Continuation...
I’ve been searching online for quite sometime now, and it seems rather unlikely that no one has tackled this before. There have certainly been similar efforts, even prior to Henry Azima. It appears that Siemens undertook some work in this area at the beginning of the last century, along with a few others later on. I’ve come across some quite recent videos on YouTube, that were made just last year or so, which might be of interest.
I’ve been searching online for quite sometime now, and it seems rather unlikely that no one has tackled this before. There have certainly been similar efforts, even prior to Henry Azima. It appears that Siemens undertook some work in this area at the beginning of the last century, along with a few others later on. I’ve come across some quite recent videos on YouTube, that were made just last year or so, which might be of interest.
- Testing of flattened coil speakers.
- Testing of flattened coil speakers using beer can bottoms to enhance the treble.
- Another test with a flattened coil.
- And, testing them with a subwoofer and without.
- Speakers featuring two flattened coils and specific enhancements for treble.
- Another test with a specific enhancement for treble, but this time incorporating a subwoofer.
Continuation...
Keep a close eye on the videos with the English subtitles turned on. Rewatch them a few times, stop, rewind and rewatch. Read the introduction, which is in Russian, and translate it. Плоская катушка = flat coil.
And here’s an image of the aforementioned test prototype featuring the flattened coil in the centre.
Do take note of the panel surface; it’s practically identical to the one that TectonicLabs produced a few years back.
This is just one of the prototypes. There were numerous others featuring beer can bottoms, two flat coils in one speaker positioned at different locations, flat coils placed vertically, at an angle, or simply a round coil, some using various materials to enhance the treble. It’s all there in those videos.
All one needs is some thin gauge insulated copper wire and a few magnets. The rest is up to us.
Keep a close eye on the videos with the English subtitles turned on. Rewatch them a few times, stop, rewind and rewatch. Read the introduction, which is in Russian, and translate it. Плоская катушка = flat coil.
And here’s an image of the aforementioned test prototype featuring the flattened coil in the centre.
Do take note of the panel surface; it’s practically identical to the one that TectonicLabs produced a few years back.
This is just one of the prototypes. There were numerous others featuring beer can bottoms, two flat coils in one speaker positioned at different locations, flat coils placed vertically, at an angle, or simply a round coil, some using various materials to enhance the treble. It’s all there in those videos.
All one needs is some thin gauge insulated copper wire and a few magnets. The rest is up to us.
Hello Lekha,
The honeycomb they use/used(?) has a much bigger cell size than the standard nomex like tectonic used. Also Tectonic used carbon fibre cloth, and Mescalito paper. The picture you posted is very interesting. Where did you find it? Cheers, Hans
The honeycomb they use/used(?) has a much bigger cell size than the standard nomex like tectonic used. Also Tectonic used carbon fibre cloth, and Mescalito paper. The picture you posted is very interesting. Where did you find it? Cheers, Hans
In the post #12638, it seems more like a flat membrane pistonic speaker (see the ribs)
In the video of the post #12641 it seems more to be in the DML family.
Just for memory, the can beer was mentioned here in post 311 and 455. The subwoofer in those video is of PPD sub type.
@lekha , I have not found in those video even with subtitle the flat coil information... Maybe I watched them to quiickly? What is tha source of the picture in post 12643?
Christian
In the video of the post #12641 it seems more to be in the DML family.
Just for memory, the can beer was mentioned here in post 311 and 455. The subwoofer in those video is of PPD sub type.
@lekha , I have not found in those video even with subtitle the flat coil information... Maybe I watched them to quiickly? What is tha source of the picture in post 12643?
Christian
A fairly new video of Mescalito panels, showing absolutely nothing. Much like the carpet videos. All we know is that rice paper is involved. I haven't taken time to listen to the music critically.
I think, you made the coil similarly (4:40-7:20):
This video showcases the company's product rather than personal prototypes of the individual. Please note that the company has yet to start producing the flat coil speakers for sale.
Naturally, the idea for the beer can bottom was inspired by discussions from this forum.
Some of the ideas used in the flattened coil prototypes were drawn from the other thread I mentioned earlier, where the distances from the coil to the magnets and other details were sourced. DIY Audio is an excellent platform for brainstorming and implementing innovative concepts. This thread is filled with thoughtful individuals, so I anticipate that an interesting will emerge from it.
