Leob,So far I compared similar, not identical, plates of different thickness, so can still be a misunderstanding that indeed more mass of the same material can be more efficient. I prepared prints of the same size plate as 1 mm, 3.8 mm and 6 mm thick which I will print with same thickness skin and same density infill.
My guess is that the 3.8 mm will be the loudest, but not sure why and if I'll be any wiser as to how it really works regardless of the result
Can you share some of your printing limitations? Maybe I could suggests a print or two that would be interesting, if I better understood your material and capabilities. I know you shared some of this before, but could you tell me:
What is the highest modulus resin you have available? I mean that you currently use or get for a very reasonable price? Not some exotic resin (at least for now!)
What is the largest size you can print?
What is the thinnest solid skin you can reliably print?
What is the lowest density infill you can reliably print?
If I know these things I might be able to suggest some constructions that would be worth testing, if you like.
Eric
Sorry Leob but I haven't found the article using those words. Do you have a link?
With "my words" : here you describe what is a "linear system".
Next you seems describing more or less the behavior of a self oscillating system (no more relation between the input and the trigger) which a guitar is not but you seems under estimating the role of its soundboard which is precisely like in other instruments to transmit efficiently the vibration to the air. The vibration of the string is send to the soundboard (the top plate of the guitar) through the sound post. I can imagine the soundboard is dedicated to the frequency range of the guitar but not a sharp tuning between string and soundboard.
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Leob .
I agree with Eric and Christian, it is not a question of ganging up on you , but more to do with trying to understand what you are saying ?
You are using words and terminology that is not known, to me anyway ?
It gets very confusing and you seem to contradict yourself in the same sentence, if I'm understanding it right that is ?
It is like you are speaking in a different language.
Christian is doing a very good job of trying to decipher what you are saying, which is amazing as English is not his first language.
I wish I could help ,but I'm a little bit lost here?
How it has got onto bridges blowing in the wind I will never know ?
And please do not try to explain this to me, or I might start talking about the millennium bridge in London 😁
Steve.
I agree with Eric and Christian, it is not a question of ganging up on you , but more to do with trying to understand what you are saying ?
You are using words and terminology that is not known, to me anyway ?
It gets very confusing and you seem to contradict yourself in the same sentence, if I'm understanding it right that is ?
It is like you are speaking in a different language.
Christian is doing a very good job of trying to decipher what you are saying, which is amazing as English is not his first language.
I wish I could help ,but I'm a little bit lost here?
How it has got onto bridges blowing in the wind I will never know ?
And please do not try to explain this to me, or I might start talking about the millennium bridge in London 😁
Steve.
The stiffest filament (FDM printer, so not resin, but a strand of plastic that is melted) I have at hand is this (link to data sheet on the page):
https://www.extrudr.com/en/products/catalogue/greentec-pro-carbon_2410/
I'm using this for the tests since it is a bit cheaper and I have more left of it:
https://www.extrudr.com/en/products/catalogue/biofusion-copper_2475/
My printbed is 300x300mm. I use 295mm out of laziness since it is fiddly to squeeze every mm out of the surface.
With printer perfectly set up and using the carbon filament I can get a solid 0.1mm layer at the bottom. With Biofusion as well, but it seems much more sensitive and on my first print some of it came off when removing the plate from the bed.
The top is more tricky, since there it has to lay down the layer on the honeycomb rather than pressing it down on glass, so 3-4 layers are needed to ensure it is solid, so at best 0.3 mm. Probably I should print the top skin separately and glue it on after for ideal results.
Minimum density infill is hard to answer. Unless I print the top separately, due to the limitations I just mentioned you need a certain density for the filament to be able to bridge the cells. If I would print the top separately I could make it with 0 infill. One can also make adaptive infill to minimize the amount needed to make a good support for the top.
But typically you express the infill as a percentage, but those values are not really expressing density as you would expect, and 15% of one infill pattern can weigh more than 15% of another pattern. Also extrusion width comes in to it. So it is not so easy for me to print something of a specific density, but I could of course calculate the density of something that is already printed and eventually tweak it to an absolute value.
