Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Resistance variation with thickness

For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) =
0.004 sq mm,
if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil)
proportionally how much does the resistance change ?
and then to 0.01 * 0.4mm (1 * 40 mil) ?



--
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electronic hints and repair briefs , schematics/manuals list on
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Default Resistance variation with thickness


"N_Cook" wrote in message
...
For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) =
0.004 sq mm,
if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20
mil)
proportionally how much does the resistance change ?
and then to 0.01 * 0.4mm (1 * 40 mil) ?





AFAIK the resistance of wire is proportional to its Cross Sectional Area.
Period. If this remains unchanged, so does the resistance.



Gareth.


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Default Resistance variation with thickness

"Gareth Magennis" wrote in message
...

"N_Cook" wrote in message
...
For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) =
0.004 sq mm,
if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil)
proportionally how much does the resistance change ?
and then to 0.01 * 0.4mm (1 * 40 mil) ?





AFAIK the resistance of wire is proportional to its Cross Sectional Area.
Period. If this remains unchanged, so does the resistance.



Gareth.



That is correct, but the length also has to remain unchanged The formula for
the resistance of a conductor is
R=r*L/A
where R= Resistance
r=Resistivity of the conductor (1.7x10^-8 for copper)
L=Length
A=cross section area

As you can see, the resistance remains constant as long as L and A remain the
same, or change in a manner that produces the same ratio.

--
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address)

Life is like a roll of toilet paper; the closer it gets to the end, the faster
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Default Resistance variation with thickness


"DaveM" wrote in message
...
"Gareth Magennis" wrote in message
...

"N_Cook" wrote in message
...
For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) =
0.004 sq mm,
if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20
mil)
proportionally how much does the resistance change ?
and then to 0.01 * 0.4mm (1 * 40 mil) ?





AFAIK the resistance of wire is proportional to its Cross Sectional Area.
Period. If this remains unchanged, so does the resistance.



Gareth.



That is correct, but the length also has to remain unchanged The formula
for the resistance of a conductor is
R=r*L/A
where R= Resistance
r=Resistivity of the conductor (1.7x10^-8 for copper)
L=Length
A=cross section area

As you can see, the resistance remains constant as long as L and A remain
the same, or change in a manner that produces the same ratio.

--



So that begs the question, how much can a piece of copper wire be
compressed? If you do squash it into a different shape, does or can its
volume change significantly?


Gareth.


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Default Resistance variation with thickness

Gareth Magennis wrote in message
...

"DaveM" wrote in message
...
"Gareth Magennis" wrote in message
...

"N_Cook" wrote in message
...
For a given length of fine copper wire of diameter 0.072 mm (2.9 mil)

=
0.004 sq mm,
if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20
mil)
proportionally how much does the resistance change ?
and then to 0.01 * 0.4mm (1 * 40 mil) ?





AFAIK the resistance of wire is proportional to its Cross Sectional

Area.
Period. If this remains unchanged, so does the resistance.



Gareth.



That is correct, but the length also has to remain unchanged The

formula
for the resistance of a conductor is
R=r*L/A
where R= Resistance
r=Resistivity of the conductor (1.7x10^-8 for copper)
L=Length
A=cross section area

As you can see, the resistance remains constant as long as L and A

remain
the same, or change in a manner that produces the same ratio.

--



So that begs the question, how much can a piece of copper wire be
compressed? If you do squash it into a different shape, does or can its
volume change significantly?


Gareth.



So it may be an effect of work hardening , relative increase in the effect
of imperfections/micro fractures or some other metallurgical effect.
Mackie speaker voice coil failures due to this flattening/ribboning process
to make the tails to the outside world.
Previous failure at the juncture of round to flat (0.07mm round to about
0.02 x 0.2mm) so at the peak stress point.
This one along the length of the ribbon section, but the whole 50mm or so
run was brittleised and disintegrated on touch, not the slightest sign of
overheating on the remaining 25 turns of round wire.
broken end marked B on this pic
http://home.graffiti.net/diverse:gra...ckie_horn1.jpg
http://home.graffiti.net/diverse:gra...ckie_horn2.jpg
Cannot expore the metallurgy as that curve of "wire" as totally
disintegrated to dust.


