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Cornstarch Subwoofer!

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Avalanche

Fri Aug 04 2006, 08:19AM

Registered Member #103
Joined: Thu Feb 09 2006, 02:16PM
Location: Derby, UK
Posts: 625

I was searching through the spare room earlier, and found my old subwoofers. It reminded me of the cornstarch speakers posted here a while ago, and I wondered what would happen if I scaled it up a tad? Despite the fact that there's loads of more important things I should be doing, I decided to give it a try anyway with one of these subwoofers

I hooked one up to my Kenwood amp, and ran Adobe Audition to generate some nice low frequency sine waves. Mixed up the cornstarch and added a bit of green ink to err.. make it a bit less freaky, and then I found the most interesting effects to be 4-8Hz, and even a tiny shift in frequency (.5Hz) changed the appearence. When the frequency got just too high (about 8Hz) I got what I call the 'alternating tongue' which just turned into a mess if I increased the amplitude any further. Anyway, with the nice effects at 5-7Hz, I decided to run some music through it at the same time, observing the waveform of the music on the peaks of the low frequency. It got quite entertaining!!

5Hz:

Video Stills (6Hz)

Videos (WMV)

6Hz Increasing Amplitude (1.55Mb)

Music 1 - Chilled out with good bassline + 5Hz (1.56Mb)

Music 2 - Similar again + 5Hz (1.51Mb)

Music 3 - Drum n Bass + 5Hz (1.55Mb) < "it's heavy stuff"

The second music video is probably the best, by the time I did the other videos the stuff had dried out too much and I had to crank the volume to get it to move again. I decided to stop when the burning smell got too bad, and my amplifier was almost too hot to touch. I rinsed the sub off under the tap, not sure if it's still ok or not. About half a pint of cornstarch did load it down a bit

"I've lost track of where all the different burning smells are coming from..."
"Is the water off? I need to cut this hose" ... "That's not a hose you idiot, that's the 3-phase!"

Blackplasma

Fri Aug 04 2006, 08:27AM

Registered Member #63
Joined: Thu Feb 09 2006, 12:18AM
Location:
Posts: 1417

Great stuff Avalanche! I think this is starting a trend =-D

How did you line the woofer?

Avalanche

Fri Aug 04 2006, 08:33AM

Registered Member #103
Joined: Thu Feb 09 2006, 02:16PM
Location: Derby, UK
Posts: 625

I just used it without any lining, the diaphram is plastic - made out of 2 parts (so I just hoped it wouldn't leak

)

It seems ok now it has dried, I think it survived!

"I've lost track of where all the different burning smells are coming from..."
"Is the water off? I need to cut this hose" ... "That's not a hose you idiot, that's the 3-phase!"

Tesladownunder

Fri Aug 04 2006, 11:31AM

Joined: Thu Feb 02 2006, 03:45AM
Location: Bunbury, Australia
Posts: 1345

The photos and videos look great but I really think you are demonstrating resonance in a pool of fluid and not the same rate dependent viscosity that causes fingers to develop and grow as in the previous thread. The spooky cornstarch effects seem best at 50Hz and develop slowly.
Sorry I haven't put a video on to demonstrate the effect but my only loudspeaker available was the 4 inch one with half the surround decayed away.

Why don't you let it thicken up and try 50 Hz. It should be of the consistency that it will pour in a slow stream, but you can hit it with a spoon without splash.

Peter

..... "Power tends to corrupt, and absolute power corrupts absolutely." Lord Acton, 1887.
...................... See absolute corruption at

Steve McConner

Fri Aug 04 2006, 12:16PM

Joined: Fri Feb 03 2006, 04:52AM
Location: Glasgow, Scotland
Posts: 3930

Just think, if you listen to drum'n'bass loud on headphones, that same thing could happen to your brain!

"Common sense is holographic and common sense itself should tell you that." - the late Chris McKinstry
don't forget to visit the scopeblog!

Avalanche

Fri Aug 04 2006, 12:22PM

Registered Member #103
Joined: Thu Feb 09 2006, 02:16PM
Location: Derby, UK
Posts: 625

thanks for the input, yeah I must admit I did wonder about that, and thought about trying it with water at one point. The whole thing seemed to settle down and resonate at about 2.5 Hz, or half the frequency I was driving it at.

I guess I'll have to get the subwoofer out again and terrorize the neighbours

or probably best wait until mid-week next week when they are at work (it's loud).

wrote ...
Just think, if you listen to drum'n'bass loud on headphones, that same thing could happen to your brain!

that's a scary thought, but enough amplitude and it would be true

Another thing to try with the cornstarch - I got this idea from an open day at my old school. Pour some into a small pot, make sure it's about 2" deep then put your finger into it. When you pull out your finger, it feels like you've left it behind

"I've lost track of where all the different burning smells are coming from..."
"Is the water off? I need to cut this hose" ... "That's not a hose you idiot, that's the 3-phase!"

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