You see, Henry Azima couldn't simply glue a coil to a flat surface and place a magnet a few millimetres away to turn a profit; he had to come out with a device, and story behind it. His company sold licenses based on patents, and Tectonics employs a similar approach. While attaching a vibrating device to a flat panel may seem straightforward, getting that flat panel to produce sound or music is a different challenge altogether. There’s considerable debate here about the best materials for the panel, rather than focusing on how to make it resonate. Fortunately, this forum is home to many insightful individuals who are capable of creating remarkable solutions.
Henry Azima wrote about bending waves, which is precisely what we are aiming for. If a leading figure in a company in the East is successfully creating prototypes and possesses the necessary business acumen, then something significant is bound to emerge from that. So, why not here as well? Shouldn't you all brainstorm?
Someone mentioned earlier that they have some damaged exciters and plan to experiment with them. Why not? I’ve taken apart some kitchen radio speakers and played around with the flattened coil and magnets on various flat sheets. While I don’t have the necessary equipment to measure sound levels and such, you do. So, I encourage you all to discuss and debate among yourselves; perhaps something truly worthwhile will emerge from it.
It’s just one type of panel and its surface. They have advanced much further than Tectonics in this regard.
- Here’s another DML featuring a flat coil and three magnets. You might spot one pair that has a beer can bottom for treble enhancement at the rear. I believe the membrane is made of plywood.
- Here’s a nearly completed product. 6 months ago.
- Here's much earlier (3 year old) try using the modified WrineX method.
lehka,
You seem to have done a lot of study! Have you built anything of your own you would like to share?
Have you read any of the Bertagni patents? Not about flat coils as far as I recall, but very good patents going back well before the Azima ones.
Eric
@Veleric and Others
I've been delving into a considerable number of patents on this subject over the past few years. There are quite a few links to many of them right here in this thread. Admittedly, this thread is rather lengthy, but it’s an absolute treasure trove! I've also conducted a bit of experimentation myself. It seems one can achieve a much better return with smaller panels that have rounded corners. I've been contemplating writing about this in the thread, particularly regarding the use of flat coils and magnets separately. I do have exciters as well, though I’m not particularly keen on them. However, the concept of bending waves traversing the panel surface to create sound waves is quite fascinating to me.I’m now in my 74th year, so I’m not likely to be doing much experimenting these days. My hearing isn’t quite what it used to be. However, this thread is brimming with enthusiastic young minds—if I may refer to you all as such! I do hope you’ll grasp the concept and undertake some experiments to develop some outstanding DMLs. My visits here may not be as frequent, but I trust that in the meantime, you’ll come up with some intriguing flat panel speakers.
Here’s a frame for a dual flat coil small speaker. Take a look at the image here for comparison. The flat membrane is secured with a surround on one side, while the magnet system is positioned on the opposite side, attached to the back frame. The front will be covered with a sound-immune acoustic mesh cloth. You may have heard how it sounds in one of the videos shared here.
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In previous posts I've mentioned that the literature says that the radiation efficiency of the various plate vibration modes varies considerably, and that the so called odd,odd modes have the greatest radiation efficiency. I did some tests recently that seem to confirm that.
In these tests I compared the radiation from the fundamental (1,1) mode to the (1,2) and (1,3) modes, depicted in the images below.
The tests were all made using an XPS panel (7"x 24" x 1/2"), attached around the entire perimeter to a sturdy frame using 3M Indoor double sided mounting tape.
The basic idea was to use multiple exciters in three different configurations such that each configuration excited only one of the three modes, and neither of other two, and compare the SPL at one meter for each configuration. The image below shows the three different exciter configurations.
In these figures, the arrows represent the location and phase of the attached exciters.
Ideally, all three configurations would have used just two exciters, but there is no way to drive only the (1,3) mode that way, so I used three exciters instead. In all cases the exciters were wired in series, so the nominal impedance of configurations 1 and 2 is 8 ohm, and 12 ohm for configuration 3.
The results of several impedance tests are shown below. The ones at the bottom of the figure are tests I performed with only a single exciter mounted at various locations along the panel. The purpose of those tests was simple to establish the frequencies for each of the panel's vibration modes. As you can seen, the frequencies of the first nine (and more) are clearly revealed by that series of impedance tests. For the sake of simplicity, I identified the (1,1) mode simply as 1, and the (1,2) mode simply as 2, etc. And from now on I will refer to the (1,1) mode as the first mode, the (1,2) mode as the second mode, and so on.
