Saying that sound moves through air is a simplification. It should've been said that sound moves in the air. We all live in the air, just like fish live in water. As air is unseen, we tend to forget that the medium we live in. We walk in the air, not through the air.
Air cannot be pushed from a small place to a larger space. In front of the cone and the dust cap there is unlimited space. You cannot make pressure in an unlimited space. A piston is working in a tube, and has to have a closed volume in front of it to push the air or anything air-like pushed out of a much smaller hole(s). Air pressure can be increased by putting more air into a closed volume, like a tire, football or balloon. The little cone and the dust cap just can't push the air in front of it to the unlimited space. They just move in the air.
Pistonic is a coined word.
The little cone and the dust cap doesn't pump air into the sealed box. It doesn't push the air as in a piston chamber through a smaller hole into the sealed box. If you take the dust cap off, there's still music. There's a hole all the way through the magnet.
Sound comes from the wire, wound or otherwise in a magnetic field fed with a alternating electric current. A wound bobbin would try to get out of the way from the magnetic field when electricity goes through the wire. Search for the right hand 3-finger rule. The semi stiff 'spider' tries to hold it in place. The bobbin is empty without the dust cap.
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Pixel1.
If you use your fingers to lift up the back of the exciter to reduce the sag , does this stop the noise?
I tried using Google translate Italian, but it refuses anything longer than 32 words.
Steve.
If you use your fingers to lift up the back of the exciter to reduce the sag , does this stop the noise?
I tried using Google translate Italian, but it refuses anything longer than 32 words.
Steve.
Aether is for the light in the vaccum of space! air is known to be the vector of sound 😉
By the way as I didn't remember the history of air as the medium for sound and the origin of the bell and vaccum experiment, I found this article (basics of acoustics).
@chdsl : please forget the model of "wind" which is like trying to transmit a signal with a DC voltage; analogy between AC voltage and sound seems better. Soud is a wave, an increase and decrease of local air pressure that thanks to the elastic property of the air can propagate. The molecules move locally for denser area (higher pressure) or rarefaction (lower pressure). A vibrating surface is able to create a sound by modifying locally the pressure.
Please think also to that :
- is a string able to make sound? or in other words, is there a string instrument without a soundboard?
- is there a string instrument without resonance box?
There's no pressure in the air in front of the little bobbin front. The bobbin is just trying to get out of the way from the magnetic field. It won't "come back" if it is not held tightly by the "spider." Search for the right hand 3-finger rule of a magnetic field. It was taught in the school those days.
There's no pistonic motion. The bobbin doesn't want to come back. There's no real word 'pistonic' in English. A piston needs a chamber to work in. You can't push air to a vast unlimited space in front of anything. Most of the people, who applied and got the patents were not scientists, or engineers. And, one of them coined a word and that stayed. Most of the mistakes in patents come from this "pushing air", "air pressure growing in", "pistonic motion" etc, etc.
Have a look at any exciter lying unfixed on a table face up with an amp connected to it. The coil tries to jump out of the magnetic field. It never tries to go into the table. You can change the polarity, and you'd still see it trying to jump away. Right hand 3-finger rule.
Not quite.
Nobody is talking about "The little cone and the dust cap doesn't pump air into the sealed box." You keep on referencing large movements of air, 'wind' is the term you have used repeatedly, which nobody else has referenced.
Boxes and closed spaces are irrelevant to DML's - I don't understand why you are referencing them?
Sound waves are the compaction and rarefaction effect noted in the paper I found for you, in fact all of your questions are answered in it which is why I posted it to you. You appear to have stopped reading at the second sentence which you, incorrectly, objected to. Its a Stanford University paper so it might be worth your time to read it more thoroughly. The movement of air is, specifically, the local movement of air molecules to transmit the sound. It is a very small movement and the molecules recover to their nominal position once the sound wave has been transmitted but they certainly move. You are right, this in not wind, but it is movement.
You readily accepted the transmission of sound through other media like steel, and now accept that air is just another form of media. That is progress.
"Sound comes from the wire, wound or otherwise in a magnetic field fed with a alternating electric current" You have described the motor effect accurately but a coil without some means of coupling the coil to the air via a diaphragm of some description, be that a cone, a dome, a flat panel or a flexible membrane to name a few, makes no sound at all. The coil provides the motive force, it is not the source of the sound.
For example, from another technology, a transformer is used to drive electrostatic speakers. It raises the voltage from the amplifier to drive the charged diaphragm. A transformer contains hundreds of coils using miles of wire. Without the connection to the diaphragm you can pour hundreds of watts into the transformer and produce thousands of volts and you can put your ear right up to the transformer and you won't hear a thing.
You might get a shock so I don't advise it.
Burnt
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"Have a look at any exciter lying unfixed on a table face up with an amp connected to it. The coil tries to jump out of the magnetic field. It never tries to go into the table. You can change the polarity, and you'd still see it trying to jump away. Right hand 3-finger rule."
Not quite.
