Hello RMAM
Could you precise the plastic and thickness of your panels?
About metamaterials, some easier to read articles would be welcome to enter in the topic 😉
Christian
Reopening the specifications of the Tectonic DML500 (to find its directivity plot), I see: active surface 378x478mm (S = 0.18m², R = 1.26, R/S = 7). 7, magic number?
Christian
I have a strong feeling that the flat panel and the box can somehow be integrated in the manner that both Whitwell and Zenker, along with a few others, are suggesting.
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The sound of a flat panel or a standard speaker depends on the listener's hearing ability, as well as the acoustics of the room in which the speakers are used. I adjust whatever speakers I have, based on my wife's hearing, as she has a background in music education and has exceptional hearing ability when it comes to music.
A simple matter of positioning the thin 3-way speaker box, which has the woofer on one side—the flatter side that typically faces sideways to the listener—flat on its other side with the woofer now firing upwards, we significantly enhanced the soundstage in our living room, much to our surprise. It is rather peculiar that everyone seems to advocate for upright (front facing) speaker boxes.
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I had a conversation with some musically educated individuals some time ago; some of them teach music, including piano and violin. I inquired about the discussion surrounding various frequencies reaching our ears, which arrive faster or slower, particularly in our living rooms or in their auditorium. My wife chose not to participate so as not to "colour" the conversation. I also mentioned that some people create massive speakers and sell them at exorbitant prices—enough to buy a decent car or two. They were previously unaware of this second aspect regarding the strangely high prices of speakers. Well, they experience music every day, for breakfast, lunch, and dinner, and even beyond that.
Anyway, the essence of the conversation is this: you hear only what your ears permit, nothing more. Once a sound leaves the source, it disperses like a balloon in every direction. Of course, you can use certain instruments to direct the sound, but once it is emitted, it travels everywhere. It is the ears of individuals, or rather their brains, that can pinpoint the source of a sound. There are some people who can separate sound reception, so to speak, into different frequencies, but they are quite rare. Individuals such as piano tuners can differentiate sounds, but most often only one at a time and in the silence of their workspace. Conductors can easily perceive that separation of sound, yet they still regard the music they are conducting as a whole, rather than as originating from a single area. Most of us have untrained ears.
Returning to our speakers, one of them asked me what I would hear if I placed some sort of screen between the stereo speakers and myself. I attempted this by using two large pieces of cardboard about 1 metre in front of the speakers, covering the entire length and extending about 1 metre higher than the line of the speakers. Even though I knew where my speakers were, I simply couldn't pinpoint them exactly. Whether the sound reached me from above the screen or around it, I couldn't say. Neither could my wife. The room was filled with music from a set of standard shop-bought speakers, or was it our brains adjusting themselves? Do give it a try.
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The sound of a flat panel or a standard speaker depends on the listener's hearing ability, as well as the acoustics of the room in which the speakers are used. I adjust whatever speakers I have, based on my wife's hearing, as she has a background in music education and has exceptional hearing ability when it comes to music.
A simple matter of positioning the thin 3-way speaker box, which has the woofer on one side—the flatter side that typically faces sideways to the listener—flat on its other side with the woofer now firing upwards, we significantly enhanced the soundstage in our living room, much to our surprise. It is rather peculiar that everyone seems to advocate for upright (front facing) speaker boxes.
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I had a conversation with some musically educated individuals some time ago; some of them teach music, including piano and violin. I inquired about the discussion surrounding various frequencies reaching our ears, which arrive faster or slower, particularly in our living rooms or in their auditorium. My wife chose not to participate so as not to "colour" the conversation. I also mentioned that some people create massive speakers and sell them at exorbitant prices—enough to buy a decent car or two. They were previously unaware of this second aspect regarding the strangely high prices of speakers. Well, they experience music every day, for breakfast, lunch, and dinner, and even beyond that.
