You can take a look at an older variant of studio monitors that were created from distributed mode idea, understood in a different way. Those who reviewed them are not the type who are particularly fond of flat panel speakers, yet the review remains intriguing. Take note of the position of the magnets, at least one of the two that is meant to be present. Also, observe the spring (cut-out) surrounding the exciter/magnet system on the back panel.
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Now that you've had a look at that review of a standalone DML , you should revisit that jolly Brit's video with a bit more attention—you might discover an analogy between the two. It would be intriguing to consider why the main "exciter" has a large magnet, while the smaller one is tucked away.
In any case, the issue with such DMLs, or any other DMLs, is that the "rear wave" is not utilised. That "rear wave" impacts everything located at the back of such a DML and distorts the sound image. One might consider using JoskaNZ's idea or the late Stig Carlsson's to block or absorb it, or...
In any case, the issue with such DMLs, or any other DMLs, is that the "rear wave" is not utilised. That "rear wave" impacts everything located at the back of such a DML and distorts the sound image. One might consider using JoskaNZ's idea or the late Stig Carlsson's to block or absorb it, or...
Hello Lekha
This is not the main reason to have an interest about the role of the back wave of DML. Open baffles loudspeaker which have also a strong rear wave are appreciated by many DIYers. In one of his paper, M Linkwitz who is a reference in audio explained that among the dipole, cardiod and monopole type of directivity, the dipole and the cardioid are the most suitable to reduce the sensibility to the room. For a dipole some distance to the back is needed... but it is not the only condition. Think about it.
Christian
I am aware of what Mr. Linkvitz wrote during his lifetime, and he wasn't discussing DMLs. There are a few more reviews on those commercial DMLs available today, much more thorough. All DMLs must be positioned away from the back wall and any objects behind them. Furthermore, if such DMLs are used in ceilings, no ghost in the ceiling would complain about the "rear wave." Additionally, patrons in bars where some DMLs are suspended won't even notice it.
However, that was not what I was primarily referring to. It was the first paragraph of the post. Naturally, people won't notice that when something else is there easy to digest. So, here it is:
With an open mind, one might perceive the analogy.
Interesting article. The concept of spinning sound waves and orbital angular momentum has been around for some time, even though it wasn't precisely referred to in that way. As illustrated in that article, directing the sound waves through a turbine would impart a certain value. If one were to use a conventional speaker, it might be possible to harness the back wave by directing it through a turbine via a bass-reflex tube, and even towards the front, enhancing the bass. A well-known speaker manufacturer has even attempted to utilise the turbine effect in their speakers.
As shown in that article, by having a certain type of uneven flat surface, one might be able to create transverse sounds in the air.
Everyone understands company secrets in the West, don't we? Anyway, for the appetite...
A nice spider...?
I know, it’s difficult to comprehend. Have another look at the review, perhaps using a translator, and then watch the video. Maybe the image above will be of assistance...? Perhaps the spider might be of assistance to you?
This image was already shared here with the review it is from. The cut in the rear panel might create a low stiffness area to limit the transfer of vibrations to this surface and limit some not desired sounds. Other explanation? What is your point withe the video?
As always, that is the question for lekha, which he doesn't like to answer. You have to guess. Will he give you a gold star if you do? I don't know, I'm not sure that anyone ever has guessed right.
I recall those "cuts" in the support frame were discussed before, but I don't recall the details, and if they were described in a patent or not, or if someone had an explanation of what they were intended to accomplish. Does anyone recall? To me, they would seem to be a way to create some compliance in the mounting, so that if the front to back alignment of the exciter and panel are less than perfect, then the voicecoil is not accidentally pushed too far from it's ideal location in the magnetic field. But I have no idea if that is what the designer intended.
Eric
Here is another Russian patent, presumably from the the group of Herger/Sotis, as the figures, etc all look the same.
https://patents.google.com/patent/R...ОГРАНИЧЕННОЙ+ОТВЕТСТВЕННОСТЬЮ+"СИНЕМОРЕ"+(RU)
Generally, it describes a pretty common DML, but one interesting feature though is the use of a foam rubber attached directly to the back of the panel. I don't recall that from other patents. It would be nice if there were more specifics about that foam rubber. It would be interesting to try. As I have mentioned before, I think damping is generally a good thing. But how much would the added weight of the foam rubber reduce the efficiency, I wonder.
Quotes from the patent:
The proposed recessed flat loudspeaker does not have a back cover. Instead, foam rubber cushioning is provided on the back of the membrane.
2. The built-in flat loudspeaker according to claim 1 of the formula, characterized in that the damping layer, which covers the reverse side of the membrane, is made of foam rubber
Oddly, the Google patent version linked indicates that there are 7 claims in the patent, but list only two.