You are referencing DC current applied to the coil. DC current by definition does not produce an AC signal. Apply an AC signal and the coil will move up and down. It will jump out, and then it will jump " into the table" It you reverse the polarity of the DC signal the coil will not " see it trying to jump away.", it will move into the table.
Music is AC
Burnt
Not quite.
You are referencing DC current applied to the coil. DC current by definition does not produce an AC signal. Apply an AC signal and the coil will move up and down. It will jump out, and then it will jump " into the table" It you reverse the polarity of the DC signal the coil will not " see it trying to jump away.", it will move into the table.
Music is AC
Burnt
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We live in that media called air.
I've accepted that sound travels in a media more than 4-5 decades ago. 🙂 This interest in making speakers happened in the covid time. Its nice going back to experimenting again.
Quote: You can change the polarity, and you'd still see it trying to jump away. Right hand 3-finger rule."
It's always one way.
----
Now, on the question of distributed mode, I'm searching for the best way to transfer the sound from source (an amp) to the flat panel. A curvy panel appears to give even better sound, transferring it from the edge. A flat panel to gives out excellent sound transferred to it from edge. Lately, I find that a wire wound up and down all over the flat panel gives nicer sound in a magnetic field. I am watching other people experimenting, as though I am in the room with them. Once, I get a batch of magnets and other relevant material, I'm going to build them. And, this is not for me. I'm going to build them with a grandkid, quite an intelligent 8 year old. 🙂
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You can use Flemings Left Hand Rule or his Right Hand rule if you change the polarity of the DC signal the direction of travel will change.
Chdsl.
I think we are understanding why you have had problems on other forums.
Burntcoil is trying to help, but it seem to just encourage you to say more.
I have no words to help, I wish I did.
Steve.
I think we are understanding why you have had problems on other forums.
Burntcoil is trying to help, but it seem to just encourage you to say more.
I have no words to help, I wish I did.
Steve.
You may need to re-read some of your own posts. "The coil tries to jump out of the magnetic field. It never tries to go into the table." You were talking direction.
Burnt
Anybody else thinking the signal to noise ratio in this thread has taken a nose dive recently or is it just me?
It is the simple way of speaking/writing, say the visual way of writing. When a force is applied to some object it jumps away. But, it won't return. If suddenly the polarity changes, the force goes the other way. That 2nd force has to be more than the 1st force, to stop it going out and return. It may look like the 1st force was nulled, but the bobbin is on its way out gaining speed. Also the coil is partly out of the magnetic field. So, the 2nd force would be somewhat smaller. The semi rigid spider holds the top of the bobbin, feels the bobbin's pushing out, so it pushes back holding the coil always in the magnetic field. In an exciter, the voice coil is fixed in a such away it can't move, that is, restricted of any movement. It is the coil that give sound. When the coil is fixed to a panel, the panel sings.
Anyway, wind a coil around the bottom of a drinking glass, just above the thick bottom, put a magnet in the glass, connect the wires to an amp. Just put something heavy on the magnet, so it won't jump out. The drinking glass will sing. 🙂 It becomes a DML.
"In an exciter, the voice coil is fixed in a such away it can't move, that is, restricted of any movement. It is the coil that give sound. When the coil is fixed to a panel, the panel sings."
No movement, no sound
No movement, no sound
chdsl,
I think you misunderstand the meaning of "pistonic" as is is used on this forum. I must admit that I too did not understand what pistonic meant in this context when I first started reading speaker literature. So I can understand some confusion.
To be "pistonic" in the way we mean it in the context of speakers doesn't require a piston chamber etc.
In any speaker, there is pretty much always (as far as I know) a driving part (like a coil and former) and a driven part (like a plate, panel, cone, ribbon, etc). Such a speaker is said to be pistonic if the entire driven part all moves together as a rigid body, where each bit of that part moves at the same velocity and in the same direction at any given time. In other words, the vectors describing the displacement, velocity, acceleration, etc, for every location on that driven part (i.e. cone etc) are identical at all times.
On the other hand, a speaker is not pistonic if different areas of the driven part move at different speeds or in different directions at the same time. That is, if the vectors describing displacement, velocity and acceleration are different from each other at any given time.
A conventional (i.e. cone speaker) is said to be "pistonic " because the cone is a stiff shape, made of sufficiently stiff material (hopefully), and because the surround and the spider allow the cone to move freely along the axis of the cone without bending, and hence the cone moves (to a very good approximation) as a rigid body, in and out along the axis of the cone as it is driven by the coil former. Note, that there is nothing in my description here of a cylinder, in which the cone moves, or any chamber into which air is pumped. There is only a driven part that moves as a rigid body.
A bending wave speaker (also called a dml), on the other hand, is said not to be "pistonic" because at any given time, different locations on the panel are moving at different speeds and different directions. This is because the panel of a bending wave speaker (or dml) is large enough and thin enough so that (unlike a cone) it doesn't move as a rigid body. Rather, it moves by bending and rebounding as it is driven and hence different parts of the panel are all moving at different speeds and often in different directions.
Eric