I have no idea what those Bertagni patents state. I will try to read them sometime again. 🙂
I think it is fibre-reinforced copper sand, whatever that means.
As both Stealth Acoustics and Sonance are competing for the same high-end market, they are unlikely to reveal their inner secrets. We are left to make our own guesses.
DML and bending waves are unlikely to be mentioned by either party. "NXT is dead."
EDIT: Here I found something about this secretive copper sand. I have no idea if that's true.
Stanley Rich's idea is mentioned at 13:44 in that video.
At 14:30 you can see how the baffle is divided into 3 sections.
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@ Veleric The Link will show the interface material to be used as the bonding for the Stretch Skin / Honeycomb.
The adhesive film is 150g/m2 prior to the Heat Treatment needed to activate the bonding process.
Maybe, the adhesive film is enough as the stretch skin for a DML Panel?
There is also Carbon Fibre rigid sheet to be used as stretch skin, starting at 0.25mm thickness to be found on the link.
https://www.easycomposites.co.uk/xa120-prepreg-adhesive-film
In relation to your other query, in the past, there has been discussion on methods for mounting an exciter.
Suggestions have been proposed to use another material type to mount the exciter onto. I have leaned towards this method as an idea to be utilised. From recollection the intention is to attempt to discover if improved panel damping is achievable by utilising a different material to the panel where the exciter attaches.
My most recent reading of the thread is detecting weights are being looked at as additional attachments, placed in a particular configuration as an attempt to improve on the control of energies transferred into the panel?
The adhesive film is 150g/m2 prior to the Heat Treatment needed to activate the bonding process.
Maybe, the adhesive film is enough as the stretch skin for a DML Panel?
There is also Carbon Fibre rigid sheet to be used as stretch skin, starting at 0.25mm thickness to be found on the link.
https://www.easycomposites.co.uk/xa120-prepreg-adhesive-film
In relation to your other query, in the past, there has been discussion on methods for mounting an exciter.
Suggestions have been proposed to use another material type to mount the exciter onto. I have leaned towards this method as an idea to be utilised. From recollection the intention is to attempt to discover if improved panel damping is achievable by utilising a different material to the panel where the exciter attaches.
My most recent reading of the thread is detecting weights are being looked at as additional attachments, placed in a particular configuration as an attempt to improve on the control of energies transferred into the panel?
I'm pretty sure that the adhesive film itself would not be stiff enough as the skin, it's intended to be used to attach the carbon fiber rigid sheet like the one you mentioned. That would be stiff enough.
Eric
But Amina still talks about DML, despite the death of NXT. I'm assuming they licensed the NXT patents at some point, so consider them to have value.
It does sound like that's what he is saying, but I really doubt it's what he meant to say. I think he just flubbed the pronunciation of composite, and it sounded like "coppersand". "Fiber reinforced composite" is a real thing, and makes sense to use in a bending wave/DML speaker. I don't think fiber reinforced copper sand is even a real thing. But of course it is now, since we started writing about it on the internet. (haha)
Eric
Amina started operation in 1999.
Yes, the pronunciation has a somewhat Aussie accent. It could simply be composite. Yes, fibre-reinforced composite is a real thing; the question is, which fibre and which materials are used in that composite?
The original creator of flat panel speakers in our time, Dr. Jose Bertagni, discovered that it would be quite challenging to produce low frequencies from a flat panel, at least one that is flat in front, using a small voice coil. Later, the highly advertised NXT came to the same conclusion. Companies that purchased NXT licenses typically produced small so-called PC speakers, and these speaker manufacturers always offered a subwoofer alongside those tiny speakers.
Jose Bertagni and/or his sons likely utilised Stanley Rich's idea to achieve low frequencies when they ventured into the invisible speaker business. Those speakers were marketed to those who could afford their price. Jose Bertagni began his flat panel polystyrene speakers in the 1960s and managed to stay afloat until 2005, when their company was sold to Sonance.
Stealth Acoustics, or their parent company Dimensional Communications, started in 1973 and had a different perspective on hidden or semi-hidden sound systems. Stealth Acoustics was established specifically for that purpose around 20 years ago. They utilised standard speaker drivers to create a flat panel sound diffusion experience.
