I seriously suspect this is one of the previous elements who was invited to walk through Vetinari's door like Reacher Gilt did...
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Apologies for repeating this if it's been answered before: to do with the dipole effect of a DML panel....
I SUSPECT that a DML is neither dipole nor bipolar for certain frequencies.
I suspect that, below (1,2) the panel would present a dipolar pattern. And I also suspect that, above Fc, it would be... different.
Please elucidate!
I suspect, between F0 and Fc it's neither dipolar nor bipolar because of the randomness of the DML action.
Anybody care to comment?
I SUSPECT that a DML is neither dipole nor bipolar for certain frequencies.
I suspect that, below (1,2) the panel would present a dipolar pattern. And I also suspect that, above Fc, it would be... different.
Please elucidate!
I suspect, between F0 and Fc it's neither dipolar nor bipolar because of the randomness of the DML action.
Anybody care to comment?
Okay, so that's really your answer? No speakers at all work by pushing air, is that correct?
Eric
Andre,
We have been lead to believe that by NXT and Tectonics, but I really wonder how much, if any, truth there is to it.
Eric
So many similarities from chdsl's post
2020
If you knock on a steel door, you hear sound, but with no movement of air.
Vibration makes sound, not pistonic motion. The coil makes the sound. It vibrates.
2022
In a given second (or millisecond) how many sounds you hear listening to music coming from a speaker? 10s, 100s or 1000s? When a piston moves, there's only one motion at a given time in one direction. There won't be 10, 20 different movements in the same direction.
Sound is an energy. + When you are in one room, someone in another room two rooms away from your room, knocks on the horizontal table, and you hear it. Two parallel walls between you and that table. There's radio on that room, and you are sitting in the first room. You still hear the radio, behind two walls. How does that come to your ears? The door in your room is closed.
etc
Different threads, different dates and same exchanges as here those weeks.
2020
If you knock on a steel door, you hear sound, but with no movement of air.
Vibration makes sound, not pistonic motion. The coil makes the sound. It vibrates.
2022
In a given second (or millisecond) how many sounds you hear listening to music coming from a speaker? 10s, 100s or 1000s? When a piston moves, there's only one motion at a given time in one direction. There won't be 10, 20 different movements in the same direction.
Sound is an energy. + When you are in one room, someone in another room two rooms away from your room, knocks on the horizontal table, and you hear it. Two parallel walls between you and that table. There's radio on that room, and you are sitting in the first room. You still hear the radio, behind two walls. How does that come to your ears? The door in your room is closed.
etc
Different threads, different dates and same exchanges as here those weeks.
Still surprised over your conclusion since I have not found the need for 12dB cut or boost to get a smooth response. Above 16kHz can be missing, but that I don't care so much about. That is something that could possibly be fixed with dedicated treble plates though. While I do like a somewhat downwards tilted response on a PA myself, I never had any complaints that the system lacks treble though, and like I said I had a lot of comments 🙂
I'm very curious about opinions on materials with high sensitivity from a few kHz and upwards. I have not been assessing materials from that perspective before, and simply discarded materials that don't give a full response.
I think many of the materials that are hard and have a strong HF response tend to also have some problems with ringing, at least that was my experience with polycarbonate, and I think I seen similar reports about metal and glass. And are metal, glass or hard plastics actually sensitive in the top, or just trebly because they lack mid? I suspect it is better to look at for example wood or some kind of composite?
Efficiency is not as important for the HF since it doesn't become as difficult to pack enough power in limited space. I think I can use quite small plates for HF only, so could probably have a frame with 2 HF plates, say 150x120mm, above a single plate of 300x340 for the mid-low. That would give 60w for top with 2xXT25, against one160w XTB40. That is decent ratio of power for the top to mid, and while depending where the x-over is placed, it should at least give a few dB extra margin without increasing the size of the speaker much.
Sound takes place when bodies strike the air, . . . by its being moved in a corresponding manner; the air being contracted and expanded and overtaken, and again struck by the impulses of the breath and the strings, for when air falls upon and strikes the air which is next to it, the air is carried forward with an impetus, and that which is contiguous to the first is carried onward; so that the same voice spreads every way as far as the motion of the air takes place.
—Aristotle (384–322 BCE), Treatise on Sound and Hearing
+ @Andre Bellwood
Directivity measurements give for me clearly the answer : a DML behaves as a dipole. The impulse response from the rear is in opposition to the front. There is only around the 90° where there are some more or less symmetric impulses.
In addition, the directivity plots or may be in a better way the polar plots at discrete frequencies show the lobes expected from the model of a dipole.
In my understanding, the model of randomly located sources over the surface is an image proposed as a parallel to the classical piston model. When we see in Dave's video the velocity maps when the frequency becomes a bit high with an exciter off center, the "random sources" is an easy shortcut; difficult to see then the work of the modes.
As it was also a question for me, I went down some acoustics books or publications to find standard models of sources. The 2 basic ones are the monopole (point source, omnidirectional source) and the dipole which can be modeled by 2 monopoles in phase opposition separated by a certain distance (model of a point source at the center of a disc). No mention of a bipole in those publications... Neither if I remember in the paper that introduces the random source model, I think the wording was "diffuse dipole". By the way, I am still searching evidences of the diffuse character of DML. The directivity measurements show an almost constant shape of the impulse. The spectrogram don't show delays change according to the frequency... Maybe I should have a deeper look on that.