--
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electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




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Default Resistance variation with thickness

"Gareth Magennis" wrote in message
...

"DaveM" wrote in message
...
"Gareth Magennis" wrote in message
...

"N_Cook" wrote in message
...
For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) =
0.004 sq mm,
if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil)
proportionally how much does the resistance change ?
and then to 0.01 * 0.4mm (1 * 40 mil) ?





AFAIK the resistance of wire is proportional to its Cross Sectional Area.
Period. If this remains unchanged, so does the resistance.



Gareth.



That is correct, but the length also has to remain unchanged The formula for
the resistance of a conductor is
R=r*L/A
where R= Resistance
r=Resistivity of the conductor (1.7x10^-8 for copper)
L=Length
A=cross section area

As you can see, the resistance remains constant as long as L and A remain the
same, or change in a manner that produces the same ratio.

--



So that begs the question, how much can a piece of copper wire be compressed?
If you do squash it into a different shape, does or can its volume change
significantly?


Gareth.



The shape of the cross section can change to virtually any dimension so long as
the length remains the same. IOW, if you squeeze a bar of 10mmx10mm down to
2mmx50mm, its cross sectional area stayed constant (only the shape of the area
changed). Its length will remain the same, since the volume didn't change;
hence, its resistance will remain the same.
So long as material is not added or removed, the volume will remain the same.
The formula says that the ratio of length to cross-sectional area must remain
the same in order for resistance to remain unchanged. If cross sectional area
is changed, the length must change to maintain the ratio. The volume must
remain constant.

--
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MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer it gets to the end, the faster
it goes.


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Default Resistance variation with thickness

On Dec 12, 11:55*am, "DaveM" wrote:
"Gareth Magennis" wrote in message

...







"DaveM" wrote in message
...
"Gareth Magennis" wrote in message
...


"N_Cook" wrote in message
...
For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) =
0.004 sq mm,
if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil)
proportionally how much does the resistance change ?
and then to 0.01 * 0.4mm (1 * 40 mil) ?


AFAIK the resistance of wire is proportional to its Cross Sectional Area.
Period. *If this remains unchanged, so does the resistance.


Gareth.


That is correct, but the length also has to remain unchanged *The formula for
the resistance of a conductor is
R=r*L/A
where R= Resistance
r=Resistivity of the conductor (1.7x10^-8 for copper)
L=Length
A=cross section area


As you can see, the resistance remains constant as long as L and A remain the
same, or change in a manner that produces the same ratio.


--


So that begs the question, how much can a piece of copper wire be compressed?
If you do squash it into a different shape, does or can its volume change
significantly?


Gareth.


The shape of the cross section can change to virtually any dimension so long as
the length remains the same. *IOW, if you squeeze a bar of 10mmx10mm down to
2mmx50mm, its cross sectional area stayed constant (only the shape of the area
changed). *Its length will remain the same, since the volume didn't change;
hence, its resistance will remain the same.
So long as material is not added or removed, the volume will remain the same.
The formula says that the ratio of length to cross-sectional area must remain
the same in order for resistance to remain unchanged. *If cross sectional area
is changed, the length must change to maintain the ratio. *The volume must
remain constant.

--
Dave M
MasonDG44 at comcast dot net *(Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer it gets to the end, the faster
it goes.- Hide quoted text -

- Show quoted text -


What I believe Norm is questioning/proposing is that the wire may have
been made more "dense" by being compressed without lengthening, and
that would probably decrease its resistance.

Bob Hofmann
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Default Resistance variation with thickness

Needs repeating with a proper milli-ohm set up rather than DVM 0.1 ohm
resolution or preferably actively with some higher current through it.
Probably really only becomes manifest close to the current carying limit of
the original round wire, replicating the problem in speaker voice coil
production and use.

