Sound Isolation

Soundproofing and acoustically treating a room both involve controlling sound in some way. Many online sources treat these two topics as one, but the techniques and goals are sufficiently different for me to treat them separately. This page covers possible solutions to thwart sound transmission and discusses the options used in this room.​

 

Soundproofing a room involves adding elements to minimize the sound energy that leaves or enters the room. Acoustic treatment, however, consists of designing the room's interior to create optimum sound clarity throughout the listening area. Acoustic treatments may, in fact, slightly reduce sound escaping the room, but the amount of reduction is most likely negligible.

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This section covers the background and decision process for sound isolation, and a separate section deals with room acoustics design tradeoffs.

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Before going too far, I needed to determine the desired level of sound isolation. Going for near-silence would be expensive and probably require shrinking the room on each surface to increase the isolation. So, my overall goal was fairly modest. That goal was to obtain reasonable sound isolation while maintaining relatively low costs and being relatively simple to implement.   

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Before discussing what was implemented, it is helpful to summarize the background information that drove the eventual decisions. ​Sound isolation techniques can be grouped into four main categories.

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1. Decoupling/Isolation: Sound travels more easily through solid materials like wood or drywall than through air. Isolating the theater room by ensuring building materials around the room do not physically contact the rest of the building effectively prevents the sound from leaving (or entering) the room. In practice, complete isolation is challenging, so minimizing contact points and using dampening materials for those contact points (see #4) minimizes sound transmission.

2. Adding Mass: Very simply, making an object heavier, such as a wall, will allow it to absorb more sound energy and reduce sound transmission. The added mass takes more energy to vibrate, and this mass will help convert the vibrational energy into heat. A good example is using a double layer of thick drywall (sheetrock). Another example, mass-loaded vinyl (MLV), is mentioned, but some don't consider it as effective as other options.

3. Absorption:  Even though air is not the most efficient medium for sound transmission, it is desirable to make it worse by filling air space with materials that can take the air's vibrational energy and convert it to heat. Fiberglass insulation, or Rockwool, is effective at doing this.

4. Dampening: This concept is similar to absorption but typically involves placing elastic material between other construction materials. These elastic materials convert vibrational energy to heat, reducing sound transmission. Various elastic compounds, such as acoustic putty/caulk and green glue, fall into this category.

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​The above sound isolation techniques have typically been combined to achieve good results. Figure 1 shows a few of the typical applications of these methods for building walls and ceilings. This is not an exhaustive list. This figure shows a top-down cross-section view of 4 walls. Also, this figure does not show that the wall's back side may have added soundproofing. These examples are arranged from less sound blocking on the left to more blocking on the right. All of these methods have superior sound blocking compared to standard drywall.

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