Hello Lekha,
From your post it is not clear to understand which frequency band you propose to redirect? The type of enclosure you show on the picture is well known. One part missing on the picture is the stuffing material which is mandatory on such a design. The principle being to load the speaker with pipe around its resonance frequency but not to allow frequencies above to go into the pipe which creates and uneven response.
Another point I don't understand is "the better sound from the rear". Which evidence of that? The exciter, less than a standard loudspeaker makes a mask to the highest frequency (roughly 10k and above for a DML). There is also in the case of a DML open on both side a strong emission in the 2k range to the rear. Maybe the mask help to hide the effect of a too low coincidence frequency?
Christian
Hello Christian.
I'm sorry to say that we have been down this road before.
Words strung together without any coherence.
Last time I put him on ignore, and I would advise everyone to do the same.
You will just be going around in circles, and getting nowhere.
Steve.
I'm sorry to say that we have been down this road before.
Words strung together without any coherence.
Last time I put him on ignore, and I would advise everyone to do the same.
You will just be going around in circles, and getting nowhere.
Steve.
If you are referring to the Polish-made transmission line speakers, they will not provide you with information on where the damping would be. They are called OGY, and you can take a look at them here.
Regarding DML, I shall wait until someone shows another practical speaker like the one by JoskaNZ, which effectively blocked the "rear wave." That speaker is something that others could replicate. I hope he will share its dimensions.
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I tried some sound absorbing ceiling panels, but not fiberglass like yours. The panels were certainly less open than your fiberglass, so the effect may be different. I do hate handling fiberglass, but maybe I could try some polyester batting.
Eric
Lekha,
This thread is mainly experimental where you have to find your own way. We try to find design rules and the best practices but the field of choices remains wide. The difference of material locally available adds to the difficulty.
Christian
Image from a patent found in this lengthy discussion.
The voice coil (in its original state) is fixed to the flat panel at the front, while the magnet system, spider, and so forth are secured to the back panel/support. The entire DML is enclosed within a frame. The front panel is secured to a type of suspension #7. It resembles a standard speaker, but instead of a cone, we have a flat panel. Therefore, we can say that the panel exhibits bending waves, or distributed mode; whereas, if it were a cone, it would be referred to as pistonic motion.
I looked hard to find any part where he did anything to block the voice coil. I didn't see it. So I have to assume you meant that placing it on the table, or glass plate, or ceiling tile was "blocking" it. Is that what you meant? But neither the suspension spring nor any of the things he contacts with it are really stiff enough to "block" the coil former. It can still move, even if only slightly. If it didn't move, there would be no sound, no matter how much current was in the coil.
Eric
Well, the aforementioned patent (along with a few others) is available in this lengthy forum. Interestingly, they originate from a member of this forum, even though that member did not bring it to the attention of this discussion. When they were introduced into the conversation, it appears that most of the members opposed the ideas presented, claiming that they are contrary to science. However, these speakers that incorporate the concepts outlined in those patents are the only DMLs commercially available in the world today. They are showcased at high-end exhibitions in Europe and receive top accolades. The biggest issue for the average customer is the exorbitant price tag, which is difficult to justify given the value of the materials used in their construction and our market environment, where selling more items would generate greater revenue, rather than selling a single item at a high price. They are, of course, designed in such a way that dismantling them would simply destroy the speaker.
In any case, clones are relatively easy to replicate in a DIY project, even if one lacks extensive carpentry skills. You may not achieve the exact same membrane, but you can come quite close. There’s no need to suspend them from strings to the soffit; you can place them on stands, even on a bookshelf, or fix them to a wall with certain measures to block the "rear wave." Most importantly, they are not large; some could even be smaller than A4 size. As I mentioned earlier, this discussion is a goldmine, if only one could discover where to dig.
Hello Lekha,
I don't remember this patent. Could you give a link to it please and remind me which commercial DML you point here?
The drawing seems showing a "simple" close box.
Christian
This figure could be used in other patents too, but in the one I found and linked, there is no mention of a closed box. The back panel may simply be an exciter support. It is not even mentioned in the body of the patent, except possibly as being part of a "support frame". The claims describe a pretty typical DML:
honeycomb panel, 5/9 aspect ratio, exciter, frame, damping foam around the perimeter. A pretty basic DML as far as I'm concerned.
The body of the patent does make reference to "transverse acoustic waves in the air" (see italic quote below), which is probably the "contrary to science" aspect that lehka was referring to. It is accepted science as far as I know that acoustic waves in the air are only longitudinal waves, never transverse. Of course that doesn't mean their speaker doesn't work, but it may not work for the reasons they think it works. Or possibly the translation is not a 100% accurate representation of the meaning in Russian.
