safer but still need to be handled with care. I think the epoxy composties are a little tougher and stronger.
The epoxy also bonds better to certain matrix materials like fiberglass and carbon fiber.
Please let us know if anyone decides to use one of these methods to build a cabinet as we would be very interested in your results.
Hezz
Thanks for your exellent and informative follow up. In particular the safety information is very useful.
Please be aware anyone working with epoxy resins also that they can be a ventilation hazard and take necessery steps to be safe. Polyester resins can also be used as a substitute for epoxy and are a bit safer but still need to be handled with care. I think the epoxy composties are a little tougher and stronger.
The epoxy also bonds better to certain matrix materials like fiberglass and carbon fiber.
Please let us know if anyone decides to use one of these methods to build a cabinet as we would be very interested in your results.
Hezz
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