Foam and rubber... Here's something I am all too familiar with. I will explain in general terms that apply to my job and in theory should transition over - seeing that sound is always measured the same. Being an audio engineer/producer there are a lot of misconceptions behind these two products. This misconception is incredibly common – so if you are reading this thinking to yourself, “Well, self, doesn’t foam stop sound? Isn’t foam used for even soundproofing a room? Everyone knows that, right?” Unfortunately I have to tell you that you are wrong. Foam does not stop sound, foam absorbs echo. Don’t feel bad. There are lots and lots of people out there that share this idea.
You Can’t Build an Aquarium With Sponges...
A much wiser man came up with an analogy that I have found useful in helping people understand this whole idea in a very generic way. Imagine you are building an aquarium. You want to keep the water in, right? I know I do, at least. What do you think will be more effective, glass panels and seals or pillows and sponges? Sound acts very similar to water when you are trying to control it. If you used sponges as the walls, they would fill with water and let all of it through to the other side. Now if, instead, you used thick glass and good seals, that would keep the water in place. Acoustical materials made from soft, squishy things like sponges are going to absorb. Dense, heavy, air-tight glass and rubber will block. That is the basics right there. Now you can impress all your friends by knowing this.
Absorbing
Products that are designed and intended to absorb echo (not block sound) are soft, light, fluffy products. They will generally feel soft to the touch. They are designed to soften up the surfaces within a room and reduce the echo in that space.
I like analogies, I think they help people visualize and relate to an idea, so here goes another one. Let’s say you are finishing a room in your basement. You have installed the studs that will frame the wall and you are to the point where you are ready for sheetrock. Instead of using sheetrock, though, you decide you are going to put up some 2″ thick “egg crate” foam on the studs. Keep in mind this foam has almost no mass or density, it is mostly air. After you’ve got this installed, you tell one of your helpers to go stand on the opposite side of the wall and begin talking. You will be able to clearly hear each other as if there were no wall in front of you.
Blocking
Products that are designed to block sound from entering or leaving a space are almost always found inside the wall construction. These products are heavy, dense, cumbersome, or designed to decouple the wall so that one side of the wall doesn’t have hard surface contact with the either.
Remember that last analogy? The one in your basement? Let’s go back there. Now, instead of foam this time, you decide it would be a better option to use 2 layers of 5/8″ rubber vinyl on either side of the wall. 2 layers on the inside, 2 layers on the outside. You send your help to the other side again and have them start talking. I would be willing to bet that you can not hear much of what they are saying because you have added so much mass into that wall.
Echo...Echo..….Echo….…..Echo…...…..Echo
You guessed it, I’ve got another analogy! Let’s head to the gym. It’s currently under construction because they are adding some real nice racquetball courts. Let’s check them out. The room is made out of concrete and is the size of a standard racquetball court – 20′ wide x 40′ long x 20′ tall. The walls of this room are two-feet thick. You clap your hands in the room and the echo seems to go on forever. Let’s have some fun in here. You have, in your hands 100 new super bouncy balls of varying colors. (You must have really big hands.) You throw them in every direction and they keep bouncing and bouncing everywhere through the room. After a few minutes, they eventually stop bouncing and hopefully you remembered to wear your helmet or you may be dealing with a big headache. Now imagine that you brought some 2″ thick foam with you. You line the walls, ceiling and floor. After that is done, you throw the same 100 super bouncy balls. This time when they hit the wall/ceiling/floor they don’t bounce. The energy from the ball was absorbed into the room, more specifically, the foam. A sound wave inside this room is just like that super bouncy ball. It will reflect, or “bounce”, of any hard surface but will be absorbed by a soft surface.
Now what?
If you made it this far, I congratulate you for making it through my fairly crude examples. My intent was to help paint a picture to help you understand more clearly the general differences between absorbing and blocking sound (soundproofing). I’m sure there are lots and lots of people out there that are excessively smarter than I am who are shaking their heads because I did not touch on the technical side of things – explaining wavelength and frequency, etc. I don’t care. I am trying to simplify things to give those non-technical individuals a basis to begin educating themselves on their noise problem(s).
In my opinion, foam ear brands are good, but they need to be changed often. There are other products made of harder rubber/plastic that will last longer and provide more dB reduction. Overall, look at the dB reduction ratings to see which one knocks down the noise the best. My money is it will be the rubber ones in theory. The higher the dB rating means the less noise going to your ear, but they have to be placed in your ears correctly. Find one that doesn't cut enough that it isn't safe, but that is the right fit. User reviews might be your best bet when it comes to that.