The other three curves are the impedance results for the three different exciter configurations I described above. And indeed, as expected, configuration 1 has an impedance peak at mode 1, but not modes 2 or 3. Likewise, configuration 2, has an impedance peak at mode 2, but not modes 1 or 3. Further, configuration 3 has an impedance peak at mode 3, but not modes 1 or 2. These results seem to confirm that the three different configurations each excite only one of the three lowest order modes, exactly as intended.
IMPEDANCE TESTS
The figure below compares the SPL results at 1 meter for the first two exciter configurations. The impedance curve for the first configuration tells us that the panel's first mode (fundamental) resonance frequency is at about 220 Hz. And the SPL results for configuration 1 show that the SPL for configuration 1 peaks strongly at that frequency, as expected.
For configuration 2, however, the results are much different. The impedance curve for the second configuration tells us that the panel's second mode resonance frequency is at about 285 Hz. But the SPL output for this configuration is much weaker than that of the first configuration, even at the 285 Hz resonance frequency of the very mode that it was designed to excite most effectively. In fact, the first configuration produces about 18 dB more output at this frequency than configuration 2.
This result confirms that the 1,1 mode (an odd,odd mode) produces much more output than the 1,2 mode.
It's getting late, so that's all for now. I'll share the results for configuration 3 soon.
Eric
In these tests I compared the radiation from the fundamental (1,1) mode to the (1,2) and (1,3) modes, depicted in the images below.
The tests were all made using an XPS panel (7"x 24" x 1/2"), attached around the entire perimeter to a sturdy frame using 3M Indoor double sided mounting tape.
The basic idea was to use multiple exciters in three different configurations such that each configuration excited only one of the three modes, and neither of other two, and compare the SPL at one meter for each configuration. The image below shows the three different exciter configurations.
In these figures, the arrows represent the location and phase of the attached exciters.
- In configuration 1, the two exciters were placed at L/6 (4") on either side of the midline of the panel length, and driven in phase. This should excite only the (1,1) mode neither of the other two modes.
- In configuration 2, the two exciters were moved to L/4 (6") on either side of the midline, and driven out of phase. This should excite only the (1,2) mode and neither of the other two modes.
- In configuration 3, three exciters were used: two were placed at L/3 (8") on either side of the midline, and driven in phase, while a third was added at the center, but driven out of phase with the other two. This should excite the (1,3) mode well, without exciting the (1,2) mode. It's not necessarily obvious if this configuration would drive the (1,1) mode or not, but impedance testing should confirm one way or the other.
Ideally, all three configurations would have used just two exciters, but there is no way to drive only the (1,3) mode that way, so I used three exciters instead. In all cases the exciters were wired in series, so the nominal impedance of configurations 1 and 2 is 8 ohm, and 12 ohm for configuration 3.
The results of several impedance tests are shown below. The ones at the bottom of the figure are tests I performed with only a single exciter mounted at various locations along the panel. The purpose of those tests was simple to establish the frequencies for each of the panel's vibration modes. As you can seen, the frequencies of the first nine (and more) are clearly revealed by that series of impedance tests. For the sake of simplicity, I identified the (1,1) mode simply as 1, and the (1,2) mode simply as 2, etc. And from now on I will refer to the (1,1) mode as the first mode, the (1,2) mode as the second mode, and so on.
The other three curves are the impedance results for the three different exciter configurations I described above. And indeed, as expected, configuration 1 has an impedance peak at mode 1, but not modes 2 or 3. Likewise, configuration 2, has an impedance peak at mode 2, but not modes 1 or 3. Further, configuration 3 has an impedance peak at mode 3, but not modes 1 or 2. These results seem to confirm that the three different configurations each excite only one of the three lowest order modes, exactly as intended.
IMPEDANCE TESTS
The figure below compares the SPL results at 1 meter for the first two exciter configurations. The impedance curve for the first configuration tells us that the panel's first mode (fundamental) resonance frequency is at about 220 Hz. And the SPL results for configuration 1 show that the SPL for configuration 1 peaks strongly at that frequency, as expected.
For configuration 2, however, the results are much different. The impedance curve for the second configuration tells us that the panel's second mode resonance frequency is at about 285 Hz. But the SPL output for this configuration is much weaker than that of the first configuration, even at the 285 Hz resonance frequency of the very mode that it was designed to excite most effectively. In fact, the first configuration produces about 18 dB more output at this frequency than configuration 2.
This result confirms that the 1,1 mode (an odd,odd mode) produces much more output than the 1,2 mode.
