"new" speaker idea

I have an idea for creating a new "omni-directional" speaker and was
wondering what you guys think and how practical it is. (in theory it works).

The a simple implementation might be: Take a balloon and a metal sphere
along with a insulated rigid wire. Attach the wire to the metal sphere and
put the sphere inside the balloon through its opening. Coat the balloon with
a conductive paint and attach an electrode to it. Put a charged gass with an
inert gas into the balloon and seal it with the insulated wire comming out
the opening of the balloon. Attach the two wires to to an amplifier and play
some music. The balloon should contract and expand to the sound.

How it works: The balloon holds the charged particles and seperates them
from the outside world while providing a diaphram that can move. The metal
sphere and conductive coating provide a method of applying an electric field
to the charged particles. When the field is pointing away from the metal
sphere there is a net force on the balloon's surface that will cause it to
expand by all the impluses of the charged particles and when the field is
directed inwards then they will cause the balloon to contract(due to the
elasticity of the balloon's surface).

Now there are technical issues involved that I'm not sure of but it seems
like it could work.

One could also use a parallel plate like device where the plates are movable
but enclose a charged gass(or possibly a liquid but I think this is
impractical).

The main issue seems to be the charged gas. The gas has to be dense enough
to supply a strong enough pressure to the balloons surface to cause it to
expand. The balloons elasticity also as to be taken into account. I'm just
not sure if its possible get a gas that isn't to "heavy" yet still will have
enough momentum generated by the electric field to increase the internal
pressure on the balloon.

I thought about trying to implement this but I wouldn't know where to get
the charged gas and it might require a lot of fiddling around with.

So I'll see what you guys think.

Thanks,
Jon

Posted by Rich Grise on November 16, 2006, 2:13 pm

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On Thu, 16 Nov 2006 18:49:30 +0000, Jon Slaughter wrote:

> I have an idea for creating a new "omni-directional" speaker and was
> wondering what you guys think and how practical it is. (in theory it works).
>
> The a simple implementation might be: Take a balloon and a metal sphere
> along with a insulated rigid wire. Attach the wire to the metal sphere and
> put the sphere inside the balloon through its opening. Coat the balloon with
> a conductive paint and attach an electrode to it. Put a charged gass with an
> inert gas into the balloon and seal it with the insulated wire comming out
> the opening of the balloon. Attach the two wires to to an amplifier and play
> some music. The balloon should contract and expand to the sound.

...

> So I'll see what you guys think.
>
> Thanks,
> Jon

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

Posted by Zak on November 16, 2006, 4:03 pm

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Rich Grise wrote:

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

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

Posted by John Popelish on November 16, 2006, 2:24 pm

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Jon Slaughter wrote:

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

> Attach the two wires to to an amplifier and play
> some music. The balloon should contract and expand to the sound.
>
> How it works: The balloon holds the charged particles and seperates them
> from the outside world while providing a diaphram that can move. The metal
> sphere and conductive coating provide a method of applying an electric field
> to the charged particles.

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

> When the field is pointing away from the metal
> sphere there is a net force on the balloon's surface that will cause it to
> expand by all the impluses of the charged particles and when the field is
> directed inwards then they will cause the balloon to contract(due to the
> elasticity of the balloon's surface).

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.

> Now there are technical issues involved that I'm not sure of but it seems
> like it could work.
>
> One could also use a parallel plate like device where the plates are movable
> but enclose a charged gass(or possibly a liquid but I think this is
> impractical).
>
> The main issue seems to be the charged gas. The gas has to be dense enough
> to supply a strong enough pressure to the balloons surface to cause it to
> expand. The balloons elasticity also as to be taken into account. I'm just
> not sure if its possible get a gas that isn't to "heavy" yet still will have
> enough momentum generated by the electric field to increase the internal
> pressure on the balloon.

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 thought about trying to implement this but I wouldn't know where to get
> the charged gas and it might require a lot of fiddling around with.

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.

> So I'll see what you guys think.
>
> Thanks,
> Jon

Posted by Jon Slaughter on November 16, 2006, 2:44 pm

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> Jon Slaughter wrote:

>> I have an idea for creating a new "omni-directional" speaker and was
>> wondering what you guys think and how practical it is. (in theory it
>> works).
>>
>> The a simple implementation might be: Take a balloon and a metal sphere
>> along with a insulated rigid wire. Attach the wire to the metal sphere
>> and put the sphere inside the balloon through its opening. Coat the
>> balloon with a conductive paint and attach an electrode to it. Put a
>> charged gass with an inert gas into the balloon and seal it with the
>> insulated wire comming out the opening of the balloon.

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

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.

>> Attach the two wires to to an amplifier and play some music. The balloon
>> should contract and expand to the sound.
>>
>> How it works: The balloon holds the charged particles and seperates them
>> from the outside world while providing a diaphram that can move. The
>> metal sphere and conductive coating provide a method of applying an
>> electric field to the charged particles.

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

yes?

>> When the field is pointing away from the metal sphere there is a net
>> force on the balloon's surface that will cause it to expand by all the
>> impluses of the charged particles and when the field is directed inwards
>> then they will cause the balloon to contract(due to the elasticity of the
>> balloon's surface).

>
> 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.

?

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.

>> Now there are technical issues involved that I'm not sure of but it seems
>> like it could work.
>>
>> One could also use a parallel plate like device where the plates are
>> movable but enclose a charged gass(or possibly a liquid but I think this
>> is impractical).
>>
>> The main issue seems to be the charged gas. The gas has to be dense
>> enough to supply a strong enough pressure to the balloons surface to
>> cause it to expand. The balloons elasticity also as to be taken into
>> account. I'm just not sure if its possible get a gas that isn't to
>> "heavy" yet still will have enough momentum generated by the electric
>> field to increase the internal pressure on the balloon.

>
> 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].
>

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

> 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 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 thought about trying to implement this but I wouldn't know where to get
>> the charged gas and it might require a lot of fiddling around with.

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

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.

> Keeping the sphere precisely centered in the balloon is another.
>

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

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