Alarm volume control

Discussion in 'General Electronics Chat' started by nqtraderman, Feb 27, 2015.

  1. nqtraderman

    Thread Starter New Member

    Oct 26, 2012
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    Hi, sorry for such a basic question, but I have an internal speaker on the landing that beeps while the house alarm is being set. The problem is at night it is too loud and disturbs the kids sleep. There is no adjustment for this secondary speaker on the alarm panel so my wife has suggested sticking tape over it but I thought I'd try to wire in a variable resistor / potentiometer so I can adjust the volume to something more reasonable.

    The alarm controller appears to work on 13v dc and this internal speaker is 16 Ohm 12 Watt so from my old physics days using Ohms Law I calculate the max current to be approx 812ma.

    I assume if I can wire a similarly sized variable resistor in parallel across the terminals it will quieten the beeps down .. or am I wrong ?

    Attached is a diagram of what I was thinking
    Alarm sounder.png
    My question is can you get that size & rating of variable resistor in UK and where would I get one from ? Or are there any other ways of doing it other than hitting it with a hammer as my wife prefers

    thanks
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Not in parallel but in series.
    You can try a 4.7Ω to 8 Ω , 2W resistor in series with speaker and listen the alarm. High value resistor value will decrease the speaker output

    Putting a R is parallel will not help if the speaker driver can deliver the power. Worst case it will put an extra load on to the speaker driver and cause problems
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Put the speaker to the wiper like this... speaker.png
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    That arrangement will suffice if the pot is a wire wound type. A carbon pot will burn.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    if the "speaker" is a piezo element, the volume control will be more dificult. just put some tape over the holes the sound comes out.
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    Above two suggestions.

    1) Put the resistor in series

    or

    2) Tape over the speaker.
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I do not think it is a piezo.
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Better yet loose the speaker :D
     
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If there's any risk of you not hearing the external alarm sounder, then it would be unsafe to quieten the internal sounder.
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    I think you have to attach the photo of speaker then it would be helpful when the members give you the suggestions.
     
  11. nqtraderman

    Thread Starter New Member

    Oct 26, 2012
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    thanks for the help guys, here is the speaker, ignore the connector block that is just me messing about with it months ago. As far as I can see it's just a simple speaker held into the plastic cover by push-on serrated washers that I can't get off without breaking the mounting lugs due to the age of the plastic
    speaker1.png

    Does this help ?

    I had a brief look on eBay and I can't see any 2W 47 Ohm variable resistors, most are 1/2 w pcb mounted type. Where would I get one if that is the solution ?

    Failing that I can just go with a 4.7 ohm 2w fixed resistor in series with it ?
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    I just think if adding a pot at the input of the amplifier of the alarm circuit, that will be better, because in the power of input side will be lower and easy control as the audio amplifier, but that should be have a alarm circuit, if only adding the power supply to the speaker to make sound then you should buy a winding variable resistor then it can be afford some more power.
     
  13. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    If its an Optima panel, there is a volume preset on the alarm pcb, also you can use silent set, by press ing the SET button Twice after entering the code.
     
  14. nqtraderman

    Thread Starter New Member

    Oct 26, 2012
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    Hi Dave, unfortunately that volume control is only for the beeper in the alarm control panel and not this external speaker. and the Quick Set function just eliminates the 30 seconds grace period / beeps we need to get upstairs after setting the alarm on the control panel which is located under the stairs and if we do that the downstairs PIR see's us and triggers the alarm .. and that's even noisier !

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

    Moderator

    Oct 2, 2009
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    You don't need 2W resistors. A couple of 4.7Ω ¼W resistors in series will do.
     
  16. nqtraderman

    Thread Starter New Member

    Oct 26, 2012
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    OK, great, thank you
     
  17. nqtraderman

    Thread Starter New Member

    Oct 26, 2012
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    Hi guys, first I'd like to thank everyone who has commented, but having had recommendations from 1/4w resistors to 2w resistors I thought I'd try and work out exactly what is required using Ohms Law.

    Now the extension speaker has 2 volumes. The first and lower one, which I want to reduce, is when it beeps as the alarm is setting each evening and the 2nd much louder volume is when an alarm is actually triggered.

    From what I can work out from the manufacturers instruction sheet posted in the link earlier, the maximum voltage applied to the loudspeaker is 13v so I assume that is when the alarm is triggered and it's going full blast, therefore I assume when it is just beeping as the alarm is setting the voltage will be somewhat lower than 13v.

    If I were to install 2 x 4.7 ohm resistors in series with the loudspeaker, and basing the calculations on the full 13v being applied to the loudspeaker, I calculate the total resistance of this part of the circuit to be 25.4 ohms and the maximum current to be 0.51 amps, therefore the total power of the circuit will be 7 watts which is well within the capability of the 12w loudspeaker.

    As the voltage across all 3 resistive elements is pro-rata to the individual resistances, I calculate the voltage across each of the 2 x 4.7 ohm resistors to be 2.4v thus consuming a maximum of 1.2w each per resistor. Please see attached schematic.

    So if my calculations are correct I will need 2w rated resistors and not 1/4w as has been quoted ?

    Or am I missing something ?

    thanks

    Alarm sounder.png
     
    Last edited: Feb 28, 2015
  18. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Using 4 pcs of 0.25W will give you 2W. That is what is meant by using 0.25W R's.
    That is why I suggested to go for 2W.

    If you plan to buy on Ebay..try this
    It can be used to increase or decrease to your desire or to any sound level. Use the diagram in post #3

    If you want it faster find something similar from your area.
    A 2W wirewound pot is more effective for your situation
    100Ω 2W is typical but even 20Ω will do. Do not go for anything lower than 15Ω. Better is twice the speaker resistance
     
  19. MrChips

    Moderator

    Oct 2, 2009
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    Your calculations are on the right track.
    If you lower the volume of the beeps you also lower the volume of the alarm.
    How often is the alarm triggered? And for how long?

    How often do you have to set the alarm?
    Beep duration is a fraction of a second, not continuous. Hence 1/4W or 1/2W will do.
    Maybe you need a toggle switch to short across the series resistor when in alarm mode.
     
  20. nqtraderman

    Thread Starter New Member

    Oct 26, 2012
    11
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    OK many thanks guys, you have been very helpful and some great explanations
    cheers :)
     
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