I am looking for a "moving coil exciter" suitable for attaching to some
surface like a window glass. I want to turn a window glass into a
speaker. I don't want to achieve high sound pressures, but prefereably
be able to go down to ~35 Hz (at sound pressures quite low).
I guess signal processing and driving the exiter to it's limits is
necessary to achieve linear response down to 35 Hz.
I already have found the "soundbug" marketed as computer accessory. But
this is not what i am looking for as it is active and uses batteries. I
rather look for a passive solution which may be like a "speaker without
membrane".
Or may i be able to build such a thing on my own by buying some parts
used in a speaker ?
Where could i look for seperate speaker parts like the magnet & coil. I
could then try to attach the coil to some suction cup for attaching it
to a window.

Raymund Hofmann

raymund hofmann wrote:

I am looking for a "moving coil exciter" suitable for attaching to some
surface like a window glass. I want to turn a window glass into a
speaker. I don't want to achieve high sound pressures, but prefereably
be able to go down to ~35 Hz (at sound pressures quite low).
I guess signal processing and driving the exiter to it's limits is
necessary to achieve linear response down to 35 Hz.
I already have found the "soundbug" marketed as computer accessory. But
this is not what i am looking for as it is active and uses batteries. I
rather look for a passive solution which may be like a "speaker without
membrane".
Or may i be able to build such a thing on my own by buying some parts
used in a speaker ?
Where could i look for seperate speaker parts like the magnet & coil. I
could then try to attach the coil to some suction cup for attaching it
to a window.

Raymund Hofmann

Have you seen such an exciter? What holds it relatively stationary as
the class moves under its influence? Inertia? What would you expect its
mass to be? This is intriguing.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

raymund hofmann wrote:

I am looking for a "moving coil exciter" suitable for attaching to some
surface like a window glass. I want to turn a window glass into a
speaker. I don't want to achieve high sound pressures, but prefereably
be able to go down to ~35 Hz (at sound pressures quite low).
I guess signal processing and driving the exiter to it's limits is
necessary to achieve linear response down to 35 Hz.
I already have found the "soundbug" marketed as computer accessory. But
this is not what i am looking for as it is active and uses batteries. I
rather look for a passive solution which may be like a "speaker without
membrane".
Or may i be able to build such a thing on my own by buying some parts
used in a speaker ?
Where could i look for seperate speaker parts like the magnet & coil. I
could then try to attach the coil to some suction cup for attaching it
to a window.

Raymund Hofmann

Have you seen such an exciter? What holds it relatively stationary as
the class moves under its influence? Inertia? What would you expect its
mass to be? Do you expect the frequency response depend on the size,
shape, and thickness of the glass? This is intriguing.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

"Jerry Avins" schrieb im Newsbeitrag
...
raymund hofmann wrote:

I am looking for a "moving coil exciter" suitable for attaching to
some
surface like a window glass. I want to turn a window glass into a
speaker. I don't want to achieve high sound pressures, but
prefereably
be able to go down to ~35 Hz (at sound pressures quite low).
I guess signal processing and driving the exiter to it's limits is
necessary to achieve linear response down to 35 Hz.
I already have found the "soundbug" marketed as computer accessory.
But
this is not what i am looking for as it is active and uses
batteries. I
rather look for a passive solution which may be like a "speaker
without
membrane".
Or may i be able to build such a thing on my own by buying some
parts
used in a speaker ?
Where could i look for seperate speaker parts like the magnet &
coil. I
could then try to attach the coil to some suction cup for attaching
it
to a window.

Raymund Hofmann

Have you seen such an exciter? What holds it relatively stationary as
the class moves under its influence? Inertia? What would you expect
its
mass to be? Do you expect the frequency response depend on the size,
shape, and thickness of the glass? This is intriguing.

I have seen such a thing mentioned / described in:

http://www.tannoyna.com/commercial/pdf/wp_nxt.pdf

But I wonder if i may be able to buy some ready made moving coil exiters
somewhere.

The mass should be high enough to result in the needed forces to the
window glass without driving the voice coil too hard and thus getting
too non-linear.
Concerning the Frequency response I would have to do compensation anyway
to achieve my goal.
So the thing is mainly that it stays linear enough with the applied
power for the application.

