Most car speaker manufacturers do that these days, leaving the coil former cavity open, and tweeter above it.
You might still consider this a viable option and find a solution for the internal section of the coil former. @spedge 's ideas and the last two patents might be helpful. The conventional speaker drivers are significantly more powerful.
Thanks for checking!
As I suspected sensitivity is too low for PA applications, but of course for normal use that is fine and similar to a low efficiency hi-fi speaker...although on-axis response measurements are a bit unfair to DML.
One can find the strangest ideas in patents. This German one is currently active.
It's about using an exciter on the front side of a very shallow cone speaker, effectively blocking the internal side of the coil former area.
It's about using an exciter on the front side of a very shallow cone speaker, effectively blocking the internal side of the coil former area.
You have me confused. Are you saying that there is a "vibration" of the coil and/or coil former that is something other than pistonic? Can you draw a sketch or otherwise help me understand what these other vibrations look like?
It is normally understood that the pistonic vibration of the coil former creates transverse waves (i.e vibrations) that travel across the panel. But it isn't necessary for the coil former to have any other type of vibration other than pistonic for that to happen. Or do you believe otherwise?
Why do you need to create your own exciter to incorportate a damper? What prevents anyone from putting a circular damping pad on a panel, and installing a typical exciter right overtop it?
Eric
I very much like eps, but I have yet to have a more emotionally engaging experience than I get from my large and quite heavy (over 10 lbs each if memory serves) aluminum skinned aluminum honeycomb panels.
I think my experience points to DML technology application having variables which significantly affect sound|experience, the neither we on this forum nor industry nor academia have fully identified.
To me this makes the collective endeavor of this forum very interesting.
All said, I'd love to have the opportunity to set up your eps speakers and mine up for a comparison in the same room (or across several rooms for that matter).
Field trip?
Lots of activity, but not certain I'd call it progress.
I did rig a kind of test frame on my subwoofers to try different center channel speakers.
In the photo, you can make out the bottom edge on one of my aluminum panels.
These pseudo DMLs from Parts Express work OK, but don't inspire.
Next, I want to try another version of Steve's card panels.
Remember, I use a pair of center channel speakers.
I'll provide an update as I make actual progress.
Attachments
The wire connected to the amplifier in a magnetic field vibrates. If you wind it into a coil, it doesn't mean that the coil would only move up and down in the magnetic field; it can jump in any direction. In a speaker driver, all movement is restricted to the so-called pistonic motion. If you leave the coil free in a magnetic field when connected to an amplifier, it would move in any direction.
The coil former vibrates within that space and often strikes the walls of that area. A considerable amount of work has been undertaken by driver manufacturers to prevent this, but they have not yet been fully successful.
If that exciter permits it, you can consider that option. You can also cut a hole in the panel in that area. This inventor had understood this quite sometime ago. They actually make a good profit from the flat panel speakers. That company has been in business since 1999, and this is their line of work. A patent usually contains just enough information to secure acceptance, and it often covers various aspects to hinder competitors. This inventor provides a bit more detail as they do not really have any competitors.
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Well, I suppose the wire/coil former could move in any direction, if there was no spider. But the direction of the force on the coil former caused by the interaction of the current and the magnetic filed is determined by the cross product of the current and the magnetic field, which is only up, or down (in the figure). Is that right. or not?
And are the up and down vibrations the ones that result in the problems in the panel within the voice coil area? Or is/are there other vibrations in some other direction that are responsible for that?
Eric
lekha,
Indeed the patent literature is rich with solutions to the "problems" in the coil former area. But curiously there is little agreement on what that problem actually is. Mikalauskas thinks the problem is a dip in the high frequencies, solved by adding a "damping device" that looks more like a stiffening device. Harris thinks the problem is the opposite (too much high frequency) but proposes possibly a similar solution (also a damper, but in this case rubber). Goebel isn't clear about if it's peaks or dips he's fixing, but thinks the important feature of his puck (rubber again) is its mass, rather than its damping properties. Bank on the other hand isn't worried about the peak, but just wants to push it higher. And so on....
All,
There is no doubt (for me) that for typical panels the bulk of the HF comes from the region near the exciter. But it's never been obvious to me that any of my panels suffer from "problems" in that area. For those that have, under what conditions do they appear (panel type, exciter type, etc). And under what type of measurement would I observe them? Christian's recent work on directivity has been great at helping me to see the effects of the coincidence frequency on panel's performance. I love learning new ways to characterize and then improve my panels. How do I see recognize such coil area problems?
What about the technical literature? Do any journal articles ever mention such issues?