Both Stealth Acoustics and Sonance utilise Stanley Rich's concept of trapped air to produce low frequencies from the front surface of the flat panel before the air enclosure using pistonic motion. They both employ a very thin air enclosure to achieve this, precisely as Rich described in his patent. Additionally, both companies use a very small area to generate high and mid frequencies, employing the bending wave modal.
Conclusion:
If we need to hide the speaker in a wall, or if we want to have both resonating areas, we can create the speaker with two separate panels, thereby avoiding resource wastage. Those two resonating areas don't need to be connected at all. Alternatively, we can design quite small mid/high frequency flat panel speaker separately, using either standard exciters or conventional drivers with a coil former and foot, and utilise Stanley Rich's concept to create a low frequency (subwoofer) that is also quite flat. This would also involve using a flat panel to diffuse sound, allowing it to be placed anywhere in the room.
Jose Bertagni and/or his sons likely utilised Stanley Rich's idea to achieve low frequencies when they ventured into the invisible speaker business. Those speakers were marketed to those who could afford their price. Jose Bertagni began his flat panel polystyrene speakers in the 1960s and managed to stay afloat until 2005, when their company was sold to Sonance.
Stealth Acoustics, or their parent company Dimensional Communications, started in 1973 and had a different perspective on hidden or semi-hidden sound systems. Stealth Acoustics was established specifically for that purpose around 20 years ago. They utilised standard speaker drivers to create a flat panel sound diffusion experience.
Both Stealth Acoustics and Sonance utilise Stanley Rich's concept of trapped air to produce low frequencies from the front surface of the flat panel before the air enclosure using pistonic motion. They both employ a very thin air enclosure to achieve this, precisely as Rich described in his patent. Additionally, both companies use a very small area to generate high and mid frequencies, employing the bending wave modal.
Conclusion:
If we need to hide the speaker in a wall, or if we want to have both resonating areas, we can create the speaker with two separate panels, thereby avoiding resource wastage. Those two resonating areas don't need to be connected at all. Alternatively, we can design quite small mid/high frequency flat panel speaker separately, using either standard exciters or conventional drivers with a coil former and foot, and utilise Stanley Rich's concept to create a low frequency (subwoofer) that is also quite flat. This would also involve using a flat panel to diffuse sound, allowing it to be placed anywhere in the room.
Attachments
Speaking of Jose Bertagni, as far as I can tell, this is his first patent.
https://patentimages.storage.googleapis.com/a9/de/c5/2a486d79e60733/US3596733.pdf
It is a very interesting read. In effect, I believe his invention is essentially a flat panel bending wave/DML speaker. But he sees it quite differently from how we normally think of such speakers.
First, his panel is a granular polystyrene with a tensioned paper or woven face layer. He believes that the tensioning creates stresses in the panel that play an an important role in how the vibrations of the voice coil are turned into sound. Such a stressed panel is not typically used in any other panel speakers that I am aware of. It might sound a little like the "canvas frame" construction that is sometimes discussed, but if you read his description you will see it is not the same concept.
Secondly, and most interesting, is that his description of how the vibrations of the coil are transmitted to the panel is very unique. He believes that the vibrations are "decomposed" as they move from the back (where the voice coil is attached) to the from of the panel, and, that the vibrations are substantially parallel to the plane of the panel. Presently, we generally understand that what creates the sound waves in the air from such a speaker are transverse vibrations of the panel (vibrations perpendicular to the plane of the panel). But Bertagni apparently believed something different.
Eric
https://patentimages.storage.googleapis.com/a9/de/c5/2a486d79e60733/US3596733.pdf
It is a very interesting read. In effect, I believe his invention is essentially a flat panel bending wave/DML speaker. But he sees it quite differently from how we normally think of such speakers.
First, his panel is a granular polystyrene with a tensioned paper or woven face layer. He believes that the tensioning creates stresses in the panel that play an an important role in how the vibrations of the voice coil are turned into sound. Such a stressed panel is not typically used in any other panel speakers that I am aware of. It might sound a little like the "canvas frame" construction that is sometimes discussed, but if you read his description you will see it is not the same concept.