Tried about 1m of 0.09mm (including varnish) wire around a 15mm a side flat
and squashed between 2 flats in a protected vice and made no difference to
4.0 ohm, despite 32 theoretical, not obvious, flats.
Repeated with just a single 15mm length of that 1m long wire, reducing 0.09
mm to about 0.03 mm , and repeated further along, so 2 squashed bits of 15mm
.. May have increased to about 4.05 ohm overall but not as obvious a change
as I was expecting.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/








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Default Resistance variation with thickness

Again 1m length , ps set for constant voltage and unlimited current.
Set V for 0.5 amps , 2 flats and no change, set for 1A and 4 flats added, no
change ie less than 0.01 amp change, if any.
Set to give 1.7 amp and varnish burnt off. So no further forward.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/



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"N_Cook" wrote in message
...
Again 1m length , ps set for constant voltage and unlimited current.
Set V for 0.5 amps , 2 flats and no change, set for 1A and 4 flats added, no
change ie less than 0.01 amp change, if any.
Set to give 1.7 amp and varnish burnt off. So no further forward.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




All your testing seems to have verified that the formula for resistance vs.
cross-sectional area does work. No matter how many 'flats' you make on the
wire, you haven't changed its resistance. The small amount that it changed can
easily be contributed to variations in meter connections and/or minute changes
in length due to the squeezing of the wire to make the 'flats'. Barring any
crystalline structure changes in the metal itself, so long as the
cross-sectional area and length doesn't change, the resistance doesn't change.

I suggest that the speaker winding that you're trying to diagnose failed because
of metal fatigue, possibly due to loose mounting, broken adhesive or just an
imperfection in the coil at manufacture.

Time to move on?

--
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MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer it gets to the end, the faster
it goes.


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DaveM wrote in message
...
"N_Cook" wrote in message
...
Again 1m length , ps set for constant voltage and unlimited current.
Set V for 0.5 amps , 2 flats and no change, set for 1A and 4 flats

added, no
change ie less than 0.01 amp change, if any.
Set to give 1.7 amp and varnish burnt off. So no further forward.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




All your testing seems to have verified that the formula for resistance

vs.
cross-sectional area does work. No matter how many 'flats' you make on

the
wire, you haven't changed its resistance. The small amount that it

changed can
easily be contributed to variations in meter connections and/or minute

changes
in length due to the squeezing of the wire to make the 'flats'. Barring

any
crystalline structure changes in the metal itself, so long as the
cross-sectional area and length doesn't change, the resistance doesn't

change.

I suggest that the speaker winding that you're trying to diagnose failed

because
of metal fatigue, possibly due to loose mounting, broken adhesive or just

an
imperfection in the coil at manufacture.

Time to move on?

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters

in the
address)

Life is like a roll of toilet paper; the closer it gets to the end, the

faster
it goes.




If it was just a one off , then fair enough. But 2 separate Mackie amps with
the same problem in the same 2 squashed percent of the wire of the speaker
voice-coils ?

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




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Default Resistance variation with thickness


N_Cook wrote:

DaveM wrote in message
...
"N_Cook" wrote in message
...
Again 1m length , ps set for constant voltage and unlimited current.
Set V for 0.5 amps , 2 flats and no change, set for 1A and 4 flats

added, no
change ie less than 0.01 amp change, if any.
Set to give 1.7 amp and varnish burnt off. So no further forward.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




All your testing seems to have verified that the formula for resistance

vs.
cross-sectional area does work. No matter how many 'flats' you make on

the
wire, you haven't changed its resistance. The small amount that it

changed can
easily be contributed to variations in meter connections and/or minute

changes
in length due to the squeezing of the wire to make the 'flats'. Barring

any
crystalline structure changes in the metal itself, so long as the
cross-sectional area and length doesn't change, the resistance doesn't

change.

I suggest that the speaker winding that you're trying to diagnose failed

because
of metal fatigue, possibly due to loose mounting, broken adhesive or just

an
imperfection in the coil at manufacture.

Time to move on?

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters

in the
address)

Life is like a roll of toilet paper; the closer it gets to the end, the

faster
it goes.



If it was just a one off , then fair enough. But 2 separate Mackie amps with
the same problem in the same 2 squashed percent of the wire of the speaker
voice-coils ?



Poor quality control, or a defective manufacturing process.


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The first sign of insanity is denying that you're crazy.
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Default Resistance variation with thickness

Michael A. Terrell wrote in message
m...

