Most of what I've learned about soundproofing

[Guest guest]

Hello, my name is Jarred, and I'm a Misophonic ("Hi Jarred", everyone says, pretending like we are all sitting together, rather than over the internet, partly because several of us try to avoid "public"). I have a severe aversion to any sudden sound, no matter how loud or soft, though the loud ones particularly suck, and like the typical Misophonic, I cannot "get used to" the sounds no matter how many times I hear them.

The topic of this massive bastard is soundproofing, which, due to my brand of Misophonia, I've researched quite a lot. Unfortunately, from what I can find, there is NO cheap, easy way to soundproof to the degree that most of us overly sensitive types would prefer, Apart from wearing earbuds [i'm currently using Luxe Microbuds, which are very small (women would love them) and have a decent seal against the ear, which is very important]. Other than that, the only other easy solutions within a moderate price, are lining your house with box fans, or showing up at your neighbors' doorstep with a baseball bat, which could become expensive later. The cheapest decent soundproofing material is basically just regular fire grade 5/8 inch drywall. Beyond that, Soundproofing materials quickly become outrageously expensive.

Residential noise abatement works off of a few basic principles:

1. Add mass. The more dense a material is, the more energy it takes to move it. However, most dense materials are also stiff, and stiff materials vibrate more at the audible level. This is why a solid concrete wall has only a slightly higher STC (sound transmission class) which is a measure of how much sound a material blocks; the higher the number, the better. Limpid (flexible) materials can have a much lower resonance point (the point at which the material vibrates in perfect sync with the sound, causing the sound to be reproduced on the other side of the material as though it were not even there). Ultimately, we want the wall to resonate below the audible range.

2. Add air gap. As compression waves of matter apply pressure to one side of a wall, the air gap provides a cushion, as it is that air can compress. This causes the wall on the opposite side of the gap to vibrate at a lower frequency. The thicker the air gap, the more the space can compress, and the lower the resonance point will be (at and below the resonance point, the entire wall will behave as a solid mass, which is what we want to avoid). It is important to note here that as the air gap must be completely air tight in order to function as a cushion, it is vital to seal up perimeter edges of all walls, windows, and doors, with acoustic caulking and weather stripping. Be sure to caulk along where the wallboard meets with the subfloor or hardwood floor; there needs to be a thin gap which will be filled with acoustic caulking.

3. Decouple the structure. "Decouple" is another word for "disconnect"; if something is coupled, it's connected, and decoupled it's disconnected. This is important because if you put a solid material in front of a sound, which fundamentally is just moving waves of expanded and compacted matter, the way for sound to move is for the wave to impact the solid wall, causing it to vibrate, which recreates expansion/compression waves on the other side of it. The goal here, then, is to get the wall on the source side of the noise to vibrate freely from the receiving wall on the other side. Below the resonance point however, since the wall behaves as a solid mass, decoupling suffers; this is why it is critical to have the resonance below the audible range, not above.

Other than all of that, if you lined your walls with foam, and filled you walls with insulation, the sound is slowed down by friction and increased air pressure as the moving air particles (sound) is forced into the open cells. However, foam on walls will mainly just decrease echo inside the room, which is why it's used in recording studios, and insulation in the walls is limited in effectiveness because the vibrating source wall can simply bypass the insulation by vibrating the studs or joists which it is connected to. This is also a major limiting factor in the air gap principle. Both of these issues can be solved by designating separate structural members for each wall section. In other words, use alternating studs/joists, or double studs/joists. This will also increase the depth of the air gap, plus allow the addition of more insulation. If a person has some construction experience and/or isn't afraid to do-it-yourself, The materials cost for this superior soundproofing technique are much less than the ultra expensive and much less effective soundproofing materials on the market today.

On the subject, Mass Loaded Vinyl (MLV) is one such expensive product which has been used for several years now to replace lead, as it is much safer. MLV is a wonderful product for blocking out sound; then again so is glass since it too is very dense, yet our windows are horribly ineffective at blocking sound because they are so thin. The problem is, thicker glass costs more money. And though MLV is cheaper than glass per foot, it's not cheaper by much. Beyond this, MLV has a Sound Transmission Class (STC) rating of 26 or so (the higher the better), and an average wood stud wall has an STC of 35 to 40; however, the average sheet of 5/8 inch drywall also has an STC of 28. Not only this, but these STC values are not cumulative; simply doubling the drywall on one side of a wall will only increase the STC by a couple points due to the fact that the two act side by side as one solid mass. MLV is suppose to work better because it is a limp material with a low resonance point, not to mention that because it is so thin, it does not use up hardly any extra wall space. Even so, there is much controversy, because many people have asked for independent lab testing of MLV, not just by itself, but rather included in a standard wall assembly, which MLV companies have yet to provide. By the way, Acoustiblok is a MLV variant, not some new fangled technology like they like to say.

