Spice Model for Loudspeaker

Jim Thompson · Sep 23, 2004

480)460-2350 | |
| E-mail Address at Website Fax

John Woodgate · Sep 23, 2004

I read in sci.electronics.design that Jim Thompson
<thegreatone@example.com> wrote (in <ju96l0tgt7dm6rpdtvlbjn339l1p76hjva@
4ax.com&gt

about 'Spice Model for Loudspeaker', on Thu, 23 Sep 2004:

I'm looking for a Spice model for a Loudspeaker, BUT I need CONE
DISPLACEMENT as the output.

I suppose there is no point in asking why. Go to:

www.klippel.de

My esteemed colleague Wolfgang Klippel will either already have a
solution for you or will, I feel sure, help you towards one. What he
doesn't know about loudspeakers isn't known by anyone.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Jim Thompson · Sep 23, 2004

On Thu, 23 Sep 2004 21:25:51 +0100, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Jim Thompson
thegreatone@example.com> wrote (in <ju96l0tgt7dm6rpdtvlbjn339l1p76hjva@
4ax.com&gt about 'Spice Model for Loudspeaker', on Thu, 23 Sep 2004:

I'm looking for a Spice model for a Loudspeaker, BUT I need CONE
DISPLACEMENT as the output.

Moving a mirror ;-)

I suppose there is no point in asking why. Go to:

www.klippel.de

My esteemed colleague Wolfgang Klippel will either already have a
solution for you or will, I feel sure, help you towards one. What he
doesn't know about loudspeakers isn't known by anyone.

480)460-2350 | |
| E-mail Address at Website Fax

Joerg · Sep 24, 2004

Hi Jim,

I'm looking for a Spice model for a Loudspeaker, BUT I need CONE
DISPLACEMENT as the output.

Moving a mirror ;-)

And here I thought you wanted to install a huge boom box in your car,

tint the glass, put on mag wheels....

This lab might be able to help, at least when it comes to the calculations:

http://www.linkwitzlab.com/x-models.htm

Regards, Joerg

http://www.analogconsultants.com

Jim Thompson · Sep 24, 2004

On Fri, 24 Sep 2004 00:04:58 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hi Jim,

I'm looking for a Spice model for a Loudspeaker, BUT I need CONE
DISPLACEMENT as the output.

Moving a mirror ;-)

And here I thought you wanted to install a huge boom box in your car,
tint the glass, put on mag wheels....

I actually designed boom boxes in my youth (mid-40s

, bought several
ZXs, and did the whole middle-age-crazy bit, grew a beard (which I
still have, but it's salt-and-pepper now).

This lab might be able to help, at least when it comes to the calculations:

http://www.linkwitzlab.com/x-models.htm

Regards, Joerg

http://www.analogconsultants.com

480)460-2350 | |
| E-mail Address at Website Fax

E. Rosten · Sep 24, 2004

Jim Thompson wrote:

On Thu, 23 Sep 2004 21:25:51 +0100, John Woodgate
jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Jim Thompson
thegreatone@example.com> wrote (in <ju96l0tgt7dm6rpdtvlbjn339l1p76hjva@
4ax.com&gt about 'Spice Model for Loudspeaker', on Thu, 23 Sep 2004:

I'm looking for a Spice model for a Loudspeaker, BUT I need CONE
DISPLACEMENT as the output.

Moving a mirror ;-)

Interesting. What for? If you need precision, you'd be better off
designing a control loop to set the precision exactly. Of course, a
spice model would help the design...

-Ed

--
(You can't go wrong with psycho-rats.) (er258)(@)(eng.cam)(.ac.uk)

/d{def}def/f{/Times findfont s scalefont setfont}d/s{10}d/r{roll}d f 5/m
{moveto}d -1 r 230 350 m 0 1 179{1 index show 88 rotate 4 mul 0 rmoveto}
for /s 15 d f pop 240 420 m 0 1 3 { 4 2 1 r sub -1 r show } for showpage

Jim Thompson · Sep 24, 2004

On Fri, 24 Sep 2004 09:42:46 +0100, "E. Rosten" <look@my.sig> wrote:

Jim Thompson wrote:
[snip]
Moving a mirror ;-)

Interesting. What for? If you need precision, you'd be better off
designing a control loop to set the precision exactly. Of course, a
spice model would help the design...

-Ed

480)460-2350 | |
| E-mail Address at Website Fax

Rich Grise · Sep 24, 2004

On Friday 24 September 2004 07:41 am, Jim Thompson did deign to grace us
with the following:

On Fri, 24 Sep 2004 09:42:46 +0100, "E. Rosten" <look@my.sig> wrote:

Jim Thompson wrote:
[snip]
Moving a mirror ;-)

Interesting. What for? If you need precision, you'd be better off
designing a control loop to set the precision exactly. Of course, a
spice model would help the design...

-Ed

There *will* be a control loop. Model is needed to evaluate best
approach.