I will explore infill density more eventually, but for my first tests I want to figure out if adding mass can improve efficiency, or in practice get an idea about optimal thickness given the constraints I have.
https://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)
In specific this quote discusses linear resonance vs self-exciting systems:
"Could this be called a resonant phenomenon? It would appear not to contradict the qualitative definition of resonance quoted earlier, if we now identify the source of the periodic impulses as self-induced, the wind supplying the power, and the motion supplying the power-tapping mechanism. If one wishes to argue, however, that it was a case of externally forced linear resonance, the mathematical distinction ... is quite clear, self-exciting systems differing strongly enough from ordinary linear resonant ones."
Doesn't really matter what amplification is done by the soundboard or what part is done by the resonant body, the end result is an amplified signal. With linear resonance you cannot get a stronger signal.
I'm using terminology from a paper quoted in the wikipedia article about the bridge that was brought up as an example of a resonant system. I think the discussion in the article about what resonance actually means seemed pertinent to the discussion.
Of course you free to disagree and ignore the discussion if you find it confusing.
About 3D printing
For the guys like me : here is an introduction to 3D printing that might help to follow the discussion around 3D printing panels from Leob
@Leob : if you have some other links closer to your technique, it would be nice.
Christian
For the guys like me : here is an introduction to 3D printing that might help to follow the discussion around 3D printing panels from Leob
@Leob : if you have some other links closer to your technique, it would be nice.
Christian
Very good overview. 3D printing has it quirks to consider like any manufacturing system, so not easy to cover it in a few pages.
And we have some special considerations not relating to the usual requirements of strength or visual quality.
I will make a post about the example plates I'm printing which I think will explain those considerations a bit more. Takes a while to print though, about 15 hrs per plate...
First of all, I certainly am confused about the subject, and as I expressed repeatedly I don't know much about material science. So much of what I'm trying to express my intuitive understanding of how things work. No surprise if it is confusing to read, and I really appreciate the help to clear up the confusion.
I think there is a relevance in the distinction expressed between a self-exciting system and linear resonance. Both would help a plate produce sound when excited, but to amplify that sound it is not enough with linear resonance. So regardless of if the modes can be seen as 2d waves on the water or the plate acts more as a 3d body, to get an efficient panel the goal is to encourage those modes
How to do that best I'm not sure, but if it is like a resonant body, it should help with a strong skin and pretty much empty core. So for example in that case I suspect that very low grade EPS with a strong skin could be better than just dense EPS.
Probably I'm reaching for oversimplifications, and it seems like DML works in several ways at the same time in different degrees across the spectrum, making things even more confusing. My observations that led me to think of it more as body than a plane was predominantly in the mids.
About the printing questions, yes, one could print standing. It can be hard with a 1 mm thick plate though. And then instead of minimal layer height you would be limited by minimal extrusion width, which is typically wider than minimal layer height. With the carbon filament they recommend a 0.6 mm noozle, and with that it might be possible to actually print 0.3mm lines, but then you are really pushing it hoping for a solid wall.
So unfortunately printing standing doesn't seem viable in this case.
So unfortunately printing standing doesn't seem viable in this case.
Hello Leob,
I think I finally understand the vocabulary of this article... but I still disagree regarding its application to DML.
The "self exciting system" wording is used to describe the property of a system to increase by itself its output thanks to some cumulative mechanism using the providing energy. This is not amplification, this a divergent phenomena. In other domain it is named unstable to say that if something moves the system away from its resting position it does not come back; worth it goes to some extreme position or even is broken.
At the beginning of the article, it is written it is a case of negative damping which a way to say the system reinforces itself. Apart some self-oscillating system (- like oscillators!), I can't give you like that examples of system where it is a desired characteristic.
When designing system with negative feedback in electronics for audio amplifiers or switching supply or whatever, the challenge is even no to be in such a situation because the system is just out of control.
Where you make a confusion I think it is in the relation between what is produce by a string (in a guitar) or an exciter and the sound.
