Why on earth does this speaker have a tiny lightbulb inside it

Discussion in 'Electronics & Electrics' started by MoonSha, Feb 8, 2020.

  1. MoonSha

    MoonSha Member

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    JBL Control 1 speaker, bulb has never lit as far as I know because it would be visible through the bass port.

    What's this thing doing in there?

    upload_2020-2-8_22-36-7.png

    other side
    upload_2020-2-8_22-42-20.png
     
    Last edited: Feb 8, 2020
  2. Sipheren

    Sipheren Member

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    Its a fuse I think you will find, they can look similar...
     
  3. aXis

    aXis Member

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    Current limiter maybe?

    At low current the series resistance is small and efficiency loss is minimal. As current increases the filament gets hot and resistance goes up dramatically, limiting the current.
     
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  4. mtma

    mtma Member

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    A harmonic profiling device.

    In seriousness, it has been common in mid range gear to find speaker fuses or light bulbs acting as a limiter, not 100% clear in the pics to the routing but very likely to be one here as well.
     
  5. mjunek

    mjunek Member

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    Exactly this.
    And also provides a visual indicator you're pushing the speaker way too hard.
    Seen it quite a few times in PA boxes.
     
    mAJORD likes this.
  6. Technics

    Technics Member

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    They don't call them lightbulbs. They call them PTC thermistors and charge twice the price. It was a fairly common method of implementing automatic gain control in the past. In this case it's probably protecting the tweeter from clipping. It's good because short transients won't be significantly affected because of the thermal inertia but sustained overload will.
     

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