The resonant mode of the formation of amplitude modulations is characterized by the fact that they arise exclusively in the form of opposite pairs with the property of phase incoherence, which in turn creates the conditions necessary for the formation and maintenance of a transverse acoustic wave in the air by such a loudspeaker. Such a wave has a number of specific features and advantages. This improves the acoustic qualities of the product: http://selftrans.narod.ru/v2 1 / acoustics / acoustics03 / acoustics3ras.htmL
Thank you Eric
There is no information that says it is a closed box. This patent is focusing on a sub-woofer, describing what is more or less a standard DML panel with no reference to the rear load but propose a compact speaker. Strange. It seems also saying to operate above the coincidence frequency.
Interesting to see it is possible to get such a patent in 2020
They say in my country, najciemniej jest zawsze pod latarnią; the information on how to create practical, working DML was right here, without all that "hang the panel with strings" misunderstanding. One could even utilise the knowledge from those patents to create commercial-quality DMLs, rather than ridiculing them.
If everyone had adhered to the "accepted" science of the time, scientific progress would have been stifled. Every product first emerges in a person's mind, followed by the "science" that explains it, if such an explanation is necessary. When Edward Villchur invented the "Acoustic Suspension Loudspeaker" in the 1950s, every company in the speaker manufacturing industry vehemently rejected the idea. Today, however, every speaker manufacturer employs that technology. A few years later, when his patent was challenged by a competitor, he chose not to engage in a legal battle but instead focused on creating more innovative products. And he lived to the ripe old age of 94.
Interestingly, Edward Villchur held both a bachelor's and a master's degree in art history, not in science!
But the patent from which the drawing comes is not an innovative new design. It's bacially the same thing described by NXT and others before them. They pretty much described a Tectonics DML.
What is the innovation you see, that was not practiced previously by many others? Honestly, please tell me.
I happen to agree that using a suspension with damping offers benefits. But that's not a great new innovation. Virtually every commercial DML has used it.
Eric
Christian,
What is it that you think implies that? Is it this:
The resonant mode of the formation of amplitude modulations is characterized by the fact that they arise exclusively in the form of opposite pairs with the property of phase incoherence, which in turn creates the conditions necessary for the formation and maintenance of a transverse acoustic wave in the air by such a loudspeaker.
Are you thinking that when they talk about a "transverse acoustic wave in the air", they are referring to "off-axis" peaks, like above coincidence?
I don't think they are, otherwise they would be writing about the wave speed, rather than "opposite pairs of phase incoherence". But are they simply talking about normal modal behavior with portions of the panel moving in opposite directions (anti-phase) at the same time? I don't know....
Eric
PS I saw that @Alvipet was visiting the thread in the last hour. Maybe he knows and will share.
homeswinghome : It seems also saying to operate above the coincidence frequency.
"If the correct parameters of the membrane geometry are applied, the small amplitude of motion of the moving coil of the acoustic exciter develops into a much larger amplitude in the modulation zone of the corresponding frequency due to the resonant superposition of the primary surface-traveling wave, which has a propagation velocity in the membrane that significantly exceeds the speed of sound in air and the secondary (reflected from the edges of the membrane) of a surface-traveling wave. Thus, the resonant mode of operation provides a high degree of efficiency for such a loudspeaker."
It is just before what you extracted :
"If the correct parameters of the membrane geometry are applied, the small amplitude of motion of the moving coil of the acoustic exciter develops into a much larger amplitude in the modulation zone of the corresponding frequency due to the resonant superposition of the primary surface-traveling wave, which has a propagation velocity in the membrane that significantly exceeds the speed of sound in air and the secondary (reflected from the edges of the membrane) of a surface-traveling wave. Thus, the resonant mode of operation provides a high degree of efficiency for such a loudspeaker."
Ah, yes. Thanks.
Wow, that sounds like some monster panel. Heron's patent proposed an aluminum honeycomb panel 40 mm thick (!) just to lower Fc to 246 Hz. I can barely imagine a panel stiff enough to operate above coincidence at subwoofer frequencies.
Eric
https://patents.google.com/patent/EP0541646B1/en?q=(defence)&inventor=heron&oq=heron+defence+
- Design considerations are illustrated by way of example below with reference to one version of the loudspeaker which utilises a radiator panel comprising a 1m x 1m square of aluminium skinned, aluminium honeycomb cored composite. The core depth for the panel is 0.04m and the thickness of each skin is 0.0003m. For this panel B is 18850Nm, µ is 3.38kg/m², and T is 488Nm⁷/kg².
- [0020]
From the f₁ equation, f₁ is [ 18850/3.38 x 1]½, = 75 Hz. - [0021]
From the fc equation, fc is [3.38 x 340⁴ /4 x 3.1416² x 18850]½ = 246 Hz