I wonder how big this mirror is intended to be? The idea of an

electrostatic speaker springs to my mind, or maybe capacitive
feedback from the voice coil/mirror arrangement - it will need
some kind of feedback, right?

Thanks,
Rich

Joerg · Sep 24, 2004

Hi Jim,

Just one other idea: There used to be "cone-less" speakers. Basically
these were just the coils with a counter mass. This was screwed to
whatever surface needed to be insonicated. I don't know whether these
are still marketed but I remember they worked ok and were designed for
use with full size stereos. I think some vendors called them invisible
speakers.

That solution would at least take part of the components out of the
equation.

Regards, Joerg

http://www.analogconsultants.com

John Woodgate · Sep 24, 2004

I read in sci.electronics.design that Joerg <notthisjoergsch@removethisp
acbell.net> wrote (in <uj%4d.2055$nj.863@newssvr13.news.prodigy.com&gt

about 'Spice Model for Loudspeaker', on Fri, 24 Sep 2004:

Just one other idea: There used to be "cone-less" speakers. Basically
these were just the coils with a counter mass. This was screwed to
whatever surface needed to be insonicated. I don't know whether these
are still marketed but I remember they worked ok and were designed for
use with full size stereos. I think some vendors called them invisible
speakers.

They have more or less been reinvented, with a bit more science applied,
and embodied in 'flat-panel loudspeakers'.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

E. Rosten · Sep 27, 2004

There *will* be a control loop. Model is needed to evaluate best
approach.

Jim,

Could you let me know how you get on with this, if that's OK. I've just
come across something where a bass loudspeaker may be the best kind (ie
cheap, avaliable, right kind of frequencies avaliable) of actuator.

One problem is that I can't figure out the best way to atach the actuee
(if that is a real word) to the speaker. Gluing something to the center
of the cone may work, but one has to be careful since you mustn't cause
the whole thing to move off axis (lots of friction if that happens).
Also, loudspeakers are designed for moving air, which suggests that the
whole assembly is less efficient that it could be since it's moving
large amounts of air around. I can not, however think of a good way
around this since the cone also performs the job of keeping the coil in
the correct place, rather well.

One could alternatively place both sides in an air tight box to improve
the springiness that returns the speaker to the original position.

Anyway, one could presumable measure the displacement of the cone by
looking at the inductance of the coil, since the further in it is, the
more inductance it will have. However, I can't think of a good, high
precision way of measuring the displacement required to calibrate that.

Any thoughts so far?

-Ed

--
(You can't go wrong with psycho-rats.) (er258)(@)(eng.cam)(.ac.uk)

/d{def}def/f{/Times findfont s scalefont setfont}d/s{10}d/r{roll}d f 5/m
{moveto}d -1 r 230 350 m 0 1 179{1 index show 88 rotate 4 mul 0 rmoveto}
for /s 15 d f pop 240 420 m 0 1 3 { 4 2 1 r sub -1 r show } for showpage

John Woodgate · Sep 27, 2004

I read in sci.electronics.design that E. Rosten <look@my.sig> wrote (in
<41581F3C.7030006@my.sig&gt

about 'Spice Model for Loudspeaker', on Mon,
27 Sep 2004:

Could you let me know how you get on with this, if that's OK. I've just
come across something where a bass loudspeaker may be the best kind (ie
cheap, avaliable, right kind of frequencies avaliable) of actuator.

One problem is that I can't figure out the best way to atach the actuee
(if that is a real word) to the speaker. Gluing something to the center
of the cone may work, but one has to be careful since you mustn't cause
the whole thing to move off axis (lots of friction if that happens).

You can glue a tube to the rim of the voice-coil former (under the dust
cap). You keep it centred by putting a support across the open end of
the bucket, having a carefully-placed hole through which the tube
passes.

Also, loudspeakers are designed for moving air, which suggests that the
whole assembly is less efficient that it could be since it's moving
large amounts of air around. I can not, however think of a good way
around this since the cone also performs the job of keeping the coil in
the correct place, rather well.

You can (carefully!) cut holes in it. But if you want more than a few of
these, a loudspeaker manufacturer (no, not one in China!) will make you
cone-less units with a heavy-duty rear suspension or a double
suspension. For $$, of course.

If you are using the driver unbaffled, the effect of the cone is minimal
at frequencies below that at which the circumference of the driver rim
is less than half a wavelength.

One could alternatively place both sides in an air tight box to improve
the springiness that returns the speaker to the original position.

You could. The boxes might have to be quite big, and they can't be quite
air-tight because they will 'blow' the cone as the air pressure changes.

Anyway, one could presumable measure the displacement of the cone by
looking at the inductance of the coil, since the further in it is, the
more inductance it will have.

The inductance changes in a complex way with position. The magnet
structure is close to saturation, and there is sometimes a conducting
element in the pole-pieces to create electrical damping.

However, I can't think of a good, high
precision way of measuring the displacement required to calibrate that.

I posted a link to Wolfgang Klippel's site. One of the topics he has
researched in depth is the measurement of cone displacement - to high
precision. It's *difficult* - he uses a laser.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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