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speaker jamming?

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teslaguy

Mon Dec 15 2008, 10:47PM

Registered Member #617 Joined: Fri Mar 30 2007, 07:29PM
Location: Buffalo NY
Posts: 49

My understanding of radio frequencies is limited so bear with me here. I want to jam the speakers in an adjacent room in my college dorm and i was wondering if I broadcasted a 20kHz or so signal using a crystal oscillator and then mosfet, could the wire connecting their speakers from their computer to their amplifier pick up a sufficient enough signal to then cause interference to degrade the quality of their music. Also, how illegal is broadcasting on those frequencies, and if this idea actually has some validity, what type of power do you think that i would need to amplify? thank you.

Backyard Skunkworks

Mon Dec 15 2008, 11:39PM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

Mattski

Mon Dec 15 2008, 11:50PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

I can't imagine the speaker cord being particularly a very efficient antenna at those frequencies, remember that a wavelength is c/f = 15km in this case with such a low frequency. With lots of power, high gain, and short distance though you get more interference.

There are no doubt some frequencies that resonate with various parasitic antennas inside the speaker amplifier. Evidence is the well known cell phone speaker interference noise. If jamming is your goal I think aiming for a higher frequency would be more productive.

I don't know about legality, but the above link suggests other people might take exception to you using this slice of the spectrum. I suspect the fact that you would be causing intentional interference would make it illegal regardless of the regulations concerning the particular frequency range.

Proud Mary

Mon Dec 15 2008, 11:55PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Whether successful or not, this proposal is clearly illegal, and anti-social behaviour, to boot. Resolve your differences in a more responsible way!

ragnar

Tue Dec 16 2008, 05:01AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Illegal and antisocial, yes, but if you so much as talk on your mobile phone close enough to the equipment, you'll achieve a continuous, noisy and annoying hash if you're lucky.

aonomus

Tue Dec 16 2008, 06:42AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

To be honest, sort it out face to face instead of doing something that may turn around and bite you later. It makes you look more mature either way.

teslaguy

Tue Dec 16 2008, 12:09PM

Registered Member #617 Joined: Fri Mar 30 2007, 07:29PM
Location: Buffalo NY
Posts: 49

Thanks for all the help guys. I thought that attempting to jam their speakers might be a bit cooler to do because i am an electrical engineering student, and as far as I and the people around them have experienced, their is no reasoning behind them. But I was doing some math myself and I found out that I would be very lucky to have the cable pick up anything at all even if i was broadcasting 50 watts....so this project is a little less feasible than i had originally hoped.
Thank you backyard for your very useful link that i should have found myself. Also thank you mattski and matt for your suggestion of using higher frequencies, If i cant bare them I might try to do something using a frequency that would jam their speakers later (much experimentation would have to be done (and now you guys have got me thinking of audiomodulating a half bridge tuned to resonate with a speaker...I hope I have some time over christmas break...)). Well thank you again for the very quick and informative replies everybody. If I do anything ill keep you all posted.

Sulaiman

Tue Dec 16 2008, 01:41PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Really cool would be 'anti-sound',
ie a microphone that picks up the interference feeding a power amplifier and loudspeaker(s)
- with gain & phase adjusted to cancel the original.
You could try to 'quieten' your space this way, although to others you will be adding to the noise.
Noise-canceling headphones are an option too.

Keep cheap arcing-type motors away from your neighbours as they cause awful interference,
especially when the wires are long and loopy. Something to do with short Hertzian waves?

LithiumLord

Tue Dec 16 2008, 03:49PM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

I thought of active sound compensation a while ago in order to make a coil silencer, but it would need too much power in that case unless used for headphones (will probably add a mic mixing feature to my headphone amp however, it's gonna get usefull for compensating loud noises in subway, however so far I was successeful in just "silencing" them by adding more power to the amp ;) ).
20+kHz audible frequency is not much of a hit for the speakers even in case you'll use an RF modulation to make either an amplifier cord resonate or, in case they are receiving some radio, just override the station a bit. However it's extremely dangerous as can cause unexpected and harmfull mental effects. Do NOT try that out unless you want a bunch of insaners (including yourself as you will hear that sound too) by your side and probably, if detected, a really huge trouble with police! Both mental hospital and jail are not the best places to pass some time, even with them being pretty quiet by night ;)
If it comes down to war, you may try out a lot of interference-causing device concepts, but I guess the destructive activity is "a little" beyond what the forum rules permit ("I have read the site rules, and I agree to follow them." (c) :D ), by the way what I described was for the knowledge of those who wanted to assemble alike devices as they are pretty easy to construct and some people do underestimate the consequences of that.
The best way out I can find for you is just to punch those guys in the face if your talks to them fail, or use the help of local administration as making loud sounds at night is illegal in every country I guess. (however that's only for the case they do it at night - if that's at day time, sorry, I'm not on your side as I like listening to music pretty loud and hate when someone pops up asking me to stop that - that's my right after all)

@Sulaiman
The collector-based motors (cheap? hehe I wouldn't say they are - as this type is used for high-torque equipment and many industrial ones are really expensive, they don't arc that much as have arc suppression circuits however) are making short signal fronts that, due to the spectrum widening effect, cover much of the radio transmission frequencies.

ANY RF RAMMING EQUIPMENT IS ILLEGAL BECAUSE IT MAY INTERFER WITH POLICE, EMERGENCY, AIRLINE AND OTHER VITAL RADIO COMMUNICATION FREQUENCIES.

GeordieBoy

Wed Dec 17 2008, 01:15AM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

> The best way out I can find for you is just to punch those guys in the face if your talks to them fail...

That's what I like about this forum. You get a whole spectrum of answers to people's questions!

Christmas greetings to all, (and happy holidays to those who don't celebrate Christmas.)

-Richie,

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