Is this Audio Device electrically correct

[DEVICE Q] So, I have a speaker, and an audio input jack. I'm connecting the audio input jack via wires to the input ports of the speaker.

NOW, If I connect a device, say my computer's output audio or my Synthesizer's output audio to the audio input jack OF DEVICE Q with the with the proper audio cable (auxiliary cable), is everything OK/safe? will the speaker be able to power itself w/o the need to introduce an amplifier? Will my computer/synthesizer be blown out? etc...

Here are the basic parts for DEVICE Q
AUDIO JACK: http://www.radioshack.com/product/index.jsp?productId=2103452&filterName=Price&filterValue=under+%243.99

SPEAKER/DRIVER: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-270

WIRES: just alligator clips and wires, probably. Only two sets, one to the Negative (black/ground?) and to the Positive channel (red?)

basically if the computers output is amplified it need only a speaker...

there are two outputs generally on a computer one is AMPLIFIED and one is LINEOUT

line out is for headphones generally and can drive a 8 ohm speaker but will make almost NO SOUND ..

I THINK you will be ok with either connection as long as you connect only the speaker to the outputs of the connection and make sure its the ground and a signal connection you can use a voltmeter set on ac to see if there is some signal there grnd should have 0 SIGNAL and the live or signal wire should have some kind of voltage very low but discerable..

when i was in school we connected speakers to the output parallel ports to make sounds ..

by varying the length of time the signal was 5 volts or 0 we could change to tone gneratated..

so I know connecting to the speaker or sound wires will be completely safe especially if you connect a simple 8 or 4 ohm speaker to it...