Don't waste your money on solid CF panels. Probably they could work okay, but not not any better than 3-5mm plywood panels at 1/10th (or less) the price.
I'm not sure exactly what you mean by "breaking up", but if you mean it flexes with lots of resonant modes rather then moving simply as a piston, well then, breaking up is exactly what we want!
Regardless of the power, the only benefit (efficiency!) of CF comes when it is used as a skin on a lightweight core. I have not tried CF over honeycomb for the same reason as you, but CF over balsa works pretty well, and doesn't require prepreg. So far I like about 0.23 mm carbon on both sides of a 1.6 mm balsa core. I think thinner carbon on thinner cores may be even better, as it should permit smaller panel size for the same frequency range, but thinner carbon tends to be more expensive...
Eric
I'm not sure what supplier you re talking about, but for most of the commercially available panels like this I have seen, they would need to be much larger (say, 24x36?) to get down below 200 Hz. The problem is they are intended for different purposes that require more strength and stiffness than we need.
Eric
Hmm. I don't recall this, or have any idea why it would be so. Can you share where you got this impression?
Eric
Sorry Eric, but I think you are wrong. Resonance happens when you have a body. Sure, that body doesn't have to have "cavities" as such (of course wood and foam has lot of cavities), that is not something I have claimed, but a dense body will dampen the resonance and having a thin plate with hardly any body will not give you an efficient panel. I'm quite confident that is true from my experiments printing panels so far.
You have to give the plate enough body to get efficiency. If it was only the flexural properties as you suggest, DML would be a misnomer, and it should be called Distributed Wave Loudspeaker. And we would have more examples of really thin plates that work well.
What do you base you size vs frequency calculations on?
I don't have a lot of experience with different materials and exciters, so perhaps that statement is true for some materials. But you can for example look at the graph from my 295x205mm plate a few pages back to see that is not generally true. And I have seen several examples of people getting much below 200 Hz with small plates.
Perhaps the skin could be even thinner if designing you own sandwich composite to use, but standard nomex honeycomb as used in aviation certainly should have the right properties. What I understand the whole research at NXT started with that they noticed the exceptional resonant properties of that material in actual fighter jets.
NaRenaud
Spedge wrote about a 7ft EPS, he is happy with. I wrote about an XPS with not so good results probably because the XPS I found didn't have the right properties. Spedge has also good results with a thin XPS epoxy coated. I tested 9mm material said to be XPS PVA coated, the results were bad. So in this area, there is dispersion I don't know the reason.
Most of the panels shown can go down 300Hz easily, 150Hz seems more difficult because it needs a lower 1st mode and probably a bigger size (ie a height in the meter or above).
About the high frequency, material like appropriate PS, plywood, balsa, CF/balsa don't show a lack of high frequencies. It is even possible to use them without EQ. Some materials can show a roll off. I had that with the 9mm XPS like panel I tested (my 2nd prototype).
Your are probably right mentioning compression. It might explain the dispersion in results around PS for example. In my case, high grade PS is not available in a standard DIY store.
Have you started to experiment ?
Christian
Quick question. I have heard in many vidoes guy from tectonic mention the phenomenon that sound from the panel when it reaches the room wall, nothing happens. No reflection. This does not make sense.
Is there any evidence for this claim?
For example you posted a graph of a 44x35cm canvas panel here #4,177
Seems to reproduce below 150Hz just fine.
I constantly see this claim that you need large plates for bass response, but all the data I see and my own experience contradicts that. And you now make the same claim despite having experience yourself that disproves it. What am I missing?
Basically the waveform generated is already diffuse. So instead of one solid wave as you get from a piston speaker, you have many waves next to each other. When a solid wave first hits your ear directly, and then hits your ear reflected a bit later, you experience the reflection as an acoustic phenomenon. But when a diffuse wave hits a wall, it will disperse even more, making lots of individual reflections which becomes undistinguishable when they reach you.
In one of Tectonics videos they explain by drawing a bunch or parallel arches from the speaker hitting a nearby wall and there reflecting. You then end up with a grid where you clearly see points where direct and reflected waves intersect. If you draw the same with wiggly lines instead, you don't see the same clear intersections, but a wiggly mess being filled up with more wiggly mess instead.
Narenaud.
The 7ft panel was EPS , the smaller 5mm panel with epoxy was XPS .
The epoxy on the XPS makes for a far better sounding and performing panel .
Once again ,this was my old gallery at NXT RUBBISH.
click on the 5ft panels to pictures to enlarge.
