I have the same attitude NaRenaud...it is great not to just accept the conventional wisdom when learning a new subject, and definitely many things left to explore with DML it seems.
But I still think those panels will not be a worthwhile investment. See if you can get figures for density for those plates, but whatever resin type and ratio you have, that will only make a slight difference, and all solid carbon plates will be in the same ballpark. In this case I think it is likely that you would be spending $100 for a plate that is not particularly good sounding nor efficient. For $122 they have 12"x12" nomex honeycomb sandwich plates. I would bet you get both louder and better sound with that.
But I still think those panels will not be a worthwhile investment. See if you can get figures for density for those plates, but whatever resin type and ratio you have, that will only make a slight difference, and all solid carbon plates will be in the same ballpark. In this case I think it is likely that you would be spending $100 for a plate that is not particularly good sounding nor efficient. For $122 they have 12"x12" nomex honeycomb sandwich plates. I would bet you get both louder and better sound with that.
Leob,
It is where I am too!
We are looking for light membrane which is the key for efficiency.
The stiffness has not be as high as possible but adapted to the membrane aerial density to meet the 1st mode target and in the same time the critical frequency.
Association of a light material with some more rigid one but in low quantity to limit the weight effect is for me today the right way.
In the light material, I am not convinced that all are good because of too poor capacity against shear strength. This an opinion but it meets some poor results from variant of XPS, maybe foamboard and it is shown in papers that the shear modulus lowers the speed the waves can reach. Far from me to give the idea I fully manage the topic!
Christian
Efficiency is key point for PA with the robustness of the membrane for power handling. For home application, yes it has less importance. Nobody seems mentioning a lack of power with the current 10 to 25W exciters. Nevertheless, efficiency in home application is a general way to limit distortion. Not a must have but a nice to have?
At the opposite we could wonder if there is a drawback in too light membrane like the risk of transparency to unwanted rear wave coming to the front?
Christian
Hello NaRenaud
You should find in Veleric post information about CF/balsa panels and also thickness, how to proceed (it is the one I have in mind, there perhaps others). Search in my previous post about the "history file". You will get direct links to different posts.
To say plywood is incorrect is really for me wrong. It is in my opinion the material which has the best performance/availability/cost balance. It is what I have for now with a 3mm poplar plywood. There are good feedback in this thread with 5mm birch or other wood. You should find in the posts an agreement to say its drawback is the efficiency. It is the reason I started with XPS, the result was for me no very good so I have given a chance to plywood. I think one advantage of plywood is there is less different material behind in the different regions of the world than for XPS. To keep plywood panels not too big there is the possibility to get it in low thickness, down to 0.4mm this from birch. It is used in aircraft models, not available in standard DIY store. I was thinking to go that way but I more looking around how to use balsa which need some additional rigid material as I am quite happy (and my wife too) with our current 3mm plywood panels. I am not aware of panel in very low thickness plywood.
Reading your "specifications" which are closed of mine, I would advice to give a chance to plywood as a not too expensive basis.
Christian
@NaRenaud. I agree. Search also for Cheapvega posts some weeks or months ago. I remember a test of CF plate with no good results.
Just let him go and find out for himself. He started out by saying he read the thread but still wants to use multiple exciters so he has no regard for anything that's been written and proven over and over, so let him go.
There is no guarantee that any material will sound good, whether the price is 5p or £500 !
tectonic do an awful lot to their panels to get the performance they want , including EQ.
as Christian says , they must be robust , and not warpe over time and take a lot of punishment.
their panels seem to be a good compromise , but would I be happy with the sound in my room ? With my experience with other materials, I'm not sure.
I wouldn't be surprised if 5mm or thinner xps with a surface coating of epoxy , would sound better for home use ?
Or even may be just as good a material if for pro use if glass fibre strengthening was was used ?
It would be interesting to hear the carbon panels compared to my veneer of card panels, which would sound better ?
They would have to be very very good ,to do this.
And these are not Even my favourite panels.
Steve.
tectonic do an awful lot to their panels to get the performance they want , including EQ.
as Christian says , they must be robust , and not warpe over time and take a lot of punishment.
their panels seem to be a good compromise , but would I be happy with the sound in my room ? With my experience with other materials, I'm not sure.
I wouldn't be surprised if 5mm or thinner xps with a surface coating of epoxy , would sound better for home use ?
Or even may be just as good a material if for pro use if glass fibre strengthening was was used ?
It would be interesting to hear the carbon panels compared to my veneer of card panels, which would sound better ?
