I would like to share some of what I have learned in regard to the construction of a recording booth. I am no expert, but I have 3 trades and extensive experience in building many weird and wonderful contraptions, from rotational mold tooling to vehicles to construction work. Coupled with some research into the behaviour of sound, some great advice from people in the music industry as well as my own experience in studios and with this project, I might be able to save someone some time and, possibly, expense. I always limit my posts to around 1,000 words, so this may result in a mini-series, as it were. Some of this may be obvious to many, but, as any good technical writer should, I assume my reader knows nothing and work from there. Of course, should anyone find fault in the basic principles outlined here, please leave a comment, and I will edit the post if required.
Well, first of all, why bother with a treated recording space? There are a plethora of “simple” solutions out there for recording narrative. From little fabric cubes of eggshell acoustic foam, to sitting in a clothes closet covered in a blanket, possible compromises abound. However, the only way to then get your recording to a high enough standard for Audio-books is to fix it in the post-mix, and that means time. Narrators are often paid by the page, so all that time fiddling digitally is going to munch on your hourly rate something awful. Even if you’re just doing your own work, a whole book is a long task, and any reduction in that time means more time writing.
My own booth is as small as possible, and built to break down into components that can fit into a standard box trailer, because we rent. I am not sharing my own design, because it may influence others down the wrong track. It is definitely faulted, but looks like it will deliver a good, balanced sound regardless.
Bear in mind too, that many will say booths are a horrible idea in the first place, but this is about recording narrative for Audio-books, and on a tight budget at that. Recording vocals for narrative requires a ‘dead’ room. That is, just the voice, with no reverberation, ambience or any sign of the fact you are in a room at all. Ideally, this would be done in a wide open space with no outside sound – good luck with that.
To understand why size is important, its critical to understand how sound actually works. I suggest that, if you don’t understand the basic principles of sound, you start here. You will need a basic understanding of both soundproofing (prevention of outside noise) and acoustic treatment (improvement of a room’s acoustic properties). You must also understand that, as with everything, opinions vary. I am merely sharing what I have learned, and that is based on certain opinions. On the fundamental principles, however, the science these days is fairly solid.
Most important of all – do your research and design before you do anything else. But, as you research, don’t let all the varied and conflicting ideas get you down. At the end of the day, you’re going to have to make do with the best you can do, and accept it will not be perfect. All we are trying to do is reduce the time spent on post-mixing, not record a hit album.
Now, about size. Your booth (for the sake of brevity, any other term to describe a designated area for recording voice will be considered a booth) should have varied dimensions and, if possible, irregular walls. If you Google “Ideal size for a recording studio”, you will find a raft of excellent sites that will explain the formulae and ratios behind a good room.
A cube is the very WORST shape for recording in. It will have resonant frequencies that make acoustic treatment almost impossible. My own booth is wider than it is deep, and much taller than it is wide. The front walls are angled as well. The best quality portable booths are often hexagonal, or even just pentagonal – it’s all about those bouncy sound waves. The ideal dimensions for a recording room for voice are much bigger than is practical for nearly everyone, and its interesting that, while vocal booths are seen as desirable in some music studios, a lot of vocals are actually recorded in the control room, rather than a booth. Opinion is divided, and, as I said before, irrelevant to the purposes of this post.
With a booth, size is the enemy. A small enclosure is a terrible place to record, so acoustic treatment is a nightmare. Check out the ratios, and make the area as close as is practical to those . Always remember, though, the smaller this thing is, the worse your problems will get.
To reduce the amount of sound, we must ‘catch’ or ‘trap’ the sound waves, to prevent them from reflecting and returning to the microphone. The slight repetition of the sound is reverberation, and undesirable. To do this requires that the energy from the vibration that is sound be converted and thus eliminated. One way to do this is to convert the sound to heat, as with Green Glue. This, and materials like it, remain in the liquid state, i.e. they don’t set or harden. The website explains this process in detail.
The most common way to trap sound, though, is with mass. The more mass a sound wave has to travel through, the more energy is lost. This is where size again becomes an issue. While acoustic panels and acoustic foam (more on that in another post) are effective at trapping high to mid-range frequencies, they cannot dissipate low-frequency waves, some of which measure multiple feet in length. Music studios often have at least one ‘bass trap’ wall, which may be more than 6 feet wide. See the problem? You may start off with a room, and end up with a telephone booth.
Again, we face a compromise between the ideal and the practical. At the end of the day, you must decide your booth’s size based on the available room, the impact the size will have on your budget (bigger = more materials) and also the time you are willing to spend building this thing. Irregular angled walls will have a heavy size cost attached, too, but you must avoid parallel walls as much as possible.
In the next post, we’ll have a look at some possible material choices for both soundproofing and acoustic treatment.