What if you build a sub with helium in it?

hilbren · 9th October 2005, 04:00 PM

I was wondering (not that is possible):
You build a sub with helium in it, the weight of helium is a factor 7 lighter then the air. So the speed of sound in helium is much slower. In fact if the speed is also a factor 7 slower then it is in the air then it should do ~47m/Sec.
That means that if you build a TLsub for about 30 Hz it would normally takes a tube of ~2,75meter, but with helium it should only take 0,39meter.
But because its helium and you want to keep the helium inside, you want to build a closed sub. And if you want to build a closed TL you must build it twice as long. But even then you get a sub thats only 0,78meter.

Just a theory... but is it true?

wes-ninja250 · 9th October 2005, 04:03 PM

When you fill your lungs with helium and speak, you speak in a very high voice. Remember that your voice is given by resonant properties in your larynx, sinuses, etc as well as the frequency of vibration of your vocal chords.

This suggests to me, then, that the Fs of the enclosure will go *up* when filled with helium.

Just a guess, though. It's possible that there's some kind of frequency shift going on when the expelled helium meets regular air, I don't know enough physics to know for sure.

Wes

hilbren · 9th October 2005, 05:43 PM

So what you are saying is that I have to use a gas thats heavier than air to create the effect?

bigwill · 9th October 2005, 08:31 PM

I just looked on google and it turns out the speed of sound in helium is 970 m/s..

In argon it's 319 m/s, neon is 435 m/s.

hilbren · 9th October 2005, 08:34 PM

okay so with helium the sub gets even longer (that can't be good)
I could not find that with google (wich keyword did you use?)

so I have to look for a gas thats heavier...

but still the big question; would this work?

bigwill · 9th October 2005, 08:41 PM

I searched for 'speed of sound in helium' etc

454Casull · 9th October 2005, 09:12 PM

How do you keep it sealed?

Rademakers · 9th October 2005, 10:08 PM

The speed of sound in sulfurhexafluoride would be about half that of the speed of sound in air. Due to it's inertness and price it would probably be the best choice.

Wkr Johan

tade · 9th October 2005, 10:43 PM

you live with a billionth of a part of your air as sulphure hexafluoride. I bet it has a terribly bad odor! I would go for uranium hexafluoride. Much better smelling. go ahead, smell it.

BassAwdyO · 9th October 2005, 11:19 PM

If the sub were completely sealed(which it would HAVE to be for this idea to work) then you wouldnt be smelling what was inside. Take for instance a bottle of colonge, if the bottle is COMPLETELY sealed, can you smell colonge through it? Not unless some is on the outside

9th October 2005, 04:00 PM	#1
hilbren diyAudio Member Join Date: Jul 2003 Location: utrecht	What if you build a sub with helium in it? I was wondering (not that is possible): You build a sub with helium in it, the weight of helium is a factor 7 lighter then the air. So the speed of sound in helium is much slower. In fact if the speed is also a factor 7 slower then it is in the air then it should do ~47m/Sec. That means that if you build a TLsub for about 30 Hz it would normally takes a tube of ~2,75meter, but with helium it should only take 0,39meter. But because its helium and you want to keep the helium inside, you want to build a closed sub. And if you want to build a closed TL you must build it twice as long. But even then you get a sub thats only 0,78meter. Just a theory... but is it true?

9th October 2005, 04:03 PM	#2
wes-ninja250 diyAudio Member Join Date: Feb 2005 Location: Kingston, ON	When you fill your lungs with helium and speak, you speak in a very high voice. Remember that your voice is given by resonant properties in your larynx, sinuses, etc as well as the frequency of vibration of your vocal chords. This suggests to me, then, that the Fs of the enclosure will go up when filled with helium. Just a guess, though. It's possible that there's some kind of frequency shift going on when the expelled helium meets regular air, I don't know enough physics to know for sure. Wes __________________ Do daemons dream of electric sleep()?

9th October 2005, 11:19 PM	#10
BassAwdyO diyAudio Member Join Date: Jun 2004 Location: Illinois	If the sub were completely sealed(which it would HAVE to be for this idea to work) then you wouldnt be smelling what was inside. Take for instance a bottle of colonge, if the bottle is COMPLETELY sealed, can you smell colonge through it? Not unless some is on the outside __________________ The golden rule of DIY: Build nice, or build twice!

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9th October 2005, 05:43 PM	#3
hilbren diyAudio Member Join Date: Jul 2003 Location: utrecht	So what you are saying is that I have to use a gas thats heavier than air to create the effect?

9th October 2005, 08:31 PM	#4
bigwill diyAudio Member Join Date: Dec 2004 Location: Cornwall	I just looked on google and it turns out the speed of sound in helium is 970 m/s.. In argon it's 319 m/s, neon is 435 m/s.

9th October 2005, 08:34 PM	#5
hilbren diyAudio Member Join Date: Jul 2003 Location: utrecht	okay so with helium the sub gets even longer (that can't be good) I could not find that with google (wich keyword did you use?) so I have to look for a gas thats heavier... but still the big question; would this work?

9th October 2005, 08:41 PM	#6
bigwill diyAudio Member Join Date: Dec 2004 Location: Cornwall	I searched for 'speed of sound in helium' etc

9th October 2005, 09:12 PM	#7
454Casull diyAudio Member Join Date: Jan 2004 Location: Toronto, ON, Canada	How do you keep it sealed?

9th October 2005, 10:08 PM	#8
Rademakers diyAudio Member Join Date: Jan 2005 Location: Rotterdam, NL	The speed of sound in sulfurhexafluoride would be about half that of the speed of sound in air. Due to it's inertness and price it would probably be the best choice. Wkr Johan

9th October 2005, 10:43 PM	#9
tade diyAudio Member Join Date: Feb 2005 Location: Ralieigh nc	you live with a billionth of a part of your air as sulphure hexafluoride. I bet it has a terribly bad odor! I would go for uranium hexafluoride. Much better smelling. go ahead, smell it.

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