Secondly, and most interesting, is that his description of how the vibrations of the coil are transmitted to the panel is very unique. He believes that the vibrations are "decomposed" as they move from the back (where the voice coil is attached) to the from of the panel, and, that the vibrations are substantially parallel to the plane of the panel. Presently, we generally understand that what creates the sound waves in the air from such a speaker are transverse vibrations of the panel (vibrations perpendicular to the plane of the panel). But Bertagni apparently believed something different.
Eric
Bertagni's company is no longer in operation; Sonance has taken its place. For Sonance, those invisible speakers are just one aspect of their business, but not the primary focus. In contrast, for Stealth Acoustics, it is their main business, and they don't typically cater to those with thin wallets.
But the idea is the same: the low frequency area is vibrated by a trapped air enclosure using pistonic motion modal (Stanley Rich), while the high/mid frequency area, which is quite small, is vibrated by the bending wave modal, with the actuator making direct contact with the panel in that region (Bertagni, NXT or whatever).
What we need is a relatively small flat panel for that, and we would never achieve those low frequencies, even if we had a wall or door excited by an exciter(s). Not even with the peculiar physics principles that the Russians are apparently employing.
If you're interested, here are, most probably, all the Bertagni patents.
https://patents.google.com/patent/US3596733A/en
https://patents.google.com/patent/US3722617A/en
https://patents.google.com/patent/US3767005A/en
https://patents.google.com/patent/US3779336A/en
https://patents.google.com/patent/US3792394A/en
https://patents.google.com/patent/US3801943A/en
https://patents.google.com/patent/US4003449A/en
https://patents.google.com/patent/US4184563A/en
https://patents.google.com/patent/US4257325A/en
https://patents.google.com/patent/US6929091B2/en
https://patents.google.com/patent/US5693917A/en
https://patents.google.com/patent/US5991424A/en
https://patents.google.com/patent/US5539835A/en
https://patents.google.com/patent/US5425107A/en
https://patents.google.com/patent/US5007707A/en
https://patents.google.com/patent/US5615275A/en
This could be interesting to some PETTaLS it's a youtube video from someone who has developed software to model DML flatpanel speakers. Sounds like he has a good background and a lot of knowledge, I haven't watched all 3 videos yet.
Interesting finding!
Those videos are from D. David Anderson.
His website mozartandcircuits.com
His publications : D Anderson's publications
Christian
If you are interested in David Allan Anderson's patents as an inventor, here are the links.
https://patents.google.com/patent/US20200120414A1
https://patents.google.com/patent/US11438704B2
And by his co-inventor, Mark Frederick Bocko
https://patents.google.com/patent/US11012784B2
https://patents.google.com/patent/EP3864860A1
https://patents.google.com/patent/WO2024006738A1
Michael Charles Heilemann was involved in one or more of those patents. All these patents are owned by the University of Rochester, USA. They will remain that way until some company decides to utilise the ideas contained within them. When you thoroughly examine those patents, you may find that all those 'new' ideas are actually present in those old expired patents.
https://patents.google.com/patent/US20200120414A1
https://patents.google.com/patent/US11438704B2
And by his co-inventor, Mark Frederick Bocko
https://patents.google.com/patent/US11012784B2
https://patents.google.com/patent/EP3864860A1
https://patents.google.com/patent/WO2024006738A1
Michael Charles Heilemann was involved in one or more of those patents. All these patents are owned by the University of Rochester, USA. They will remain that way until some company decides to utilise the ideas contained within them. When you thoroughly examine those patents, you may find that all those 'new' ideas are actually present in those old expired patents.
This PETTaLS software seems like a really great start to the kind of simulation software we all want. At the moment it still unclear what materials or exciters are catered for, but I am sure this can be fine tuned quite easily with the correct input or feedback from actual users.
At the end (from about 26:45) of the Part 1 video, Dr Anderson says a few interesting things. It is still unclear when or how this software will be made available. He invites some feedback on what we (as flat panel speaker builders) think about it, what would be useful, what changes can be made, etc. It would be great if the forum members could establish a more direct feedback line to him. Maybe invite him to join this thread?
Dr Anderson acts as a consultant to companies that make these speakers. It would be very interesting to know who those companies are - so that we can go and check out their products.
