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Determining power handling of a speaker ?

Discussion in 'Electronic Repair' started by N Cook, Jan 11, 2007.

  1. N Cook

    N Cook Guest

    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 ?
     
  2. Ron(UK)

    Ron(UK) Guest

    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)
     
  3. Eeyore

    Eeyore Guest

    RMS continuous ? What model.

    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
     
  4. Ron(UK)

    Ron(UK) Guest

    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)
     
  5. Rick

    Rick Guest

    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
     
  6. Arfa Daily

    Arfa Daily Guest

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

    Arfa
     
  7. N Cook

    N Cook Guest

    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 ?
     

  8. 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?


    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

    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.


    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
     
  9. N Cook

    N Cook Guest

    Surely if confined on a coil then lower current handling?

    8 ohms
     

  10. 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
     
  11. N Cook

    N Cook Guest

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

    Meat Plow Guest

    Most high power voice coils I've seen use flat wire. I would assume this
    adds to the watt rating.
     
  13. 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
     

  14. 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
     
  15. N Cook

    N Cook Guest

    Exactly my problem , I cannot square the blurb statement with analysed
    physical reality.
     
  16. Ron(UK)

    Ron(UK) Guest

    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)
     
  17. N Cook

    N Cook Guest

    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.
     
  18. N Cook

    N Cook Guest

    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.
     
  19. Arfa Daily

    Arfa Daily Guest

    There ya go !!

    Arfa
     
  20. Eeyore

    Eeyore Guest

    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
     
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