so making a box from construction hard foam
1" or 2" thick,then when its cut out,"glue" with epoxy and seal it up? im wondering if epoxy would "eat" the foam board. or disolve it a bit? i know some paint rollers cant be used with epoxy because they degenerate and breakdown during use. i have to say id the epoxy works well,it seems to me(what do i know) like a interesting way to build a speaker.
what about the weight? shouldnt the speaker be heavy for some reason? if so,mayube it could be sand loaded on the bottom.
im just guessing.
roy
1" or 2" thick,then when its cut out,"glue" with epoxy and seal it up? im wondering if epoxy would "eat" the foam board. or disolve it a bit? i know some paint rollers cant be used with epoxy because they degenerate and breakdown during use. i have to say id the epoxy works well,it seems to me(what do i know) like a interesting way to build a speaker.
what about the weight? shouldnt the speaker be heavy for some reason? if so,mayube it could be sand loaded on the bottom.
im just guessing.
roy
"Sheet aluminum glued to this stuff would work very well, I think.
http://www.duraboard.com/"
Not stiff and too heavy.
"what about the weight? shouldnt the speaker be heavy for some reason?"
A light stiff box attached to a massive sandfilled bass ought to work well.
It will help some things, like the enclosure moving in reaction to the woofer mass.
Another good reason to have a sub; its box can have a much lowerresonant freq, say 150 Hz for one used at 80 Hz and below.
Well, maybe higher since most XO's aren't very steep.
http://www.duraboard.com/"
Not stiff and too heavy.
"what about the weight? shouldnt the speaker be heavy for some reason?"
A light stiff box attached to a massive sandfilled bass ought to work well.
It will help some things, like the enclosure moving in reaction to the woofer mass.
Another good reason to have a sub; its box can have a much lowerresonant freq, say 150 Hz for one used at 80 Hz and below.
Well, maybe higher since most XO's aren't very steep.
Hi there. To begin: I did my masters paper on cabinet design and I did a lot of research.
The big question is, what do you want to achieve?
I turned out that over a certain thickness or structure there is no audible improvement anymore. Keep this in mind. It is no use to go overboard with your cabinets to improve on inaudible imperfections!
The MAIN thing is still the speaker cone, that is the part that produces the most distortion and non linearities.
I also tried sandwhich cabinets (filled with sand). Yes, they are very good and pretty much the best option for the price, but awfully heavy and really not worth the trouble because the difference to a 22mm MDF cabinet is minimal!
By the way one material is not per se good. Like MDF or plywood for example. There are BIG diferences. Plywood for example comes in various qualities. The better quality has thinner layers! The plywood with 1-2mm thick layers is usually inferiour to MDF. MDF also comes in different qualities...
What you want is a reasonably stiff cabinet that does not react like a balloon. But also you do not want a cabinet that has resonances in the audible frequency band, like marble for example, because then you have big trouble with resonances in the midrange with a high Q and those are easy to hear..
What you need is a material with a high damping factor. Combined with a reasonably stiff wall this means that you need relativly heavy materials. Light foam won't do much here...
There is a formula to calculate the fres of the cabinet (approximately). I am happy to share..
The big question is, what do you want to achieve?
I turned out that over a certain thickness or structure there is no audible improvement anymore. Keep this in mind. It is no use to go overboard with your cabinets to improve on inaudible imperfections!
The MAIN thing is still the speaker cone, that is the part that produces the most distortion and non linearities.
I also tried sandwhich cabinets (filled with sand). Yes, they are very good and pretty much the best option for the price, but awfully heavy and really not worth the trouble because the difference to a 22mm MDF cabinet is minimal!
By the way one material is not per se good. Like MDF or plywood for example. There are BIG diferences. Plywood for example comes in various qualities. The better quality has thinner layers! The plywood with 1-2mm thick layers is usually inferiour to MDF. MDF also comes in different qualities...
What you want is a reasonably stiff cabinet that does not react like a balloon. But also you do not want a cabinet that has resonances in the audible frequency band, like marble for example, because then you have big trouble with resonances in the midrange with a high Q and those are easy to hear..
What you need is a material with a high damping factor. Combined with a reasonably stiff wall this means that you need relativly heavy materials. Light foam won't do much here...
