Well, I have played with all sorts of bowls available at home. Some perform better than others. It was particularly interesting to test the sound of a polystyrene bowl, especially from the convex side with an exciter/transducer inside the bowl. I also found that cone-shaped candle cup holders produced interesting music, despite having a thicker base, of course with the exciter on the outside and the candle cup holder facing up. It hadn't occurred to me to dampen the inside of those bowls. I must give that a try.
Here’s an interesting convex "DML" from the 1920s, even though they didn’t recognise it as a DML at the time. Clair Loring Farrand was the inventor of those radio speakers and held more than 250 patents. He was the president of Farrand Industries Inc. in Valhalla, N.Y., and his companies controlled approximately 1,000 patents.
It is also intriguing to transfer vibrations to the panel—whether flat, convex, or concave—using a spike. It seems that the spike can be rigidly connected to the panel.
Yes, it is the "point force driven" plate in Dave's video, the idea behind the Jazzman loudspeaker and the interface or concentrator part proposed some posts ago and more in the past the phonograph.
In all of that, keep in mind the target of a minimal set of requirements : bandwidth (roughly some few hundreds to ten thousand - 100 /300Hz to 10kHz?) over 60° (?, more if the target is an omni), ), FR and directivity even enough to allow EQ, not to bad efficiency nor distortion. Short list with few words but challenging.
Christian
There’s a wealth of fascinating information in those 1920s speakers, particularly regarding the membranes, spikes and so on. You’ll discover something quite intriguing at the end of this video.
While watching a certain YouTube video that appeared in another thread, and subsequently researching one of the topics mentioned in it, a particular idea emerged regarding those DML speakers with a frame around them. There has always been an issue with those "bending waves" or "distributed mode waves" reflecting back from the edges, distorting the soundstage of the DMLs. What if we line the DML's edge with a strip of sound-absorbing material, ideally on both sides of the frame? Duntech Audio has extensively employed this concept in their very expensive speakers.
Hello Lekha
Reflecting waves from the edges is the nature of those speakers. There are 2 mechanism of damping : the material damping, the suspension damping (when there is a suspension). In my opinion it is the next step to try to learn more about them. A certain damping is needed in order to smooth the FR. From Steve, it seems that too many damping is not the goal. The good results he has with the polypropylene with round flutes (which a material with a certain degree of damping = not a ringing one) might be a way to get a target.
About the sound stage, what was reported here by some is the lack of precision of the sound stage with DML. It is for that, that I posted recently the 2 videos from Audioholics about directivity. Those videos propose an interesting link between the appreciation of the sound stage according to the speaker dispersion. A precise sound stage comes from a relative low dispersion speaker while a large sound stage not extremely precise, without sweet spot comes from a wide dispersion speaker. The key point being the amount of room reflections. The nature of DML is to have a wide dispersion, almost +/-90°, the back in addition for an open baffle. The target is to get this dispersion as homogeneous as possible.
People wanting something more precise for the sound stage should look at other designs like horns or wave guides.
It would be interesting to get the same thing from loudspeakers with wide dispersion using for example BMR (-7dB @60°) or a bending wave driver like the Manger (directivity pattern?).
The solution you linked is a counter-measure to edge diffraction. The source of that being the waves in the air which when they come to a strong change of the direction in the geometry create secondary sources. This is the theory. I just had a look to some measurements of a full range and I wonder how this is visible on it and in what measure a DML with its complex vibration of the plate is impacted.
Christian
I messed around with these a while back with the pink insulation stuff and they definitely do something magical, but the distortion and screechiness at 2k was unbearable.
Does anyone have raw measurements on their setups including distortion? I tried a quick search and didnt see anything thats why i ask. And since im already asking.
Whats your current favorite "diaphragm" material and why?
Does anyone have raw measurements on their setups including distortion? I tried a quick search and didnt see anything thats why i ask. And since im already asking.
Whats your current favorite "diaphragm" material and why?
Those who have succeeded in creating loudspeakers and established a reputation in the audio industry ( John Dunlavy, Alan Show etc) have always been concerned about diffractions and reflections from the edges of the enclosure to which the speaker was attached. They recognised the presence of some form of "bending waves" or "distributed mode waves" along the surface, even if they did not explicitly state it. In their work, they refer to these sound movements and vibrations along the surfaces and sought solutions to address them.
