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I just discovered the greatest acoustic treatment!..
Old 2nd October 2011
  #31
Lives for gear
 
🎧 10 years
Yeah I'm curious myself now. I totally missed this thread 2 years ago
Old 2nd October 2011 | Show parent
  #32
Lives for gear
 
mcgruff's Avatar
 
🎧 10 years
I've got a set of inflatable speakers (not the bud ones in the image but same idea). A something-or-other in the base vibrates the air inside and the skin radiates the sound (I think).

Perhaps balloons really do work well as diffusers. Maybe vibrations picked up at one region of the balloon's surface would be transmitted to the body of air inside and then radiated out equally from all parts of the surface as sound waves.

Any acoustic engineers here?
Old 2nd October 2011 | Show parent
  #33
Gear Nut
 
🎧 10 years
Quote:
Originally Posted by The Byre ➑️
As sound travels through helium three times faster than through air, I am assuming that what happened in this case was some kind of extreme example of refraction-reflection, similar to the effects found within temperature inversion at an open-air rock concert, where the sound travels through the cold air above the audience and bounces off the warm air of the audience and returns to the cold air. The audience complains the sound was not loud enough, but people living five miles away, trying to get some sleep, think it is more than loud enough.
My understanding leaves me to believe sound would travel slower through helium as the denser the material the faster it travels. Sound travels faster in water
Old 2nd October 2011 | Show parent
  #34
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Rick Sutton ➑️
Don't helium balloons deflate in a few days?
The Mylar ones can last if they don't fail somewhere and leak, which they usually seem to after a few days.. Standard rubber balloons usually deflate within a day. Those small helium atoms get through the pores in the stretched rubber balloon pretty easily.

Cheers,

Otto
Old 2nd October 2011 | Show parent
  #35
Gear Addict
 
🎧 10 years
Actually there is some real science to support this and I have used balloons as acoustic treatment several times with good results. It doesn't have to be inflated with helium. I usually just blow up the balloons and tape them to the ceiling.

Got the idea from an experiment in an old high school physics class. If you take a hoop, like a large embroidery hoop or something similar, and put a plastic membrane on each side and inflate it with CO2 it takes the shape of a convex lens. Just like a glass lens focusses light, the lens shaped "balloon" focusses sound waves passing through it at a specific focal length. The key is that the gas inside is a different density than the air in the room.

Balloons, being more or less round, are equivalent to passing light through a glass ball. If you hold a glass ball up to a light bulb, you will see how the shape refracts light quite dramatically. A balloon filled with a gas of a different density than the surrounding air will do exactly the same thing to sound. Blowing up a balloon with your lungs fills the balloon with a much higher concentration of CO2 than the surrounding air. Of course inflating with pure CO2 or helium with have a more pronounced effect but in my experience it's not really necessary so I don't bother with it.

With balloons placed against a wall or ceiling, the sound will be strongly refracted and focussed on the wall. The refracted concentrated sound bounces off the wall and back into the balloon which refracts the sound waves again on the way out, basically scrambling them up so they cancel against themselves, functioning as a strong diffusor and phase canceler. To "see" what this does to sound, take a glass ball and hold it up to a mirror and shine a light through it in a dark room. The light passing through the glass ball, bouncing off the mirror and then back through the glass results in very little light making it's way back out of the ball.

Balloons work quite well to tame a live ceiling or wall. It's temporary and looks kinda cheap, but comes in really handy for location recording in a less than desirable room.
Old 2nd October 2011
  #36
Founder
 
Jules's Avatar
Quote:
Originally Posted by Robert Randolph ➑️
I have a helium balloon in my house that's been floating for 6 years now and shows no sign of ever coming down
Almost a family member then?!!!

That's great!
Old 2nd October 2011
  #37
Founder
 
Jules's Avatar
Quote:
Originally Posted by Gamelan ➑️
Balloons work quite well to tame a live ceiling or wall. It's temporary and looks kinda cheap, but comes in really handy for location recording in a less than desirable room.
Am I on crack or did I once read about an inflatable acoustic product?

Balloon traps!

Ok they were on display at the Vienna AES show (but I missed them)

http://www.flexac.com/index.html
Old 2nd October 2011
  #38
Gear Head
 
🎧 10 years
just fill the room with laughing gass, everything will sound awesome!
Old 2nd October 2011 | Show parent
  #39
Lives for gear
 
3 Reviews written
🎧 10 years
I've always mixed a few percent of xenon in with the helium. For recording hardcore, I go with 66.6% xenon and then fart in their general direction.
Old 2nd October 2011 | Show parent
  #40
Lives for gear
 
3 Reviews written
🎧 10 years
Quote:
Originally Posted by Gamelan ➑️
Actually there is some real science to support this
Can you post a reference?