There is a formula to calculate the fres of the cabinet (approximately). I am happy to share..
well it seems alot of you guys
know more about cabinet design than i ever will. the one thing id like to point out,,though it seems obvious is this,,as DIYers we can aford to spend time building a cabinet that if bought would be cost prohibitive. but even if the cab takes us three weeks to build with our spare time,,in reality it still "costs" us nothing,well except for parts. i happen to like that idea.
so armed with a plan,we CAN realy build loudspeakers that otherwise would be out of reach.
the thing with plywood. the thinner vrs thicker/quality thing. from what i have read while researching boatbuilding,,the quality goes down because of "voids" or spaces in between the plys. the high cost stuff,im pretty sure osent have any. they have very high quality controll,and in fact garanteed by loydes of london. i cant remember the the number of it. bs"somthing". it is pretty expensice though, i though if i built a set of speeks that i realy liked,then i might build another pair with this high quality ply. it has a mahogany surface. and i happen to like that anyways.
"BS 1088 British Standard Specification for Marine Plywood manufactured from selected untreated Tropical Hardwoods"
http://www.glen-l.com/wood-plywood/okoume.html
if you do a search for boat building or dinghy building,,youll get a ton of site from DIYers that use this type of plywood,most important though,there will be tons of decent pictures to show what it looks like when finneshed. mostly covered with epoxy(looks clear) the a few coats of marine sparvarnish for UV protection. in other words,,ittl look just like any woodworking project,but tough as nails.
oh,as far as carbon fiber,, for the home builder that wont use a ton of it,,,its not "that" expensive to use. im just not sure its called for in loudspeaker uses. maybe it is shrug shrug
i like this thread. there are alot of answers out there other than the ply/osb box.
roy
know more about cabinet design than i ever will. the one thing id like to point out,,though it seems obvious is this,,as DIYers we can aford to spend time building a cabinet that if bought would be cost prohibitive. but even if the cab takes us three weeks to build with our spare time,,in reality it still "costs" us nothing,well except for parts. i happen to like that idea.
so armed with a plan,we CAN realy build loudspeakers that otherwise would be out of reach.
the thing with plywood. the thinner vrs thicker/quality thing. from what i have read while researching boatbuilding,,the quality goes down because of "voids" or spaces in between the plys. the high cost stuff,im pretty sure osent have any. they have very high quality controll,and in fact garanteed by loydes of london. i cant remember the the number of it. bs"somthing". it is pretty expensice though, i though if i built a set of speeks that i realy liked,then i might build another pair with this high quality ply. it has a mahogany surface. and i happen to like that anyways.
"BS 1088 British Standard Specification for Marine Plywood manufactured from selected untreated Tropical Hardwoods"
http://www.glen-l.com/wood-plywood/okoume.html
if you do a search for boat building or dinghy building,,youll get a ton of site from DIYers that use this type of plywood,most important though,there will be tons of decent pictures to show what it looks like when finneshed. mostly covered with epoxy(looks clear) the a few coats of marine sparvarnish for UV protection. in other words,,ittl look just like any woodworking project,but tough as nails.
oh,as far as carbon fiber,, for the home builder that wont use a ton of it,,,its not "that" expensive to use. im just not sure its called for in loudspeaker uses. maybe it is shrug shrug
i like this thread. there are alot of answers out there other than the ply/osb box.
roy
"Low density is a requisite characteristic?"
It is for the strategy of having high resonances that can be effectively damped with relatively thin material.
There's the brute force method, like concrete or brick, which will have high stiffness by virtue of its thickness.
Its resonances will be in the audible range, but the sheer magnitude of its mass and stiffness means it will essentially be an immovable object to the low pressures involved (a fraction of a psi).
"But also you do not want a cabinet that has resonances in the audible frequency band,"
Good like trying to achieve that. But it's probably not necessary beyond a certain frequency, where the energy is low enough that it will be as per above.
It is for the strategy of having high resonances that can be effectively damped with relatively thin material.
There's the brute force method, like concrete or brick, which will have high stiffness by virtue of its thickness.
Its resonances will be in the audible range, but the sheer magnitude of its mass and stiffness means it will essentially be an immovable object to the low pressures involved (a fraction of a psi).
