Determining power handling of a speaker ?

[N Cook]

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 ?

 

[Ron(UK)]

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)

 

[Eeyore]

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

 

[Ron(UK)]

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)

 

[Rick]

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

 

[Arfa Daily]

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]

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
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 ?

 

[Michael A. Terrell]

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

 

[N Cook]

Surely if confined on a coil then lower current handling?

8 ohms

 

[Michael A. Terrell]

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

 

[N Cook]

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

 

[Meat Plow]

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.

 

[Michael A. Terrell]

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

 

[Michael A. Terrell]

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

 

[N Cook]

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.

 

[Ron(UK)]

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)

 

[N Cook]

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.

 

[N Cook]

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.

 

[Arfa Daily]

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

 

[Eeyore]

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