If you just look at the pressure aspect it is an amplification (no sound to sound you can hear) but in fact it is a kind of transformation of power. The pressure is increase while an other physical quantity is reduced, I would say the speed (sorry I haven't make deep preparation or research to be 100% sure, this might be to simplistic but the principle is here). This is a full passive transformation. The magic of soundboards!
So yes it is a linear resonance to keep the previous wording or a linear system which is the way to get control on the transformation and not some divergent system.
Here are some links picked (to selected!) in a quick search "how soundboard works"
So, with that Leob, I think I am at the end of the time to invest on the topic and will focus on other aspects.
Waiting from news (with data
) about the panels you are preparing.Christian
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Leob,
I won't come back to the "self exciting" versus "linear resonance"...
It took time to me to find a representation of what are the bending waves which produce sound. There is one drawing below extract from STRUCTURAL ACOUSTICS TUTORIAL—PART 1: VIBRATIONS IN STRUCTURES Stephen A. Hambric
M Warnaka's patent introcuces a way for that. 1966! (the patent gives also by the way the basic formulas that govern DML)
So what is expected by the core is more than to be light and what is expected from the skin is not to be stiffer as possible.
It was well summerized by Steve in #4823 "As long as you get the combination of rigidity and weight correct they seem to work well."... with some condition on the core to be added. Unfortunately I won't be able to give you those conditions... Refer to some foam core panel that don't work. It is where I am.
I let perhaps Steve to comment on the low density EPS because he tested so many material. DML is also a matter to experience, some with success, some not.
About the difference according the frequency in the spectrum, the key is more in my understanding in the efficiency of the different frequency regions described in the analysis of vibrating plates than in existence of a body. This also a point where we don't have enough understanding or evidence.
Christian
I agree, more actual observations than my uninformed ramblings I just thought the distinction that was expressed was interesting, because in my mind resonance was resonance.
The 6mm plate will take a while to print and take a lot of material, but I have the 1mm and 3.8mm ready now with exciters mounted.
Size of the plates are 295x205mm, and the 1mm plate weighs 36g, and the 3.8mm 76.3g.
Both plates have one 0.1 layer at the bottom, which is the side the exciter is fixed on. The infill is 17% honeycomb, and at the top I have 3 layers a 0.1mm each. These settings was pushing it with the BioFusion filament, and the surface at the top didn't become fully solid everywhere, and little bit came off at the bottom of the 3.8mm getting stuck to the glass as I removed the plate. But it was the settings I found best for for the carbon filament, so used the same for these plates.
The extrusion with is 0.6 mm as nozzle size, but infill has 50% extrusion.
This is the 3.8 mm plate during printing to give you an idea about the structure:
Also you can see the thick walls. I added those for some damping. Maybe not ideal from a efficiency standpoint, but seems like some damping will smoothen the FR and reduce ringing, and I'm planning to tie it in all 4 corner mounts only for suspension.
First of all which is louder?
Using "check levels" before measuring the FR in REW, the noise registers as 93dB for the 1mm plate and 99dB for the 3.8mm. So as expected the ticker plate is loudest despite having double the mass.
Since this material is not that stiff to start with, the 1mm plate is very bendy though, and wobbles as you wave it in the air. The 3.8mm is fairly stiff, and takes some actual force to bend it.
When it comes to FR, the 1mm is surprisingly close I would say...it feels so flimsy that I expected it to be a disaster. Actually it is, but because it distorts badly in the low mids, more on that later...
First I measured with them just hanging from strings, with orange being the 3.8mm and turquoise the 1mm:
The bass response is stronger with the thin plate, but some strong modes in the low mids makes the 3.8mm win in peak SPL.
To drift away in speculations a bit, this kind of response is what I seen before that makes me think why the thickness tends to push up those modes in particular. The lower bass frequencies depend more on pure wave bending of the plane, and hence become louder with the thinner plate. But the lack of body means weaker modes in the mids. That's my hypothesis anyway and I'm sticking with it!
