Is it possible to convert a self-powered speaker into a passive one? (and if yes, how?)
My scenario: I have an old pair of PC speakers i'd like to use with my portable MP3 player even if there is no power outlet nearby...
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1\$\begingroup\$ How do you plan to power the speakers without a power outlet? Do you have some sort of battery-powered amplifier? An MP3 player alone does not supply enough power to drive a standard set of bookshelf speakers. Otherwise your headphones would be incredibly loud and the battery would drain awfully quick. \$\endgroup\$– Justin TrzeciakMar 2, 2014 at 23:33
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\$\begingroup\$ i've seen some passive speakers recently for sale (like the Sony SRS-P7), so i thought it would be possible. Also, i don't mind about low volume and battery draining... \$\endgroup\$– eadmasterMar 2, 2014 at 23:37
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\$\begingroup\$ If you aren't too worried about volume or battery life, you might be ok. What you would have to do is investigate the circuit in the existing speakers to see what is doing the amplifying and what is conditioning the signal. Then, you would have to isolate the amplifier such that your new input would only feed into any built in crossover (if there is more than one driver for each speaker assembly) and equalization before reaching the speaker(s). It's hard to say without a schematic or picture though. \$\endgroup\$– Justin TrzeciakMar 2, 2014 at 23:57
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3 Answers
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Passive speakers like the Sony SRS-P7 are cheap headphone type speakers combined with acoustic amplification. A carefully designed sound channel amplifies the audio. Like cupping your hands to make your yelling louder, or sticking a cellphone in a bowl (I use a roll of blue painters tape, it really works well). There's a limit to what can be done based on the size of the enclosure. Active speakers on the other hand, are typically directly facing the outside.
To modify an active speaker into a passive one, would need new speakers and some manufacturing of a sound channel (Using a router or plastic injection moulding or 3d printer, etc)
The best thing you can do would replace the power and amplifier circuits with a battery powered one. And the speakers themselves will need to be resized. Essentially, the only thing you would keep is the audio cable and the case. Not practical or pragmatic.
Hit a dollar store. Buy a portable mp3 player speaker case, or a set of passive speakers...
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\$\begingroup\$ My friend connected a 12V 2Ah Lead-acid battery to his desktop speaker set and used it as portable active speakers. \$\endgroup\$ Mar 3, 2014 at 5:06
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Most headphone amplifiers are designed to drive at least 8 Ohm load. The speakers can have different resistance, but 4 and 8 Ohm speakers are quite widespread, and 2, 16, 60 Ohm or even more are rare.
If your speakers' resistance is at least 8 Ohm, it's possible to use them with your MP3 player just like headphones. The use of this application is another question - the volume will be so low that you will need to hold the speakers close to your ears, just like headphones :)
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I have an old pair of PC speakers i'd like to use with my portable MP3 player even if there is no power outlet nearby...
You could build a battery-powered power supply. This could be a few AA batteries or lithium-ion battery with a regulator and a separate charging circuit.
There is likely to be spare space inside at least one of the enclosures (though this might affect accoustics).
answered Mar 3, 2014 at 10:06