Making the light vs. sound physics comparisons is fine as a sort of visualization exerciuse, but really, I've worked in the field of UV, vis, IR and electron optics for a long time and I don't believe that a balloon is creating an acoustic lens or anything of the sort. I would believe that balloons taped to the ceiling would have diffusive properties and possibly some absorption.

I just don't think your discussion holds much air.
Old 2nd October 2011 | Show parent
  #41
Lives for gear
 
🎧 15 years
Mods should move this thread to the Acoustics section and maybe some of the experts will chime in or experiment themselves.
Old 2nd October 2011 | Show parent
  #42
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by aabbey1 ➑️
My understanding leaves me to believe sound would travel slower through helium as the denser the material the faster it travels. Sound travels faster in water
In general, the velocity of sound in a medium varies inversely as the square root of the density of the medium, so it actually travels slower in a denser medium, other things being equal (which they usually aren't). However, the velocity is also proportional to the square root of the coefficient of stiffness, and the combination of all this does produce a higher velocity of sound in water. However, it's the stiffness of the medium (a condensed state versus a gas), not the density that increases the velocity.

For a gas, the velocity varies inversely as the square root of the molecular weight, so as noted previously, the velocity in pure helium (MW about 4) is nearly three times higher than air (MW about 29).

Cheers,

Otto

Last edited by ofajen; 3rd October 2011 at 08:16 PM.. Reason: Corrected MW data
Old 2nd October 2011
  #43
Lives for gear
 
🎧 10 years
is there a leak in the room or did the singer actually hit the right notes?
Old 2nd October 2011 | Show parent
  #44
Lives for gear
 
dabigfrog's Avatar
 
🎧 10 years
Quote:
Originally Posted by mwikkid ➑️
i'll bet no, for 2 reasons:


1. nitrous oxide has a different density than helium
2. you'll never get around to actually recording because of the wah wah wah WAH WAH WAH WAH WAH WAH WAH WAH

if you do them long enough, it's not wah wah wah......its All-Ah, All-Ah, All-ha....imho, fyi, ymmv, etc.....
Old 2nd October 2011 | Show parent
  #45
Gear Addict
 
🎧 10 years
Quote:
Originally Posted by Syncamorea ➑️
Can you post a reference?

Making the light vs. sound physics comparisons is fine as a sort of visualization exerciuse, but really, I've worked in the field of UV, vis, IR and electron optics for a long time and I don't believe that a balloon is creating an acoustic lens or anything of the sort. I would believe that balloons taped to the ceiling would have diffusive properties and possibly some absorption.

I just don't think your discussion holds much air.
Sound and Waves Activities

Scroll to the bottom of the page. It's a 5th grade science experiment. Many more references out there if you care to look them up. Do a search for "CO2 sound lens" (as you should have before posting) and you will see it's for real.
Old 2nd October 2011 | Show parent
  #46
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by ofajen ➑️
For a gas, the velocity varies inversely as the square root of the molecular weight, so as noted previously, the velocity in pure helium (MW about 2) is nearly three times higher than air (MW somewhat higher than 14).
Whoops! MW for He is around 4. MW for air is about 29. Actual velocity in He at 300K is about 1010 m/sec, versus 347 m/sec for air.

Cheers,

Otto
Old 2nd October 2011 | Show parent
  #47
Lives for gear
 
Ernest Buckley's Avatar
 
1 Review written
🎧 15 years
Quote:
Originally Posted by Dean Roddey ➑️
I've just begun using overweight people for sound treatment. With the economic downturn and whatnot, it's not too expensive these days.
Old 3rd October 2011 | Show parent
  #48
Registered User
 
1 Review written
🎧 10 years
This is what every studio needs ...

Air Swimmers
Old 3rd October 2011 | Show parent
  #49
Lives for gear
 
Rotaholic's Avatar
 
🎧 10 years
Would the ballons in the box sound as good or close to the real thing heh
What sort of pumps is everyone using, vintage? all tube?
Old 3rd October 2011
  #50
Here for the gear
 
🎧 5 years
I want to see the room pic with the baloon, please
Old 3rd October 2011 | Show parent
  #51
Lives for gear
 
MREVOL's Avatar
 
🎧 15 years
I just discovered this thread and must say you guys are all late. I added a couple inflatable girls to my room and now my mixes and ego are bigger then they ever were.
Old 3rd October 2011
  #52
Gear Head
 
🎧 5 years
Helium balloons will also help if you record some high pitched choruses
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