Anyway, the essence of the conversation is this: you hear only what your ears permit, nothing more. Once a sound leaves the source, it disperses like a balloon in every direction. Of course, you can use certain instruments to direct the sound, but once it is emitted, it travels everywhere. It is the ears of individuals, or rather their brains, that can pinpoint the source of a sound. There are some people who can separate sound reception, so to speak, into different frequencies, but they are quite rare. Individuals such as piano tuners can differentiate sounds, but most often only one at a time and in the silence of their workspace. Conductors can easily perceive that separation of sound, yet they still regard the music they are conducting as a whole, rather than as originating from a single area. Most of us have untrained ears.
Returning to our speakers, one of them asked me what I would hear if I placed some sort of screen between the stereo speakers and myself. I attempted this by using two large pieces of cardboard about 1 metre in front of the speakers, covering the entire length and extending about 1 metre higher than the line of the speakers. Even though I knew where my speakers were, I simply couldn't pinpoint them exactly. Whether the sound reached me from above the screen or around it, I couldn't say. Neither could my wife. The room was filled with music from a set of standard shop-bought speakers, or was it our brains adjusting themselves? Do give it a try.
Hello Lekha
From the videos, I have in mind the questions about the front/rear cancellation. I have also in mind M Zenker's paper about a rear load close to the panel to smooth the DP but I am not convinced he pushed enough to listening tests, it might be more a theoretical solution than something for a high quality speaker... have you seen other possibilities?
About the 2 "experiences" you relates, it might be a question of directivity.
In a standard loudspeaker, the vertical directivity has accidents (depanding of the design, the crossover frequency...) due to the distance between the sources mid and tweeter, the crossover. Having that horizontal may reduce an unpleasant reflection... This is a tentative of explanation... It is in the way a dipole is said to be a good solution as the null at 90° limits the reflections to the side and back wall (see M Linkwitz drawings).
In the second experience, the screen you added has attenuated the direct sound from the speaker making it difficult to localize. A DML radiates from the front at about +/-90°, with no big difficulties up to 10kHz, probably in an uneven manner. A loudspeaker designed for a stable directivity seems to be in +/-60° (see the spinorama.org site). For a loudspeaker which was not designed for a constant directivity, some areas can be as low as +/-30°. This are tendencies, not a real study. One quality of the DML is "it disappeared" in the room and, as it was said before, they allow to have a pleasant sound with no localization of the source even if you are not just at the sweet spot. I wonder if a loudspeaker designed for a constant directivity "disappears" also from the room.
The rear radiation of DML seems more chaotic... the exciter itself makes a mask in the highs, the parts like a spine can create a mask even in the mids. I don't have ideas of what FR is expected from the rear except maybe a dipole in the low frequency. Goebel mentions a cut off of the rear at 4kHz when some open baffle designs add a rear tweeter.
I have search for directivity plot or spinorama of open baffles made from classical drivers, but not found.
Christian
I have a feeling that Zenker spoke at length but didn’t provide much in the way of details. He didn’t mention how, or whether, the flat panel is fixed on all four sides, or even if the fixing is rigid or flexible. He merely discussed one idea, most likely hoping for further discussion in that podcast. I have no idea whether that podcast was free or paid, but it’s probably a paid one. I’ve subscribed, so I’ll be notified when he or Whitwell might appear again. As you know, the concept of using a flat panel as a sound diffuser has been around for ages, perhaps since the time people learned to use drums for communication.
The drum skin is, of course, elastic, so striking it causes it to vibrate and produce sound. In those days, drum sounds could travel long distances. Most musical instruments, apart from drums, have rigid bodies, yet they are rarely square or rectangular, with the exception of perhaps Cajons. There is also a fascinating musical instrument called the Hang, which resembles two pans welded together—people have used single pans to create music, often at village fairs or drinking parties. There are others, such as Ghatam from India. And, many other stiff surface music instruments.