There is also a small 10mm vh grade eps panel with a response similar to a ply but obviously more efficient.
https://www.audiocircle.com/index.php?action=gallery;area=browse;album=2453
Steve.
The 7ft panel was EPS , the smaller 5mm panel with epoxy was XPS .
The epoxy on the XPS makes for a far better sounding and performing panel .
Once again ,this was my old gallery at NXT RUBBISH.
click on the 5ft panels to pictures to enlarge.
There is also a small 10mm vh grade eps panel with a response similar to a ply but obviously more efficient.
https://www.audiocircle.com/index.php?action=gallery;area=browse;album=2453
Steve.
Thanks for detailed explanation. Some of it still does not compute.
Would not diffused sound wave qualify as distortion? They claim clean sound. But any wave which differs from electrical signal is distortion.
Wheather its one solid wave or many diffused waves, reflection will happen.
I am still not convinced about what he said.
Adason.
I have seen a few tectonic salesman in videos getting a little over excited and claiming no reflections from their panels.
This is obviously not true.
What they should be saying is that the reflections from the wall are not interfering badly with the sound going towards the wall.
If in piston or wave mode the reflections will interfere with each other and cause peaks and troughs (cancellations) causing a mess.
now the sound hitting the wall has already been badly altered and it too will be reflected, and do the same to the sound still traveling to the wall !
dml does not produse large waves(well it can, but that's another story ?) It is diffuse (random) this has little affect on the sound going to and from the wall.
This improves the intelligibility ,as tectonic are always claiming.
The waves do interfere with each other but not in such a bad way.
But it can go wrong if you have a panel with a side peak close to a wall, I know this from experience !
I'm being harassed by my wife so I must leave it there.
Steve.
Sorry had to correct some predicted text.
I have seen a few tectonic salesman in videos getting a little over excited and claiming no reflections from their panels.
This is obviously not true.
What they should be saying is that the reflections from the wall are not interfering badly with the sound going towards the wall.
If in piston or wave mode the reflections will interfere with each other and cause peaks and troughs (cancellations) causing a mess.
now the sound hitting the wall has already been badly altered and it too will be reflected, and do the same to the sound still traveling to the wall !
dml does not produse large waves(well it can, but that's another story ?) It is diffuse (random) this has little affect on the sound going to and from the wall.
This improves the intelligibility ,as tectonic are always claiming.
The waves do interfere with each other but not in such a bad way.
But it can go wrong if you have a panel with a side peak close to a wall, I know this from experience !
I'm being harassed by my wife so I must leave it there.
Steve.
Sorry had to correct some predicted text.
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You don't get typical harmonic distortion, but phase distortion with the multiple waves interacting. If you look at for example an impulse response it clearly is less clean than what you get from a regular speaker.
Tectonic claims that since it is still within the first few ms of the impulse, it is perceived as part of the initial transient. While it is true that we cannot separate the tail that DML will give, I'm not so sure it doesn't affect how we perceive the sound.
Obviously DML can be perceived as clean sounding, and can get very low THD. But it does have a slightly reverberant character that usually is not disturbing, but rather the opposite and can be quite pleasant. And when you put it in a room, the actual reflections is the room become less noticeable and disturbing, so it is good trade off it seems to start with a diffuse signal.
Reflection will happen regardless, but the difference is how we perceive it psychoacoustically. If the individual reflections are masked by the direct signal, we don't notice them. So they are still there, but so spread out that we cannot identify them as reflections.
When I first read about this my reaction was that it is surprising how good DML sounds since it breaks so many norms regarding sound. Having something building up a diffuse signal from lots of resonant modes really sounds like a bad idea, with potential for lots of issues in both time and frequency domains. Those issues are identifiable when you look at both FR and IR, but at least the unclean IR seems to not be a problem in how the sound is perceived.
Loeb,
I'm not sure I understand exactly what you mean by "body". If you mean low density, then probably we are largely in agreement. Note also that I listed density as one of the flexural properties. In fact, I submit that it may be the most important one!
For a homogeneous material, efficiency is determined mainly by the factor E/rho^3, where E is the material's elastic modulus (also called Youngs modulus), and which is a measure of inherent stiffness, and rho is the density. So efficiency depends on both stiffness (more is better) and density (lower is better). But since it depends on density cubed, density might be considered even more important than stiffness.
For composites such as your printed plates, there is a similar efficiency factor: D/mu^3, where D is the panel's flexural rigidity and mu is the panel's areal density (weight per unit area). But similarly, it depends on stiffness (higher is better) and density (lower is better), just like for homogeneous materials. By printing solid skins with a honeycomb core, you are reducing "mu" significantly, while reducing D only slightly, compared to a similar solid panel. That's why the efficiency of your printed panels is pretty good.