Here, we only consider those "bending waves" or "distributed mode waves" along the surface and nothing else. Well, not entirely; some have thought about perimeter suspension and experimented with it. Perhaps that suspension absorbed some of the edge diffractions and reflections. However, I am not entirely convinced, as the standard cone speaker diffuser is also connected to a perimeter suspension, yet vibrations still travel along the baffle surface and reflect back. And every known audio industry business is striving to find solutions to combat that issue.
If a flat panel relies solely on "bending waves" or "distributed mode waves" along the surface to create a full-scale loudspeaker, then we must find a way to eliminate edge diffraction, or at least absorb most of it. Perhaps that is why all those companies with funding for R&D have abandoned the pursuit a long time
ago.
Some suggest that silicone might help to reduce that diffraction, while others believe that leather could be effective as well. Perhaps you could come up with a solution.
Hello,
I have some but as I am not sure of their real mean SPL I propose to make one of my plywood panel on Monday.
I have a pair of 3mm poplar plywood (with a full peripheral foam suspension - weather strip). Even if from my last measurements, I think the coincidence frequency is a bit low (13k, see post 13130), they have been working almost daily for more than 3 years now, with no EQ, without being "tired" of their sound.
For me here (France) it is probably the easiest material to source with good enough sound.
My first panel was a 20mm thick XPS. It is with them I discovered the sound of DML. They had some resonances I can't explained. I changed for plywood. Maybe I should do some additional measurements with them to try to understand how they behave. I don't think it is a material in use among the regular contributors of this thread.
Among the possible source of distortion or resonance there is what was called here the cavity noise due to the air trap in the voice coil area and source of a strong emission in the 2 to 3k to the rear.
A panel without a full suspension may show a higher distortion figure (to be confirmed).
Among the other material here there is the EPS (Expanded Polystyrene). Personally, I haven't get a nice HF extension from it. Steve got also good results from thin light ply.
A possibility might also be acrylic or a plain clear polystyrene (available here in different thickness, fully transparent as a kind of glass or white) in 2 or 3mm thick. The drawback of this one is it is heavy so the efficiency is lower.
Christian
Last edited:
Have you replaced here their wording by yours? What is the exact wording of the sources?
You mean of wave propagation in the air along the surface?
There are 2 waves at play : the one in the plate (or the cone), the one in the air. Diffraction relates to what happens in the air because of a change in the geometry or, to refer to S Linkwintz words, a change of volume. See : Diffraction from baffle edges + Q8 - Diffraction. Would a narrower (<12.5") main panel give sharper stereo imaging, due to reduced delay of edge diffraction?
How to draw a conclusion from solutions against diffraction in the air at edge of cabinet to bending wave absorption at the edge of a plate (2 different things) ?
Hello Christian 👋
The main difference in sound stage between a small 8inches dml compared to a large 7ft dml panel .
Is the scale and soundstage depth.
It seems obvious to me , probably because i have been testing DML's for some time,that if you are sitting 10ft from a 7ft x 2ft panel you will get a huge soundstage with less depth than a 6x9inch .
Let's face it, the panels are cutting off half of my front wall.
In a very large room this would not be a problem.
The 6x9inch will have a point source with huge amounts of depth but will not have the huge scale of the large panels.
You can compensate for this with a higher low frequency crossover and a powerful sub.
But it will not be the same as the 7ft tall panel with sub.
I like both scenarios so that is why I intend to always have both in my system, so I can choose which I want to listen to.
The beauty of dml panels is that I can be anywhere in a room and enjoy the full sound performance without having to clamp my head in one single point in the room.
Relaxed freedom to lie back and enjoy the music.
Instead of sitting in a fixed point position getting neck ache and usually frowning with concentration.
My main concern is , do the instruments and soundstage sound realistic.
I find dmls far superior to ordinary speakers in this respect, that is why I can never go back.
When I go to audio shows with my friends, we always end up shuffling around on different chairs trying to find the central point.
Sitting on the seats either side of these centre seats always loses one channel.
It is very annoying.
It's like playing musical chairs 😃
Must go.
Steve.
This thread has a number of posts, including measurements, on the impact of different kinds of damping materials (in the context of constrained-edge DMLs). So that aspect has been rather thoroughly explored.
Based on that information I currently am putting together some DMLs using butyl rubber tape to attach the panels to the frames. It will be interesting to hear them. I have a couple of Dayton 40W exciters and two of the "coin" style exciters on hand if I decide I need some additional "oomph" in the higher frequencies. My 73YO ears may not need them though.....