Eric
Egidijus Mikalauskas has been the Research and Development Chief Engineer at Amina Technologies Ltd for the past 14 years or so. The managing director, Richard Newlove, no longer writes patents; it is now Mikalauskas who handles that. Amina has been in operation for the last 25 years, consistently engaged in the business of creating "DMLs" the hard way, specialising in invisible speakers, and they have been quite successful in this endeavour. Göbel is no longer active in that sector, and Neil Harris is not doing much in this area anymore. Whom should we listen to?
When searching for answers in patents, one must also consider those that have been abandoned. Most were abandoned because the inventor did not pay the fees or could not find an investor. However, the ideas are still present, some really worthwhile.
Neil Harris was the obvious assumption, but it was the patent by Ken Harris, cited by Miskalauskus, that I was referring to:
https://patents.google.com/patent/WO2006078247A1
But I'm still wondering about your explanation about which wire/former vibrations it is that cause the problems in the panel vibrations within the voice coil area. Or the measurements I could do to find the problems in that area.
Eric
The simplest experiments I could find on YouTube involving direct current in a hurry
Merry Christmas!
Subtitles are available
And, Richard Newlove speaking at CEDIA 5 years ago.
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And, last year at CEDIA
And some (if not most) of our conventional thinking on DMLs seems to be dissolving...
And some (if not most) of our conventional thinking on DMLs seems to be dissolving...
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Amina does not conceal anything, except for the exciter, which is their product. You could likely dismantle it, but doing so might damage the speaker. In any case, Amina speakers seem to challenge our conventional thinking on DMLs, as the same Amina speaker can accommodate additional surfaces that are completely different from one another, such as skim coat, wood panels, engineered wood panels, and even leather... all with just an $89 Amazon amplifier! Additionally, there is that thin tall subwoofer with only one opening for "bass reflex" (there has been some discussion regarding a very old patent on flat panel subwoofer boxes somewhere in this thread, though I can't recall where), along with those integrated "I" speakers. I've also seen an internal view of one of their older speakers with integrated low frequencies somewhere in this thread, which was promptly dismissed. I didn't make a note of that; perhaps someone else did?
It's interesting how they position their exciters right along the middle vertical line, symmetrically on both sides of that line. Zenker talks a lot but doesn't have a DML to demonstrate. The Russians have something to showcase and sell, but they have their own theory. I believe there is another company in Germany that produces invisible flat panel speakers, but I can't recall the name.
It's interesting how they position their exciters right along the middle vertical line, symmetrically on both sides of that line. Zenker talks a lot but doesn't have a DML to demonstrate. The Russians have something to showcase and sell, but they have their own theory. I believe there is another company in Germany that produces invisible flat panel speakers, but I can't recall the name.
I tried a few things that people are proposing, because I have a peak at about 3kHz that I want to get rid of. I tried to damp the center point, put little weight on it, make a hole but it only seems to lessen the mid/high freq output, and leaving the peak intact (although on a different freq?).
I tried this stiffening (made a 3d printed cone like the amina solution). Doesn't seem to have benefits for my panel. Only the high freq seems to be dampened....
I think the disk should provide more high freq output (like the Spedge beer can solution that works really well!), and the damper is used to tame the effect down a bit? The center of the panel is working pistonic and the rest dml?
I try "solutions" I see on the internet because I think the inventors/manufacturers must have their reason to make/use/patent them. But they don't seem to help in my setup. Maybe the effect is too subtle?
On the other hand, copying things like using a foam tape around the edge of the panel made a big difference.
I did notice them too, but suspect it to be something to bind the front and back layer of the honeycomb to the exciter foot. The picture of the inside of the Tefra speakers with the voice coil covered with tape made me curious though. They don't conceal using standard Chinese exciters, and a simple first order high pass for the "tweeter".
And Amina says in a video that this is a aluminium honeycomb, but it looks a lot like nidaplast.....(?) Edit : in the prototype they show it looks metalic, so probably aluminium.
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The Russians certainly manufacture their own exciters; they have the capability to do so. They seem to have over 25 years of experience in the DML field as well. Both Amina in the UK and DPK in Russia are commercial entities, so they are unlikely to disclose their "highly" secret information. @spedge can visit Amina, as it is located in the UK, and try to gather more information.
What is particularly intriguing is that the Amina panel can accommodate another panel or surface on top of it, glued to it, and still produce "immersive" sound. Skim coat, leather, wood panel, or even some metal surface are all completely different materials, yet they are using more or less the same flat panel. Or, they may know how to tune them for the specific surface, which is equally intriguing.
Amina most likely has their honeycomb panels manufactured to their own specifications. Or, they may manufacture the panels themselves.