There isn’t a day that goes by that I don’t hear someone using the application of the soundproofing term incorrectly. Sometimes they miss use the definition itself and almost always they confuse the methodologies available to deal with real soundproofing issues that are inherent in the definition. Lets define the term soundproofing and then examine current methodologies for dealing with genuine soundproofing issues.
The actual definition of soundproofing deals with sound pressure and reducing that sound pressure between the source that is generating the actual sound pressure.
Lets use the example of a garbage truck emptying the large container of trash into its back section. You are in your apartment next to the garbage truck. Following the definition, you want to reduce the sound pressure levels between you and the truck. If a motorcycle goes by and generates a pressure wave of a certain frequency and that wave travels to your house, it will be heard and possibly felt depending on the frequency generated by the motorcycle. American bike manufacturers produce the pressure waves of greatest intensity.
Pressure reduction can also be defined and the term soundproofing applied inside of a room. In a room where we live our lives, hopefully only part of our lives, we have another soundproofing example. We want to reduce the sound pressure between the source and the receiver. If we have a listening room, home theater, or professional recording studio environment, we want to reduce the pressure between our low frequency drivers and our room. The speakers generate low frequency energy which is injected into our rooms and depending on our room size, will produce resonant distortions within the room. These distortions color the audible part of the signal for both playback and recording purposes.
How To Sound Proof
How do we reduce sound pressure, so that we can actually apply the term soundproofing? We can first increase the distance between ourselves and the source of the high pressure waves. We could move to another apartment away from the garbage receptacle or we could leave the apartment complex and move to another one with the knowledge learned from the last apartment. We could move away from streets that have motorcycles on them and through traffic of any nature.
We could use noise barriers to disrupt the signal path between us and the source. This is where barrier or sound isolation technologies come into play. Noise barriers reflect or absorb some of this unwanted sound pressure. We could add barrier technology to our apartment on the walls and ceiling which is between us and the garbage truck. This would create a barrier that would disrupt the signal path between us and the source. We could do the same to our home by building barrier technology between the house and the road where sound pressure generating traffic exists. Barrier technology and its costs must be weighed against the sound pressure levels one is trying to avoid.
Inside Our Rooms
Inside our rooms, we can use damping structures to absorb excess sound pressure energy. This is a different methodology than barrier technology. In barrier technology, we are using reflection to reduce sound pressure transmission between the source and receiver. When sound pressure strikes the barrier, part of it is reflected off the barrier. With damping technologies we are using absorption. Remember from our basic physical science courses that only three things happen to sound pressure. It is absorbed, reflected, or diffused. With damping technologies, we convert the existing sound pressure energy from the electromechanical energy generated by our loudspeakers to heat through the process of absorption. Open celled and closed cell acoustic foams use this process for middle and high frequencies. Low frequency absorbers also use this technique for lower frequency wavelengths.
Noise cancellation technologies can attack the soundproofing issue at the source itself if you will. Using sophisticated electronic signal generator, one can cancel certain unwanted sound pressures electronically by introducing an inverted wave form of the noise and thus producing noise cancellation. Noise cancellation headphones are an example of this electronic sound pressure reducing technology.
Soundproofing is all about reducing sound pressure from source to receiver. We can use noise barriers or damping technologies depending on the particular soundproofing problems we are faced with. We can use damping processes such as sound absorption technologies within a room to reduce sound pressure levels at our listening or monitoring positions. We can build barrier technologies in our control rooms to keep street traffic noise from entering our mixes. Soundproofing deals with noise from outside and inside our rooms. Different soundproofing methods are used to deal with different soundproofing issues. We don’t want to put acoustic foam on our apartment walls which is a damping soundproofing process to stop the pressure waves generated from the garbage truck. This soundproofing issue would require that we use barrier technology. Better yet, just move away.