N_Cook wrote:

DaveM wrote in message
...
"N_Cook" wrote in message
...
Again 1m length , ps set for constant voltage and unlimited current.
Set V for 0.5 amps , 2 flats and no change, set for 1A and 4 flats

added, no
change ie less than 0.01 amp change, if any.
Set to give 1.7 amp and varnish burnt off. So no further forward.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




All your testing seems to have verified that the formula for

resistance
vs.
cross-sectional area does work. No matter how many 'flats' you make

on
the
wire, you haven't changed its resistance. The small amount that it

changed can
easily be contributed to variations in meter connections and/or minute

changes
in length due to the squeezing of the wire to make the 'flats'.

Barring
any
crystalline structure changes in the metal itself, so long as the
cross-sectional area and length doesn't change, the resistance doesn't

change.

I suggest that the speaker winding that you're trying to diagnose

failed
because
of metal fatigue, possibly due to loose mounting, broken adhesive or

just
an
imperfection in the coil at manufacture.

Time to move on?

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate

characters
in the
address)

Life is like a roll of toilet paper; the closer it gets to the end,

the
faster
it goes.



If it was just a one off , then fair enough. But 2 separate Mackie amps

with
the same problem in the same 2 squashed percent of the wire of the

speaker
voice-coils ?



Poor quality control, or a defective manufacturing process.


--
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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.



Its more than that.
In both Mackie cases the main active coils showed absolutely no overheating
let alone burning. In all other odd o/c speakers I've poked my nose in, have
had large sections of charring or completely burnt and broken coil formers.
Not failure in the tail sections because they are usually different / larger
conductors soldered or welded to the main coil. These Mackie tails are
acting as fuses, protecting the voice coil, which is ridiculous.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/




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Default Resistance variation with thickness


N_Cook wrote:

Michael A. Terrell wrote:

Poor quality control, or a defective manufacturing process.


Its more than that.
In both Mackie cases the main active coils showed absolutely no overheating
let alone burning. In all other odd o/c speakers I've poked my nose in, have
had large sections of charring or completely burnt and broken coil formers.
Not failure in the tail sections because they are usually different / larger
conductors soldered or welded to the main coil. These Mackie tails are
acting as fuses, protecting the voice coil, which is ridiculous.



No, it isn't. Who would manufacture speakers that way for Mackie? If
they did, all of them would fail. They would have to pay extra, and get
no warranty. It sounds like the tinsel wire was the wrong type for the
power level and was likely got through due to poor QC. Poor quality
tinsel wire also suffers from work hardening, and broken strands. When
enough break, the rest burn. Also, if they are a few percent too short,
they get more mechanical abuse, which destroys them. Since you didn't
see them when they were brand new, you have absolutely no idea what
really happened.

I have worked in failure analysis in electronics manufacturing, and I
can tell you that production people can be some of the biggest idiots in
the world. Monday mornings they have hangovers, and Fridays they don't
give a damn what they do, as long as they can leave on time to drink
their paychecks.


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Default Resistance variation with thickness

Michael A. Terrell wrote in message
m...

N_Cook wrote:

Michael A. Terrell wrote:

Poor quality control, or a defective manufacturing process.


Its more than that.
In both Mackie cases the main active coils showed absolutely no

overheating
let alone burning. In all other odd o/c speakers I've poked my nose in,

have
had large sections of charring or completely burnt and broken coil

formers.
Not failure in the tail sections because they are usually different /

larger
conductors soldered or welded to the main coil. These Mackie tails are
acting as fuses, protecting the voice coil, which is ridiculous.



No, it isn't. Who would manufacture speakers that way for Mackie? If
they did, all of them would fail. They would have to pay extra, and get
no warranty. It sounds like the tinsel wire was the wrong type for the
power level and was likely got through due to poor QC. Poor quality
tinsel wire also suffers from work hardening, and broken strands. When
enough break, the rest burn. Also, if they are a few percent too short,
they get more mechanical abuse, which destroys them. Since you didn't
see them when they were brand new, you have absolutely no idea what
really happened.

I have worked in failure analysis in electronics manufacturing, and I
can tell you that production people can be some of the biggest idiots in
the world. Monday mornings they have hangovers, and Fridays they don't
give a damn what they do, as long as they can leave on time to drink
their paychecks.


