Converting PC speakers to portable speakers.

Discussion in 'General Electronics Chat' started by H3x0S, Aug 13, 2012.

  1. H3x0S

    Thread Starter New Member

    Aug 13, 2012
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    I've been wanting to do this for a long time. Portable speakers are often very expensive and not loud enough. I got my hand on some old speakers and I would like to turn them into a portable speakers. What are the main steps I should do to achieve this? Could this be done by only removing the 230V -> 9V converter and simply connecting a battery to the place where I cutted the wires. Could you give me an approximate time of how long would a 9V Alkaline battery last on a 18W speaker considering that it would be on 80% power most of the time? Thanks. :)
     
  2. #12

    Expert

    Nov 30, 2010
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    If a 9 volt battery could deliver that kind of power, it would last 16.5 minutes...but it can't. Try something with more current like NiMh AA's or alkaline "C" cells.
     
  3. H3x0S

    Thread Starter New Member

    Aug 13, 2012
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    What would you consider to be a cheap and effective solution for this that could provide enough power to supply the speakers? Also, do you think that they would work just by removing the converter without any additional work?
     
  4. KJ6EAD

    Senior Member

    Apr 30, 2011
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    For the lowest long-term cost of operation I'd use a 12V sealed lead acid (SLA) battery.
     
  5. Audioguru

    AAC Fanatic!

    Dec 20, 2007
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    An audio amplifier with a 9VDC supply provides:
    1) Single-ended amplifier into 8 ohms= 0.77W.
    2) Single-ended amplifier into 4 ohms= 1.1W.
    3) Bridged amplifier into 4 ohms= 3.9W.
    Maybe the rating of 18W is actally 18 Whats which are imaginary.

    Nobody plays an amplifier at 80% average output power. If it plays music or speech at clipping then its average output power is 10% or less.
    If it is class-AB then its idle current is fairly low.
    If it is class-A then its idle current is huge.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    NiMH batteries are likely the best power source. The batteries are relatively inexpensive and are lighter than an SLA battery.

    You should be able to just remove the AC adapter and supply 9V with 8 NiMH batteries.

    If you measure the 9V current with a multimeter when the speakers are playing music at a typical volume level, you can estimate how long the batteries will last. AA NiMH batteries have a capacity of about 2000mAh to use for the estimate.
     
  7. vpoko

    Active Member

    Jan 5, 2012
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  8. Audioguru

    AAC Fanatic!

    Dec 20, 2007
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    If the TDA2003 has a fully charged 12V lead-acid battery at 13.2V then its output into an 8 ohm Minimus 7 speaker is only 2.2W at clipping. Its output will be 4W into 4 ohms.

    It is spec'd to produce 10 Whats into 2 ohms at a horrible-sounding 10% distortion (clipping like mad) when its supply is 14.4V.
     
  9. #12

    Expert

    Nov 30, 2010
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    Just a note: Some NiMH AA batteries are up in the 2700 maHr range.
     
  10. H3x0S

    Thread Starter New Member

    Aug 13, 2012
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    Seems like SLA batteries are the best option. I'll be going with them. 7Ah battery + charger will cost me 40$.
     
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