Muting a loudspeaker

Discussion in 'The Projects Forum' started by nqtraderman, Nov 22, 2012.

  1. nqtraderman

    Thread Starter New Member

    Oct 26, 2012
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    I have an old house alarm, its an Optima XM, which as well as the beeper in the Control Box also has an external Speaker upstairs. Both beep at "low" volume when you Set/Unset the alarm and go off at High volume when an alarm is triggered.

    The problem is the external speaker is too loud even when its on the low level beeping mode. Within the Control panel there is a Volume adjustment pot and that is turned down as low as it will go but it's still too loud. The Instruction sheet shows the external speaker connected across pins 13&14

    http://www.moretonalarms.com/pdf_engineer_manuals/ADE_Optima_xm4.pdf

    I thought of taking the external speaker enclosure off and stuffing it with something to damp it down a bit but the thing is a sealed unit. So I will need an electronic solution .. or a hammer

    I am going to assume it works on about 13v, the spec sheet quotes the external speaker as 16 ohms / 130ma. I disconnected both wires to the external speaker and tested the voltage across them when it was beeping at low volume (set/reset) and it was around 600mv. I assume when the Alarm is triggered the voltage is increased to 13v ?

    Can I wire a potential / variable resistor in Series with the external speaker to quieten it down a bit and if so what value .. or should it be connected in Parallel with the speaker ?

    I know doing so would also reduce the High volume when the alarm triggers as well but the external Siren will more than make up for that

    thanks
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    use a 100 ohms pot
     
  3. nqtraderman

    Thread Starter New Member

    Oct 26, 2012
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    In series ?
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
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    put the pot across the supply, and the speaker to the wioer and one of the other terminals.
     
  5. nqtraderman

    Thread Starter New Member

    Oct 26, 2012
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    OK, thank you
     
  6. crutschow

    Expert

    Mar 14, 2008
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    3,235
    You can also buy a speaker volume control such as one of these, which are similar to what Dodgydave suggested.
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    You might need a 500 ohm pot (wirewound type) as it's a 16 ohm speaker and 100 ohms in series might still be too loud. Speaker attenuators can be funny like that.
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    Dodgydave suggested using the pot as a potentiometer, not a rheostat, in which case a 100 ohm pot should work since the volume can be adjusted to zero.
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Thanks Crutschow and sorry DodgyDave.

    I've never seen a commercial attenuator unit used as a 3 pin "pot", typically they use a series wirewound resistance. I'm not sure why.
     
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