The blurb technical said 300W RMS handling for this 12 inch speaker.
Now it is blown and I've opened up
2 layers of 90 turns , so 180 turns of .16mm or 6.3 mil/thou diameter wire
on 64 mm diameter former.
300 Watt ?


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

N Cook wrote:
The blurb technical said 300W RMS handling for this 12 inch speaker.
Now it is blown and I've opened up
2 layers of 90 turns , so 180 turns of .16mm or 6.3 mil/thou diameter wire
on 64 mm diameter former.
300 Watt ?

What make and model speaker is it? what`s failed? is the voice coil
burnt? What was diving it when it blew? and what signal content?
Ron(UK)

N Cook wrote:

The blurb technical said 300W RMS handling for this 12 inch speaker.

RMS continuous ? What model.


Now it is blown and I've opened up
2 layers of 90 turns , so 180 turns of .16mm or 6.3 mil/thou diameter wire
on 64 mm diameter former.
300 Watt ?

The temperature rating of the former ( and the glue ) is the relevant issue. Not
to mention ventilation too !

Some ppl push 2-1/2 inch formers to 300W - personally I'm happier with 3".

Graham

N Cook wrote:
The blurb technical said 300W RMS handling for this 12 inch speaker.
Now it is blown and I've opened up
2 layers of 90 turns , so 180 turns of .16mm or 6.3 mil/thou diameter wire
on 64 mm diameter former.
300 Watt ?


The field strength of the magnet assembly has a lot to do with the power
handling, also the cooling arrangements and the cabinet design.

Ron(UK)

N Cook wrote:

The blurb technical said 300W RMS handling for this 12 inch speaker.
Now it is blown and I've opened up
2 layers of 90 turns , so 180 turns of .16mm or 6.3 mil/thou diameter wire
on 64 mm diameter former.
300 Watt ?

Who knows? There are so many design factors that come into play. Let
alone what the manufacturer meant by "300W RMS handling" - Peak RMS? If
so, for how long? Continuous RMS? 300W at what frequency?

Rick

"Rick" wrote in message ...
N Cook wrote:

The blurb technical said 300W RMS handling for this 12 inch speaker.
Now it is blown and I've opened up
2 layers of 90 turns , so 180 turns of .16mm or 6.3 mil/thou diameter
wire
on 64 mm diameter former.
300 Watt ?

Who knows? There are so many design factors that come into play. Let
alone what the manufacturer meant by "300W RMS handling" - Peak RMS? If
so, for how long? Continuous RMS? 300W at what frequency?

Rick

What is " peak " RMS ? That is an oxymoron ...

Arfa

N Cook wrote in message
...
The blurb technical said 300W RMS handling for this 12 inch speaker.
Now it is blown and I've opened up
2 layers of 90 turns , so 180 turns of .16mm or 6.3 mil/thou diameter wire
on 64 mm diameter former.
300 Watt ?


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



My trusty 1941 Electrical Engineer's Companion has the following data
Resistivity for 0.0063 inch diameter wire 0.76 ohm per yard
Safe current carying capacity of the smallest gauge listed of 0.044 inches
diameter of 5 amps in air.
No reason to suspect this data.

This voice coil of 180 turns on 64 mm
gives 1425 inches = 40 yards
so resistance 30 ohms

Scaling by areas, current carying capacity is reduced by ratio of squares of
44 to 6.3 giving about 0.1 amp, only, in free air
I*I*R = 0.3 Watt

Where is my error ?

N Cook wrote:

N Cook wrote in message
...
The blurb technical said 300W RMS handling for this 12 inch speaker.
Now it is blown and I've opened up
2 layers of 90 turns , so 180 turns of .16mm or 6.3 mil/thou diameter wire
on 64 mm diameter former.
300 Watt ?

My trusty 1941 Electrical Engineer's Companion has the following data
Resistivity for 0.0063 inch diameter wire 0.76 ohm per yard


That would be AWG34 wire, much too small for a speaker like this. How
did you measure the wire, and did you slip a decimal place?

How many turns per inch?


Safe current carying capacity of the smallest gauge listed of 0.044 inches
diameter of 5 amps in air.
No reason to suspect this data.