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

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your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.


The problem is not at the tinsel wire, ie the flexible bridge. But before
that, a flattening of the voice coil wire into ribbon. Production seems to
be a precise length of say 2.5m with the ends squashed giving some precise
run of round voice coil wire. One end has the ribbon fixed to the tinsel in
the ideal spot but the other end arrives at maybe half a turn from ideal and
has to make a half turn to join the tinsel for the other termination.
Tinsel ribbon is presumably higher current carying than the crresponding
voice coil wire, so no problems there.
This Mackie problem is something to do with a run of same gauge but
squashed wire.
Remember the whole half-turn of ribbon disintegrated so not due to a nick or
rubbing on metalwork.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


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Default Resistance variation with thickness

Perhaps it is chemistry . Bear in mind that the wire is silver and not
copper and the surface area of a squashed wire is more than when it was
round and any corrosion on that surface will have proportionally more effect
on the thin flats than the bulky round.

The voice coil wire looked like copper because it was under a coppery brown
lacquer. But, before it disintegrated, the ribbon section was darker brown
than the round section.
Now if air could get under the lacquer and tarnish the silver to black
copper sulphide, or whatever that blackening is, then that would explain
it.
Unfortunately none of that section remains as it literally turned to dust
after photographing it, you could not pick it up even with fingers, it was
little more than a wraithe.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/



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Default Resistance variation with thickness

N_Cook wrote:
Perhaps it is chemistry . Bear in mind that the wire is silver and not
copper and the surface area of a squashed wire is more than when it was
round and any corrosion on that surface will have proportionally more effect
on the thin flats than the bulky round.

The voice coil wire looked like copper because it was under a coppery brown
lacquer. But, before it disintegrated, the ribbon section was darker brown
than the round section.
Now if air could get under the lacquer and tarnish the silver to black
copper sulphide, or whatever that blackening is, then that would explain
it.
Unfortunately none of that section remains as it literally turned to dust
after photographing it, you could not pick it up even with fingers, it was
little more than a wraithe.


Are you sure that voice coil isn't aluminium? Some aluminuium v/cs are
copper coated btw.

Ron(UK)
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Ron Johnson wrote in message
...
N_Cook wrote:
Perhaps it is chemistry . Bear in mind that the wire is silver and not
copper and the surface area of a squashed wire is more than when it was
round and any corrosion on that surface will have proportionally more

effect
on the thin flats than the bulky round.

The voice coil wire looked like copper because it was under a coppery

brown
lacquer. But, before it disintegrated, the ribbon section was darker

brown
than the round section.
Now if air could get under the lacquer and tarnish the silver to black
copper sulphide, or whatever that blackening is, then that would

explain
it.
Unfortunately none of that section remains as it literally turned to

dust
after photographing it, you could not pick it up even with fingers, it

was
little more than a wraithe.


Are you sure that voice coil isn't aluminium? Some aluminuium v/cs are
copper coated btw.

Ron(UK)



The voice coil remains unaffected, do you know of a simple test for silver v
aluminium ? I would say it looked brighter, more silvery indeed, than
aluminium but I am not familiar with seeing .07 to 0.09 mm diameter Al wire
or silver wire for that matter.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/





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Default Resistance variation with thickness

N_Cook wrote:
Ron Johnson wrote in message
...
N_Cook wrote:
Perhaps it is chemistry . Bear in mind that the wire is silver and not
copper and the surface area of a squashed wire is more than when it was
round and any corrosion on that surface will have proportionally more

effect
on the thin flats than the bulky round.

The voice coil wire looked like copper because it was under a coppery

brown
lacquer. But, before it disintegrated, the ribbon section was darker

brown
than the round section.
Now if air could get under the lacquer and tarnish the silver to black
copper sulphide, or whatever that blackening is, then that would

explain
it.
Unfortunately none of that section remains as it literally turned to

dust
after photographing it, you could not pick it up even with fingers, it

was
little more than a wraithe.

Are you sure that voice coil isn't aluminium? Some aluminuium v/cs are
copper coated btw.