The plan is like I said to actually suspend from all four corner mounts, and to emulate that I pulled slightly at the bottom corner mounts while doing the test (orange 3.8mm and green 1mm):
We see that the bass response especially becomes smoother, and is much more similar for both plates. It makes sense if the damping constricts the planar wave motion, but we still see those mid peaks in the 3.8mm, and they don't seem to be much affected by damping the boundaries. This does seem to indicate that there are different principles at play here in different parts of the spectrum.
However, like mentioned before the 1mm distorts badly in the low mids. I'm not sure why that is, but think I want to revise the process and see if that can be fixed by printing the top layer separately and glue or iron it on. Improving on the 1mm plate might help improving the thicker plates as well.
I just thought the distinction that was expressed was interesting, because in my mind resonance was resonance.The 6mm plate will take a while to print and take a lot of material, but I have the 1mm and 3.8mm ready now with exciters mounted.
Size of the plates are 295x205mm, and the 1mm plate weighs 36g, and the 3.8mm 76.3g.
Both plates have one 0.1 layer at the bottom, which is the side the exciter is fixed on. The infill is 17% honeycomb, and at the top I have 3 layers a 0.1mm each. These settings was pushing it with the BioFusion filament, and the surface at the top didn't become fully solid everywhere, and little bit came off at the bottom of the 3.8mm getting stuck to the glass as I removed the plate. But it was the settings I found best for for the carbon filament, so used the same for these plates.
The extrusion with is 0.6 mm as nozzle size, but infill has 50% extrusion.
This is the 3.8 mm plate during printing to give you an idea about the structure:
Also you can see the thick walls. I added those for some damping. Maybe not ideal from a efficiency standpoint, but seems like some damping will smoothen the FR and reduce ringing, and I'm planning to tie it in all 4 corner mounts only for suspension.
First of all which is louder?
Using "check levels" before measuring the FR in REW, the noise registers as 93dB for the 1mm plate and 99dB for the 3.8mm. So as expected the ticker plate is loudest despite having double the mass.
Since this material is not that stiff to start with, the 1mm plate is very bendy though, and wobbles as you wave it in the air. The 3.8mm is fairly stiff, and takes some actual force to bend it.
When it comes to FR, the 1mm is surprisingly close I would say...it feels so flimsy that I expected it to be a disaster. Actually it is, but because it distorts badly in the low mids, more on that later...
First I measured with them just hanging from strings, with orange being the 3.8mm and turquoise the 1mm:
The bass response is stronger with the thin plate, but some strong modes in the low mids makes the 3.8mm win in peak SPL.
To drift away in speculations a bit, this kind of response is what I seen before that makes me think why the thickness tends to push up those modes in particular. The lower bass frequencies depend more on pure wave bending of the plane, and hence become louder with the thinner plate. But the lack of body means weaker modes in the mids. That's my hypothesis anyway and I'm sticking with it!
The plan is like I said to actually suspend from all four corner mounts, and to emulate that I pulled slightly at the bottom corner mounts while doing the test (orange 3.8mm and green 1mm):
We see that the bass response especially becomes smoother, and is much more similar for both plates. It makes sense if the damping constricts the planar wave motion, but we still see those mid peaks in the 3.8mm, and they don't seem to be much affected by damping the boundaries. This does seem to indicate that there are different principles at play here in different parts of the spectrum.
However, like mentioned before the 1mm distorts badly in the low mids. I'm not sure why that is, but think I want to revise the process and see if that can be fixed by printing the top layer separately and glue or iron it on. Improving on the 1mm plate might help improving the thicker plates as well.
Forgot to mention what was the biggest surprise to me. That the 3.8mm plate actually works quite well. In the earlier test I did with this filament I got bad HF response, but must been the mounting of the exciter that was bad, or that I had double as thick bottom skin.
Efficiency is also on par with the carbon. The carbon sounds a bit tighter somehow, but the double stiffness according to the specs doesn't seem to have nearly as much impact as I would have thought.
I will print identical panel to the BioFusion when I honed some things down to get a more direct comparison.
Efficiency is also on par with the carbon. The carbon sounds a bit tighter somehow, but the double stiffness according to the specs doesn't seem to have nearly as much impact as I would have thought.
