Magneplanar Tympani IV bass panels with Rotary
For extending the response of Magneplanar Tympani bass below 25 hz,
a rotary subwoofer is the answer. A rotary subwoofer is both efficient
and is capable of reproducing infra bass to 1 hz! I have used a rotary
subwoofer for 4 years with Magneplanar Tympani bass panels and the
results are stunning. Transient response, coherency, and efficiency with
all the power one could ever ask for.
For extending the response of Magneplanar Tympani bass below 25 hz,
a rotary subwoofer is the answer. A rotary subwoofer is both efficient
and is capable of reproducing infra bass to 1 hz! I have used a rotary
subwoofer for 4 years with Magneplanar Tympani bass panels and the
results are stunning. Transient response, coherency, and efficiency with
all the power one could ever ask for.
Attachments
Excellent, about 1/6 of a wavelength. Now what fraction of a wavelength would you need for the backwave to not destructively interfere with the front wave? And do you get constructive or destructive interference when the speaker is in open space?
(Coming up next: consideration of panel width)
(Coming up next: consideration of panel width)
When two waves interfere they must be in opposition of phase to destruct each other.
If i try to understand this mechanism, and if i imagine that destruction begins with the beginning of the two waves and finish with the end of the two waves, i can't imagine what happens if one of the two waves has not the same length.
How can they interfere if they are not complete? And what doest it mean a fraction of wave ? If i consider a classic representation of a wave, a wave on the surface of water, i can't imagine what is a fraction of wave... Either you have a complete one, or no wave at all. Which phenomenon can cut a wave? Reflexion on a wall can not cut the wave, it changes its direction and lowers its amplitude. That does not cut a part of it as you cut your bread. A special stuff can absorb whole or part of amplitude, but cannot cut a wave in portions.
Explain, please.
If i try to understand this mechanism, and if i imagine that destruction begins with the beginning of the two waves and finish with the end of the two waves, i can't imagine what happens if one of the two waves has not the same length.
How can they interfere if they are not complete? And what doest it mean a fraction of wave ? If i consider a classic representation of a wave, a wave on the surface of water, i can't imagine what is a fraction of wave... Either you have a complete one, or no wave at all. Which phenomenon can cut a wave? Reflexion on a wall can not cut the wave, it changes its direction and lowers its amplitude. That does not cut a part of it as you cut your bread. A special stuff can absorb whole or part of amplitude, but cannot cut a wave in portions.
Explain, please.
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You're getting it now! The backwave will be out of phase with the front wave, and the pathlength from wall reflection will not be long enough to cause the phase to reinforce the front wave. So you get cancellation.
If you were in a really, really big room and could space the dipole 1/4 wavelength from the back wall, you wouldn't get cancellation from that mechanism (the backwave phase shifts a half wavelength, thus constructively interfering with the front wave), but you would still get cancellation from the back wave and front wave "meeting" at the edges of the baffle or plane radiator, so that would determine the bass rolloff. This is why putting the speaker in open air will not show the inevitable cancellation that you get in a room, and likewise why putting the mike really close to it will not show the rolloff- the frontwave is being generated only a few centimeters from the mike, the backwave maight be generated a meter or so away, so the cancellation at that spot is minimal. Back off to listening position and the deep bass goes away. Note that we're considering a single frequency- what you'll see in real life is a comb filter effect superimposed on the rolloff from the baffle or driver width.
When dimensions between boundaries are small with respect to wavelength, your visualization of waves bouncing around is not valid. Essentially, all the air pressurizes and depressurizes as one. So the backwave and front wave cancel and that's why planar dipoles- ANY planar dipole- inevitably have a bass rolloff. There are tricks to compensate (e.g., very high Q woofers, H baffles), but you'll never get the same bass extension that you will from a monopole or bipole source using the same size driver.
about bass at home
Hello,
quite surprised that my last messages were "trapped out",
a dipolar in "the low" (one square meter of active membrane), is "really" different in termes of "rendu" than one or two 15" or 18" in box (sealed,vented or horn loaded)
it's just obvious...I am just a physicist, musician and develloping speakers for many years
Best regards
JYS
Hello,
quite surprised that my last messages were "trapped out",
a dipolar in "the low" (one square meter of active membrane), is "really" different in termes of "rendu" than one or two 15" or 18" in box (sealed,vented or horn loaded)
it's just obvious...I am just a physicist, musician and develloping speakers for many years
Best regards
JYS
Sure, the theory sounds unassailable. But I have to side with Tiburce2, after building a biggish cone-driver OB. The sound (and the measurements) are a whole lot more wonderful than you'd think by measuring wave-lengths. Much more wonderful.
One reason is that the theory is too simple. The waves that meets are just not neatly 180-degrees or any specific degrees. There's a large surface area (for these speakers), stuff that creeps around the odd shape of your baffle (any shape that isn't circular is odd), and stuff that bounces off back walls a few times, etc.
My Dayton-Wright ESLs are in a box a meter square. But they pump out lots of bass down to maybe 60 or 65 Hz before diminishing. (OK, I use a different number each time I post.) Try that in your theory!