In any case, I believe that rigidly connected flat panels could transmit good music; for instance, an exciter touching a table would also produce sound. Perhaps we should, for a time, set aside the idea of elastic surround suspension and consider firmly fixing the flat panels to the frame? There were ideas in the 1980s about securing flat panels with cork strips instead of rubber suspension to achieve a sort of stiff suspension, but with a degree of softness. I suppose you’ve heard of Dr. Carl Pinfold, who experimented with a longitudinal voice coil and a flat panel. It seems he never left any documentation of his ideas or filed a patent for them. By the way, that longitudinal voice coil reminds me of the flattened coil I mentioned some time ago.
lehka,
He may or may not have said it out loud, but for all his examples and simulations he was taking about panels with rigid fixed edges around all four sides. You can see it noted on some of his slides, for example at about 15 minutes(see below). It's also clear from the modal response simulation he shows at the same time into the video (15 minutes) As I recall it is also the case for all his technical papers. In one of his papers he describes the actual boundary conditions where about 50 mm of the panel is clamped around the entire perimeter, I suspect that was also the case here.
Eric
Thanks lekha for posting the Zenker video, and the Whitwell videos too. Those are indeed worth watching.
I have wondered why Zenker seems to favor clamped edges. My own preference is for boundary conditions that are close to what engineers refer to as "simple" supports, and what might be thought of in simple terms as "fixed, but flexible". The modal shapes and frequency distributions for the two cases (i.e. fixed rigid vs fixed flexible) are very, very similar, except that the fixed rigid case requires a larger panel to get the same response, as a smaller panel with fixed, flexible supports. So it's hard for me to see what the advantage might be.
I did try clamped edges once. It was a long time ago so I don't recall the details other than that it confirmed the obvious, which is that the natural frequencies were pushed higher. That is, the clamped panel essentially acted like it was a smaller panel.
Eric
I was very interested in Zenker's discussion of aspect ratio, as that is something I have studied a lot myself. I was curious when he talked about the ratio of 1.25 as if it was a well known "golden ratio" for panel aspect ratio. The best aspect ratio according to NXT was 1.134, and maybe there was another at 1.37 IIRC. Of course Tefra claims 9/5 (1.8) is best. But where was 1.25 ever published? Is that familiar to anyone else, and from where?
But the part of his results concerning aspect ratio that I found most interesting was one that he didn't emphasize at all. And that is that the very best overall performance was for aspect ratio's of 4 to 5. I've been talking about the benefits of high aspect ratio panels for some time now. It's nice to see his results confirm the same thing.
Eric
But the part of his results concerning aspect ratio that I found most interesting was one that he didn't emphasize at all. And that is that the very best overall performance was for aspect ratio's of 4 to 5. I've been talking about the benefits of high aspect ratio panels for some time now. It's nice to see his results confirm the same thing.
Eric
The simple support is actually fixed but has the ability to move horizontally if necessary. A fixed support, on the other hand, does not permit any movement or rotation in any direction from its fixed position. The surround suspension is somewhat akin to a spring support (with a semi-rigid support that possesses some rigidity), but it is not entirely rigid, which is why cone breakage occurs. Even around a flat panel, such a semi-rigid, predominantly elastic suspension would allow it to move erratically in response to the vibrations or bending waves occurring in that region or at any other edge at a given time, resembling cone breakage in a flat panel context.
Perhaps Dr. Pinfold's idea of using a cork surround could create an edge that is fixed with a softer material, which would be more stable than the standard surround. Alternatively, one might consider fixing the edges with silicone or double-sided silicone tape.
The term fixed is actually a bit vague. But usually it means the same as clamped, or cantilevered, as in: prevented from displacement and rotation.
A simple support prevents motion in the direction of the applied force at a particular point, but allows rotation about that point. So because of the freedom to rotate, I think it's technically not correct to say a simple support is fixed, although it is indeed prevented from motion in one direction. Yes, a simple support allows horizontal motion if necessary. But in the case of small deformations, the freedom (or restraint) of horizontal motion has no practical impact.
Eric
Fixed, or simple support, or support at the 4 corners only... - are we talking about edge damping here?
