What is in a gel sac? Would it be any good at sound proofing?

So yeah, I was thinking about making a sound-proof box as part of a project and wondered: would a gel sac make good sound insulating material.  You know the stuff I mean - the little sac like things you can't help but prod about on posh mouse mats and on gel bike saddles. 

Thinking about that I also realised I didn't really know what the 'gel' material actually is?  Is it possible to easily make a similar or substitute substance at home?  Thanks.

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Proper sound treatment is a combination of three elements: absorption, reflection, and diffusion.

A bunker doesn't allow sound to escape because the walls are far too dense for air to impart much energy to them.  The sound, in turn, reflects between the walls.  However, recording studios are not bunkers - not only because bunkers are impractical to build, but because they bottle in sound.  Since the air doesn't lose much energy hitting those thick walls, it bounces back in a harsh slap that sounds awful.  Furthermore it exaggerates room modes, which are resonant peaks in frequency based on the dimensions of the room.  These peaks color the sound in unpleasant ways.

An anechoic chamber relies heavily on absorption by using open-cell foam.  This kind of foam is useful for absorption because the open cells give little caverns for air to get lost in, thereby converting the sound energy into heat.  However, anechoic chambers are unnatural sounding spaces because they are too dead; even talking in one gives you the sense that the air is being sucked from your lungs.

Diffusion occurs when sound hits an irregular surface.  A good analogy is that a flat wall behaves much like shining a flashlight against a mirror; a diffusive surface, on the other hand, is like a frosted mirror.  Not only does diffusion smooth reverberation, but due to the fact that the energy is spread instead of focused, there is a significant drop in loudness.  However, too much diffusion in a room is like turning reverb up too high - it smears the sound until it is unintelligible.

Smart acoustical engineering not only gives you a nice balanced sound in a room with minimal leakage, but it also give you the best bang for your buck during construction.  Recording studios employ all three techniques to not only sound good inside but to sound silent outside.

First, absorption can be achieved by mechanically isolating the room, thereby dampening low-frequency vibration.  This is usually done by "floating" the room, or rather building a room within a room where there are few if any contact points.  This forces the sound energy to get trapped in the air between the rooms.

Then, the walls of the inner room are splayed to reflect sound energy in ways that prevent hot-spots from forming.  By creatively angling the walls, reflected sound has a longer distance to bounce around and can be redirected so that modal build-ups don't occur.

Next it's back to absorption.  Using only patches of foam, the inner room (where the magic happens) is treated at critical points along the walls and ceiling where reflected energy may get too intense.  Also, absorptive panels (basically, wood paneling fixed so it vibrates freely at a specific frequency) are placed in modal hot-spots to smooth out any ringing.

Finally, diffusive surfaces can be built (or purchased) and placed at specific points in the room.  This helps give the room ambiance, breaks up remaining flutter echoes, and disperses energy even more.

Depending on your budget and space limitations, there are many ways you can achieve all this.  There are actually quite a few Instructables that can give you some ideas.  Furthermore, I recommend reading F. Alton Everest's Master Handbook of Acoustics as a great source of knowledge (with surprisingly little math to grok).

I know.  I don't mean to scare you into thinking how hard this will be.  I will tell you though, that you will not only save money but be much happier (as will your neighbors) with careful planning and construction.  My apartment home studio has an 82 year-old lady (who is rather sweet) through one wall and an 86 year-old lady (who is itching to call my landlord over anything) through the floor.  The room sounds great, and I have no complaints.
bongodrummer (author)  MahavishnuMan7 years ago
Wow, thanks MahavishnuMan, such a detailed answer.  I was not particularly looking for noise to sound good inside this sound-proof box, just to block it out so anything inside the box is can't be heard outside.  I am only talking about 1m x 1.5m x 1.5m box here, I should have made that more clear, sorry. 

I have read through the studio making instructables - good stuff.  Any thoughts on the sound absorption, reflection, and diffusion properties of liquids or gels?

As part of the box, I do need to have air coming in and out though- I had a thought that maybe I could reduce this problem by bubbling it through a liquid, to help close off the gap to sound. 

Thanks,
B.
     
I'm sorry about the confusion.  I naturally assumed that, since your handle is BongoDrummer, that you were trying to avoid noise issues from neighbors (as most drummers would).

Oh, well, that changes things.  Changes them quite a bit actually.

You won't be able to get much in the way of soundproofing inside that small a space, so if dimensions you gave pertain to the outside of the box, you won't have much room inside it.  Furthermore, if you require fresh air supply in and out of the box, the design gets more complex.

