Forums

Moving coil exciter

Started by raymund hofmann January 8, 2004
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" <jya@ieee.org> schrieb im Newsbeitrag
news:3ffdcb7c$0$6756$61fed72c@news.rcn.com...
> 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 <jya@ieee.org> wrote in message news:<3ffdcb7c$0$6756$61fed72c@news.rcn.com>...
> 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" <jya@ieee.org> 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 (&#2013266083;20; 2 for &#2013266083;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. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
Ken Asbury wrote:

> Jerry Avins <jya@ieee.org> wrote in message news:<3ffdcb7c$0$6756$61fed72c@news.rcn.com>... > >>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
I think I missed something. *BUT* "scares deer, raccoons, etc" caught my attention. My brother's garden suffers from feeding the local wildlife. What all is required? How big a window is required to make an effective/efficient transducer? I could be a HERO to a whole neighborhood if I solved the problem.
Richard Owlett wrote:

   ...

> I think I missed something. > > *BUT* "scares deer, raccoons, etc" caught my attention. > My brother's garden suffers from feeding the local wildlife. > What all is required? How big a window is required to make an > effective/efficient transducer? I could be a HERO to a whole > neighborhood if I solved the problem.
How about a cheap piezo or electrostatic horn tweeter? The brilliant part is the motion detector that makes the noise conditional. I can't test it here for fear of scaring off the birds I feed. Compromises! Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;