Windows 7: How do i make sound activated LEDs 70watt speaker 120v

ok, so i talk to best buy and what they said is that theoreticaly it would work to just take the negitive and positive leads, connect resistors and LEDs... good to go, but without a series of switchs, when i crank the volume it would blow the resistors and leds. the guy i talked to said hes done it and it would be too hard to do as a one man job, but obviously it works for some people online without needing all the switches, so what will work for me. i calculated the max voltage for my speaker system is 120 volts, so if i resisted that much, wouldnt it still work, if the max is 120, turning the volume up wouldnt put it past 120 volts. so why would it blow? radio shack advised me to go to a car sterio installer and see what they say. one thing geek squad mention is that one of them a while back bought some sound activated leds from NewEgg that plug directly into the sound card audio out and are like a third party device that just bypasses the audio but reads the signal and plays the leds to the tune. that might be cool if anyone could help me try to find. or if anyone knows enough about the speaker modding im trying to do to give me some clear cut directions on how to do it. i know these things are really hard somtimes to do because they are so individualized but accentually what i need is for someone to make me a blue print of sort. i need clear cut verry defined reasoning behind why things are done a certain way. what they are protecting me against. and how it would turn out if i follow step by step. i hate when people are vague, it leads to screw ups so. if you think you can help, thank you so much.

The max voltage for you speaker system is most definitely NOT 120 volts.
If you proceed from incorrect assumptions you'll surely end up with incorrect results.

Best bet ... google-search for what you want.

Sounds like you're referring to a color organ. If that is what you're referring to you can either buy one something like this,

3-Channel AC Color Organ - Cana Kit

or build your own (I made a basic 3 channel one about 30 years ago in high school) using schematics found online, from easy to complex,

LED Color Organ Triple Deluxe

it is, 110-120

WOW maybe your speakers are 120w (thats watts) and the electrical input of your amplifier will almost certainly be 110v (120vmax) or UK 230v (240vmax) but the system does not send this much voltage to the speakers unless its some epic festival PA.

For example your 120volts pushing 4ohm speakers would require a current of 30A, you touch those speaker cables and you are going to die!

that looks really cool, i like the one on instructibles, however, i am woried, at 70 watts, what some modders told me was that you would need a series of switches not to blow your speaker, otherwise when you crank the volume fast it will kill the whole thing i guess. i dont know enough about it to know what that meens, but i know that blowing my speaker, and blowing a resistor i generaly bad juju, so do u know if i would run ito that problem here?

no, 70 watts, 120volts i did the math and then looked at the back of the box, and i did infact think of unplugging it first and waiting about 30 sec?

on the back of the box is it referring to input voltage?

A 4Ohm system running 120v would produce 3600watts

all i know is the whole system is only 120 watts, the bass subwoofer, the part im actualy modding is only 70 watts of that "it claims" you sound like u might know more about it than i do. but it didnt give me much information, if you wanna look it up yourself they are logitech x540s i belive

is it for your PC? you could always connect it to an empty output on your soundcard with no amplification, this would give you a maximum of 2 volts to worry about