How does soundproofing work?

Anyone who has spoken to people online through services like Zoom or Discord is probably familiar with how much variance there is in audio recording quality. Even the uninitiated can probably notice the difference in quality between the average consumer headset mic and a professionally made audio recording.

While this difference is partially caused by the quality of the mic being used, a much more noticeable factor is the environment in which the recording was created. Background noise is a major detractor for sound quality, so one of the most common tips for start-up voice actors and sound engineers is to learn how to soundproof a room, a process that is worth examining. 

Why sound-proof?

Although soundproofing a room isn’t necessarily difficult, it is still a process that requires effort, so a reasonable question would be, why bother with soundproofing?

For someone that works in audio design, it’s an easy enough question; Reducing background noise helps get as clean of a recording as you can, making it easier to edit down the line. But for everyone else, the answer is a bit more abstract. 

As can be seen in other articles on this site, spaces with a low acoustic comfort can have some very major impacts on our performance, health and wellbeing. These impacts, ranging from increasing stress levels to mental health problems, should ideally be dealt with on a more widespread level, but can be mitigated through the use of soundproofing. 

So how does soundproofing work?

Although the mechanics of how it propagates can be complicated, sound itself is a fairly simple phenomenon. It’s caused by the vibration of a medium at a certain frequency, which our ears can then pick up and interpret as needed. Although we mostly think of sound as propagating through air, it can propagate through other materials, including metal and wood. However, when sound moves from one medium to another, say from air to wood, the frequency it moves with also changes in what we call distortion. 

This distortion is caused by the fact that different materials are able to vibrate to different extents. Air, for example, is really easy to vibrate, whereas wood or metal is slightly more difficult to vibrate. Some materials, such as certain types of foam and vinyl, are extremely difficult to vibrate, and transfer almost no sound through them. These are the materials that are used to be sound-proof, although the exact application of these materials can be different, depending on what the exact use case is. 

Studio vs. general sound-proofing

Sound-proofing is only really defined as controlling the environmental sound, so there are different ways that it can be used, depending on what the exact end goal is.

Acoustically isolating a room

The general use case is trying to prevent noise from outside of a room from reaching into the room. This is usually done by inserting sound-deadening materials, such as the foam mentioned earlier, into the walls of a room so that sound has a difficult time passing through the wall. Since most sound-deadening materials are also good insulators for temperature, it’s not usually too difficult to incorporate them into construction projects, as they have multiple benefits.

Improving the sound quality in a room

If you’ve ever been in a studio though, you might have noticed panels like the ones pictured above hung around the walls of the studio. These panels are part of the specific use case that studios have.

See, while studios also tend to have general soundproofing to prevent outside noise from getting in, they also need to deal with noises made within the room, including those made by the recording subject themself.

The voice of a singer in a studio will naturally bounce off a wall, causing what is known as reverb, which makes the recording more difficult to work with post-production, as well as generally making the recording sound lower quality.

These sound waves bouncing around the room from surface to surface are one of the main reasons why those zoom calls we were talking about can have such poor sound quality. People seating in an empty office surrounded by cold, hard materials, will have a lot more of these reverbs than other people who attend the call from more cozy spaces, smaller, with more furniture and finished with softer and warmer materials such as wood, which absorb the sound instead of bouncing it back to the room.

So these panels are placed in specific points where reverb is most likely to occur, in order to deaden the sound before it has the chance to reverb. This way the recording device will only hear the singer’s voice itself, not the sound bouncing off the wall. 

This concept can be taken one step further in the use-case for concert halls, where sound from the stage needs to be funneled towards the audience as much as possible, without also funneling sounds from the audience back towards them. This is done through two methods.

The first is to build the room in a wedge shape that, even without any sound-proof panels, will naturally reflect sound back into the audience.

The second is to use sound-proof panels along the walls beside the seats at specific points to deaden any reflected sound from the audience.

Since most concert halls try to fit a certain aesthetic, these sound panels are usually cleverly hidden by creative design choices, as is the case in the above picture of the Sydney Opera House.

An interesting side effect of this sound-proofing process is that sound doesn’t tend to get reflected back to the stage, meaning that it can be difficult to hear other people on the same stage. There can even be specific dead zones on a stage where no sound is audible at all, because there’s no way for it to be reflected there. 

Conclusion

It may be tempting to think of soundproofing as a technique only truly useful to professionals working in the audio industry. And while it certainly finds more extensive use in those fields, sound-proofing is a useful technique for a wide variety of use cases.

As can be seen in other articles on this site, being able to mitigate background noise can be incredibly helpful for our own health and peace of mind, so learning how best to apply these techniques in your own space can be greatly beneficial. Maybe it’s time to add a rug to your office, or some heavy curtains. All these soft materials will absorb sound waves and reduce the reverb of the room.