"new" speaker idea

...

Why not just use air and call it an electrostatic? That's what you're trying to accomplish anyway.

The rubber balloon would have to be excruciatingly precisely made so that it would stay an equal distance from the sphere all the way around.

Or, you could fill a balloon with water, and use a solenoid to pump the water in and out at an audio rate...

Have Fun! Rich

I don't understand what you mean by "a charged gass".

If the "charged particles" are a gas, they are free to move under the influence of an electric field.

I think you are confusing the forces a stationary charge would produce, and the force a movable charge would produce, under the influence of an electric field.

Here is a variation that may have fewer problems. Just fill the space between the sphere and the balloon with any ordinary gas. Apply a sum of a large DC voltage and the signal AC voltage between the sphere and metalized balloon. This produces a unidirectional, but variable force of attraction between the sphere and balloon. Google [electrostatic speakers].

Or you could coat the sphere with an electret (charged solid dielectric, the electrostatic equivalent of a permanent magnet) that produces the same bias field as the DC voltage. Then the balloon would be attracted or repelled by the potential applied between the inside surface of the balloon and the sphere. But the surface of the electret would have to be perfectly insulating, to keep it from getting coated with an equal and opposite charge that would neutralize its effect.

I agree that a charged gas is a problem. Keeping it from attracting an equal and opposite neutralizing charge is also a problem.

Keeping the sphere precisely centered in the balloon is another.

you cannot use a normal gas because the gas will not be effected by the electic field. Or if it is, it is to slight and only comes from the polarity of the particles. This polarity is due to the fact that there will be a gradient across the particles... although it would surely be completely insignificant. The charged gas exists so that the particles will be attracted to or repelled alway from charged sphere.

yes?

I'm not sure if there is some confusion. What I mean is that you will supply a force to the charged particles due to the voltage difference given between the balloon and the metal sphere.

i.e.,

it is approximately equal to

F = qE and E = -grad(V)

Since V is radially symmetric one has V(r) = Ar

and F = -qA.

here V depends on t ofcourse but we are looking at any instant.

Hence there is a force proportional to the potential difference(which we call A) between the balloon and metal sphere that is acting on each particle.

This force gives a momentum to the particles and eventually they will strike the balloons surface assuming they are moving away from the metal sphere. Since they have a momentum they exert a pressure on the inner surface of the balloon. The sum total of all these ineractions exert a total pressure on the inner surface and it might be enough to cause the balloon to expand.

yeah, I see this but how large will the voltage have to be?

I think the issues tend to be how long the charge will stay charged and if its possible easily generate that charge in some manner. I have no idea though. Not sure how well it is to keep things insulated so they don't loose there charge.

I don't see what you mean here. Are you essentially saying the gas will loose its charge over time due to leakage? This would be an issue in the long term. One could coat the surfaces to try to reduce this but I'm not sure how practical it would be.

I don't think this is an issue as it would just add to nonlinearities in the sound wave produced. I mean, it might not be an optimal solution but can't be to bad in general.

Thanks, Jon

Actually, a balloon filled with a lighter or heavier gas than air mounted over a speaker would make an interesting lens.

Think about it: in your example you think of water as something rigid, i.e. having infinite speed of sound.

A balloon with helium would not be perfect but at least be practical :)

Thomas

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That is a version of an elecrostatic speaker. Been there, done that is my main comment. It is not clear what your details of how it is constructed with a charged gas, coated balloon, etc. bring to the table or improve on existing electrostatic design. The main problem with them is the small electric forces are not sufficient for speakers of any power and they work poorly in the bass requiring a large surface area. Electrostatic speakers do fill a high end nitch, however. If you are serious, work out the details and build a prototype.

Please define "charged gas".

Thanks, Rich

A buddy of mine at MIT, Robert A. Hirschfeld, did his bachelor's thesis under Professor Bose... a metallized balloon inside a perforated sphere made from two metal colanders.

...Jim Thompson

sheesh. An ionized gas. For example, Hydrogen with each atom's electron removed or some other element or molecule. For the field to apply a force there much be a charge. To get a charge one must used something that is charged. One could use a plasma such as a flame in the plasma speakers and this is what is used for plasma speakers. The problem here is that is an impractical means to create a charged gas for normal use.

The field will not interact with air in normal circumstances and so some other means are used.