They would have to be very very good ,to do this.
And these are not Even my favourite panels.
Steve.
"He started out by saying he read the thread but still wants to use multiple exciters so he has no regard for anything that's been written and proven over and over, so let him go." 😂
I also listened to comparison recordings and to my ears the multiple exciters always sound better.
I also listened to comparison recordings and to my ears the multiple exciters always sound better.
If everyone will just get the same ply or xps boards because we know they work, this thread is a bit pointless, and we might miss out on even better materials. But still some directions can be helpful, also when wanting to break new ground. No one has really showed conclusively that carbon sheets doesn't work, but some have left subjective impressions, and I been arguing against it on (admittedly fairly weak) theoretical grounds.
However, I haven't seen much on people getting premade nomex/carbon sandwich either, and personally I would be more interested in the results of the mentioned 12"x12" plate than the carbon sheet, but would love to see data on a carbon sheet as well.
I must also say I have not really seen anything conclusive against multiple exciters. In fact I would say the opposite. Tectonic for example is using multiple exciters successfully.
Spedge,
If I'm following right, the XPS does actually produce pretty good sound in a very limited frequency range. Presumably the reason it can't produce good highs is because of the compressibility of the material and being generally thick. It fails on lows for a different reason, which to me seems likely to be related to energy return. To make it thinner then it loses stiffness too much...so my first plan was to put a thin hard skin of fiberglass or carbon fiber on XPS. That was when, per Tech Ingredients it seemed the panels worked largely as a piston and to many waves bouncing in the panels was bad (which would make sense if he got good sound from 1 inch thick XPS). Then I got to the Tectonic videos which seemed to support the idea because they were using CF honeycomb...a more expensive and resilient version of skinned foam it seems for higher power. I got the fiberglass and was waiting on the right foam to start building....
Then I looked deeper into their stuff and based on their explanations Im not convinced the foam or honeycomb is nec at low power. A very thin CF plate has a lot of the same character as a very thin plywood panel except it is stronger and tougher and can be made larger without breaking up, so I want to try that.
I do appreciate the idea that cf skinned honeycomb might be a better place to start but a 12 inch piece won't tell me anything. The size definitely matters as materials don't behave the same at scale...Tectonic states this, in a smaller panel the material has to be more flexible so you could make a very small DML panel with good sound but the panel would have to be very floppy and thin and so it would fall apart. With that in mind, it seems no test of a CF panel is really a test unless it's a somewhat large panel...I don't mind $100 for a large CF panel experiment, but a large CF honeycomb panel is 3-4 times as much in price, so not keen to start there.
I could make my own CF of FG skinned foam which I probably will eventually, but no way I'm trying to make honeycomb as it requires prepreg and prepreg requires a heated curing with temperature control I don't have in my shop.
I want to get good response down to 180 Hertz which seems to require a somewhat largish panel.
Going back to the picture frames: I have thought of doing a fiberglass layup essentially stretched over a large wood frame...maybe 3 to 4 feet on a side? The edges would be a dry single layer 1.2 ounce cloth for support to act as a surround and also prevent bass leeching and the center would have layers built up with epoxy...maybe with a tapered edge blending to the dry cloth? Or maybe not...Not seeing any reference to tapered designs and their possible pitfalls.
If I'm following right, the XPS does actually produce pretty good sound in a very limited frequency range. Presumably the reason it can't produce good highs is because of the compressibility of the material and being generally thick. It fails on lows for a different reason, which to me seems likely to be related to energy return. To make it thinner then it loses stiffness too much...so my first plan was to put a thin hard skin of fiberglass or carbon fiber on XPS. That was when, per Tech Ingredients it seemed the panels worked largely as a piston and to many waves bouncing in the panels was bad (which would make sense if he got good sound from 1 inch thick XPS). Then I got to the Tectonic videos which seemed to support the idea because they were using CF honeycomb...a more expensive and resilient version of skinned foam it seems for higher power. I got the fiberglass and was waiting on the right foam to start building....
Then I looked deeper into their stuff and based on their explanations Im not convinced the foam or honeycomb is nec at low power. A very thin CF plate has a lot of the same character as a very thin plywood panel except it is stronger and tougher and can be made larger without breaking up, so I want to try that.