This same issue holds true for a product referred to commonly as `soundboard'; one of the more popular soundboards is called Homasote. Soundboard was originally an attempt at decoupling a wall: It is a light weight material which one attaches to the studs or joists. Then the drywall is screwed only to the soundboard, not through the soundboard and into the studs/joists. However, this product has had more than enough time to be independently tested, but good luck finding those tests. The unanimous consensus of soundproofing experts everywhere is that soundboard sucks; yet, the product sells because it is cheap, and people don't do their homework. One final point here, is that if you're looking for decoupling, a product called Resilient Channel (RC) has been time and laboratory tested and is known to work well enough in many cases. A resilient channel is basically a long thin metal strip bent along its width into the shape of an `S'. The RC is attached to the studs/joists and the wallboard is then attached to the RC, which acts as shock absorption to limit the transfer of vibration. A product with even higher votes, accolades, and reliable testing is a newer product which combines hat channel (metal strips bent along their width in the shape of a hat) with vibration damping clips. The clips are attached to every other stud/joist in a 2 foot or so grid pattern, and the hat channel is attached to that. Even so, a double or alternating stud/joist partition has better performance and costs a little less.

I've used the word `damping', to describe the action of canceling out vibration. This is the primary action used by visoelastic damping compounds also used in soundproofing; visoelastic meaning that a substance is both viscous like cold honey, as well as being elastic, meaning that if stretched, it will eventually conform back to its original shape. The most popular brand used is called Greenglue, which comes in caulking tubes and is applied in between 2 layers of wallboard. As was stated before, rigid materials resonate at higher frequencies, limpid materials at lower frequencies. Though the two layers of wallboard act as one mass, the walls will not hold a vibration very well because the compound resists vibration at the frequencies that the rigid materials want to vibrate at. As such, this compound lowers the resonance of the wallboard, lessens the ability of the wallboard to resonate at all, and converts some of the vibration energy into heat from the internal friction of moving particles of the flexible compound. The product may seem too good to be true, however, it has wonderful STC ratings from independent testers used in various wall assemblies, and is highly recommended by most professionals that I've heard from. Beside which, it really isn't too good to be true, since Greenglue is actually still a little expensive at $12 a tube, and it requires at least 2 tubes per 4x8 sheet of wallboard. A similar product is called Quietglue, and is much cheaper at $9 or so (you'll have to buy a lot of it, and the savings start adding up fast). Lab results show that Quietglue and Greenglue have performance that is too close to call. The good thing about these products is that, not only are they cheaper products and also have a lot of momentum backing them up, but they are also the easiest to install, can be installed over current drywall, and can also be used after the fact with staggered or double stud/joist assemblies for the best results. One thing I need to clarify is that a decoupled wall works so well with these vibration damping compounds precisely because they both work on different principles. Regardless of what the Greenglue company will say (to make its product seem like the ultimate end-all solution), this product does not `decouple', it only `dampens'. I can prove this with simple deductive reasoning: Resilient channel works as a shock absorber, just like air (though not as good), yet if a careless individual zips his/her screws all the way through the wallboard, through the channel, and into the studwork, the decoupling property (which is the only property that RC exhibits) is completely ruined. This is the major shortcoming of resilient channel, it's propensity to being improperly installed. You see, the screws rigidly fasten the wallboard to the structural members, shorting the system as though it were an electrical circuit. However, one thing that the Greenglue company touts as a wonderful benefit of its product is the fact that drilling screws through its wallboard/Greenglue/wallboard assembly and into the structural members (which is how you are suppose to attach it anyway) does very little to lower its performance. Rigid fasteners will short any decoupled system, so if it does little to nothing with Greenglue, this shows that the property it exclusively uses is damping. By the way, air decouples many times better than any solid substance because of simple physics. Anywho, that's my mamma. Like how I just abruptly ended this with no conclusion?