At the end (from about 26:45) of the Part 1 video, Dr Anderson says a few interesting things. It is still unclear when or how this software will be made available. He invites some feedback on what we (as flat panel speaker builders) think about it, what would be useful, what changes can be made, etc. It would be great if the forum members could establish a more direct feedback line to him. Maybe invite him to join this thread?
Dr Anderson acts as a consultant to companies that make these speakers. It would be very interesting to know who those companies are - so that we can go and check out their products.
As far as I know, they are not Sonance, Stealth Acoustics, Cersonar, Amina Sound, FlatPanel Audio, or DPKSound, as they have their own 'scientists' and rarely discuss such matters on YouTube, aside from marketing talk. All of them have been in this business for a long, long time.
Maybe here?
Hey y'all - this is Dave... creator of the PETTaLS software videos. Thanks for the invite Veleric!
I worked mainly as a consultant for smartphone companies that were turning the phone cover glass into a speaker using piezoelectric transducers instead of the moving-coil devices that most DML makers use. I'm not 100% sure that I'm allowed to say which companies I've worked with because of the NDAs, but here's an article that might be related: https://spectrum.ieee.org/piezoelectric-speakers.
I've also worked with companies that were creating DML-ish things, like SonicSensory/DropLabs.
Because my work was so concerned with glass as the audio medium, I haven't done quite as much investigation as all of you have into the effects of non-isotropic materials. I've mostly worked on modeling the effects of exciter arrays and enclosures (sealed and ported) on the resonances of panels, as well as piezoelectric transducers and other higher-order things like using arrays of exciters to do beamforming and shaping surface vibrations. If you're interested in reading any of those papers (and it seems like the folks on this forum probably are), you can find links at my google scholar site: https://scholar.google.com/citations?user=Dpw7u9IAAAAJ&hl=en&authuser=1
These days my research lab at work is mostly focused on hearing protection and spatial audio, but I like developing loudspeaker tools as my side gig (as well as making guitar effects, my other hobby!)
I'm already working to incorporate some of the suggestions into my software. I'll be heading out of town on vacation in a couple days, but I'll post some new videos when I have updates! (Also now that I'm part of this forum I'll check in regularly)
I worked mainly as a consultant for smartphone companies that were turning the phone cover glass into a speaker using piezoelectric transducers instead of the moving-coil devices that most DML makers use. I'm not 100% sure that I'm allowed to say which companies I've worked with because of the NDAs, but here's an article that might be related: https://spectrum.ieee.org/piezoelectric-speakers.
I've also worked with companies that were creating DML-ish things, like SonicSensory/DropLabs.
Because my work was so concerned with glass as the audio medium, I haven't done quite as much investigation as all of you have into the effects of non-isotropic materials. I've mostly worked on modeling the effects of exciter arrays and enclosures (sealed and ported) on the resonances of panels, as well as piezoelectric transducers and other higher-order things like using arrays of exciters to do beamforming and shaping surface vibrations. If you're interested in reading any of those papers (and it seems like the folks on this forum probably are), you can find links at my google scholar site: https://scholar.google.com/citations?user=Dpw7u9IAAAAJ&hl=en&authuser=1
These days my research lab at work is mostly focused on hearing protection and spatial audio, but I like developing loudspeaker tools as my side gig (as well as making guitar effects, my other hobby!)
I'm already working to incorporate some of the suggestions into my software. I'll be heading out of town on vacation in a couple days, but I'll post some new videos when I have updates! (Also now that I'm part of this forum I'll check in regularly)
Dave,
You also mentioned in your reply on YouTube that you hope to do make empirical measurements of the material parameters in your lab. Probably this is well known to you already but the impulse excitation method is a great way to get the elastic constants for both isotropic and orthotropic materials. If you are not already using this in your lab, I would recommend adding it. I think it's a great excercise for engineering students.
My homebrew version of the method is here:
and there are commercial units like this:
https://resonalyser.com/
But with FEA and a microphone you don't really even need the "instrument". It would be a great project for your students to write the code to extract the elastic properties that best fit the measured resonances.