I do appreciate the idea that cf skinned honeycomb might be a better place to start but a 12 inch piece won't tell me anything. The size definitely matters as materials don't behave the same at scale...Tectonic states this, in a smaller panel the material has to be more flexible so you could make a very small DML panel with good sound but the panel would have to be very floppy and thin and so it would fall apart. With that in mind, it seems no test of a CF panel is really a test unless it's a somewhat large panel...I don't mind $100 for a large CF panel experiment, but a large CF honeycomb panel is 3-4 times as much in price, so not keen to start there.
I could make my own CF of FG skinned foam which I probably will eventually, but no way I'm trying to make honeycomb as it requires prepreg and prepreg requires a heated curing with temperature control I don't have in my shop.
I want to get good response down to 180 Hertz which seems to require a somewhat largish panel.
Going back to the picture frames: I have thought of doing a fiberglass layup essentially stretched over a large wood frame...maybe 3 to 4 feet on a side? The edges would be a dry single layer 1.2 ounce cloth for support to act as a surround and also prevent bass leeching and the center would have layers built up with epoxy...maybe with a tapered edge blending to the dry cloth? Or maybe not...Not seeing any reference to tapered designs and their possible pitfalls.
Oh, also...
Based on reading here it seems the surface it very important. I would assume a gloss CF sheet would not sound good. Even a smooth "matte" sheet might be wrong. The Tectonic panels have a unidirectional surface with a visible grain meaning the top layer at least it laid very dry to let the texture through. That makes sense based on what others here have reported on surfaces so in my search I am avoiding the smooth gloss options (Yes, I could sand the surface but I'm not sure that would actually yield a similar result to a textured layip
Based on reading here it seems the surface it very important. I would assume a gloss CF sheet would not sound good. Even a smooth "matte" sheet might be wrong. The Tectonic panels have a unidirectional surface with a visible grain meaning the top layer at least it laid very dry to let the texture through. That makes sense based on what others here have reported on surfaces so in my search I am avoiding the smooth gloss options (Yes, I could sand the surface but I'm not sure that would actually yield a similar result to a textured layip
An important factor with sandwich materials is probably the ability to control surface stiffness, density and resonant abilities much more freely than a sheet of a single material. With the right equipment and skills that means that you can finetune it to more suit what you want out of the speaker. I think for a PA application you need to use EQ even with a really good panel, since you have to be able to maximize the output, and DML will not give a flat enough response because its nature of amplifying signal through resonant modes. But a good sandwich composite probably helps getting as close as possible.
Of course for home use, first of all experimenting with sandwich materials it seems complicated and costly, especially if you should make the plates yourself. Secondly you might not be after a technically excellent speaker, but something that colours the sound in a pleasant way and that efficient enough to fill up a room from a reasonable panel area and a regular power socket.
Actually, size of panel might matter less that many sources indicate. See the FR of my 295x205mm carbon plastic plates a couple of pages back. With xover at 180hz I would say you don't really need large panels.
There are some posts comparing panels of same material and different size, and effect on both FR and loudness was not that great.
I worry about the coverage and distance sound travels with a smaller panel for what Tectonic does, PA systems, but not for a living room.
Otherwise it seems advantage with large panels is subbass response (below 80hz or so) and a somewhat smoother FR, at least when we are talking plates with longest side less than 40cm.
Some good points there.
For power...I just discovered PartsIND cancelled my order which is why they didn't arrive so Im shopping exciters again...but 20-40watts per exciter is what I'm shopping and with two exciters per panel and a small room...likely power will never be an issue even if somehow I managed to dampen my panels down to 85Db@1 watt. I should have plenty of headroom on the exciters and am more likely I thing to have distortion at higher volumes because of the panel design rather than the exciters.
As to transparency to rear waves I have thought a lot about that. I even considered designs with a reflective surface at a specified distance behind the panel to add to lowe end power and I think there is probably good use for that, but I decided that at my level of tech I would be overcomplicating the design without having the tools to tune in the results.
I would love to see someone comercially make such a panel...a very light membrane hanging in a large shallow box with curved edges as wave guides. I can picture some beautiful designs...but I know people spend years working out the complexities of such things so not bold enough to think I can tackle it.
Well that's all that really counts in the end if it's for personal consumption. I wish you the best and look forward to the results if you pursue this. I've settled (for a while) on EPS but definitely test different materials as I come across them. Good luck.
Narenaud.
In your prepreg plate link it shows a panel weight of 1. 16 LBS .
Even if this is per square metre , it is still very heavy .
Even my 1mm card and veneer panels 6x9inch can go down to 100hz in a domestic environment comfortably.
How rigid does it need to be ?