The most synthetic paper I found about monopole, dipole and cardioid : The beneficial coupling of cardioid low frequency sources to the acoustic of small rooms
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Christian,
Your link took me to the author, but not the particular paper. This may be more direct:
The_beneficial_coupling_of_cardioid_low_frequency_sources_to_the_acoustic_of_small_rooms
Eric
Christian,
What would you say are the implications of that, for us as builders of DMLs?
Is it that we should be putting them in enclosures, or especially a "semi-open back" enclosure to turn them from dipole to cardioid?
Rummaging through my collection of papers, I found this Azima paper, maybe you have seen it before:
Ditributed Mode Loudspeakers in Small Enclosures
Eric
Hello Eric,
Those questions are central in my current thinking for a next design.
It is what I had in mind in the post #13008
From the directivity tests, I think the open back DML falls in the category of the dipoles like the "classical" open baffle.
Technically there are probably possibilities to design some closed box or maybe cardioid even if we don't have many examples (or I don't remember about them).
@Eucyblues99 : is it you who tested a back plate with a central hole?
The papers proposing a closed box generally try to deal with the problem of an open back close to a wall or a way to smooth the modes but none because of the specific directivity pattern of a dipole.
I made some preliminary test closing more or less the back of a DML, some cardioid patterns seem possible.
In front of that, as for all the loudspeakers there is the question of what we may prefer. Which directivity pattern suit the best to our taste, to our possibility of loudspeaker placement. The technical drawbacks of the open baffle are known, despite that there are widely appreciated. I think most of us appreciate the sound of the open baffle DML, the fact they disappear from the room.
What will be the sound of a DML in a closed box or a cardioid one? I mean the perception we will have in our rooms. The closed box is probably a risky design.
I have in mind remarks in this thread of a boxy sound from tentative of attenuating the rear wave. I am not sure to understand what is a boxy sound but this week doing some tests, I had a small closed box with a full range Visation; clearly the sound came from the loudspeaker. Just after I tested a plywood panel and even if the band was limited, the FR not really straight, the sound was really pleasant, filling the room.
What I have in mind currently is what ever our choice as load (open, close...) is or more precisely as directivity pattern, the questions of the coincidence frequency and of the drum effect have to be closed which is I think almost done (at least we have elements to decide).
Then for an open baffle mainly (maybe also but not as much for a cardioid), the problem of the cavity noise has to be solved. Here we are at the beginning with some tests of concentrators or let say interface parts.
Next will be the rear load : open, attenuated rear, cardioid, closed...
I rely on you to choose the best arrangemnt for a smooth low frequency extension!
DML is a technology, the real question is a matter of loudspeaker architecture. Recently I posted video #13148 about directivity. Seems a matter of taste but my experience on that is very limited.
Christian
Hi guys
Lekha appears to have been wiped from the thread.
I answered his post on a Technics speaker earlier, and was puzzled that it was missing. I looked at alerts and saw it had been deleted. Reason being ..."Lekha was a puppet account of a previous member".
I suspect it was chsdl in drag.
Lekha appears to have been wiped from the thread.
I answered his post on a Technics speaker earlier, and was puzzled that it was missing. I looked at alerts and saw it had been deleted. Reason being ..."Lekha was a puppet account of a previous member".
I suspect it was chsdl in drag.
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Yes... My Viridian build has a hole behind the exciter with a pad of acoustic fibre secured across it. It also has filtered openings top and bottom, and to partial depth down the sides. It took many hours of trial and error to arrive at that arrangement.
The sound is different to the open panels. There is some degree of closing in and a more mellow sound with more low mid tones. I like it but some listeners preferred the open panel. The best way to resolve this is to copy the design for testing purposes. It can also probably be further improved.
Eucy
He was trying to be the thread, annoying as hell in my book, getting a kick out of dragging everyone in circles. "Moving air has nothing to do with sound"... like the "glass doesn't bend" dude.... is that the same guy, I can't remember, and don't want to.
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That's possible! I've read through the bulk of posts in this thread and there seemed to be a lot of similarities. Too bad, a lot of bandwidth wasted along the way.
On a very different note, I'm close to firing up a 22x24 inch XPS panel to evaluate the concept. I have acquired most of the components, made a frame and I'm currently working on a mounting system for it. Hopefully before long I will have additional results to share.
Christian, I'm not sure that one can determine whether an open-back DML panel is strictly a dipole in the classical sense simply by taking directivity responses. A dipole is a dipole because front and rear waves cancel out at the edges at the relevant frequencies, but I don't think that's everything that's happening with a DML panel. If one looks at high-order modes at higher frequencies on a DML panel, then it's clear that there are multiple "micro-diploes" operating simultaneously, any one of which will be in or out-of-phase with its neighbouring dipoles and obviously out-of-phase with its own wave on the opposite face of the panel (but which will be acoustically isolated because of the size of the panel relevant to the acoustic wavelengths.)
Any one "micro-dipole" on the front of the panel will simultaneously have an IN-phase micro-dipole operating on the rear of the panel. Which makes it a micro-BIpole...
So, as far as the whole panel is concerned, I think we might be looking at a diffused BiDipole? ... 😎
And I also think that the edges of a panel reveal an acoustic null because the surface waves cannot project in-line with the plane of the panel, and maybe because the individual micro-dipoles do short-circuit at the edges? Also, the relevant micro-dipoles might only be active closer to the exciter than they are to the edges anyway, depending on the damping factor of the panel itself.
Leob is that maybe because use set up your system all around your dance-floor listening area? Iif so, then I'd assume that the maximum distance, ear-to-speaker, might be no more than 5metres or so for a 100sqm dancefloor?
When I run my panels outdoors, I sometimes have to project over 20 or 30m to the furthest seats, and they do end up sounding a bit dull.