Eric
Here is the link to Dave's thesis : Driver-array based flat-panel loudspeakers: theoretical background and design guidelines
@EarthTonesElectronics
Dave, maybe to start to give a rough picture of the DML here... most of our DML are based on materials available in general DIY stores like plywood, EPS, XPS (expended or extruded polystyrene), cardboard, corrugated flute polypropylene. There are also designs with composite (CF/GF on balsa) and some tenative of 3D printing. This is not exhaustive. The exciters are from Dayton audio, Tectonic and some now from Xcite. The panels are most of the time with an open back. The suspension can be in one or 2 points at the top (suspended) or full peripheral with some double side foam tape or weather foam. There is generally some support (spine) for the exciter.
Recently, I started and described here the way to make directivity measurements. They are very informative. With that we have the first picture of the coincidence frequency and so a possible decision about the choice of the material, its thickness.
As those measurements are for now almost from open back panels, they seem to show also the dipole behavior of the panel with a peak, a first null and then as the frequency increases 4 lobes, 6 lobes and more generally, a SPL at high angle higher than on axis (this before any coincidence frequency).
I don't have in mind papers explaining the combination of the 2 mechanisms : the dipole (as know for cone driver in open baffle configuration) and the DML with its modes.
Is it correct to interpret the behavior of an open back DML in that way?
From this question, I was thinking that our main question is to design a DML, either in an open back configuration but then with an almost constant figure of eight directivity (as open baffle designers do in a multy way configuration with a minimal baffle) or in a closed back configuration to get a cardioid type directivity. In the DIYer threads about DML, the second family (closed back) is associated to a "boxy sound".
Do you have some advice to improve one or both of those families of loudspeakers?
There are for sure other questions but it is probably already more than enough!
Happy new year to all! Best wishes!
Christian
@EarthTonesElectronics
Dave, maybe to start to give a rough picture of the DML here... most of our DML are based on materials available in general DIY stores like plywood, EPS, XPS (expended or extruded polystyrene), cardboard, corrugated flute polypropylene. There are also designs with composite (CF/GF on balsa) and some tenative of 3D printing. This is not exhaustive. The exciters are from Dayton audio, Tectonic and some now from Xcite. The panels are most of the time with an open back. The suspension can be in one or 2 points at the top (suspended) or full peripheral with some double side foam tape or weather foam. There is generally some support (spine) for the exciter.
Recently, I started and described here the way to make directivity measurements. They are very informative. With that we have the first picture of the coincidence frequency and so a possible decision about the choice of the material, its thickness.
As those measurements are for now almost from open back panels, they seem to show also the dipole behavior of the panel with a peak, a first null and then as the frequency increases 4 lobes, 6 lobes and more generally, a SPL at high angle higher than on axis (this before any coincidence frequency).
I don't have in mind papers explaining the combination of the 2 mechanisms : the dipole (as know for cone driver in open baffle configuration) and the DML with its modes.
Is it correct to interpret the behavior of an open back DML in that way?
From this question, I was thinking that our main question is to design a DML, either in an open back configuration but then with an almost constant figure of eight directivity (as open baffle designers do in a multy way configuration with a minimal baffle) or in a closed back configuration to get a cardioid type directivity. In the DIYer threads about DML, the second family (closed back) is associated to a "boxy sound".
Do you have some advice to improve one or both of those families of loudspeakers?
There are for sure other questions but it is probably already more than enough!
Happy new year to all! Best wishes!
Christian
This firm appears to be a startup in 2023, boasting about creating the thinnest DML panels. I posted a video of it earlier. If you click on the Buy icon, you'll find the product specifications, such as this. The panel size is based on the golden ratio. They claim that the exciters and their placement are proprietary, but I'm sure you can guess their placements. That's quite an exorbitant price for a piece of balsa wood, an expanded PVC sheet, and two exciters, though. Anyway, it has the most modern website out of all those "DML" manufacturers.
Their largest hidden speaker,
And Amina from nine years ago, featuring that exciter array.
And, the Chinese copy (?) of it five years ago,
Happy New Year to all! I hope it brings peace for all of us living on this Planet Earth!
Their largest hidden speaker,
And Amina from nine years ago, featuring that exciter array.
And, the Chinese copy (?) of it five years ago,
Happy New Year to all! I hope it brings peace for all of us living on this Planet Earth!