Eric
https://patents.google.com/patent/R...ОГРАНИЧЕННОЙ+ОТВЕТСТВЕННОСТЬЮ+"СИНЕМОРЕ"+(RU)
Generally, it describes a pretty common DML, but one interesting feature though is the use of a foam rubber attached directly to the back of the panel. I don't recall that from other patents. It would be nice if there were more specifics about that foam rubber. It would be interesting to try. As I have mentioned before, I think damping is generally a good thing. But how much would the added weight of the foam rubber reduce the efficiency, I wonder.
Quotes from the patent:
The proposed recessed flat loudspeaker does not have a back cover. Instead, foam rubber cushioning is provided on the back of the membrane.
2. The built-in flat loudspeaker according to claim 1 of the formula, characterized in that the damping layer, which covers the reverse side of the membrane, is made of foam rubber
Oddly, the Google patent version linked indicates that there are 7 claims in the patent, but list only two.
Eric
Hello Eric,
The back plate is said to be from MDF in the review. even if it is another material, the spring created might be much stiffer than the exciter spider so not helping for misalignment. The other hypothesis I made in the post above is to avoid the vibrations to go the back plate. Other hypothesis : don't you have in your tests more bass extension with no spine?
Christian
No, it's identical, with or without the spine supporting the exciter, in every test (many!) that I have made. Of course, it could be different if the design is somehow of a different cless/type than what I normally design. That is, where the fundamental of the panel is somewhat higher than the magent resonance of the exciter. For example, most of the typical exciters have a magnet resonance, of around 20-40 Hz, and my panels (as mounted) have a fundamental of 70 to 100 Hz, typically. In that type of case, there is no effect of the spine on the bass response. The spine only acts to support the magnet and avoid distorting the alignment of the voice coil and stressing the attachment of the exciter to the panel.
I understood it to be that the perimeter frame is MDF, rather than the back plate. the back plate looks to be plastic, but who knows how thick? But you could be correct in any event about it's stiffness. I'm just guessing about the point of the cuts.
Eric
The "cuts" are not important. They are merely for appearance... and for misdirection. It appears to have achieved what was intended.
Really? Up to the risk to create a potential mechanically weak zone just at the exciter... without speaking of machining cost (maybe marginal depanding of the process). Still waiting for your answer.
Here's another Herger patent, US this time.
https://patentimages.storage.googleapis.com/f2/ca/50/b0acdb771157e4/US11849295.pdf
No foam on the back this time, though. But this patent gives a description of the preferred aspect ratio of that panel as 9/5. And further indicates that the aspect ratio of 9/5 applies only for the case where the stiffness is identical in both directions. Indeed it makes sense that the aspect ratio should change when the panel stiffness in the two directions differs.
Also, there is this description of how to adjust the aspect ratio when the panel is anisotropic:
It seems at first glance to be simple and reasonable, but after trying to apply the rule, it's hard to understand exactly what they really meant. It's possible that the confusion arises from the translation, I don't know.
Can someone help me figure out what they mean exactly? Let's take a specific example. Consider that the stiffness in the long direction is 10 MPa in one direction, and 20 MPa in the other, then what is "k"? Is it 200? or 100? or 2.0 or 1.0 or other?
The thing that makes the most logical sense to me would be that k=2.0, and then that the adjusted aspect ratio would be 18/5 instead of 9/5. Do you think that is right?
Eric
https://patentimages.storage.googleapis.com/f2/ca/50/b0acdb771157e4/US11849295.pdf
No foam on the back this time, though. But this patent gives a description of the preferred aspect ratio of that panel as 9/5. And further indicates that the aspect ratio of 9/5 applies only for the case where the stiffness is identical in both directions. Indeed it makes sense that the aspect ratio should change when the panel stiffness in the two directions differs.
Also, there is this description of how to adjust the aspect ratio when the panel is anisotropic:
It seems at first glance to be simple and reasonable, but after trying to apply the rule, it's hard to understand exactly what they really meant. It's possible that the confusion arises from the translation, I don't know.
Can someone help me figure out what they mean exactly? Let's take a specific example. Consider that the stiffness in the long direction is 10 MPa in one direction, and 20 MPa in the other, then what is "k"? Is it 200? or 100? or 2.0 or 1.0 or other?
The thing that makes the most logical sense to me would be that k=2.0, and then that the adjusted aspect ratio would be 18/5 instead of 9/5. Do you think that is right?
Eric
Wow, they win. I wasted years trying to copy those cuts exactly! Thank you lekha for sparing me from wasting even more time on that.
Eric