Resonance?

Tater Rocket

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Anyone know much about the subject? I downloaded a program where I can put in a frequency and it plays it. Who wants to help me find the resonate frequency of my dorm floor? I found the frequency of my room, around 40-45 htz. The floor is approximately 100-150 feet long. But I am wondering about the method to find the frequency. Should I just aim the sub at the wall and keep hitting numbers until somebody at the end of the floor tells me they hear it (if volume is kind of low) or what?

Thanks for helping me in this joke,
Spud
 

Tater Rocket

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Well..nevermind, I am close
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I found what I thought was the resonant frequency of my room, but apparently it is the same frequency as the room below me and a couple doors down ;-) It wasn't LOUD in other rooms like it was in mine, but it was everpresent in any room on this side of the hall. The girl below me said her entire room was shaking and she couldn't tell where the sound was coming from, which means it wasn't just the bass, it was resonating. She said the way she found out was she came up here because a friend of hers was up here and she heard people talking about how "chris has something in his room that is shaking the whole building". Hehe. And that is with the sub facing forward, not toward the side that is the length of the floor. I may later re-arrange it so the sub is facing the wall and see if it will show up better in other rooms.

Oh, and it was about 45.7 htz.

Spud
 

x-ray

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Spud,

This sounds like fun
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any chance of a link to the program you downloaded ?

Thanks
 

Tater Rocket

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http://download.com.com/3000-2169-10177949.html?tag=lst-0-1

There ya go
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Have a good subwoofer ;-) Just start as low as your sub will go and go up a htz at a time until it gets louder (keep going as it may just be your sub getting into its effective range). There should be about a 5htz region where it just fills the sound. Go up in that 5htz area slowly until it gets the loudest. I'll have to do this experiment after I go home too
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Fun stuff.

Edit: Hey look, post 555, only 111 more to go until I will be transformed to satan.
 

x-ray

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Thanks

Now this board is responsible for eye and ear damage
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Tater Rocket

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Hehe, no, more like brain damage. It doesn't hurt your ears, it hurts your head and drives you insane ;-) I still have a slight headache from it, but it was well worth it
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That is the second time I have had the whole floor talking about my computer speakers. The main speakers I bought a cheap 2.1 set, but off all the speakers, and hooked up 6.5 inch pioneers (only $20 a pair) to it. When testing I turned the volume up and started playing music. I had one song that had an air raid siren...apparently it sounded real enough and loud enough that everyone came out of their room and one guy got off the phone with his mom saying "mom, I have to go, I think we may have to evacuate". Hehe, so much fun.

Spud
 

Nerd

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Now I will have to try resonating my house... hope that nothing happens to my hdd...
 

Tater Rocket

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The easiest way is set on sweep to go from around 150 htz down to 10 for a 5 second duration, then undo the mute button. Note if it gets real loud close to the end or beginning, then close the parameters in around 20 htz a time. Some time I should stick the sub out in the hall where there are no walls as obstructions and try to find the resonance there. Should make for an interesting weekend here in this crappy town.

Spud
 

Icebreak

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Tater Rocket-

My microphone input stops when I fire up the program but the program has a place for microphone input. Do you know what that is for?
 

Nerd

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my speaker only produces sound at 50 hz and above... oh well... the table's integrity was compromised at 67 hz. Computer casing was rattling at higher volumn.. test terminated when brother complain of headaches... lol
 

Albany Tom

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You may want to look at the video of the Tacoma Narrows bridge before you play too much with that.
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I think someone from the college I went to designed it. When the wind blew just right, it setup a little vibration that got bigger, and bigger, and....well let's just say it tore the bridge apart in a most interesting manner.

This happens every few years when someone decides to have a party on an overhead structure that wasn't quite built well enough.
 

binky

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Tater -- You'll get a 'resonant frequency' at even intervals of some integer n times 1/2 the wavelength. The value at 1/2 the wavelength is a nice base to quote so that's what's called resonant frequency. The wavelength of the sound is a function of how fast it travels in the medium that it's giving a pressure wave to.

In air that's the speed-o-sound which we all know at around (I can't remember exactly so help me here) 550mph. Crud. Metric system would really help here but I learned part in one system, part in another. The speed is a function of the density of the medium. It's linearly proportional to that, in fact.

Anyway, obviously if you know the speed the wave travels and its frequency (frequency = how long it takes to make one full sine wave pattern) then you can divide speed/freq = (m/sec) / sec to get the length of the wave in meters.

Am I making any sense here? Am I just telling you something you know already?

You're floor's fixed around its edges (we hope). You want to find the minimum wavelength that makes the middle of the floor go up & down the most. That's the resonant frequency of the floor. At that time when the subwoofer is making the floor move the most, you'll be creating the biggest pressure fluctuation in your room. That also means that the microphone's transducer will be shoved the hardest, and you're hearing the loudest sound for a given amount of power input (power set by volume control). The computer is probably looking for where that maximimum volume is for the very lowest frequency, thus pinpointing your 1/2 wavelength value. That's your resonant frequency, and that's why you need a microphone to gather the feedback.

I hope this helps somewhat. Good luck!

Now if you can help me write a big report on SAN vs NAS...
 

Tater Rocket

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When I mean the floor, I mean the entire 10th floor...not my room's floor ;-) What I'll do next weekend is put the subwoofer in the hall and run the sound down the 100-200 feet of hall and find that pitch. Should work better as there is nothing blocking it until it gets to the wall on the other end. Don't have time this weekend...but next weekend heck yeah, hehe. Should be fun...that and watching war movies with it hooked up.

Spud
 

binky

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Well, it really must be giving you the resonance of your floor and lots due to your whole room because you can't completely isolate the floor from the rest of the effects.
 

Icebreak

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I have heard of successful and unsuccessful attempts at using this concept as a detection device and as a weapon.

A powerful and controlled voice can destroy a crystal champagne glass.

A powerful and contolled device should be able to detect the resonant fingerprint of a ship at sea amd conceiveabley rattle it.
 
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