I will print identical panel to the BioFusion when I honed some things down to get a more direct comparison.
I have been trying to follow some of the patents, a lot of it is over my head for sure. But looking at the Warnaka patent, it is intended for low frequency loudspeakers. I'm not saying there is no bending wave. You can almost see it with your bare eyes for low bass, but I suspect that principle becomes less and less dominant higher up in the spectrum.
Yes, it is way to thin for this material, but only intended as an experiment. But I'm really surprised how well such a flabby plate works...apart form the distortion, the difference to the much stiffer 3.8mm is relatively small.
I don't have XPS to compare with, and like mentioned it is a cheap uncalibrated measuring mic, so I don't trust the HF response especially. But it is a bit less bright than the plywood or polycarbonate I tried.
Leob.
With my 1mm card and veneer panels I had to use pva to stiffen the panels to prevent flapping and wobble.
This helps when using the panel further down to about the 120hz mark..
The panel is well into piston mode at these lower frequencies , actually it is in piston mode all the way up to 20k.
You said it yourself, these panels work in many ways, to my knowledge they first produce pistonic motion in the central area then bending wave through the panel and then dml , in that order.
Which makes me think , as you are using 3d printing, you could easily print a dome in the centre to aid hf response, with solid ring mounting to mate with the coil former.
Although I prefer using a thin fabric dome coated in a 50x50 mix of pva to help prevent resonance in the coil cavity area.
The dome should, I believe (depending on the material) give a good response up to 20k ?
Not that my veneer of card panels need help reaching 20k
Just an idea of mine, that works for me.
Steve.
With my 1mm card and veneer panels I had to use pva to stiffen the panels to prevent flapping and wobble.
This helps when using the panel further down to about the 120hz mark..
The panel is well into piston mode at these lower frequencies , actually it is in piston mode all the way up to 20k.
You said it yourself, these panels work in many ways, to my knowledge they first produce pistonic motion in the central area then bending wave through the panel and then dml , in that order.
Which makes me think , as you are using 3d printing, you could easily print a dome in the centre to aid hf response, with solid ring mounting to mate with the coil former.
Although I prefer using a thin fabric dome coated in a 50x50 mix of pva to help prevent resonance in the coil cavity area.
The dome should, I believe (depending on the material) give a good response up to 20k ?
Not that my veneer of card panels need help reaching 20k
Just an idea of mine, that works for me.
Steve.
Leob.
You made a comment earlier about using a thin skin on low grade eps .
I only use a very thin mix of 50x50 pva and water, this does sink into the eps a little and creates a hard surface but is incredibly light when all the water evaporates.
As for gluing a hard skin on to the eps, yes this would work , but it is not something I would do personally as this would loose so much of the sound I love from my eps panels.
The applied skins would dominate the sound of eps, and rob the panel of minute detail ,which is what I love about eps.
Xps would be a better candidate for this I believe , and would benefit from the harder skin, as I have found using epoxy.
DML is very complicated, that is why I prefer to use the old name, soundboard.
You vibrate the panel to make sound, the panel material will have its characteristic sound, which can be manipulated and controlled.
What methods are used would depend on the use for the panel and the sound preferred.
I know it is very simplistic attitude but it works for me and has helped me understand dml better.
Steve.
You made a comment earlier about using a thin skin on low grade eps .
I only use a very thin mix of 50x50 pva and water, this does sink into the eps a little and creates a hard surface but is incredibly light when all the water evaporates.
As for gluing a hard skin on to the eps, yes this would work , but it is not something I would do personally as this would loose so much of the sound I love from my eps panels.
The applied skins would dominate the sound of eps, and rob the panel of minute detail ,which is what I love about eps.
Xps would be a better candidate for this I believe , and would benefit from the harder skin, as I have found using epoxy.
DML is very complicated, that is why I prefer to use the old name, soundboard.
You vibrate the panel to make sound, the panel material will have its characteristic sound, which can be manipulated and controlled.
What methods are used would depend on the use for the panel and the sound preferred.
I know it is very simplistic attitude but it works for me and has helped me understand dml better.
Steve.