Obviously, you won't get sound isolation from a gaping hole in the box to allow air, so the solution you proposed to bubble air through a liquid is a great way to handle this.  The liquid (I'm assuming water), being dense and non-porous, will reflect sound within the box and transfer very little energy to the outside air.  You will, however, also need to bubble the air going to the outside of the box somehow.

Otherwise, I imagine a thick metal box lined with at least 2-3" open-cell foam and a similar (albeit smaller) metal box inside it should do the trick.  Isolating the noise source on a bed of more foam will help prevent transferring vibration to the inner box.  If you really want to get fancy, you can arrange the foam in a way that is also diffusive (since no surface is 100% absorptive, there is always energy bouncing back - diffusion is reflection made random).  To do this, the innermost foam can be cut into a pattern following a two-dimensional maximum length sequence; the pattern and dimensions of the foam pieces will depend on the most problematic frequencies, and the math gets a bit complicated, but doing so can give you an additional 6-18 dB attenuation with less material used.

Of course, this entirely depends on how loud the sound source is.  Keep in mind that it is scientifically impossible to make anything "soundproof"; it merely attenuates the vibration (and, thus, the volume) by enough of a factor to where the sound blends in with the ambient sound in an environment.

While sound intensity is often measured in dB (decibels), keep in mind that this is a dimensionless unit of measurement, and therefore is relative to some standard measure.  Decibels are also a logarithmic unit; for every 6 dB decrease in volume, the sound is perceived as being half as loud.  The average home living room has an ambient noise floor (with all electronic devices off, of course) of about 18-24 dB.  With a television on at a comfortable volume, the intensity is usually about 36-42 dB.  The difference is 18 dB; if intensity doubles for every 6 dB, then this means the average TV set is about 8 times louder than ambient noise (18/6=3, and 2^3=8).

You can pick up an SPL meter from an electronics supply store and measure the difference your box makes.  It's a handy tool to have anyhow, and fun to aim at things to see just how loud they are.

If you really want to know about maximum length sequences and how to use them, let me know.

designerdd6 years ago
I know this is an old thread, but I thought you should know about aerogel - this is the little gel granules that are inside Kalwall. Here is a link:
http://www.cabot-corp.com/Aerogel/Building-Insulation
It is pretty cool stuff with impressive credentials and acoustic insulation properties as well as thermal insulation. It is translucent, so it is also good for daylight transmission.
jeff-o7 years ago
Those little sacs probably wouldn't do much.  They are far too hard and light to absorb sound.

You could either use foam or fiberglass to absorb sound, or something really heavy like sand or concrete.  It depends on what your goal is:  Do you want to prevent sound from escaping the box, or sound from getting in?
bongodrummer (author)  jeff-o7 years ago
Thanks for the answers. I want to prevent sound from escaping.
I know that foam is a good absorber. But I was under the impression that it works best with a blocker as well - something dense like lead right?

So I my first thought was to go with 'eggcrate' style foam on the inside, backed with something particularly hard and dense, like a layer lead followed by plasterboard and ply (which would also useful for the box structure).  Though in reality I don't think I will be getting enough lead sheet any time soon.  

Also toying with the idea of having two separate boxes, one suspended inside the other, for good isolation.   

I just got curious about gel, and liquid as well I suppose...  Know how deadened all the noise goes when you put your head underwater?  

Perhaps some gel sacks might be useful as isolating material as part of an overall solution? What is in them anyway? Any easy home-brew versions? 
Dense materials transmit sound well, it's how the sound penetrates them (or not) that counts. The surface exposed to sound is important. E.g. if sound "bounces" off concrete it's a good insulator. Thin metal will absorb sound energy and vibrate, transmitting it. Lead would possibly reflect, and damp vibration, but it's not great sound proofing.
Cotton-wool would be much better.


L
I don't think you have to go so far as building a lead-lined box!  But, perhaps your idea of a box within a box, with the internal box either suspended in foam or held in place by dense sand would do the trick.

Honestly I'm not sure which would work better.  I suppose you could try both, since neither is really permanent.
lemonie7 years ago
Sound travels better through dense materials, it's the surface you want to modify in general. Classically: foam-spikes and broken-up surfaces.
Not gel, try foam


L


___ lemonie7 years ago
Yes, I think foam would be the best solution for you.  You would get the most  "bang for your buck" so to speak.