Here is a basic AWG wire chart. I have to add a the other columns for
transformer and coil winding.

http://home.earthlink.net/~mike.terrell/RefAWG.html


This voice coil of 180 turns on 64 mm
gives 1425 inches = 40 yards
so resistance 30 ohms

Scaling by areas, current carying capacity is reduced by ratio of squares of
44 to 6.3 giving about 0.1 amp, only, in free air

It isn't in free air, its a wound inductor, and 6.3 mil wire is rated
at .057 amps at 700 circular mils per amp. This is a common value for
continuous duty coils and transformers.


I*I*R = 0.3 Watt

Where is my error ?


What is the rated impedance of the speaker?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Surely if confined on a coil then lower current handling?

8 ohms

N Cook wrote:

Surely if confined on a coil then lower current handling?

8 ohms


That 700 circular mils per amp is for transformer/coil calculations.
6.125 amps * 8 ohms = 49 volts * 6.125 =300.125 watts. This would
require a 14 AWG wire for 700 circular mils per amp. which is ten times
the diameter you quoted. It is 63 mils, or about 15 turns per inch.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Michael A. Terrell wrote in message
...
N Cook wrote:

Surely if confined on a coil then lower current handling?

8 ohms


That 700 circular mils per amp is for transformer/coil calculations.
6.125 amps * 8 ohms = 49 volts * 6.125 =300.125 watts. This would
require a 14 AWG wire for 700 circular mils per amp. which is ten times
the diameter you quoted. It is 63 mils, or about 15 turns per inch.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

It is 90 turns in 15 mm , 2 layers, 1 over the other, so 180 turns

N Cook wrote:

Michael A. Terrell wrote in message

N Cook wrote:

Surely if confined on a coil then lower current handling?

8 ohms


That 700 circular mils per amp is for transformer/coil calculations.
6.125 amps * 8 ohms = 49 volts * 6.125 =300.125 watts. This would
require a 14 AWG wire for 700 circular mils per amp. which is ten time0
the diameter you quoted. It is 63 mils, or about 15 turns per inch.


It is 90 turns in 15 mm , 2 layers, 1 over the other, so 180 turns

15 millimeters = 0.590551181 inches

1/.59055 * 90 = 152.400 turns per inch.

That would be AWG 34 (143 TPI) or 35 (158 TPI), or British SWG 38 or
39. I don't see how it could handle 300 watts at 8 ohms.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Meat Plow wrote:

On Fri, 12 Jan 2007 18:23:30 +0000, N Cook Has Frothed:

Michael A. Terrell wrote in message

N Cook wrote:

Surely if confined on a coil then lower current handling?

8 ohms


That 700 circular mils per amp is for transformer/coil calculations.
6.125 amps * 8 ohms = 49 volts * 6.125 =300.125 watts. This would
require a 14 AWG wire for 700 circular mils per amp. which is ten times
the diameter you quoted. It is 63 mils, or about 15 turns per inch.

It is 90 turns in 15 mm , 2 layers, 1 over the other, so 180 turns

Most high power voice coils I've seen use flat wire. I would assume this
adds to the watt rating.


If it is square wire, multiply the current rating times 1.27



--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Michael A. Terrell wrote in message
...
N Cook wrote:

Michael A. Terrell wrote in message

N Cook wrote:

Surely if confined on a coil then lower current handling?

8 ohms


That 700 circular mils per amp is for transformer/coil
calculations.
6.125 amps * 8 ohms = 49 volts * 6.125 =300.125 watts. This would
require a 14 AWG wire for 700 circular mils per amp. which is ten
time0
the diameter you quoted. It is 63 mils, or about 15 turns per inch.


It is 90 turns in 15 mm , 2 layers, 1 over the other, so 180 turns

15 millimeters = 0.590551181 inches

1/.59055 * 90 = 152.400 turns per inch.

That would be AWG 34 (143 TPI) or 35 (158 TPI), or British SWG 38 or
39. I don't see how it could handle 300 watts at 8 ohms.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Exactly my problem , I cannot square the blurb statement with analysed
physical reality.

N Cook wrote:
Michael A. Terrell wrote in message
...
N Cook wrote:
Michael A. Terrell wrote in message

N Cook wrote:
Surely if confined on a coil then lower current handling?

8 ohms

That 700 circular mils per amp is for transformer/coil
calculations.
6.125 amps * 8 ohms = 49 volts * 6.125 =300.125 watts. This would
require a 14 AWG wire for 700 circular mils per amp. which is ten
time0
the diameter you quoted. It is 63 mils, or about 15 turns per inch.
It is 90 turns in 15 mm , 2 layers, 1 over the other, so 180 turns
15 millimeters = 0.590551181 inches

1/.59055 * 90 = 152.400 turns per inch.

