Acoustic Treatment and Sound Proofing

Most of you probably got into this course thinking that you will be dealing with electronic audio devices and how to use them when working with digital audio. You would be correct. However, you may not have anticipated that you will be directly dealing with acoustics as well.

Understanding acoustics can be an extremely complicated task. So many things can happen to sound by the time it reaches your ears. Let’s say you are in your living room, watching TV. The sound you hear while watching is not solely the product of the speakers’ output. The soundwaves from the speakers move at around 340 meters per second. That is fast. The sound that reaches your ears at any given moment is a composite of the sound that directly came from the speakers and dozens, if not hundreds of reflections of its reflections, bouncing of walls and furniture. Each object the sound bounces from will effect a certain change in sound, depending on the materials’ properties. Chances are, you are not exactly hearing the sound the way it was truly meant to be heard. It may or may not be significant to you personally, but the difference is there.

Acoustics may not be a big issue for casual listeners, but it is a critical factor to consider in audio production. We’re usually not aware of how sound bounces in small spaces like offices or editing rooms because the reflections arrive very quickly.  But they can cause major problems if you want to record or critically listen in the room, because of how they combine with the original sound. Conventional wisdom dictates that sound must be recorded cleanly and clearly. Two things prevent that — unwanted ambient noise and reflections. This is what acoustic treatment is all about.

It is not possible to discuss acoustic treatment without coming across another term — sound proofing. They are often used interchangeably, especially by those with an insufficient level of familiarity towards sound engineering. Therefore, let us be clear: sound proofing is not synonymous with acoustic treatment. How the two terms are differentiated isn’t consistent, though. Sound proofing is the more popular term and it deals with means to isolate a room by preventing sound and noise from the outside to pass through its walls. Acoustic treatment, on the other hand, deals with reducing reflections that occur within a room. This manner of definition implies that these are two separate terms with very different intentions. On the other hand, the more classic definition of acoustic treatment is that it is the application of acoustic or sound-absorbing material to a room or enclosure to obtain the desired acoustic characteristics (Tremaine, 1969). By this definition, one can argue that sound proofing can be considered as a subset of acoustic treatment. Regardless of the school of thought you will choose to employ, you should always bear in mind that acoustic treatment and sound proofing does not mean the same exact thing.

With ambient noise levels in urban areas getting higher and walls in modern buildings getting thinner and less dense, sound proofing has become more and more important for us. While awareness is still insufficient overall, the noisy home syndrome is a constant issue in buildings as a threat to our well-being. Sound proofing is the primary means of addressing this issue. However, the process of sound proofing a building, or even a room in a building often involves significant renovation making the proposition particularly expensive.

Acoustic treatment itself unavoidably entails a certain amount of cost, which increases with the gravity of a room’s acoustic issues and how much of it you want to resolve. Neutralizing how a room colors sound from within can be complicated. But if we are primarily concerned in reducing reflections, then there are a lot of practical and inexpensive means to do so. Sometimes, it only involves re-arrangement of furniture or the addition of wall fixtures.

Studios often have non-parallel walls to control reflections so that sound do not keep echoing between them to cause hollowness by reinforcing individual frequencies.  If the sound can bounce at an angle, the reflections follow a different direction each time, and the hollowness gets smoothed out.

The reflections that really matter are the ones that the sound source or talent is facing  – usually the wall behind the microphone.  The most common solution is the use sound blankets, drapes, fabrics and alike.  They are hug on the offending wall, at about the same height as the talent’s mouth. The ability of the fabric to cut down reflections can be enhanced by hanging them on a stand and allow for some gap from the wall. A couple of inches between wall and fabric allow for the trapping of more sound as opposed to having the fabric in direct contact with the wall.

You can also soften a reflective surface by closing drapes and moving a sofa.  Another technique is diffusion, it can also conquer some of the offending echoes.  That is because the biggest problem with a hard wall is that it reflects all the sound back in the same direction.  If you can break up the surface so some of the reflections go elsewhere, there’ll be less noticeable echo.  If you do not  have a book shelf handy, try stacking up cases or boxes at random angles.

Acoustic treatment is a fairly large topic to cover. It can also be fun for do-it-yourself and home improvement enthusiasts. Treatment tricks and tips will be discussed further, but you can start learning from initial readings, such as this article.

Let us be clear with one thing, though. Professional studios are purposefully designed and constructed from scratch. Achieving a comparable level of acoustic qualities will be tricky, if not practically impossible through retrofitting otherwise ordinary rooms. Therefore, trying to do so is probably more trouble than it’s worth. The goal with existing rooms is to reduce noise and reflections to levels low enough to allow us to produce good audio recordings.

 

References:

E-Home Recording Studio. (n.d.). Acoustic treatment 101: getting your room to sound great. Retrieved from http://ehomerecordingstudio.com/acoustic-treatment-101/.

Mayes-Wright, C. (2009). A beginners’ guide to acoustic treatment. Retrieved from http://www.soundonsound.com/sos/dec09/articles/beginnersacoustics.htm.

Sound on Sound. (2009). Soundproofing & acoustic treatment: frequently asked questions. Retrieved from https://www.soundonsound.com/sos/jul00/articles/faqacoustic.htm.

Tremaine, H. (1969). Audio Cyclopedia. Howard W. Sams and Co., Inc., Indiana, IN, USA.

Vandervort, D. (2016). 7 soundproofing secrets for a quieter home. Retrieved from http://www.hometips.com/buying-guides/soundproofing-insulation.html.