Not really. Its more closely related to a plasma speaker than an electrostatic speaker. Here I use the momentum of the gas particles to move the diaphram instead of an electric field. Its true that the electric field moves the particles but it is on step away from an electrostatic speaker uses which doesn't use in intermediate medium. (although this method actually uses a conductive diaphram it is not needed as it can be done other ways.)

The whole point is to accelerate the particles in the gas and have them impact a surface. If the there are enough impacts then they will move that surface.

Now is it more efficient or more practical than an electrostatic or normal speaker? I have no idea. This is why I asked.

I would love to do a prototype but my means are not great and there are several technical issues involved that I don't probably have the time and knowledge to deal with. Now I thought about working out some of the math to see if its feesible but it still requires some knowledge about things I have no idea.

I'm thinking about trying to work out the mathematics as it seems like it might be pretty interesting but its been a long time since I've done any physics and I'm sure to make many mistakes ;/ Might turn out to be a big waste of time.

Jon

And how exactly do you intend to hold a plasma ball inside a rubber balloon? Pressurize the plasma? If that's what you think you're going to do, I believe you still have some reading to catch up on.

Good Luck! Rich

And the permeability of the balloon ( it'll go flat ).

It could be an entertaining experiment !

Graham

Ionised gas does not have to be hot

Rich, come to Taco Bell with me some day for lunch, and I'll show you...;-)

Bob M.

First off no one said one had to use protons. You use could a large molecule with a net charge on it(even if its small).

This is where you are going wrong. The gas doesn't HAVE to be affected by the field. The BALLOON is the acoustic diaphragm, and IT is what moves the air outside the speaker. It will be moved by the electric field and produce sound.

The balloon needs to be very close to the sphere, and therefore needs to have a VERY uniform thickness so that it forms a true sphereical shape. The balloon and sphere will have a large DC bias applied, on the order of 1000-1500 Volts. The music voltage will be added to that, so the instantaneous voltage will go from near zero to near 2000-3000 V. The tricky thing is to get the balloon VERY close to the sphere so the elecrical field strength is very high, but not so close that the electrostatic attraction overcomes the gas pressure and pulls the balloon into the sphere.

I have built planar, bipolar-driven electrostatic speakers. I ran about

• and - 1000 V bias on the outer screens and used the thinnest aluminized mylar film for the diaphragm. I used filament transformers wired backwards to develop several hundred volts of music signal, and the things were just barely audible. These used a 2 x 4' panel. The spacing was about .2" between each screen and the diaphragm. If I could have aligned the thing flatter, I could have reduced the spacing a bit.

Jon

I was afraid that was where you thought you were going....

A volume of ionized gas is not "charged" as a whole, although it is made up of individual particles (ions and electrons) which are. If you intend to contain such a volume, how to you intend to keep the particles from recombining? Or if what you meant is a collection of, say, hydrogen atoms with the electrons not only stripped off but physically removed from the entire volume (in other words, your "gas" is simply a bucket of protons), what keeps this extremely positively-charged "pile of stuff" from simply grabbing whatever electrons would happen to be available - from, oh, I don't know - your center "sphere" electrode?

Or here's a fun experiment. Let's assume we are talking about "ionized hydrogen" (again, "bucket of protons"), and we have enough of these which we've maintained, someone in gaseous form to fill a reasonable "balloon-sized" volume. Call it a couple of liters of protons at at least one atmosphere (probably signficantly more, since the plan was to support an elastic balloon). Do you foresee any problems arising from this big pile of positive charge sitting around, assuming, of course, that it WOULD simply "hang around" in the first place?

Bob M.

(snip)

The force of a surface on the movable charged particles integrates to the opposite of the force generated when those particles impact the surface. There is no net force.

(snip)

Probably quite large, hundreds of volts, at least.

This is all solved by building the electric field with application of an external voltage source. the only current that source has to provide is the leakage.

I mean I have no idea how you introduce and maintain a charged gas. For instance, you might introduce a gas of naked protons. But they will very quickly grab any available electrons ant turn into neutral hydrogen atoms.

Yes. They will very quickly grab opposite charges and become neutral.

"Long term" might be measured in microseconds.

The conductivity would have to approximate zero, almost perfectly, and that wouldn't stop charges from accumulating on top of those insulated surfaces, canceling the local electric field.

Naw, all we need is an elastic material which is impermeable to protons....should be a piece o' cake.....;-)

Bob M.

It does if you intend to contain any significant quantity at 15 PSI. :-)

Cheers! Rich