Ron(UK)



The voice coil remains unaffected, do you know of a simple test for silver v
aluminium ? I would say it looked brighter, more silvery indeed, than
aluminium but I am not familiar with seeing .07 to 0.09 mm diameter Al wire
or silver wire for that matter.


Are you saying that the part of the coil which failed is a separate wire
from the actual voice coil or in some way 'free floating'?
In most speakers - of the single rear suspension type, the v/c is wound
on the former with the ends coming up the cone on the inside then
soldered to the pigtails where they pass through the cone. The tails of
the v/c and soldered joints are glued to the cone inside and the
pigtails glued on the outside. All this is usually covered on the inside
by the dust dome. There should be little fatigue of the v/c wire
anywhere as it should be secured to the v/c former or cone.
The pigtails and often silvered and do fail either through gross
overexcursion or fatigue leading to overheating. I`ve seen pigtails
melted where the voice coil is intact.

You can sometimes rescue a speaker from this condition with some new
pigtails and a dust dome. At one time you could buy pigtail wire from
Goodmans, you probably still can from Wembley Loudspeakers if you ask
nicely.

A speaker which has been seriously overdriven often shows no voice coil
damage other than an obvious open circuit in the 'straight' part of the
v/c winding. Chances are, your customer was pushing the amps well into
clipping and simply overcooked the voicecoils which melted at the
weakest point.

Wembley Loudspeakers will repair the drivers at a reasonable cost no doubt.

Ron
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Default Resistance variation with thickness

Ron Johnson wrote in message
...
N_Cook wrote:
Ron Johnson wrote in message
...
N_Cook wrote:
Perhaps it is chemistry . Bear in mind that the wire is silver and not
copper and the surface area of a squashed wire is more than when it

was
round and any corrosion on that surface will have proportionally more

effect
on the thin flats than the bulky round.

The voice coil wire looked like copper because it was under a coppery

brown
lacquer. But, before it disintegrated, the ribbon section was darker

brown
than the round section.
Now if air could get under the lacquer and tarnish the silver to black
copper sulphide, or whatever that blackening is, then that would

explain
it.
Unfortunately none of that section remains as it literally turned to

dust
after photographing it, you could not pick it up even with fingers, it

was
little more than a wraithe.
Are you sure that voice coil isn't aluminium? Some aluminuium v/cs are
copper coated btw.

Ron(UK)



The voice coil remains unaffected, do you know of a simple test for

silver v
aluminium ? I would say it looked brighter, more silvery indeed, than
aluminium but I am not familiar with seeing .07 to 0.09 mm diameter Al

wire
or silver wire for that matter.


Are you saying that the part of the coil which failed is a separate wire
from the actual voice coil or in some way 'free floating'?
In most speakers - of the single rear suspension type, the v/c is wound
on the former with the ends coming up the cone on the inside then
soldered to the pigtails where they pass through the cone. The tails of
the v/c and soldered joints are glued to the cone inside and the
pigtails glued on the outside. All this is usually covered on the inside
by the dust dome. There should be little fatigue of the v/c wire
anywhere as it should be secured to the v/c former or cone.
The pigtails and often silvered and do fail either through gross
overexcursion or fatigue leading to overheating. I`ve seen pigtails
melted where the voice coil is intact.

You can sometimes rescue a speaker from this condition with some new
pigtails and a dust dome. At one time you could buy pigtail wire from
Goodmans, you probably still can from Wembley Loudspeakers if you ask
nicely.

A speaker which has been seriously overdriven often shows no voice coil
damage other than an obvious open circuit in the 'straight' part of the
v/c winding. Chances are, your customer was pushing the amps well into
clipping and simply overcooked the voicecoils which melted at the
weakest point.

Wembley Loudspeakers will repair the drivers at a reasonable cost no

doubt.

Ron



This is a high power horn so tinsel ribbon instead of pigtails. Instead of
the voice coil of round wire going from one tinsel to the other there are
short runs of flattened wire. Unnecessary here , assuming it is to save
overlap, so fouling the gap in the magnet, because the magnet is milled out
on both sites of the lead-in and lead out tinsels. In pics of earlier post.
If the wire had not been flattened it would not have failed, at least as how
it was being used, is what I am suggesting.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/



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N_Cook wrote:

Perhaps it is chemistry . Bear in mind that the wire is silver and not
copper and the surface area of a squashed wire is more than when it was
round and any corrosion on that surface will have proportionally more effect
on the thin flats than the bulky round.