I must admit I'm a bit jealous of your printing capability, what fun that would be!
Eric
Adason.
If you have come from years of living with piston type units, it is hard to imagine anything else.
You will probably have to listen to a dml panel first before you can start to understand how they work.
Most audio people dismiss dml as noise or distortion because they do not understand how they work.
In the tectonic video posted earlier the audio engineer on the right came from many years understanding pistonic drivers and their problems.
In the video he is still amazed at how dml works and all the problems dml solves.
Until you listen to a good quality dml for yourself you probably won't believe they actually work either.
When I say that a singer sounds like she is in the room singing will a dml panel, I mean she sounds like she is really, really, in the room, in front of me.
Dml is that good.
Steve.
If you have come from years of living with piston type units, it is hard to imagine anything else.
You will probably have to listen to a dml panel first before you can start to understand how they work.
Most audio people dismiss dml as noise or distortion because they do not understand how they work.
In the tectonic video posted earlier the audio engineer on the right came from many years understanding pistonic drivers and their problems.
In the video he is still amazed at how dml works and all the problems dml solves.
Until you listen to a good quality dml for yourself you probably won't believe they actually work either.
When I say that a singer sounds like she is in the room singing will a dml panel, I mean she sounds like she is really, really, in the room, in front of me.
Dml is that good.
Steve.
Leob.
My small panels are only 1mm thick, and perform perfectly from at least 200hz to 20k.
They are more efficient than heavy panels but not as efficient as eps types.
I just measured a 8inch paper pulp cone drivers material and it was just under 1mm.
What is too thin and too small to be a dml ?
As long as you get the combination of rigidity and weight correct they seem to work well.
Steve.
My small panels are only 1mm thick, and perform perfectly from at least 200hz to 20k.
They are more efficient than heavy panels but not as efficient as eps types.
I just measured a 8inch paper pulp cone drivers material and it was just under 1mm.
What is too thin and too small to be a dml ?
As long as you get the combination of rigidity and weight correct they seem to work well.
Steve.
Yes, I basically mean low density. Everything has a body, but a really thin plate has too little body to resonate, or create modes, regardless of the material. And a really dense material has a body that will dampen the modes due to the inertia introduced.
I would say you do need cavities, that is how materials can be stiff and light at the same time. In foam or wood those cavities are really small and spread uniformly in the material. In a nomex honeycomb we are talking cells of space that we actually can see, but that is not required to create a body with good resonance (although the honeycomb pattern helps give compressive strength in the direction that matters compared to if one could make aramid foam somehow with the same density).
Like I keep repeating, I'm not very experienced with neither DML nor material science, so I might be way off base. But I am experienced with sound, and my intuitive impression combined with some course analysis of FR from the panels I have is that the ones lacking a really light core with enough thickness is much less efficient. If I have 3mm core instead of 1 mm core, other parameters the same, it is more mass to drive for the exciter. Yes the g/m3 of the material overall becomes less, but it is still seems very strange that add more mass for the exciter to drive means louder output. I can really only explain it with resonance anyway.
You can indeed get well below 200 Hz with small plates, but I was talking specifically about with typical commercially available carbon/nomex plates.
Also, realize that it's one thing to get output at say, 50 Hz, but yet another thing entirely to get reasonably flat response beginning at 50Hz. Typically, there will be isolated output at some low frequency, but then a huge dip or dips before the response becomes reasonably flat. The frequency that matters is not the lowest frequency your panel can produce, but rather, the frequency above which the response is reasonably flat.
There is a rule of thumb that the minimum useful frequency of a panel is about 2.5 times the panel's fundamental frequency. And there is an approximation for the panel's fundamental frequency. Combining those gives this approximation for a panel's minimum useful frequency:
Fmin=2.5*(pi/A)*(D/mu)^0.5
For the 5.5 mm carbon nomex panel you found (https://shop1.r-g.de/en/art/6195K), I used their specifications to estimate D and mu. Then re-arranging the above equation and setting Fmin to 200 Hz and solving for A (panel area), the resulting area is 0.6 m2. That is, the estimated area required to get flat response with this panel above 200 Hz is about 0.60 m2.
That's a pretty big panel (and expensive).
Doing the same for the 3.5 mm panel, the required area is closer to 0.4 m2, so that's a little better.
And that's just for smooth output above only 200 Hz. You may want a lower Fmin than that, and hence might need even larger panels, with this type of construction.
Eric