That would be AWG 34 (143 TPI) or 35 (158 TPI), or British SWG 38 or
39. I don't see how it could handle 300 watts at 8 ohms.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Exactly my problem , I cannot square the blurb statement with analysed
physical reality.


It`s not a pure resistor, it`s an inductor, operating in a strong
magnetic field, and theoretically with forced air cooling. Also, some
manufacturers lie about their specs!

You still haven't disclosed what make and model of speaker it is.

Ron(UK)

Ron(UK) wrote in message
...
N Cook wrote:
Michael A. Terrell wrote in message
...
N Cook wrote:
Michael A. Terrell wrote in message

N Cook wrote:
Surely if confined on a coil then lower current handling?

8 ohms

That 700 circular mils per amp is for transformer/coil
calculations.
6.125 amps * 8 ohms = 49 volts * 6.125 =300.125 watts. This would
require a 14 AWG wire for 700 circular mils per amp. which is ten
time0
the diameter you quoted. It is 63 mils, or about 15 turns per inch.
It is 90 turns in 15 mm , 2 layers, 1 over the other, so 180 turns
15 millimeters = 0.590551181 inches

1/.59055 * 90 = 152.400 turns per inch.

That would be AWG 34 (143 TPI) or 35 (158 TPI), or British SWG 38 or
39. I don't see how it could handle 300 watts at 8 ohms.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Exactly my problem , I cannot square the blurb statement with analysed
physical reality.


It`s not a pure resistor, it`s an inductor, operating in a strong
magnetic field, and theoretically with forced air cooling. Also, some
manufacturers lie about their specs!

You still haven't disclosed what make and model of speaker it is.

Ron(UK)

I agree the aerodynamics of air forced through a narrow slot to produce
cooling is going to be highly significant, I hadn't considered that. I need
to find the current carying capacity of copper wire if allowed maximum
foprced-air cooling. Then come back a bit from that as the covered layer is
not cooled as efficiently as the outer layer.

I've been on Usenet long enough not to deliberately add material , not
relevant to the thread, it will divert of its own course usually anyway.


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

I'm coming round to thinking that as these pots are easily openable and
there is no wear at all on the tracks, then clean out all the lubricant with
meths or something, coat the wiper with something to stiffen it up a bit and
re-assemble, with no lubricant at all, maybe just "dry lubricant" of fine
graphite powder laid in the track area instead.

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

"N Cook" wrote in message
...
I'm coming round to thinking that as these pots are easily openable and
there is no wear at all on the tracks, then clean out all the lubricant
with
meths or something, coat the wiper with something to stiffen it up a bit
and
re-assemble, with no lubricant at all, maybe just "dry lubricant" of fine
graphite powder laid in the track area instead.


There ya go !!

Arfa

N Cook wrote:

Michael A. Terrell wrote in message

That would be AWG 34 (143 TPI) or 35 (158 TPI), or British SWG 38 or
39. I don't see how it could handle 300 watts at 8 ohms.


Exactly my problem , I cannot square the blurb statement with analysed
physical reality.

Oh for heaven's sake guys, it's *force cooled* !

Certain manufacturers have also demonstrated their voice coils operating red
hot, the materials are that good.

Graham

N Cook wrote:

maybe just "dry lubricant" of fine graphite powder laid in the track area
instead.

That'll change the resistance won't it ?

Graham

Eeyore wrote:

N Cook wrote:

Michael A. Terrell wrote in message

That would be AWG 34 (143 TPI) or 35 (158 TPI), or British SWG 38 or
39. I don't see how it could handle 300 watts at 8 ohms.


Exactly my problem , I cannot square the blurb statement with analysed
physical reality.

Oh for heaven's sake guys, it's *force cooled* !

Certain manufacturers have also demonstrated their voice coils operating red
hot, the materials are that good.

Graham


Really? How do they maintain the impedance? The resistance would go
up quite a bit, and the insulation wouldn't last very long. It sounds
like another audiofools dream.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

"Michael A. Terrell" wrote in message
...
Eeyore wrote:

N Cook wrote:

Michael A. Terrell wrote in message

That would be AWG 34 (143 TPI) or 35 (158 TPI), or British SWG 38
or
39. I don't see how it could handle 300 watts at 8 ohms.