"But also you do not want a cabinet that has resonances in the audible frequency band,"
Good like trying to achieve that. But it's probably not necessary beyond a certain frequency, where the energy is low enough that it will be as per above.
cabinet resonances are often in the audible (midrange) frequecies and this is where the ear is most sensitive. You have basically 3 options if you want to avoid colouration
(did not understand the thing with "having resonances", do you say you want them??)
1. you can "shift" the resonances over the audible range
2. you can "shift" the resonances below the audible range
3. you can dampen them
solutions for no:
1. you make the cabinet light and stiff (B&W did that with their matrix range)
2. you make the cabinet heavy and use materials that are not stiff (concrete does not do the trick since it is heavy AND stiff, if you use 3cm concrete or marble ( even worse), you get awful resonances above 500Hz were it is most noticable). If the material is too soft though then the walls bend at low frequencies (like a ballon) which takes the punch out of the bass
3. you use materials with a high damping factor (heavy rubber for example or sand) and you then need relativly high mass to make it work. This construction often needs another material to give you the framesupport (for sand especially)
For those who want more details or facts I am happy to supply more...
PS: I am a member of the audio engineering society and had a longer chat with Mr Thiele recently.
(did not understand the thing with "having resonances", do you say you want them??)
1. you can "shift" the resonances over the audible range
2. you can "shift" the resonances below the audible range
3. you can dampen them
solutions for no:
1. you make the cabinet light and stiff (B&W did that with their matrix range)
2. you make the cabinet heavy and use materials that are not stiff (concrete does not do the trick since it is heavy AND stiff, if you use 3cm concrete or marble ( even worse), you get awful resonances above 500Hz were it is most noticable). If the material is too soft though then the walls bend at low frequencies (like a ballon) which takes the punch out of the bass
3. you use materials with a high damping factor (heavy rubber for example or sand) and you then need relativly high mass to make it work. This construction often needs another material to give you the framesupport (for sand especially)
For those who want more details or facts I am happy to supply more...
PS: I am a member of the audio engineering society and had a longer chat with Mr Thiele recently.
Re: one more idea
Or just go to a pet shop and buy lizard sand it's already sterilized
faustian bargin said:...that i've heard of people doing, is to build a box-within-a-box, such that the space between the boxes is filled with sand, or sand + lead shot. i suppose you could even make some wild cement concoction, to really make it dense and heavy - maybe use a glue-sand-shot mixture. (yuck.) however the vibration damping might not be as good as with dry sand.
(btw if you try this, sterilize the sand first in the oven.)
/andrew
Or just go to a pet shop and buy lizard sand it's already sterilized
"(did not understand the thing with "having resonances", do you say you want them??)"
Want them or not, you'll have them, it's just a question of where; as you obviously know.
I was alluding to your option 1.
I don't see how it's possible to get them above the audio range, but if you can get far enough above the bass/mid's passband I'd think the tweeter's low mass wouldn't give any significant panel excitation.
I'm guessing that'd only be possible with thick honeycomb sandwhich panels or ones with a lot of curvature.
Want them or not, you'll have them, it's just a question of where; as you obviously know.
I was alluding to your option 1.
I don't see how it's possible to get them above the audio range, but if you can get far enough above the bass/mid's passband I'd think the tweeter's low mass wouldn't give any significant panel excitation.
I'm guessing that'd only be possible with thick honeycomb sandwhich panels or ones with a lot of curvature.
The most interesting new approach that would be realatively cost effective is to build the cabinet out of rigid building foam about 1- 1.5 inches thick and then skin both the inner and outer cabinet with about .25 inch fiberglass woven mat and epoxy resin.
This would be both relatively light internally and have a high stiffness and a high internal dampening factor.
This would be both relatively light internally and have a high stiffness and a high internal dampening factor.
Another Solution.... for a 3-Way
Build a rigid, braced (matrix) and undamped box for the Bass with the resonance above its operating range. And a separate box with thin panels (1/4" inner and outer) and say 1/2" to 3/4" of sand (unbraced) for the midrange/tweeter cabinet with the resonance lower than the midrange handles.
I am assuming the crossover should be around 200Hz or so.
You should have steeper crossovers to avoid any out of passband soundwaves being able to resonate the respective panels.