Often used in this thread is weather strip. Eric had good results with Poron 92. I tried natural latex tubing.
But it appears that canvas supported panels still hold a lot of promise and good results. And it's easy to implement.
Directivity measurements
Here is a link to a page from MiniDSP showing how to transfert measurements from REW to VirtuixCAD for plotting.
Christian
Here is a link to a page from MiniDSP showing how to transfert measurements from REW to VirtuixCAD for plotting.
Christian
About Dr. Carl Pinfold's novel speaker design.
Dr. Pinfold mentioned a cement-based inorganic plastic, but I couldn't find any information on that anywhere.
Dr. Pinfold mentioned a cement-based inorganic plastic, but I couldn't find any information on that anywhere.
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lehka,
I also wondered if you know anything about Kenneth Heron, of this patent:
https://patents.google.com/patent/EP0541646B1/en?inventor=kenneth+heron&oq=kenneth+heron
It's also from the British Defence department and predates (I think) all the NXT patents. Did he work with Bank and those guys? Was Heron the original mastermind?
You may notice, this one has a different view of the main operating principal than the later NXT patents. Heron envisioned his panel to work primarily above the coincidence frequency. So his panels were very, very thick and stiff. One example was 40 mm thick panel using aluminum skins and aluminum honeycomb core. You will love that it is shown hanging from strings!
Eric
I also wondered if you know anything about Kenneth Heron, of this patent:
https://patents.google.com/patent/EP0541646B1/en?inventor=kenneth+heron&oq=kenneth+heron
It's also from the British Defence department and predates (I think) all the NXT patents. Did he work with Bank and those guys? Was Heron the original mastermind?
You may notice, this one has a different view of the main operating principal than the later NXT patents. Heron envisioned his panel to work primarily above the coincidence frequency. So his panels were very, very thick and stiff. One example was 40 mm thick panel using aluminum skins and aluminum honeycomb core. You will love that it is shown hanging from strings!
Eric
I think it doesn't actually make any sense to talk about whether a panel is large, or small, or whatever, without considering also its thickness, elastic modulus and density. I was little disappointed that Zenker didn't take that into account.
My view of whether a panel is large or small depends on the panel's fundamental (lowest) natural frequency, and not on its raw size. And I would consider any panel with a fundamental in the range of say, 50 to 150 Hz to be "normal" size, and any panel with a fundamental lower than 50 to be "large" and any panel with a fundamental higher than 150 Hz to be "small". These are obviously arbitrary cutoffs, but it demonstrates the idea. By this definition, a panel only 0.1 m2 could be considered "large" if it is thin, low modulus, and high density, while a panel over 1.0 m2 could be "small" if it is very thick, high modulus, and low density.
Probably the best "engineering" way to characterize a panel's "size" would be to scale the panel area by a factor which combines the effects of area, thickness, and elastic modulus, and density, on its fundamental natural frequency. This would be akin to the use of dimensionless parameters like the Mach number or Reynolds number in fluid mechanics.
I'd propose something like this:
Ve = A/{t*(E/ρ)^1/2}
where:
A=panel area
t=thickness
E=Elastic Modulus
ρ=panel density
Eric
Hello Eric,
I think your analysis is correct. What M Zenker shown is under the condition of the characteristics of the panel of his tests and what you explain here goes deeper in the topic.
Currently the communication of Zen or Xcite is it is much too general, too on the surface of the subject from my point of view I already posted this opinion on the SoundImport site some weeks ago when a first Xcite paper was published.
Anyway, congratulation for the invention of the Veleric number. Let's test it!
I think there is another dimension to take into account which is the dipole nature of the open back DML which creates a link between the low frequency cut off and some physical dimensions (combinaition od width, heigth, depth of the frame).
Combining both, we may end with a reduce range of thickness.
This is opinion for now. If the directivity measurements helped a lot to about the coincidence frequency, it is not clear for me about the low frequency cut off. Maybe because it is a question with at least 2 dimensions... The modes in the panel and the acoustics in the air.
Christian