Exactly my problem , I cannot square the blurb statement with analysed
physical reality.

Oh for heaven's sake guys, it's *force cooled* !

Certain manufacturers have also demonstrated their voice coils operating
red
hot, the materials are that good.

Graham


Really? How do they maintain the impedance? The resistance would go
up quite a bit, and the insulation wouldn't last very long. It sounds
like another audiofools dream.

I seem to recall some manufacturer in the 1980s demonstrating something like
this, touting the durability of their kapton voice coil formers. I am not
sure that the demo was using actual voice coil wire.

Leonard

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Michael A. Terrell wrote:
Eeyore wrote:
N Cook wrote:

Michael A. Terrell wrote in message
That would be AWG 34 (143 TPI) or 35 (158 TPI), or British SWG 38 or
39. I don't see how it could handle 300 watts at 8 ohms.

Exactly my problem , I cannot square the blurb statement with analysed
physical reality.
Oh for heaven's sake guys, it's *force cooled* !

Certain manufacturers have also demonstrated their voice coils operating red
hot, the materials are that good.

Graham


Really? How do they maintain the impedance? The resistance would go
up quite a bit,

It does, that`s why power compresion occurs.

and the insulation wouldn't last very long.

probably not, I have seen coil formers baked very brown by the heat
from the coil without the coil itself failing, I doubt the actual voice
coil could withstand glowing red, specially as they are almost always
copper or aluminium. Maybe the term red hot was meant as a
colloquialism for 'very very hot', certainly above 100c

I`m quite prepared to be educated tho.

Ron(UK)

"Michael A. Terrell" wrote:

Eeyore wrote:
N Cook wrote:
Michael A. Terrell wrote in message

That would be AWG 34 (143 TPI) or 35 (158 TPI), or British SWG 38 or
39. I don't see how it could handle 300 watts at 8 ohms.


Exactly my problem , I cannot square the blurb statement with analysed
physical reality.

Oh for heaven's sake guys, it's *force cooled* !

Certain manufacturers have also demonstrated their voice coils operating red
hot, the materials are that good.

Graham

Really? How do they maintain the impedance? The resistance would go
up quite a bit,

It does ! The effect is usually called 'power compression' and it can typically
knock up to 3dB off the speaker sensitivity with prolonged high power use. That'll
give you some inkling as to the temp rises involved.

Since such speakers are invariably used with 'active crossovers' on the inputs to
the amplifiers it doesn't cause any adverse issues with crossover responses.

The company that first made that 'red hot' claim was Precision Devices. You can
find a 1000W continuous rated speaker of theirs here.

http://www.precisiondevices.co.uk/showdetails.asp?id=17


and the insulation wouldn't last very long. It sounds
like another audiofools dream.

Kapton voice coil formers are now the norm for decent quality speakers.

I have *never* seen a purely thermal failure in any *modern* voice coil.

Graham

Eeyore wrote:

"Michael A. Terrell" wrote:

Eeyore wrote:
N Cook wrote:
Michael A. Terrell wrote in message
That would be AWG 34 (143 TPI) or 35 (158 TPI), or British SWG 38 or
39. I don't see how it could handle 300 watts at 8 ohms.

Exactly my problem , I cannot square the blurb statement with analysed
physical reality.
Oh for heaven's sake guys, it's *force cooled* !

Certain manufacturers have also demonstrated their voice coils operating red
hot, the materials are that good.

Graham
Really? How do they maintain the impedance? The resistance would go
up quite a bit,

It does ! The effect is usually called 'power compression' and it can typically
knock up to 3dB off the speaker sensitivity with prolonged high power use. That'll
give you some inkling as to the temp rises involved.

Since such speakers are invariably used with 'active crossovers' on the inputs to
the amplifiers it doesn't cause any adverse issues with crossover responses.

The company that first made that 'red hot' claim was Precision Devices. You can
find a 1000W continuous rated speaker of theirs here.

http://www.precisiondevices.co.uk/showdetails.asp?id=17


and the insulation wouldn't last very long. It sounds
like another audiofools dream.

Kapton voice coil formers are now the norm for decent quality speakers.

I have *never* seen a purely thermal failure in any *modern* voice coil.

Graham


I`ve seen the pigtails melt before the voice coil does.

Ron(UK)

--
Lune Valley Audio
Public Address Systems
Hire Sales Maintenance
www.lunevalleyaudio.com