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Old 15th October 2005, 06:02 PM   #1
Soulwax is offline Soulwax  United Kingdom
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Default Vacuum loudspeaker

Possibly a silly question but here goes anyway.

What would happen if you were to take an acoustic suspension enclosure, make it airtight, and then evacuate the air inside to create a partial vacuum? What would happen to the rear wave since it would have no medium through which to propagate?

Would this reduce cabinet colourations?
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Old 15th October 2005, 06:23 PM   #2
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Here are some recent thoughts...

http://www.diyaudio.com/forums/showt...374#post741374

-Casey Walsh
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Old 15th October 2005, 06:41 PM   #3
Tweeker is offline Tweeker  United States
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One thing that will happen is that the cone will no longer be resting at the mid point of a normal suspension/surround but will be pushed well into the cabinet side. Using a gas of different mass but the same pressure wont have this.
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Old 15th October 2005, 07:08 PM   #4
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Default Re: Vacuum loudspeaker

Quote:
Originally posted by Soulwax
What would happen to the rear wave since it would have no medium through which to propagate?

Would this reduce cabinet colourations?


the rear wave wouldn't exist if there was a vacuum there...

I don't see how this is possible though given that speakers themselves leak air
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Old 15th October 2005, 07:14 PM   #5
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For one thing it would make it much easier for incredibly degenerate, stupid people who attend stereo stores to push in and damage the dust caps in the middle of exposed loudspeaker drivers!
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Old 15th October 2005, 07:21 PM   #6
Soulwax is offline Soulwax  United Kingdom
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Good link Casey. I obviously have some reading to catch up with.
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Old 15th October 2005, 08:27 PM   #7
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Well, multiply the pistonic surface area of the cone by atmospheric pressure. That number is the force applied to the cone [inward].

I don't think any kind of speaker can handle that kind of ridiculous abuse.

EDIT: However, if you do have a cone/suspension that can handle it, I believe you could achieve a response like that of an infinite baffle (but in sealed enclosure with a volume of virtually zero).
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Old 15th October 2005, 09:33 PM   #8
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you would need over 500kgs of force to move a 12 woofer.thats one big magnet and alot of watts
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Old 15th October 2005, 10:44 PM   #9
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Actually, it would not necessarily take a lot of force to move it. You would just need a suspension with the right spring constant and a lot of play.

Think of it this way- if you had a really long spring (hundreds of feet), it might have 500 pounds hanging from it, but another ounce of force could move it an inch or more. That's assuming a linear spring constant.

I think it sounds reasonable as far as the physics of it go, but I'm not sure if you could arrange a geometry that would be able to take advantage of it. Perhaps a really funky spring constant could do it; or a servo motor with a DSP controlled displacement/force curve.

I wouldn't call the vacuum woofer a physical impossibility yet, but I doubt it's within the range of the DIY community, nor will it be within the next 10 years.

Edit- change units to metric

Disclaimer- I am a fan of science fiction
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Old 1st August 2007, 01:07 PM   #10
APi is offline APi  Finland
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What if you make loudspeaker box U-shaped, put some elastic foil on it and suck the air away. The foil bend inside the box until it has enough tensile elongation. Pressure is "only" 1/5-1/10 what you have in bicycle wheel. Not anything that the right material wont stand.

And there you have the "cone". Box can be very thin, very tall and/or wide.

But how to move the "cone" since its not stiff enough for a point force?

ESL?
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