Why would they use silver? It is very soft, and malleable. More than
likely it is aluminum, or bright tin plated copper.


The voice coil wire looked like copper because it was under a coppery brown
lacquer. But, before it disintegrated, the ribbon section was darker brown
than the round section.
Now if air could get under the lacquer and tarnish the silver to black
copper sulphide, or whatever that blackening is, then that would explain
it.


If the piece cracked, it could have arced and heated. That can spread
and damage the surface.


Unfortunately none of that section remains as it literally turned to dust
after photographing it, you could not pick it up even with fingers, it was
little more than a wraithe.



--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.
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Default Resistance variation with thickness

N_Cook wrote:
Ron Johnson wrote in message
...
N_Cook wrote:
Ron Johnson wrote in message
...
N_Cook wrote:
Perhaps it is chemistry . Bear in mind that the wire is silver and not
copper and the surface area of a squashed wire is more than when it

was
round and any corrosion on that surface will have proportionally more
effect
on the thin flats than the bulky round.

The voice coil wire looked like copper because it was under a coppery
brown
lacquer. But, before it disintegrated, the ribbon section was darker
brown
than the round section.
Now if air could get under the lacquer and tarnish the silver to black
copper sulphide, or whatever that blackening is, then that would
explain
it.
Unfortunately none of that section remains as it literally turned to
dust
after photographing it, you could not pick it up even with fingers, it
was
little more than a wraithe.
Are you sure that voice coil isn't aluminium? Some aluminuium v/cs are
copper coated btw.

Ron(UK)

The voice coil remains unaffected, do you know of a simple test for

silver v
aluminium ? I would say it looked brighter, more silvery indeed, than
aluminium but I am not familiar with seeing .07 to 0.09 mm diameter Al

wire
or silver wire for that matter.

Are you saying that the part of the coil which failed is a separate wire
from the actual voice coil or in some way 'free floating'?
In most speakers - of the single rear suspension type, the v/c is wound
on the former with the ends coming up the cone on the inside then
soldered to the pigtails where they pass through the cone. The tails of
the v/c and soldered joints are glued to the cone inside and the
pigtails glued on the outside. All this is usually covered on the inside
by the dust dome. There should be little fatigue of the v/c wire
anywhere as it should be secured to the v/c former or cone.
The pigtails and often silvered and do fail either through gross
overexcursion or fatigue leading to overheating. I`ve seen pigtails
melted where the voice coil is intact.

You can sometimes rescue a speaker from this condition with some new
pigtails and a dust dome. At one time you could buy pigtail wire from
Goodmans, you probably still can from Wembley Loudspeakers if you ask
nicely.

A speaker which has been seriously overdriven often shows no voice coil
damage other than an obvious open circuit in the 'straight' part of the
v/c winding. Chances are, your customer was pushing the amps well into
clipping and simply overcooked the voicecoils which melted at the
weakest point.

Wembley Loudspeakers will repair the drivers at a reasonable cost no

doubt.
Ron



This is a high power horn so tinsel ribbon instead of pigtails. Instead of
the voice coil of round wire going from one tinsel to the other there are
short runs of flattened wire. Unnecessary here , assuming it is to save
overlap, so fouling the gap in the magnet, because the magnet is milled out
on both sites of the lead-in and lead out tinsels. In pics of earlier post.
If the wire had not been flattened it would not have failed, at least as how
it was being used, is what I am suggesting.


It`s more likely to fail on the straight, horn drivers usually do,
either because it`s that part of the winding isnt in the magnetic gap or
there`s nothing close by to help sink the heat away - Eitherway it
almost certainly failed due to being overdriven, maybe a burst of loud
feedback or the internal amp being driven into clipping.

Are you sure that the v/c is round wire with only the leadouts being
flattened? Most half decent speakers these days are wound with flat wire
anyway.

Of course, being Mackie, anything could happen!

Ron
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