What if you build a sub with helium in it?

[Tehrasha]

Aleast some of those heavy boxes would be easier to move. 😀

 

[tade]

Sulfurhexafluoride is oderless and inflammable, so no problems there (could have found that out yourself btw)

Thanks for the tip. i didnt know i could learn information by myself.

 

[xplod1236]

With Helium you'd need to build a much bigger box.

dave

I'm not sure what kind of box we're talking about, but for a sealed one, you would need a smaller box.
According to the ideal gas law, "One mole of an ideal gas at STP occupies 22.4 liters." That applies for all gasses, so you would have the same amount of helium as air. The pressures inside and outside the box would be the same, but helium would be a lot easier to compress (because of the smaller molecule size) than air, which would be like having a bigger box filled with air.

the weight of helium is a factor 7 lighter then the air.

So you would get away with using a helium-filled box to get the same response as you would from a box that is 7 times bigger and holds 7 times more air.

This should be correct according to the ideal gas law, but in my mind it just doesn't seem right, and I can't figure out why.

Anybody want to add to the confusion?

 

[mike.e]

A guy online called MuriloP,he had a site with equations proving why in theory,a box of something other than air could prove useful I forget what it was.

What about loosely filling a gastight thin bag with gas inside the box?

One or two companys have done it commercially.

 

[rcavictim]

Sulfurhexafluoride is oderless and inflammable, so no problems there (could have found that out yourself btw).


Wkr Johan

Due to a quirk in the english language, there are many, both words flamable and inflamable mean that the substance will burn. Non-flamable, or uninflamable mean no fire. I'm not sure if unflamable is a real word. The meaning seems to be clear though if it is. No fire.

 

[ralphs99]

In the 70's Cerwin Vega made a system with a Nitrogen filled bladder inside the box.

Cheers,
Ralph.

 

[jadenlinkletter]

i'd say this calls for a project,

if anyone has any useful information.
links,
specs,
company,

post your info.

thanks,

 

[Rademakers]

i didnt know i could learn information by myself

Meditation perhaps would do that for you, however you could have checked with Google first 🙄

Due to a quirk in the english language, there are many, both words flamable and inflamable mean that the substance will burn. Non-flamable, or uninflamable mean no fire. I'm not sure if unflamable is a real word. The meaning seems to be clear though if it is. No fire.

Thanx for the pointer 🙂

Non-flam(m)able it is.

Wkr Johan

 

[phase_accurate]

Re pressurizing box:

Apart form causing problems with coil displacement and challenging a driver's mechanical rigidity it would only do one thing: make the air-volume "stiffer". I.e. it would rise the in-box resonance frequency (fc) of the driver which you don't want - I assume. This effect can be had much cheaper by using a smaller box from the beginning !


Re articifially increasing the internal volume:

There was once a closed-box speaker model by Cerwin Vega (late seventies beginning of the eighties) that had a bag inside which was filled with some inert gas to achieve exactly what is discussed here.
Apart from that I once read about using some stuff that easily changes between fluid and gaseous state at room temperature to achieve the same.

Regards

Charles

 

[SY]

SF6 is indeed non-toxic, inert, non-inflammable, and dense. It does have one disadvantage- any sparks or arcs will cause it to break down into some VERY toxic components.

 

[Tweeker]

On the bright side SF6 is harder to arc in than most gases. SF6 is also a very potent greenhouse gas.

 

[Rademakers]

SF6 is indeed non-toxic, inert, non-inflammable, and dense. It does have one disadvantage- any sparks or arcs will cause it to break down into some VERY toxic components.

Are you sure?

It's used in electric insulators, even in the breakers of 100kV+ devices.

If it would break down, it could only break down to the elements it consists of. Perhaps my chemical knowledge isn't extended enough but it seems strange that it would break down from a very stable compound into one of the most reactive elements possible (totall 2 of course).

In other words the opposite of the foundation for predicting the behaviour of molecules by means of electronnegativity and sharing electrons.

In electrical insulators by example, it would mean that it wouldn't insulate at all, but would attack and eventually destroy the metals it would be assumed to protect, unless the reaction is irreverseble enough to immidiatly react to the compound ones again.

On basic chemical and physical properties I would put it in the same class as CFK's and Teflon (carbon surrounded by fluorine). All substances that are known and used for there great thermal stability and overall chemical inertness.

Btw, what does 'arc' mean (couldn't find it)?

Wkr Johan

 

[phase_accurate]

Btw, what does 'arc' mean (couldn't find it)?

Maybe something like that ?

http://teslamania.delete.org/frames/mpg/500kV_Switch.mpg

Regards

Charles

 

[Tweeker]

The elements it consists of are very nasty. The plasma is hot indeed. S-F bonds arent incredibly strong (as F bounds go). The dielectric strength in power applications is sometimes increased by using N2 to pressurize it. SF6 dielectric strength is about three times that of air.

In electrical insulators by example, it would mean that it wouldn't insulate at all, but would attack and eventually destroy the metals it would be assumed to protect, unless the reaction is irreverseble enough to immidiatly react to the compound ones again.

Its insulates very well, until it doesnt. Only after its been broken will you have nasties about.

 

[Rademakers]

But is the temperature in a closed bag, inside a closed or vented system, high enough to initiate this?

Wkr Johan

 

[jadenlinkletter]

So one guy sais a gas thats lighter then air will make the internal volume seem bigger

another guy sais that a gas tahts heavier then air will make the internal volume of a box seem bigger,

which is it??

if i go to the store and buy 20 baloons filled with helium, is it going to work?

we all know we can realize huge dynamic peaks in bass in massive ported boxes, i want to put theese in a 5 cubic foot enclosure that has a 15 inch pa woofer in it.

if anyone can help me decide if this will work, i'll have results withtin 3 or 4 hours

 

[SteveCallas]

Maybe I'm just being cynical, but if you would go to all the work of deciding upon the optimal gas, figuring out a way to remove the air in the enclosure and replace it with said gas, seal off the enclosure completely, and be assured of no ill effects to the driver in order to get the enclosure to act like a bigger enclosure.....why not just build a bigger enclosure instead?

 

[jadenlinkletter]

good point,

one answer in my oppinion

more bass, less space.

very practical for DJ'ing and car audio

 

[xplod1236]

So one guy sais a gas thats lighter then air will make the internal volume seem bigger

another guy sais that a gas tahts heavier then air will make the internal volume of a box seem bigger,

which is it??

I'm saying that helium is gonna make the internal volume seem bigger. I did a lot of thinking about this, and the theory seems to be correct.

I think that the other guy says that in a gas that's heavier than air, sound will travel slower, which would be useful in the port of a ported box and in a tl.

Somebody correct me if I'm wrong

 

[Svante]

The acoustic compliance of a box is

Ca=V/(rho0*c^2)

for helium rho0=0.1785 kg/m3 and c=970 m/s, V is the box volume. This means that the compliance is 0.85 times that of an air filled box, that is it appears 0.85 times as big. In turn this means that the box would have to be 1/0.85=1.18 times larger to give the loudspeaker the same frequency response as the air filled box.

On the other hand, since the velocity of sound is 970/345=2.8 times higher, all the box resonaces would occur at 2.8 times the frequencies of the air filled box. This is good. In the cases where standing waves is a problem, filling the box with helium could shift these frequencies to a region where they are less of a problem.

However, I think that the main reason that helium is never used is that the gas will eventually leak out of the case, and then the dimensioning of the box will become completely wrong.

And bass-reflex would be out of the question. 😉