Build a rigid, braced (matrix) and undamped box for the Bass with the resonance above its operating range. And a separate box with thin panels (1/4" inner and outer) and say 1/2" to 3/4" of sand (unbraced) for the midrange/tweeter cabinet with the resonance lower than the midrange handles.
I am assuming the crossover should be around 200Hz or so.
You should have steeper crossovers to avoid any out of passband soundwaves being able to resonate the respective panels.
"skin both the inner and outer cabinet with about .25 inch fiberglass woven mat and epoxy resin.
This would be both relatively light internally and have a high stiffness and a high internal dampening factor."
.5 in. of fiberglass weighs as much as about 1 in. of wood.
Once you have skins of enough mass to render the core mass negligible,say 10X, further increasing the fiberglass has little further effect.
At that point you're not changing the stiffness/mass ratio, which determines resonance freq.
This would be both relatively light internally and have a high stiffness and a high internal dampening factor."
.5 in. of fiberglass weighs as much as about 1 in. of wood.
Once you have skins of enough mass to render the core mass negligible,say 10X, further increasing the fiberglass has little further effect.
At that point you're not changing the stiffness/mass ratio, which determines resonance freq.
I once went to a stone mason who is experienced in speaker building itself. He had about 50 to 100 stone boards in his showroom and he said he has made the best experiences with black granite. Unfortunately this is 250 Euro per squaremeter stuff. Basalt has similar density, I don`t know whether it is cheaper. Apart from weight and stiffness a third advantage is that the speed of sound is close to steel and aluminium, which improves the draw-off of the magnet/basket resonances.
A more modern alternative to sand filling is the following:
http://www.korff.ch/e/hawaphon.htm
Regards
Charles
http://www.korff.ch/e/hawaphon.htm
Regards
Charles
re: fibreglass
Hi Noah,
I am not sure what you meant with:
Usually fibreglass and resin do not have a high internal dampening factor, that is why fibreglass cones (or kevlar for that matter) have problems with cone resonances. The resin that is normally used does not have a good dampening factor and actually overshadows all the acoustical qualities of the fibreglass. Maybe you are talking about a different resin, which would be interesting...
Fibreglass is also quite light and to dampen a wall you would need a few times the mass of the wall. Therefor I cannot see what you want to achieve with fibreglass. In my experience rubber matts or bitumen does a much better job, it is both heavy and has a very high dampening factor.
(If anyone has problems finding rubber matts, then you could use the car rubber matts, there are some relatively thick and cheap ones available)...
However, as I mentioned before, with adding a lot of mass to the walls you will shift the resonance frequencies downwards and this can result in less resonances but within a more sensitive frequency band than before, which can leed to a worse sound again...
PS: somebody was interested in the formula for calculating resonances: I will post this next week...
Hi Noah,
I am not sure what you meant with:
Usually fibreglass and resin do not have a high internal dampening factor, that is why fibreglass cones (or kevlar for that matter) have problems with cone resonances. The resin that is normally used does not have a good dampening factor and actually overshadows all the acoustical qualities of the fibreglass. Maybe you are talking about a different resin, which would be interesting...
Fibreglass is also quite light and to dampen a wall you would need a few times the mass of the wall. Therefor I cannot see what you want to achieve with fibreglass. In my experience rubber matts or bitumen does a much better job, it is both heavy and has a very high dampening factor.
(If anyone has problems finding rubber matts, then you could use the car rubber matts, there are some relatively thick and cheap ones available)...
However, as I mentioned before, with adding a lot of mass to the walls you will shift the resonance frequencies downwards and this can result in less resonances but within a more sensitive frequency band than before, which can leed to a worse sound again...
PS: somebody was interested in the formula for calculating resonances: I will post this next week...
The main point was to gain the stiffness from the skins being spaced apart by the core.
Fiberglass is the easiest way to get compound curvature (I forget, but I think we were talking about curved surfaces).
Anyway, it's true fiberglass doesn't have as high a damping as treated paper or polypropylene, but it's higher than wood and metal.
Fiberglass is the easiest way to get compound curvature (I forget, but I think we were talking about curved surfaces).
Anyway, it's true fiberglass doesn't have as high a damping as treated paper or polypropylene, but it's higher than wood and metal.
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