It's getting late, so that's all for now. I'll share the results for configuration 3 soon.
Eric
This isn't essential problem, because the perception can be near perfect. I wish you a lot of busy years and more loudspeaker!
Hi Eric
It's late here now as well, so pardon any simplistic observations, but isn't it obvious even from your sketch that 1,1 will have more output than the other modes??. The output can be visualised by the area under the graph, and only 1,1 is fully in phase... Both of the others have anti phase components which reduce the output
Regards
Eucy
Continuing my post from last night.
Here is the result for configuration 3, compare to configuration 1.
Recall, configuration 3 is designed to drive the third mode (1,3), which, like the fundamental is an odd,odd mode. But unlike configuration 2, there is a strong peak in the SPL for this configuration in the vicinity of the 350 Hz resonance frequency of this mode, again confirming that the output of the odd,odd modes is good compared to the second mode.
It's also interesting that configuration 1, driving presumably only the fundamental mode, still produced even more SPL in the 350 Hz region than configuration 3. This shows just how strong the radiation from the first mode is, even well above it's main resonance frequency.
Although, I think it's also worth noting that since config 3 used 3 exciters, rather than 2, the nominal impedance is higher (12 ohms) than it was for the other two configurations with only 2 exciters (8 ohms). So that higher impedance alone would be expected to cause a slight reduction in the output of Config 3 across the full spectrum, right?
Eric
Here is the result for configuration 3, compare to configuration 1.
Recall, configuration 3 is designed to drive the third mode (1,3), which, like the fundamental is an odd,odd mode. But unlike configuration 2, there is a strong peak in the SPL for this configuration in the vicinity of the 350 Hz resonance frequency of this mode, again confirming that the output of the odd,odd modes is good compared to the second mode.
It's also interesting that configuration 1, driving presumably only the fundamental mode, still produced even more SPL in the 350 Hz region than configuration 3. This shows just how strong the radiation from the first mode is, even well above it's main resonance frequency.
Although, I think it's also worth noting that since config 3 used 3 exciters, rather than 2, the nominal impedance is higher (12 ohms) than it was for the other two configurations with only 2 exciters (8 ohms). So that higher impedance alone would be expected to cause a slight reduction in the output of Config 3 across the full spectrum, right?
Eric
Eucy,
Totally agree. It's just nice to get some actual measurements to see if what you expect is actually correct. Sometimes things that you assume to be true (because they seem obvious), are not in fact correct.
Eric
Continuation...
Another suggestion is to position the flattened panel on the front side of the flat panel / membrane, while retaining the magnets at the back. Although having a coil visible in front of the panel or speaker may not be particularly aesthetically pleasing, it could be concealed with a thin layer of aluminium foil. Additionally, the rear frame could be made slightly thicker to create a resonance box at the back, which would enhance the bass response, even with an opening for bass reflex.
Furthermore, it would be advisable not to place the coil at the centre; rather, it would be better positioned further down, as demonstrated in some of the videos, or perhaps at an off-centre location, as shown in this image. The coil could be flattened from left to right,
or designed to resemble an envelope with tapered sides, or turned to an angle as in this image.
You may have observed from the videos that they can be quite compact in size while still producing excellent sound quality. With your understanding of how various types of panel surfaces respond to bending waves, you might be able to determine the ideal dimensions, as well as the appropriate type of panel and its surface finish. At least, that’s my hope.
By the way, here’s an interesting experiment from about four years ago. It might serve as inspiration.
Another suggestion is to position the flattened panel on the front side of the flat panel / membrane, while retaining the magnets at the back. Although having a coil visible in front of the panel or speaker may not be particularly aesthetically pleasing, it could be concealed with a thin layer of aluminium foil. Additionally, the rear frame could be made slightly thicker to create a resonance box at the back, which would enhance the bass response, even with an opening for bass reflex.
Furthermore, it would be advisable not to place the coil at the centre; rather, it would be better positioned further down, as demonstrated in some of the videos, or perhaps at an off-centre location, as shown in this image. The coil could be flattened from left to right,
or designed to resemble an envelope with tapered sides, or turned to an angle as in this image.
You may have observed from the videos that they can be quite compact in size while still producing excellent sound quality. With your understanding of how various types of panel surfaces respond to bending waves, you might be able to determine the ideal dimensions, as well as the appropriate type of panel and its surface finish. At least, that’s my hope.
By the way, here’s an interesting experiment from about four years ago. It might serve as inspiration.
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