Determining power handling of a speaker ?
N Cook
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/
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
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
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
"Rick" <rick...@rcn.com> wrote in message news:45A6990F...@rcn.com...
What is " peak " RMS ? That is an oxymoron ...
Arfa
N Cook
news:eo5ftd$8j0$1...@inews.gazeta.pl...
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
>
> N Cook <dive...@gazeta.pl> wrote in message
> news:eo5ftd$8j0$1...@inews.gazeta.pl...
> > 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 ?
>
> 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
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.
N Cook
news:45A7CCAC...@earthlink.net...
It is 90 turns in 15 mm , 2 layers, 1 over the other, so 180 turns
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
> > 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.
Michael A. Terrell
>
> On Fri, 12 Jan 2007 18:23:30 +0000, N Cook Has Frothed:
> >> >
> >> > 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.
> >
>
> adds to the watt rating.
If it is square wire, multiply the current rating times 1.27
N Cook
Exactly my problem , I cannot square the blurb statement with analysed
physical reality.
Ron(UK)
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
news:9bSdnc8SbJpyIjXY...@bt.com...
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
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
N Cook wrote:
> Michael A. Terrell <mike.t...@earthlink.net> 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
Eeyore
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
Michael A. Terrell
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.
Leonard Caillouet
> Eeyore wrote:
>>
>> N Cook wrote:
>>
>> > Michael A. Terrell <mike.t...@earthlink.net> 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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Ron(UK)
> Eeyore wrote:
>> N Cook wrote:
>>
>>> Michael A. Terrell <mike.t...@earthlink.net> 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)
Eeyore
"Michael A. Terrell" wrote:
> Eeyore wrote:
> > N Cook wrote:
> > > Michael A. Terrell <mike.t...@earthlink.net> 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
Ron(UK)
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