Raymund Hofmann

Jerry Avins wrote in message ...
raymund hofmann wrote:

I am looking for a "moving coil exciter" suitable for attaching to some
surface like a window glass. I want to turn a window glass into a
speaker. I don't want to achieve high sound pressures, but prefereably
be able to go down to ~35 Hz (at sound pressures quite low).
I guess signal processing and driving the exiter to it's limits is
necessary to achieve linear response down to 35 Hz.
I already have found the "soundbug" marketed as computer accessory. But
this is not what i am looking for as it is active and uses batteries. I
rather look for a passive solution which may be like a "speaker without
membrane".
Or may i be able to build such a thing on my own by buying some parts
used in a speaker ?
Where could i look for seperate speaker parts like the magnet & coil. I
could then try to attach the coil to some suction cup for attaching it
to a window.

Raymund Hofmann

Have you seen such an exciter? What holds it relatively stationary as
the class moves under its influence? Inertia? What would you expect its
mass to be? Do you expect the frequency response depend on the size,
shape, and thickness of the glass? This is intriguing.

Jerry

The suction cup will damp the transfer of energy to the glass too
much. Instead, superglue the butt of the coil to the window. The
inertia of the PM tranfers the energy. Frequency response sucks
but it scares deer, racoons, etc, away from my wife's patio flower
beds when coupled to an SFO triggered by an IR motion sensor.

Ken

raymund hofmann wrote:

"Jerry Avins" schrieb:

...

Have you seen such an exciter? What holds it relatively stationary as
the class moves under its influence? Inertia? What would you expect
itsmass to be? Do you expect the frequency response depend on the
size, shape, and thickness of the glass? This is intriguing.

I have seen such a thing mentioned / described in:

http://www.tannoyna.com/commercial/pdf/wp_nxt.pdf

But I wonder if i may be able to buy some ready made moving coil exiters
somewhere.

The mass should be high enough to result in the needed forces to the
window glass without driving the voice coil too hard and thus getting
too non-linear.
Concerning the Frequency response I would have to do compensation anyway
to achieve my goal.
So the thing is mainly that it stays linear enough with the applied
power for the application.

Raymund Hofmann

I read the NXT paper on Tannoy's web site. It is clear from that paper
that achieving excellent sound quality depends greatly on the acoustic
properties of the radiating panel, and no little bit on the exciter
itself. The paper indicated that the bottom few octaves are best covered
by a more conventional woofer, crossing over at (IIRC) 3-400 Hz. You
want to go a decade below that, and I imagine they would like to know
how to do that too.

aside
I have high regard for Tannoy. I own a pair of their 15" dual-concentric
speakers in 7 ft^3 cabinets, and they are fine speakers indeed. (One of
my life regrets is that, in the 1960s, I had to move them out of the
living room to make room for the children.) On axis, their response is
flat to 30 KHz (tested in RCA Lab's anechoic chamber), but the beam
emerging from the mouth of the 12" diameter horn is so narrow that it's
easy to miss the microphone 15 feet away.

My favorite Tannoy product (as an intellectual thing) is their 48"
public-address speaker, intend to be mounted under a helicopter, and
loud enough to transmit instructions to people on the ground, overriding
the helicopter noise.
/aside

If the Soundbug produces suitable sound, by far the easiest way to make
what you want is to buy one (£20; 2 for £37) and replace the battery
with wires to a supply. To make an active one, A would buy a four- to
six-inch speaker with as heavy a magnet as feasible, and carefully
remove the cone, leaving the voice coil, dust shield (dome), and spider
intact. (I assume that the dome is not larger than the voice coil. If it
is, it will have to be carefully removed, being sure that no thing falls
or is drawn into the gap.) Make a cone of heavy aluminum foil with a
base the diameter of the voice coil and a length to project a bit beyond
the frame (or as much of the frame as you decide to leave) and glue the
cone to the voice coil. Attach 3 or four threads from the cone to the
frame to stabilize the voice coil against twisting. (The cone and its
surround provided that stability before they were removed.

Devise your own way to hold the tip of the cone (or an extension of it)
against the glass. The best way depends on too many unknowns for me to
attempt a design.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