Another reason is that sound output has a lot of hand-crafted jiggle-factors like the fudge-point where air resistance turns into mass impedance. When you have an OB, you are running a driver which gives you a big bump down in the 20-30 Hz range, and not befuddled by the type of box, since there is no box.
I have a general distaste for speaker boxes and I was very surprised to discover how much beautiful bass an OB makes. No kidding. In line with my firm belief in heterogeneous subs and locations, adding an OB sub is about as heterogeneous as you can get.
Ben
One reason is that the theory is too simple. The waves that meets are just not neatly 180-degrees or any specific degrees. There's a large surface area (for these speakers), stuff that creeps around the odd shape of your baffle (any shape that isn't circular is odd), and stuff that bounces off back walls a few times, etc.
My Dayton-Wright ESLs are in a box a meter square. But they pump out lots of bass down to maybe 60 or 65 Hz before diminishing. (OK, I use a different number each time I post.) Try that in your theory!
Another reason is that sound output has a lot of hand-crafted jiggle-factors like the fudge-point where air resistance turns into mass impedance. When you have an OB, you are running a driver which gives you a big bump down in the 20-30 Hz range, and not befuddled by the type of box, since there is no box.
I have a general distaste for speaker boxes and I was very surprised to discover how much beautiful bass an OB makes. No kidding. In line with my firm belief in heterogeneous subs and locations, adding an OB sub is about as heterogeneous as you can get.
Ben
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![Norman_M_s_Tympani_Bass_2B_3.x_CIMG021941[1].jpg](/community/data/attachments/271/271336-45ae09ce5fdf4edcda57c11381c6eaa8.jpg)
Not quite, SY.
So your aim was to explain why cancellation is more important in a room than in open space.... and the benefit to keep a quarter wave length from the walls.
I am surprised because cancellation is a fact I do not deny. And all this efforts you develop, I thought it was to make me understood and accept something I refused to accept…
What i know is that when a wave is reflected, it changes its polarity so that it does not kill the direct wave but reinforce it. What i hardly understand is why the distance of the reflecting wall is so important. When a mike can catch a wave of 17m long at 3 cm of the membrane, why the direct wave cannot be influenced by a wave that was reflected 2 meters before ?
What surprises me, in second, is that the increase of cancellation in room, owing to your demonstration, should cause decrease on spl measures in room. But that does not appear: LS150 planar was measured by Claude Lacroix and friends, in a huge auditorium and in small room at listening spot, and decrease is not on this second curve. So, where decrease is visibly maximum, it is in (near) open space, not in the small room.
Why ? Perhaps another cause like room effect can explain?
Attached docs:
Graphics are absolutely raw, without smoothing.
First : in auditorium of 12m x 9m x 4.5m. LS 150 in a corner (maxi cancellation supposed). Micro at 6m in axe. We see a regular decrease about 12 dB/oct.
Second : in a four faces pyramidal attic room, of 70 cubic meters and 50 square meters. Micro at 3 m in axe. We see immediately the benefic influence of the smaller dimensions for lower 20hz response.
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Hello Bentoro
I absolutely agree with you : pleasure cannot be measured in wave length, perhaps waves of desire ...
Things are always more complex than demonstration elements. It's true, in the other side, i cannot follow far further if scientific audio fellows begin to come in the abstruse details of their knowledge...
Nobody say a word on the fact that cancellation is a local phenomenon, not a general one : it appears not on the whole space around the planar sub but only where direct and rear waves meet after an equal length way, because this is a condition to be out of phase. The longer the difference of length of the ways, the lower cancellation appears, with a vanishing effect that surely have been measured. And this shows a domain that should be drawn in a specific graphic (does it exist?). Baffles are precisely put in this area to decrease cancellation.
When you put the planar in parallel with the wall, the wall effect is maximum on three sides : don’t forget that the base of the square is on the ground : no cancellation. If you put the planar at 90 degres with a side touching the wall, the cancellation plays only on two sides. If you can install a planar in the frame of a door (never heard that), the room behind keeps 100% of rear waves. Bur also all the waves that can be reflected and come reinforced direct ones. Final benefits?
Can we also consider that the dimension of the emitting surface, relatively to the length of borders which is cancellation main domain, can this be a factor that also counts? When the dimensions increase, the perimeter grows along a linear function when the surface follows an exponential one. When the planar is very large, the borders effect, where cancellation appears, loses importance in front of central emission with no cancellation effect. Infraplanar emits on more than one square meter surface, and yours, even more.
I absolutely agree with you : pleasure cannot be measured in wave length, perhaps waves of desire ...
Things are always more complex than demonstration elements. It's true, in the other side, i cannot follow far further if scientific audio fellows begin to come in the abstruse details of their knowledge...
Nobody say a word on the fact that cancellation is a local phenomenon, not a general one : it appears not on the whole space around the planar sub but only where direct and rear waves meet after an equal length way, because this is a condition to be out of phase. The longer the difference of length of the ways, the lower cancellation appears, with a vanishing effect that surely have been measured. And this shows a domain that should be drawn in a specific graphic (does it exist?). Baffles are precisely put in this area to decrease cancellation.