I will drive the exciters with an SAE MK3-CM I recently refurbished (new electrolytic capacitors). At 200W/ch it will have no problems running those 40W exciters.
Based on that information I currently am putting together some DMLs using butyl rubber tape to attach the panels to the frames. It will be interesting to hear them. I have a couple of Dayton 40W exciters and two of the "coin" style exciters on hand if I decide I need some additional "oomph" in the higher frequencies. My 73YO ears may not need them though.....
I will drive the exciters with an SAE MK3-CM I recently refurbished (new electrolytic capacitors). At 200W/ch it will have no problems running those 40W exciters.
Along and on the surface. They wouldn't promote DMLs, would they?
On the baffle, if you will. The concern is always about what occurs on the baffle surface, referring to the material the baffle is made from, rather than what happens in the air along the baffle—those sound waves won't return. If anything, they would bend around the edge and dissipate. There seem to be hundreds of patents attempting to address that problem. None of them, however, would refer to bending waves or distributed mode waves.
Those audio engineers and other manufacturers have been placing sound-absorbing material around the speakers on the baffle (such as Duntech and Harbeth). Some have separated the baffle board from the enclosure using sound-absorbing material (like Harbeth), while others have positioned the speakers in different planes (as seen with Japanese and Korean manufacturers, etc.). Some even place one box inside another with a gap between them. For example, Pioneer separated the speakers from the baffle using dual rubber gaskets in two different locations. In any case, I hope someone here will succeed in creating an A4-sized DML without that diffraction.
Nothing special though. Anyone can slap an exciter unto a plank and consider it a speaker. But these panels (looks like solid pine planks) probably sound better than the small speakers in the background. So, an upgrade for this guy.
Indeed, people often overlook what is evident. That’s what makes it special. Yes, he did attach a simple exciter available in the US to a 1-inch thick pine plank, but have you noticed any "bending waves" or "distributed mode waves" on its surface? What isn’t immediately apparent is that there aren’t vibrations as such to "move the air" on the front face of that plank.
He is merely a painting contractor in his town, not an engineer. He experimented with another "engineer's" idea from Tech Ingredients, without much scientific thought, just for fun. However, it turned out that the thick pine plank emitted music, and it was quite pleasant to the ear.
One way or another, his experiment effectively debunked the established understanding of "moving the air" to create the sound we hear. It also challenged the theories of "bending waves" or "distributed mode waves" on a panel surface. Just imagine such a small exciter bending the surface of a 1-inch thick pine panel!
That’s what makes this so special.
Sound is simply energy that transfers from one material to another, which our ears can detect. In this case, it passed from the coil former or its cover to the pine plank, then through it and into the air, from one source to another, where it can be heard by our ears, and interpreted by our brains individually.
Imagine someone walking down the corridor, and we can hear their footsteps inside our rooms, without the walls or floors vibrating. Or a child crying somewhere on the floor above, without the ceiling or walls vibrating.
Last edited:
Excuse the delay:
They are PMMA (just because of transparency) with 4mm, but with impresive results with the less expensive plastics.
General information article:
https://phys.org/news/2017-02-sound-shaping-metamaterial.html
About directivity, i,e, sound control (thanks @lekha for introducing the Dunlavy excellency) with metamaterials:
https://www.hosiden.com/dcms_media/...ndWaveDeflectionMetamaterialTechnology_EN.pdf
https://www.techbriefs.com/componen...transmission-and-reflection-of-acoustic-waves
Hard talK:
https://nanoconvergencejournal.springeropen.com/articles/10.1186/s40580-017-0097-y
Wish you all a reverberant new year
“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
― Nikola Tesla
Hi Freedom666.is a thin wall undamped box giving a DML like sound?
See:
fun loudspeaker in 18 liter water bottle
with heavy eq
diy double cone after removing dustcap
works astonishingly well. like other thin wall speakers
I found your threads on applying Ali foil to drive units.
Very interesting, I have not read them all yet.
I did coat an eps panel with Ali foil, but did not like it.
But I think that on some materials this would be a good way to go.
Thin ply for instance , card, veneer, and others.
Reducing the panels self noise , hopefully without changing the panels good performance would be worthwhile.
Using heavier foils could also be used to control a bad harsh sounding panel.
I tested this many years ago, maybe in the future I will look into this again, using some of my newer panel materials that I think might benefit from less self noise coloration.
Steve.