Yes size does matter , a six foot 5mm xps or 1mm card would flap and wobble about uncontrollably and would act like a sail outside in the wind.
My basic 7ft 1inch thick eps panels worked with a perfectly flat response from about 300hz to 10k in my room .
This is the loudest material I have so far encountered and is my favourite for sound quality.
But everyone has their own personal sound they are trying to achieve.
The reason I made my recordings of different panels was to try and show the sort of sound that is possible.
The recordings only show a fraction of the sound I am hearing in the room, it is not possible to make perfect recordings in an ordinary room with my phone .
It is hard to tell the difference between the different panels in the recordings but it is obvious in my room.
But one thing they all have in common is the basic dml sound, which does come across in the recordings, I believe ?
To be honest, I would not even have attempted to make the recordings of my panels, if I was not confident of the sound they produce.
If it is not perfect ,I'm not interested.
Steve.
In your prepreg plate link it shows a panel weight of 1. 16 LBS .
Even if this is per square metre , it is still very heavy .
Even my 1mm card and veneer panels 6x9inch can go down to 100hz in a domestic environment comfortably.
How rigid does it need to be ?
Yes size does matter , a six foot 5mm xps or 1mm card would flap and wobble about uncontrollably and would act like a sail outside in the wind.
My basic 7ft 1inch thick eps panels worked with a perfectly flat response from about 300hz to 10k in my room .
This is the loudest material I have so far encountered and is my favourite for sound quality.
But everyone has their own personal sound they are trying to achieve.
The reason I made my recordings of different panels was to try and show the sort of sound that is possible.
The recordings only show a fraction of the sound I am hearing in the room, it is not possible to make perfect recordings in an ordinary room with my phone .
It is hard to tell the difference between the different panels in the recordings but it is obvious in my room.
But one thing they all have in common is the basic dml sound, which does come across in the recordings, I believe ?
To be honest, I would not even have attempted to make the recordings of my panels, if I was not confident of the sound they produce.
If it is not perfect ,I'm not interested.
Steve.
I'm New to this thread and am with a very limited understanding of the discussions being had, as I have not got a hands on experience.
I am also not aware if the following material, that has come to mind, has been trialled at any time.
A material that is from the past and made from a Natural Product, has good quality damping properties (if this is needed), and is available quite cheaply as a material that can be repurposed for an investigation into the suitability for use on a flat panel, is from an Olden Era, being the 'Shellac Disc' used as a medium for recording music onto.
As their is experimentation being discussed and a non smooth fascia surface seems to be a necessity, who knows what might be discovered with the above material and the Spiralling Configurations on the Fascia Grooves.
I am also not aware if the following material, that has come to mind, has been trialled at any time.
A material that is from the past and made from a Natural Product, has good quality damping properties (if this is needed), and is available quite cheaply as a material that can be repurposed for an investigation into the suitability for use on a flat panel, is from an Olden Era, being the 'Shellac Disc' used as a medium for recording music onto.
As their is experimentation being discussed and a non smooth fascia surface seems to be a necessity, who knows what might be discovered with the above material and the Spiralling Configurations on the Fascia Grooves.
Weight: I saw that in the link and it seemed strange. 1.5mm CF shouldn't be that heavy. If it is that heavy then it seems a poor choice. I was excited about those panels in particular because they are low resin unidirectional with some of the natural texture remaining , which is what Tectonic prefers, and they are much cheaper than such panels usually cost but also probably too thick. Finding that kind of layup at a discount is hard. Those panels probably have 2-3 times as many layers as would be appropriate for this use thanks.
I missed that somehow nabout the 7 foot 1 inch XPS...I had thought you didn't like the sound of XPS. If I got good sound out of such a panel I would be happy, though I would need to fill the low gap somehow. My current subwoofer is only good to about 180 max, really better to 150. Maybe I could add a mid-woofer?
Question: how high does the frequency go on those panels? I would think they would roll off badly starting around 8k? Maybe a little piece of thin fiberglass skin near the exciters could extend that be reducing the loss to material compression? Or do your panels just not have that problem?
Loeb,
One thing you should understand is that for DML panels, the "resonances" are not actually coming from the cavities in the panel. Rather, they come from the flexural properties of the panel (stiffness, density, length, width, and boundary conditions). Honeycomb core panels are lightweight while still stiff, which provides high efficiency, But not because there are cavities, but rather simply because they are lightweight. A completely solid core material with the same density and other physical properties, should provide the same performance as a core honeycomb core.
Eric