When you put the planar in parallel with the wall, the wall effect is maximum on three sides : don’t forget that the base of the square is on the ground : no cancellation. If you put the planar at 90 degres with a side touching the wall, the cancellation plays only on two sides. If you can install a planar in the frame of a door (never heard that), the room behind keeps 100% of rear waves. Bur also all the waves that can be reflected and come reinforced direct ones. Final benefits?
Can we also consider that the dimension of the emitting surface, relatively to the length of borders which is cancellation main domain, can this be a factor that also counts? When the dimensions increase, the perimeter grows along a linear function when the surface follows an exponential one. When the planar is very large, the borders effect, where cancellation appears, loses importance in front of central emission with no cancellation effect. Infraplanar emits on more than one square meter surface, and yours, even more.
Footnote: perhaps modeling OBs with Monte Carlo methods (very large number of data points chosen kind of randomly) would be productive. Starting with something basic like a square baffle parallel to the back wall at a distance equal to the baffle edge dimension.
You know, I really don't think there is an accepted model (or calculation) for OBs (except maybe circular ones hanging in free air). Just the intuitive feeling that when out of phase sounds meet......... But even for the simplest baffles, as soon as you start drawing ray-diagrams the situation is anything but simple anywhere even in an anechoic chamber.
Ben
You know, I really don't think there is an accepted model (or calculation) for OBs (except maybe circular ones hanging in free air). Just the intuitive feeling that when out of phase sounds meet......... But even for the simplest baffles, as soon as you start drawing ray-diagrams the situation is anything but simple anywhere even in an anechoic chamber.
Ben
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Hi bentoro
"You know, I really don't think if there is an accepted model (or calculation) for OBs..."
I think so, too. You know, my problem is not measuring, nor building an accepted model. I am relatively sure of what my ears give to me.
I am only unhappy each time a member of a forum condemns a planar or an OB because of the cancellation principle. And always comes back to the elementary school demonstration of the two waves coming from an only point of the membrane surface and arriving on a single point of space to meet and cancel themselves.
As if the planar surface had no effect.
As if reflected waves had no effect.
As if room had no effect.
As if what seems to be far out of easy calculation was by the way not to be considered.
And they always explain that science is always true, so OB cannot work, so they are good for garbage.
And you who love planar sound because you have heard it, you are judged donkeys by those who never saw one.
"You know, I really don't think if there is an accepted model (or calculation) for OBs..."
I think so, too. You know, my problem is not measuring, nor building an accepted model. I am relatively sure of what my ears give to me.
I am only unhappy each time a member of a forum condemns a planar or an OB because of the cancellation principle. And always comes back to the elementary school demonstration of the two waves coming from an only point of the membrane surface and arriving on a single point of space to meet and cancel themselves.
As if the planar surface had no effect.
As if reflected waves had no effect.
As if room had no effect.
As if what seems to be far out of easy calculation was by the way not to be considered.
And they always explain that science is always true, so OB cannot work, so they are good for garbage.
And you who love planar sound because you have heard it, you are judged donkeys by those who never saw one.
Bonjour,
still surprised (more often upsetted), about "The Evidence" that dipolar is the wrongest way to produce low frequencies (in large or small listening rooms)
I have Never read any consistent paper about the physic's of that kind of speaker and it's coupling whith room acoustics...So "simplified Ideas" for a scientist is an example of the "copy, paste" attitude...It Just Can't Work
I have calculated, realised and measured a lot of "Bass Speakers", from "Shoe Boxes" up to cubic meter's of enclosures animated by large diameter cone speakers in number (2,4,8)...
Until I encountered my friend Lacroix with the delight of realising a powerfull bass unit abble to give a "light and extended low" without this penible sound of box
To SY, I suppose that the "Models" you are so proud of are Totally out of the physic's because of their abusive simplifications
It's a largely more complex problem than "cancellation" which gives no explanation because based on unreal descriptions of generation and propagation of acoustic waves
Young Doctor in Fluid Mechanic's, I wrote (for my students) on the door of my labo (in the 80's)
"Let's prefer a good experiment to a wrong calculation"
Best Regards
JYS
still surprised (more often upsetted), about "The Evidence" that dipolar is the wrongest way to produce low frequencies (in large or small listening rooms)
I have Never read any consistent paper about the physic's of that kind of speaker and it's coupling whith room acoustics...So "simplified Ideas" for a scientist is an example of the "copy, paste" attitude...It Just Can't Work
I have calculated, realised and measured a lot of "Bass Speakers", from "Shoe Boxes" up to cubic meter's of enclosures animated by large diameter cone speakers in number (2,4,8)...
Until I encountered my friend Lacroix with the delight of realising a powerfull bass unit abble to give a "light and extended low" without this penible sound of box
To SY, I suppose that the "Models" you are so proud of are Totally out of the physic's because of their abusive simplifications
It's a largely more complex problem than "cancellation" which gives no explanation because based on unreal descriptions of generation and propagation of acoustic waves
Young Doctor in Fluid Mechanic's, I wrote (for my students) on the door of my labo (in the 80's)
"Let's prefer a good experiment to a wrong calculation"
Best Regards
JYS
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